SOLAR PHYSICS BRANCH (7660)

Publications, 1995-1997


Title: The Relationship of Green-Line Transients to White-Light Coronal Mass Ejections

Authors: Plunkett, S. P.; Brueckner, G. E.; Dere, K. P.; Howard, R. A.; Koomen, M. J.; Korendyke, C. M.; Michels, D. J.; Moses, J. D.; Moulton, N. E.; Paswaters, S. E.; Cyr, O. C. St.; Socker, D. G.; Wang, D.; Simnett, G. M.; Bedford, D. K.; Biesecker, D. A.; Eyles, C. J.; Tappin, S. J.; Schwenn, R.; Lamy, P. L.; Llebaria, A.

Journal: Solar Physics, v. 175, Issue 2, p. 699-718.

Publication Date: 10/1997

Abstract: The authors report observations by the Large Angle Spectrometric Coronagraph (LASCO) on the SOHO spacecraft of three coronal green-line transients that could be clearly associated with coronal mass ejections (CMEs) detected in Thomson-scattered white light. Two of these events, with speeds >25 km s/sup -1/, may be classified as whip-like' transients. They are associated with the core of the white-light CMEs, identified with erupting prominence material, rather than with the leading edge of the CMEs. The third green line transient has a markedly different appearance and is more gradual than the other two, with a projected outward speed <10 km s/sup -1/. This event corresponds to the leading edge of a streamer blowout' type of CME. A dark void is left behind in the emission-line corona following each of the fast eruptions. Both fast emission-line transients start off as a loop structure rising up from close to the solar surface. The authors suggest that the driving mechanism for these events may be the emergence of new bipolar magnetic regions on the surface of the Sun, which destabilize the ambient corona and cause an eruption. The possible relationship of these events to recent X-ray observations of CMEs is briefly discussed.

Article: Not Available


Title: First results from EIT

Authors: Clette, F., Delaboudiniere, J.-P., Artzner, G.E., Brunaud, J., Gabriel, A.H., Hochedez, J.-F., Millier, F., Song, X.Y., Au, B., Dere, K.P., Howard, R.A., Kreplin, R., Michels, D.J., Moses, J.D., Defise, J.-M., Jamar, C., Rochus, P., Chauvineau, J.-P., Marioge, J.-P., Catura, R.C., Lemen, J.R., Shing, L., Stern, R.A., Gurman, J.B., Neupert, W.M., Maucherat, A., Cugnon, P., Van Dessel, E.L.

Journal: Astron. Soc. Pac. Conf. Ser. (USA), Astronomical Society of the Pacific Conference Series, vol.118, p. 268-72

Publication Date: 1997

Abstract: The Extreme-UV Imaging Telescope has already produced more than 15000 wide-field images of the corona and transition region, on the disk and up to 1.5 Rsun above the limb, with a pixel size of 2.6". By using four different emission lines, it provides the global temperature distribution in the quiet corona, in the range 0.5 to 3*10/sup 6/ K. Its excellent sensitivity and wide dynamic range allow unprecedented views of low emission features, even inside coronal holes. Those so-called "quiet" regions actually display a wide range of dynamical phenomena, in particular at small spatial scales and at time scales going down to only a few seconds, as revealed by all EIT time sequences of full- or partial-field images. The initial results presented here demonstrate the importance of this wide-field imaging experiment for a good coordination between SOHO and ground-based solar telescopes, as well as for science planning.

Article: Not Available


Title: Imaging the solar corona in the EUV

Authors: Delaboudiniere, J.-P. Stern, R.A., Maucherat, A., Portier-Fozzani, F., Neupert, W.M., Gurman, J.B., Catura, R.C., Lemen, J.R., Shing, L., Artzner, G.E., Brunaud, J., Gabriel, A.H., Michels, D.J., Moses, J.D., Au, B., Dere, K.P., Howard, R.A., Kreplin, R., Defise, J.M., Jamar, C., Rochus, P., Chauvineau, J.P., Marioge, J.P., Clette, F., Cugnon, P., van Dessel, E.L.

Journal: Adv. Space Res. (UK), Advances in Space Research, vol.20, no.12, p. 2231-7

Publication Date: 1997

Abstract: The SOHO (Solar and Heliospheric Observatory) satellite was launched on December 2 1995. After arriving at the Earth-Sun (L1) Lagrangian point on February 14 1996, it began to continuously observe the Sun. As one of the instruments onboard SOHO, the EIT (extreme ultraviolet imaging telescope) images the Sun's corona in 4 EUV wavelengths. The He II filter at 304 Angstrom images the chromosphere and the base of the transition region at a temperature of 5 - 8*10(4) K, the Fe IX-X filter at 171 Angstrom images the corona at a temperature of 1.3*10(6) K, the Fe XII filter at 195 Angstrom images the quiet corona outside coronal holes at a temperature of 1.6*10(6) K, and the Fe XV filter at 284 Angstrom images active regions with a temperature of 2.0*10(6) K. About 5000 images have been obtained up to the present. In this paper, we describe also some aspects of the telescope and the detector performance for application in the observations. Images and movies of all the wavelengths allow a look at different phenomena present in the Sun's corona, and in particular, magnetic field reconnection.

Article: Not Available


Title: Ultraviolet jets and bright points in the solar chromosphere. II. Statistical correlations

Authors: Hoekzema, N.M.; Rutten, R.J.; Cook, J.W.

Journal: Astrophysical Journal, vol.474, no.1, pt.1, p. 518-28

Publication Date: 1 Jan. 1997

Abstract: We use HRTS--VI rocket observations of the solar chromosphere to search for relationships between high-Dopplershift "jets" observed in the C I lines near lambda = 156 nm and internetwork "bright points" observed in the lambda = 160 nm continuum, in sequel to the analysis by Cook et al. which failed to find a direct connection between these phenomena. We now use the same data to establish statistical correlations between C I Dopplershift and 160 nm brightness modulation in internetwork areas. These mean relations emerge only after extensive spatial averaging and have small amplitude, but are definitely significant. They show that both C I Dopplershift and 160 nm brightness participate in oscillatory behavior with 3 minute periodicity and mesoscale (8 Mm wavelength) as well as small-scale (1.4 Mm wavelength) spatial patterning. We find spatial and temporal phase relations between Dopplershift and brightness that confirm that jets and bright points should not be interpreted as isolated entities. Rather, they are chromospheric manifestations, with much pattern interference, of the oscillatory acoustic shock dynamics in the internetwork which also cause Ca II K2V grains. Additional small-scale modulation is present which we attribute to waves with f-mode character.

Article: Available from ADS


Title: EIT and LASCO Observations of the Initiation of a Coronal Mass Ejection

Authors: Dere, K.P., Brueckner, G.E., Howard, R.A., Koomen, M.J., Korendyke, C.M., Kreplin, R.W., Michels, D.J., Moses, J.D., Moulton, N.E., Socker, D.G., Cyr, O.C. St., Delaboudiniere, J.P., Artzner, G.E., Brunaud, J., Gabriel, A. H., Hochedez, J. F., Millier, F., Song, X. Y., Chauvineau, J. P., Marioge, J. P., Defise, J. M., Jamar, C., Rochus, P., Catura, R. C., Lemen, J. R., Gurman, J. B., Neupert, W., Clette, F., Cugnon, P., Van Dessel, E. L., Lamy, P. L., Llebaria, A., Schwenn, R., Simnett, G. M.

Journal: Solar Physics, v. 175, Issue 2, p. 601-612.

Publication Date: 10/1997

Abstract: The authors present the first observations of the initiation of a coronal mass ejection (CME) seen on the disk of the Sun. Observations with the EIT experiment on SOHO show that the CME began in a small volume and was initially associated with slow motions of prominence material and a small brightening at one end of the prominence. Shortly afterward, the prominence was accelerated to about 100 km/s and was preceded by a bright loop-like structure, which surrounded an emission void, that traveled out into the corona at a velocity of 200-400 km/s. These three components, the prominence, the dark void, and the bright loops are typical of CMEs when seen at distance in the corona and are shown to be present at the earliest stages of the CME. The event was later observed to traverse the LASCO coronagraphs fields of view from 1.1 to 30 Rs. Of particular interest is the fact that this large-scale event, spanning as much as 70 deg in latitude, originated in a volume with dimensions of roughly 35" (2.5*10E4 km). Further, a disturbance that propagated across the disk and a chain of activity near the limb may also be associated with this event as well as a considerable degree of activity near the west limb.

Article: Not Available


Title: MHD Interpretation of LASCO Observations of a Coronal Mass Ejection as a Disconnected Magnetic Structure

Authors: Wu, S. T., Guo, W. P., Andrews, M. D., Brueckner, G. E., Howard, R. A., Koomen, M. J., Korendyke, C. M., Michels, D. J., Moses, J. D., Socker, D. G., Dere, K. P., Lamy, P. L., Llebaria, A., Bout, M. V., Schwenn, R., Simnett, G. M., Bedford, D. K., Eyles, C. J.

Journal: Solar Physics, v. 175, Issue 2, p. 719-735.

Publication Date: 10/1997

Abstract: We present a qualitative and quantitative comparison of a single coronal mass ejection (CME) as observed by LASCO (July 28-29, 1996) with the results of a three-dimensional axisymmetric time-dependent magnetohydrodynamic model of a flux rope interacting with a helmet streamer. The particular CME considered was selected based on the appearance of a distinct tear-drop' shape visible in animations generated from both the data and the model. The CME event begins with the brightening of a pre-existing coronal streamer which evolves into a tear-drop' shaped loop followed by Y-shaped structure. The brightening moves slowly outward with significant acceleration reaching velocities of 450 km/s at 30 Rs. The observed CME characteristics are compared with the model results. On the basis of this comparison, we suggest that the observed features were caused by the evacuation of a flux rope in the closed field region of the helmet streamer (i.e., helmet dome). The flux rope manifests itself as the cavity of the quasi-static helmet streamer and the whole system becomes unstable when the flux rope reaches a threshold strength. The observed tear-drop' structure is due to the deformed flux rope. The leading edge of the flux rope interacts with the helmet dome to form the typical loop-like CME. The trailing edge of this flux rope interacts with the local bi-polar field to form the observed Y-shaped structure. The model results for the evolution of the magnetic field configurations, velocity, and polarization brightness are directly compared with observations. Animations have been generated from both the actual data and the model to illustrate the good agreement between the observation and the model.

Article: Not Available


Title: LASCO Observations of Disconnected Magnetic Structures Out to Beyond 28 Solar Radii During Coronal Mass Ejections

Authors: Simnett, G. M., Tappin, S. J., Plunkett, S. P., Bedford, D. K., Eyles, C. J., Cyr, O. C. St., Howard, R. A., Brueckner, G. E., Michels, D. J., Moses, J. D., Socker, D., Dere, K. P., Korendyke, C. M., Paswaters, S. E., Wang, D., Schwenn, R., Lamy, P., Llebaria, A., Bout, M. V.

Journal: Solar Physics, v. 175, Issue 2, p. 685-698.

Publication Date: 10/1997

Abstract: Two coronal mass ejections have been well observed by the LASCO coronagraphs to move out into the interplanetary medium as disconnected plasmoids. The first, on July 28, 1996, left the Sun above the west limb around 18:00 UT. As it moved out, a bright V-shaped structure was visible in the C2 coronagraph which moved into the field-of-view of C3 and could be observed out to beyond 28 solar radii. The derived average velocity in the plane of the sky was 110+or-5 km/s out to 5 solar radii, and above 15 solar radii the velocity was 269+or-10 km/s. Thus there is evidence of some acceleration around 6 solar radii. The second event occurred on November 5, 1996 and left the west limb around 04:00 UT. The event had an average velocity in the plane of the sky of 54 km/s below 4 Rs, and it accelerated rapidly around 5 Rs up to 310+or-10 km/s. In both events the rising plasmoid is connected back to the Sun by a straight, bright ray, which is probably a signature of a neutral sheet. In the November event there is evidence for multiple plasmoid ejections. The acceleration of the plasmoids around a projected altitude of 5 solar radii is probably a manifestation of the source surface of the solar wind.

Article: Not Available


Title: First View of the Extended Green-Line Emission Corona At Solar Activity Minimum Using the Lasco-C1 Coronagraph on Soho

Authors: Schwenn, R., Inhester, B., Plunkett, S. P., Epple, A., Podlipnik, B., Bedford, D. K., Eyles, C. J., Simnett, G. M., Tappin, S. J., Bout, M. V., Lamy, P. L., Llebaria, A., Brueckner, G. E., Dere, K. P., Howard, R. A., Koomen, M. J., Korendyke, C. M., Michels, D. J., Moses, J. D., Moulton, N. E., Paswaters, S. E., Socker, D. G., Cyr, O. C. St., Wang, D.

Journal: Solar Physics, v. 175, Issue 2, p. 667-684.

Publication Date: 10/1997

Abstract: The newly developed Cl coronagraph as part of the Large Angle Spectroscopic Coronagraph (LASCO) on board the SOHO spacecraft has been operating since January 29, 1996. The authors present observations obtained in the first three months of operation. The green-line emission corona can be made visible throughout the instrument's full field of view, i.e., from 1.1 Rs out to 3.2 Rs (measured from Sun center). Quantitative evaluations based on calibrations cannot yet be performed, but some basic signatures show up even now: (1) There are often bright and apparently closed loop systems centered at latitudes of 30 degrees to 45 degrees in both hemispheres. Their helmet-like extensions are bent towards the equatorial plane. Farther out, they merge into one large equatorial streamer sheet' clearly discernible out to 32 Rs. (2) At mid latitudes a more diffuse pattern is usually visible, well separated from the high-latitude loops and with very pronounced variability. (3) All high-latitude structures remain stable on time scales of several days, and no signature of transient disruption of high-latitude streamers was observed in these early data. (4) Within the first 4 months of observation, only one single fast' feature was observed moving outward at a speed of 70 km/s close to the equator. Faster events may have escaped attention because of data gaps. (5) The centers of high-latitude loops are usually found at the positions of magnetic neutral lines in photospheric magnetograms. The large-scale streamer structure follows the magnetic pattern fairly precisely. Based on their observations the authors conclude that the shape and stability of the heliospheric current sheet at solar activity minimum are probably due to high-latitude streamers rather than to the near-equatorial activity belt.



Article: Not Available


Title: Origin and Evolution of Coronal Streamer Structure during the 1996 Minimum Activity Phase

Authors: Wang, Y.-M., Sheeley, N. R., Jr., Howard, R. A., Kraemer, J. R., Rich, N. B., Andrews, M. D., Brueckner, G. E., Dere, K. P., Koomen, M. J., Korendyke, C. M., Michels, D. J., Moses, J. D., Paswaters, S. E., Socker, D. G., Wang, D., Lamy, P. L., Llebaria, A., Vibert, D., Schwenn, R., Simnett, G. M.

Journal: Astrophysical Journal v.485, p.875

Publication Date: 08/1997

Abstract: We employ coronal extrapolations of solar magnetograph data to interpret observations of the white-light streamer structure made with the LASCO coronagraph in 1996. The topological appearance of the streamer belt during the present minimum activity phase is well described by a model in which the Thomson-scattering electrons are concentrated around a single, warped current sheet encircling the Sun. Projection effects give rise to bright, jet-like structures or spikes whenever the current sheet is viewed edge-on, multiple spikes are seen if the current sheet is sufficiently wavy. The extreme narrowness of these features in polarized images indicates that the scattering layer is at most a few degrees wide. We model the evolution of the streamer belt from 1996 April to 1996 September and show that the effect of photospheric activity on the streamer belt topology depends not just on the strength of the erupted magnetic flux, but also on its longitudinal phase relative to the background field. Using flux transport simulations, we also demonstrate how the streamer belt would evolve during a prolonged absence of activity.

Article: Available from ADS


Title: Measurements of Flow Speeds in the Corona between 2 and 30 Rsun

Authors: Sheeley, N. R., Jr., Wang, Y.-M., Hawley, S. H., Brueckner, G. E., Dere, K. P., Howard, R. A., Koomen, M. J., Korendyke, C. M., Michels, D. J., Paswaters, S. E., Socker, D. G., St. Cyr, O. C., Wang, D., Lamy, P. L., Llebaria, A., Schwenn, R., Simnett, G. M., Plunkett, S., Biesecker, D. A.

Journal: Astrophysical Journal v.484, p.472

Publication Date: 07/1997

Abstract: Time-lapse sequences of white-light images, obtained during sunspot minimum conditions in 1996 by the Large Angle Spectrometric Coronagraph on the Solar and Heliospheric Observatory, give the impression of a continuous outflow of material in the streamer belt, as if we were observing Thomson scattering from inhomogeneities in the solar wind. Pursuing this idea, we have tracked the birth and outflow of 50--100 of the most prominent moving coronal features and find that: 1. They originate about 3--4 Ro from Sun center as radially elongated structures above the cusps of helmet streamers. Their initial sizes are about 1 Ro in the radial direction and 0.1 Ro, in the transverse direction. 2. They move radially outward, maintaining constant angular spans and increasing their lengths in rough accord with their speeds, which typically double from 150 km s-1 near 5 Ro, to 300 km s-1 near 25 Ro,. 3. Their individual speed profiles v(r) cluster around a nearly parabolic path characterized by a constant acceleration of about 4 m s-2 through most of the 30 Ro, field of view. This profile is consistent with an isothermal solar wind expansion at a temperature of about 1.1 MK and a sonic point near 5 Ro,. Based on their relatively small initial sizes, low intensities, radial motions, slow but increasing speeds, and location in the streamer belt, we conclude that these moving features are passively tracing the outflow of the slow solar wind.

Article: Available from ADS


Title: The Green Line Corona and Its Relation to the Photospheric Magnetic Field

Authors: Wang, Y.-M., Sheeley, N. R., Jr., Hawley, S. H., Kraemer, J. R., Brueckner, G. E., Howard, R. A., Korendyke, C. M., Michels, D. J., Moulton, N. E., Socker, D. G., Schwenn, R.

Journal: Astrophysical Journal v.485, p.419

Publication Date: 08/1997

Abstract: Images of the green line corona made with the LASCO C1 coronagraph on SOHO are analyzed by applying current-free extrapolations to the observed photospheric field. The Fe XIV lambda 5303 emission is shown to be closely related to the underlying photospheric field strength. By modeling the observed intensity patterns as a function of latitude and height above the solar limb, we derive an approximate scaling law of the form nfoot ~ <Bfoot>0.9, where nfoot is the density of the green line--emitting plasma and <Bfoot> is the average field strength at the footprints of the coronal loop. The observed high-latitude enhancements in the green line corona are attributed to the poleward concentration of the large-scale photospheric field. The strongest such enhancements occur where the high-latitude unipolar fields become reconnected to active region flux at lower latitudes, the global emission pattern rotates quasi-rigidly at the rate of the dominant active region complex. The validity of the current-free approximation is assessed by comparing the topology of the observed and simulated green line structures.

Article: Available from ADS


Title: Eruptive prominence and associated CME observed with SUMER, CDS and LASCO (SOHO)

Authors: Wiik, J. E., Schmieder, B., Kucera, T., Poland, A., Brekke, P., Simnett, G.

Journal: Solar Physics, v. 175, Issue 2, p. 411-436.

Publication Date: 10/1997

Abstract: Not Available

Article: Not Available


Title: Solar Magnetic Field Events related to CMEs observed with SOHO (MDI, EIT, SUMER, LASCO)

Authors: Schmieder, B., Van Driel-Gesztelyi, L., Wiik, J. E., Thompson, B., Deforest, C., St. Cyr, C., Vial, J.-C., Nitta, N., Simnett, G.

Journal: Physics of the Sun and Heliosphere in the Era of Space Probes: Scientific Highlights of SOHO, Ulysses, and Yohkoh, 23rd meeting of the IAU, Joint Discussion 19, 26-27 August 1997, Kyoto, Japan.

Publication Date: 00/1997

Abstract: We shall present two CMEs observed by LASCO during the minimum of activity of the Sun. These are associated with filament disparitions brusques (DB). CME and DB definitively seem to be consequences of global magnetic field instability, which causes reconnection of pre-existing field lines in the corona. We shall demonstrate how cancelling flux and converging magnetic field in photosphere may destabilize coronal streamers overlying one or two filament channels.

Article: Not Available


Title: Evidence of an Erupting Magnetic Flux Rope: LASCO Coronal Mass Ejection of 1997 April 13

Authors: Chen, J., Howard, R. A., Brueckner, G. E., Santoro, R., Krall, J., Paswaters, S. E., St. Cyr, O. C., Schwenn, R., Lamy, P., Simnett, G. M.

Journal: Astrophysical Journal Letters v.490, p.L191

Publication Date: 12/1997

Abstract: A coronal mass ejection (CME) observed by LASCO exhibits evidence that its magnetic field geometry is that of a flux rope. The dynamical properties throughout the fields of view of C2 and C3 telescopes are examined. The results are compared with theoretical predictions based on a model of solar flux ropes. It is shown that the LASCO observations are consistent with a two-dimensional projection of a three-dimensional magnetic flux rope with legs that remain connected to the Sun.

Article: Available from ADS


Title: EIT Observations of the Extreme Ultraviolet Sun

Authors: Moses, D., Clette, F., Delaboudiniere, J.-P., Artzner, G. E., Bougnet, M., Brunaud, J., Carabetian, C., Gabriel, A. H., Hochedez, J. F., Millier, F., Song, X. Y., Au, B., Dere, K. P., Howard, R. A., Kreplin, R., Michels, D. J., Defise, J. M., Jamar, C., Rochus, P., Chauvineau, J. P., Marioge, J. P., Catura, R. C., Lemen, J. R., Shing, L., Stern, R. A., Gurman, J. B., Neupert, W. M., Newmark, J., Thompson, B., Maucherat, A., Portier-Fozzani, F., Berghmans, D., Cugnon, P., Van Dessel, E. L., Gabryl, J. R.

Journal: Solar Physics, v. 175, Issue 2, p. 571-599.

Publication Date: 10/1997

Abstract: The Extreme Ultraviolet Imaging Telescope (EIT) on board the SOHO spacecraft has been operational since 2 January 1996. EIT observes the Sun over a 45*45 arc min field of view in four emission line groups: Fe IX, X, Fe XII, Fe XV, and He II. A post-launch determination of the instrument flatfield, the instrument scattering function, and the instrument aging were necessary for the reduction and analysis of the data. The observed structures and their evolution in each of the four EUV bandpasses are characteristic of the peak emission temperature of the line(s) chosen for that bandpass. Reports on the initial results of a variety of analysis projects demonstrate the range of investigations now underway: EIT provides new observations of the corona in the temperature range of 1 to 2 MK. Temperature studies of the large-scale coronal features extend previous coronagraph work with low-noise temperature maps. Temperatures of radial, extended, plume-like structures in both the polar coronal hole and in a low latitude decaying active region were found to be cooler than the surrounding material. Active region loops were investigated in detail and found to be isothermal for the low loops but hottest at the loop tops for the large loops. Variability of solar EUV structures, as observed in the EIT time sequences, is pervasive and leads to a re-evaluation of the meaning of the term quiet Sun'. Intensity fluctuations in a high cadence sequence of coronal and chromospheric images correspond to a Kolmogorov turbulence spectrum. This can be interpreted in terms of a mixed stochastic or periodic driving of the transition region and the base of the corona. No signature of the photospheric and chromospheric waves is found in spatially averaged power spectra, indicating that these waves do not propagate to the upper atmosphere or are channeled through narrow local magnetic structures covering a small fraction of the solar surface.

Article: Not Available


Title: A user friendly planning and scheduling tool for SOHO/LASCO-EIT

Authors: Paswaters, S.E.; Wang, D.; Howard, R.A.

Journal: Astron. Soc. Pac. Conf. Ser. (USA), Astronomical Society of the Pacific Conference Series, vol.125, p. 375-8

Publication Date: 1997

Abstract: The LASCO/EIT instruments aboard the SOHO satellite (launched December 1995) were developed with complicated image processing/acquisition techniques. The planning and scheduling tool was designed allow the user easily to take advantage of all available resources of the four telescopes (LASCO's three coronagraphs and the EIT) to maximize the use of the telemetry downlink. The planning tool allows users to develop customized observing sequences while monitoring compression factors and on-board processing times to realistically work within the limits of the instruments. The scheduling tool then graphically displays scheduled sequences and highlights potential resource conflicts. Sequences are saved in database tables as "as planned observations" and are available to be retrieved at any later date. Outputs include: database updates, inputs to the SOHO science activity plan, and the command loads themselves. Statistics are gathered after the images are received so the tool is constantly improving its estimate of processing time and compression factor.

Article: Not Available


Title: QDB: an IDL-based interface to LASCO databases

Authors: Esfandiari, A.E.; Paswaters, S.E.; Wang, D.; Howard, R.A.

Journal: Astron. Soc. Pac. Conf. Ser. (USA), Astronomical Society of the Pacific Conference Series, vol.125, p. 353-6

Publication Date: 1997

Abstract: QDB is a collection of IDL and C routines that provides a query interface to the Large Angle Spectrometric Coronograph (LASCO) databases maintained under the Sybase database management system. IDL widgets are used extensively to display the databases, tables, columns, and on-line help. This is a fully automated process-no code modification is required to reflect database changes such as adding/dropping databases, tables, or columns. Standard Query Language (SQL) is used to build a query based on the user selection. This query is then passed via remote shell (rsh) to two C routines that access the Sybase Open Client Database library to execute the query. The result is returned in an IDL structure. Another set of IDL routines optionally displays or manipulates the data in this structure.

Article: Not Available


Title: The LASCO data archive

Authors: Wang, D.; Howard, R.A.; Paswaters, S.E.; Esfandiari, A.E.; Rich, N.

Journal: Astron. Soc. Pac. Conf. Ser. (USA), Astronomical Society of the Pacific Conference Series, vol.125, p. 282-5

Publication Date: 1997

Abstract: The data archive for the Large Angle Spectrometric Coronagraph (LASCO) and the Extreme Ultraviolet Imaging Telescope (EIT) is designed to contain 1 B of image data in an easy to use recordable CD-ROM based archive. This paper discusses the planning, implementation and cost considerations of designing the archive. The problem of getting data into the archive and distributing data to co-investigator institutes is also discussed.

Article: Not Available


Title: In-orbit calibration of the distortion of the SOHO/LASCO-C2 coronagraph

Authors: Llebaria, A.; Aubert, S.; Lamy, P.; Plunkett, S.

Journal: Astron. Soc. Pac. Conf. Ser. (USA), Astronomical Society of the Pacific Conference Series, vol.125, p. 435-8

Publication Date: 1997

Abstract: This paper describes distortion calibration procedures for the SOHO/LASCO-C2 coronagraph, based on in-orbit data and extensive image processing methods. It addresses specific problems of externally occulted coronagraphs (obstructed center of field-of-view, strong vignetting, and presence of stray light) and limitations inherent to space-based instrumentation (cosmic rays and limited number of reference points).

Article: Not Available


Title: CHIANTI an atomic database for emission lines. I. Wavelengths greater than 50 Angstrom

Authors: Dere, K.P.; Landi, E.; Mason, H.E.; Monsignori Fossi, B.C.; Young, P.R.

Journal: Astronomy & Astrophysics Supplement Series, vol.125, no.1, p. 149-73

Publication Date: Oct. 1997

Abstract: A comprehensive set of accurate atomic data is required for analyses of astrophysical and solar spectra. CHIANTI provides a database of atomic energy levels, wavelengths, radiative data and electron excitation data for ions which are abundant in cosmic plasmas. The most recent electron excitation data have been assessed and stored following the method of Burgess and Tully (1992). The current version is essentially complete for specifying the emission spectrum at wavelengths greater than 50 Angstrom. A list of observed lines in the spectral region between 50 and 1100 Angstrom has been compiled and compared with the lines predicted by the CHIANTI database. The CHIANTI database reproduces the vast majority of lines observed at these wavelengths. CHIANTI includes IDL (Interactive Data Language) routines to calculate optically thin synthetic spectra for equilibrium conditions. IDL routines to calculate theoretical line intensities required for electron density or temperature diagnostics and emission measure studies are also included. The CHIANTI atomic database and supporting IDL routines are available by anonymous FTP. Table 3 is only in electronic form at CDS via anonymous ftp to cdsarc.u.strasbg.fr (130.79.128.5).

Article: Not Available


Title: Synthetic images of the solar corona from octree representation of 3-D electron distributions

Author: Vibert, D.; Llebaria, A.; Netter, T.; Balard, L.; Lamy, P.

Journal: Astron. Soc. Pac. Conf. Ser. (USA), Astronomical Society of the Pacific Conference Series, vol.125, p. 230-3

Publication Date: 1997

Abstract: Empirical and theoretical modeling of 3-D structures in the solar corona is confronted by the tremendous amount of data needed to represent phenomena with a large dynamic range both in size and magnitude, and with a rapid temporal evolution. Octree representation of the 3-D coronal electron distribution offers the right compromise between resolution and size, allowing computation of synthetic images of the solar corona.

Article: Not Available


Title: Association of Extreme-Ultraviolet Imaging Telescope (EIT) Polar Plumes with Mixed-Polarity Magnetic Network

Authors: Wang, Y.-M., Sheeley, N. R., Jr., Dere, K. P., Duffin, R. T., Howard, R. A., Michels, D. J., Moses, J. D., Harvey, J. W., Branston, D. D., Delaboudiniere, J.-P., Artzner, G. E., Hochedez, J. F., Defise, J. M., Catura, R. C., Lemen, J. R., Gurman, J. B., Neupert, W. M., Newmark, J., Thompson, B., Maucherat, A.

Journal: Astrophysical Journal Letters v.484, p.L75

Publication Date: 07/1997

Abstract: SOHO EIT spectroheliograms showing the polar coronal holes during the present sunspot minimum are compared with National Solar Observatory (Kitt Peak) magnetograms taken in Fe I lambda 8688 and Ca II lambda 8542. The chromospheric lambda 8542 magnetograms, obtained on a routine, near-daily basis since 1996 June, reveal the Sun's strong polar fields with remarkable clarity. We find that the Fe IX lambda 171 polar plumes occur where minority-polarity flux is in contact with flux of the dominant polarity inside each polar hole. Moreover, the locations of "plume haze" coincide approximately with the patterns of brightened He II lambda 304 network within the coronal hole. The observations appear to be consistent with mechanisms of plume formation involving magnetic reconnection between unipolar flux concentrations and nearby bipoles. The fact that minority-polarity fields constitute only a small fraction of the total magnetic flux within the polar holes suggests that plumes are not the main source of the high-speed polar wind.

Article: Available from ADS


Title: Observations of CMEs from SOHO/LASCO

Authors: Howard, R.A., Brueckner, G.E., Koomen, M.J., Korendyke, C.M., Michels, D.J., Moses, J.D., Socker, D.G., Dere, K.P., St. Cyr, O.C., Lamy, P.L., Llebaria, A., Bout, M.V., Schwenn, R., Simnett, G.M., Plunkett, S.P.

Journal: "Coronal Mass Ejections", N. Crooker, J.A. Joselyn, J. Feynman, eds., Geophysical Monograph 99, pages 17-26.

Publication Date: 1997.

Abstract: The LASCO experiment on board the SOHO satellite has been making observations of the solar corona out to 30 R since first light on 29 December 1995, and routinely since 15 May 1996. Over 120 coronal mass ejections have been observed to date. LASCO represents a significant advance over previous coronagraphs in many ways, but principally in an expanded field of view, increased sensitivity and increased dynamic range. The satellite, orbiting about the Lagrangian point, L1, is in continual sunlight, providing the opportunity to view the corona continuously, uninterrupted by orbit night as is common with near-Earth orbits. While the CMEs observed by LASCO are similar to those observed with previous coronagraphs, there are several new aspects: (1) Many are accompanied by a global response of the solar corona, (2) Many show acceleration to the edge of the field, (3) Disconnection is a frequent occurrence, (4) CMEs are occurring more frequently than had been expected at this minimum phase of the solar activity cycle, and (5) CMEs undergo extensive internal evolution as they move outward.

Article: Not Available


Title: Origins of the Slow and the Ubiquitous Fast Solar Wind

Authors: Habbal, S. R., Woo, R., Fineschi, S., O'Neal, R., Kohl, J., Noci, G., Korendyke, C.

Journal: Astrophysical Journal Letters v.489, p.L103

Publication Date: 11/1997

Abstract: We present in this Letter the first coordinated radio occultation measurements and ultraviolet observations of the inner corona below 5.5Rs, obtained during the Galileo solar conjunction in 1997 January, to establish the origin of the slow solar wind. Limits on the flow speed are derived from the Doppler dimming of the resonantly scattered component of the oxygen 1032 and 1037.6 A lines as measured with the ultraviolet coronagraph spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO). White light images of the corona from the large-angle spectroscopic coronagraph (LASCO) on SOHO taken simultaneously are used to place the Doppler radio scintillation and ultraviolet measurements in the context of coronal structures. These combined observations provide the first direct confirmation of the view recently proposed by Woo & Martin that the slow solar wind is associated with the axes, also known as stalks, of streamers. Furthermore, the ultraviolet observations also show how the fast solar wind is ubiquitous in the inner corona and that a velocity shear between the fast and slow solar wind develops along the streamer stalks.

Article: Available from ADS


Title: Nonthermal velocities in the solar transition zone and corona

Authors: Doyle, J.G.; O'Shea, E.; Erdelyi, R.; Dere, K.P.; Socker, D.G.; Keenan, F.P.

Journal: Solar Physics, vol.173, no.2, p. 243-58

Publication Date: July 1997

Abstract: Nonthermal velocities are presented for spectral lines covering the temperature range 10^4 -10^6 K, measured from high-spectral-resolution data for several solar features observed at the limb by the high resolution telescope and spectrograph (HRTS), including a coronal hole, quiescent regions' and several small-scale active regions. These results are compared with predictions based on acoustic waves and heating via Alfven waves. It is likely that more than one mechanism is operating simultaneously, in particular, resonant Alfven wave heating, which is very sensitive to background plasma motions.

Article: Not Available


Title: In-orbit diagnostics of EIT EUV CCD radiation-induced aging

Authors: Defise, J.-M., Clette, F., Moses, J. D., Hochedez, J.-F. E.

Journal: Proc. SPIE Vol. 3114, p. 598-607, EUV, X-Ray, and Gamma-Ray Instrumentation for Astronomy VIII, Oswald H. Siegmund, Mark A. Gummin, Eds.

Publication Date: 10/1997

Abstract: The extreme UV imaging telescope (EIT) on-board SOHO is performing a global survey of the extreme ultraviolet (EUV) solar corona. Operating since January 96, EIT has been producing tens thousands of images of the Sun in four narrow channels (171, 195, 284 and 304 angstrom). orbiting around the L1 Lagrangian point and oriented permanently towards the Sun, the EIT mission is a unique opportunity to study an instrument continuously exposed to solar EUV radiations. The backside thinned CCD detector is showing significant changes in its overall signal and in local 'burn in' regions. Periodic bakeouts allowed to restore a good efficiency. However, a specific observation program has been set up to diagnose the origin of the signal decay. In this framework, photon transfer analyses are performed on solar EUV images, providing good indications on the local charge collection efficiency status. Calibration lamp images are also used to eluate the signal recovery in the visible range. The signal degradation seems to be the result of two competing effects: periodic deposition of a contamination layer, and charge mobility change in the CCD Si layer as a function of the accumulated EUV dose. In this paper, the CCD quantum properties evolution is discussed, as well as the contamination issue. Preliminary diagnostics on the CCD aging under EUV radiations are exposed.

Article: Not available


Title: Polar Plume Anatomy: Results of a Coordinated Observation

Authors: Deforest, C. E., Hoeksema, J. T., Gurman, J. B., Thompson, B. J., Plunkett, S. P., Howard, R., Harrison, R. C., Hassler, D. M.

Journal: Solar Physics, v. 175, Issue 2, p. 393-410.

Publication Date: 10/1997

Abstract: Not Available

Article: Not available


Title: Comparison of solar flare emission measures from broadband soft X-ray and ultraviolet spectrograph observations

Authors: Cook, J.W.; Waljeski, K.; Moses, D.; Brueckner, G.E.

Journal: Adv. Space Res. (UK), Advances in Space Research, vol.17, no.4-5, p. 101-4

Publication Date: Feb.-March 1996

Abstract: Joint observations of a solar flare were obtained by the AS&E Imaging X-ray Telescope and the NRL High Resolution Telescope and Spectrograph (HRTS). We compare emission measures from soft X-ray and HRTS data. A small isolated X-ray loop close to the HRTS slit position has an emission measure Ne^2 Delta L of 3.5*10^29 cm(^- 5), compared to an emission measure of 2.7*10^29 cm(^-5) obtained from the intensity of flaring Fe XXI 1354 Angstrom plasma along the HRTS slit.

Article: Not Available


Title: Wide-angle stray-light reduction for a spaceborne optical hemispherical imager

Authors: Buffington, A., Jackson, B.V., Korendyke, C.M.

Journal: Applied Optics, vol.35, no.34, p. 6669-73

Publication Date: 1 Dec. 1996

Abstract: The authors describe a simple visible-light stray-background-reducing baffle, suitable for use on a stabilized interplanetary platform. The design is a corral-like enclosure with five concentric walls. The baffle reduces direct sunlight and reflections from illuminated portions of the spacecraft by a factor of 10/sup -12/, provided that all these lie beyond at least a hemisphere centered on the viewing aperture. With this condition these bright sources do not directly illuminate within the outermost wall of the corral, and diffraction over the wall tops is the dominant mechanism by which light reaches the corral interior. The authors present design calculations for such a corral, as well as a laboratory measurement confirming the basic design assumption.

Article: Not Available


Title: STEREO: a solar terrestrial event observer mission concept

Authors: Socker, D. G., Antiochos, S. K., Brueckner, G. E., Cook, J. W., Dere, K. P., Howard, R. A., Karpen, J. T., Klimchuk, J. A., Korendyke, C. M., Michels, D. J., Moses, J. D., Prinz, D. K., Sheeley, N. R., Jr, WU, S. T., Buffington, A., Jackson, B. V., Labonte, B., Lamy, P. L., Rosenbauer, H., Schwenn, R., Burlaga, L., Davila, J. M., Davis, J. M., Goldstein, B., Harris, H., Liewer, P. C., Neugebauer, M., Hildner, E., Pizzo, V. J., Moulton, N. E., Linker, J. A., Mikic, Z.

Journal: Proc. SPIE Vol. 2804, p. 50-61, Missions to the Sun, David M. Rust, Ed.

Publication Date: 11/1996

Abstract: A STEREO mission concept requiring only a single new spacecraft has been proposed. The mission would place the new spacecraft in a heliocentric orbit and well off the Sun- Earth line, where it can simultaneously view both the solar source of heliospheric disturbances and their propagation through the heliosphere all the way to the earth. Joint observations, utilizing the new spacecraft and existing solar spacecraft in earth orbit or L1 orbit would provide a stereographic data set. The new and unique aspect of this mission lies in the vantage point of the new spacecraft, which is far enough from Sun-Earth line to allow an entirely new way of studying the structure of the solar corona, the heliosphere and solar-terrestrial interactions. The mission science objectives have been selected to take maximum advantage of this new vantage point. They fall into two classes: those possible with the new spacecraft alone and those possible with joint measurements using the new and existing spacecraft. The instrument complement on the new spacecraft supporting the mission science objectives includes a soft x-ray imager, a coronagraph and a sun-earth imager. Telemetry rate appears to be the main performance determinant. The spacecraft could be launched with the new Med-Lite system.

Article: Not Available


Title: Measurement of near-specular visible-wavelength scattered light from two superpolished "coronagraph quality" mirrors

Authors: Korendyke, C.M., Socker, D.G., Brueckner, G.E., Schwenn, R.

Journal: Optical Engineering, vol.35, no.4, p. 1170-4

Publication Date: April 1996

Abstract: Several coronagraphs with mirror objectives are planned or have been constructed for terrestrial and space-based observatories. To justify the nontraditional choice of an internally occulted, reflective design for the inner coronal channel of the large-angle spectrometric coronagraph (LASCO) instrument constructed for the Solar Heliospheric Observatory satellite, the authors measured the near-specular (0.09 to 1.25 deg) scatter of two superpolished, spherical coronagraph mirrors with a unique geometry scatterometer. The visible stray light emanating from defect-free portions of the best mirror was measured to be 3.5*10(-7) B/Bo (coronal brightness relative to the mean solar brightness) at 2R (heliocentric distance in solar radii) and 2*10(-7) B/Bo at 3 R. These levels are well below typical sky brightnesses of 10(-5) B/Bo present at mountaintop observatories with clear skies. This stray light level would allow spectroscopic differencing observations of visible coronal emission lines (4*10(-8) B/Bo at 2 R for coronal green line features) well into the inner corona from a space-based platform. An aspheric mirror with better performance than this stray light has been installed in the LASCO flight instrument. The authors describe the scatterometer apparatus, detail the experimental results, and present a comparison between predicted coronagraph stray light levels and nominal coronal signal levels.

Article: Not Available


Title: The Large Angle Spectroscopic Coronagraph (LASCO)

Authors: Brueckner, G. E., Howard, R. A., Koomen, M. J., Korendyke, C. M., Michels, D. J., Moses, J. D., Socker, D. G., Dere, K. P., Lamy, P. L., Llebaria, A., Bout, M. V., Schwenn, R., Simnett, G. M., Bedford, D. K., Eyles, C. J.

Journal: Solar Physics, v. 162, p. 357-402.

Publication Date: 12/1995

Abstract: The Large Angle Spectroscopic Coronagraph (LASCO) is a three coronagraph package which has been jointly developed for the Solar and Heliospheric Observatory (SOHO) mission by the Naval Research Laboratory (USA), the Laboratoire dAstronomie Spatiale (France), the Max-Planck-Institut fur Aeronomie (Germany), and the University of Birmingham (UK). LASCO comprises three coronagraphs, C1, C2, and C3, that together image the solar corona from 1.1 to 30 Rs (C1: 1.1-3 Rs, C2: 1.5-6 Rs, and C3: 3.7-30 Rs). The C1 coronagraph is a newly developed mirror version of the classic internally-occulted Lyot coronagraph, while the C2 and C3 coronagraphs are externally occulted instruments. High-resolution imaging spectroscopy of the corona from 1.1 to 3 Rs can be performed with the Fabry-Perot interferometer in C1. High-volume memories and a high-speed microprocessor enable extensive on-board image processing. Image compression by a factor of about 10 will result in the transmission of 10 full images per hour.

Article: Not Available


Title: EIT: the Extreme Ultraviolet Imaging Telescope. Synoptic observations of small and large-scale coronal structures

Authors: Clette, F.; Delaboudiniere, J.-P.; Dere, K.P.; Cugnon, P.

Journal: Coronal Magnetic Energy Releases. Proceedings of the CESRA Workshop, p. 251-60

Publication Date: 1995

Abstract: The EIT will provide wide-field images of the corona and transition region, on the solar disc and up to 1 Rs above the limb. Its normal incidence multilayer-coated optics will select the spectral emission lines of four ions (Fe IX, 171 Angstrom; Fe XII, 195 Angstrom; Fe XV, 284 Angstrom; He II, 304 Angstrom), providing a sensitive temperature diagnostic in the range 6*10E4 to 3*10E6 K. This SOHO instrument will thus probe the coronal plasma on a global scale, as well as the underlying cooler and turbulent atmosphere. The EITs characteristics and performances are presented, and prospects for coordinated observations with ground-based radio observatories are outlined.

Article: Not Available


Title: Coronal structure and heating: comparison between SXT/Yohkoh observations of an active region and magnetogram

Authors: Cheng, C.-C.; Dere, K.P.; Wu, S.T.; Hagyard, M.J.; Hiei, E.

Journal: Adv. Space Res. (UK), Advances in Space Research, vol.17, no.4-5, p. 205-8

Publication Date: Feb.-March 1996

Abstract: We have studied the magnetic structure in AR 7150 (S09E06) observed on 29 April 1992 by the Soft X-Ray Telescope (SXT) on Yohkoh. The observed X-ray images are compared with force-free magnetic fields with different values of alpha, extrapolated from the MSFC photospheric magnetogram observed at the same time. The results show that the magnetic field of the active region is not potential. Different groups of loops are characterized by different values of alpha. Bright loops correspond to a field with large alpha, indicating twisting of the loop. However, there is no obvious correlation between the brightness of individual loops and the amount of twist. Further investigation of the magnetic state of the loop structure requires accurate nonlinear force-free calculations.

Article: Not Available


Title: Nonthermal velocities in the solar transition and coronal region observed with the High-Resolution Telescope and Spectrograph

Authors: O'Shea, E.; Doyle, J.G.; Dere, K.P.; Keenan, F.P.

Journal: Astron. Soc. Pac. Conf. Ser. (USA), Astronomical Society of the Pacific Conference Series, vol.109, p. 145-6

Publication Date: 1996

Abstract: Using data obtained from the fourth rocket flight of the NRL High-Resolution Telescope and Spectrograph estimates of nonthermal velocities have been calculated for spectral lines covering the wavelength range 10^4.2 to 10^6.2 K, that is, lines from the transition region and corona. Using the O IV line intensities at 1399 Angstrom and 1401 Angstrom in conjunction with theoretical line ratios we derived electron density along the whole slit length of the spectrograph. Also consiDered in this work are the redshifts and blueshifts of the different lines observed above quiet and coronal hole regions.

Article: Not Available


Title: A model for active region emission at centimeter wavelengths

Authors: Nindos, A.; Alissandrakis, C.E.; Gelfreikh, G.B.; Kundu, M.R.; Dere, K.P.; Korzhavin, A.N.; Bogod, V.M.

Journal: Solar Physics, vol.166, no.1, p. 55-87

Publication Date: June 1996

Abstract: Presents multi-frequency observations and model computations of the microwave emission of a solar active region. The radio observations were obtained with the RATAN-600 at several wavelengths between 0.8 and 31.6 cm and with the VLA at 6 and 20 cm. The active region was also observed in the EUV O IV lines by the HRTS instrument aboard the Space Shuttle Spacelab-2 mission. These lines are formed in the chromosphere-corona transition region and their intensity ratio is sensitive to pressure. Photospheric magnetograms provided both the longitudinal and the transverse component of the magnetic field. The microwave observations were checked against model computations taking into account both the free-free and the gyro-resonance emission mechanisms and using the pressure data from the O IV lines. The magnetic field was computed through constant- alpha force-free extrapolations of the longitudinal photospheric field. The authors computed both the flux from 2 to 20 cm and the spatial structure of the microwave emission at 6 and 20 cm. The comparison of the computed and observed flux spectra are used to estimate the magnetic field strength at the base of the transition region and in the low corona, as well as the values of the conductive flux and the height of the base of the transition region.

Article: Not Available


Title: Enhancing the Spatial Resolution of Solar Coronagraph Observations Using Dynamic Imaging

Authors: Zaccheo, T. S., Karovska, M., Cook, J. W., Howard, R. A., Brueckner, G. E., Korendyke, C. M., Schwenn, R.

Journal: Astrophysical Journal v.471, p.1058

Publication Date: 11/1996

Abstract: The Large Angle and Spectrometric Coronagraph (LASCO) C1 coronagraph on board the Solar and Heliospheric Observatory (SOHO) is designed to image the corona from 1.1 to 3.0 R. The resolution of C1 is defined by the size of its CCD pixels, which correxpond to 5.6" and not by the diffraction limit of the optical system, which may be as small as 3". The resolution of C1 can be imprfoved using the technique of "dynamic imaging" - the process of acquiring successie images of the same scene using subpixel displacements of the steerable primary mirror. We developed a technique we call the fractional pixel restoration (FPR) algorithm that utilizes these observations to construct an image with improved resolution. Simulations were used to test this algorithm and to explore its limitations. We also applied the direct co-addition and FPR algorithms to laboratory preflight images of a wire mesh grid. These results show that the resolution of the C1 coronagraph can be sugnificantly enhanced, even in the presence of noise and modes differences between successive images. In some cases, the results can even reach the diffraction limit of the telescope.

Article: Available from ADS


Title: Next-generation EUV imaging spectrometer for solar flare observations

Authors: Moses, J. D., Brueckner, G. E., Dere, K. P., Korendyke, C. M., Moulton, N. E., Prinz, D. K., Seely, J. F., Socker, D. G., Bruner, M. E., Lemen, J. R.

Journal: Proc. SPIE Vol. 2804, p. 260-273, Missions to the Sun, David M. Rust, Ed.

Publication Date: 11/1996

Abstract: The Naval Research Laboratory Skylab SO82A slitless spectrograph provided solar flare observations that have never been equaled in diagnostic capabilities for interpreting thermal flare physics. Improvements in detector technology, optics and optical coating technology, and almost two decades of analysis of SO82A data can be combined with the basic concept of an EUV objective grating spectrograph to build an instrument to address many of the remaining mysteries of solar flares. This next generation instrument incorporates two sets of two identical, orthogonally mounted slitless spectrographic Cassegrain telescopes. Each telescope consists of a multilayer coated, Wadsworth mount objective grating and multilayer coated spherical secondary mirror, a backside illuminated CCD detector is installed at the focal plane. The orthogonal mounting changes the dispersion direction by 90 degrees on the disk image, processing on the two resulting images allows recovery of the undispersed disk image and spectral line profiles. The resulting instrument will obtain high time cadence, spectrally-dispersed images with improved spatial resolution, dynamic range, signal-to-noise ratio, and velocity discrimination.

Article: Not Available


Title: LASCO spectrometric Lyot coronagraph tunable passband filter

Authors: Socker, D. G., Brueckner, G. E., Korendyke, C. M., Lilley, D. N., Steenson, J. H., Kohn, P. M., Lyons, G. M., Owens, M. L., Moulton, N. E., Moye, R. W., Schwenn, R., Hemmerich, P.

Journal: Proc. SPIE Vol. 2804, p. 126-140, Missions to the Sun, David M. Rust, Ed.

Publication Date: 11/1996

Abstract: Spectrometric and spectropolarimetric aspects of the Lyot coronagraph flown aboard the ESA/NASA SOlar Heliospheric Observatory (SOHO) are presented. The coronagraph is one of the three channels comprising the LASCO coronagraph and the only channel with spectroradiometric capabilities. Among the primary science objectives assigned to the Lyot coronagraph are the determination of the mechanisms responsible for the acceleration of the solar wind and the heating of the corona. Spectrometric and spectropolarimetric coronal observations made with the Lyot coronagraph are used in support of these and other objectives. We describe the Lyot instrument design from the imaging coronal spectrometer perspective. The rationale for use of a tunable Fabry-Perot interferometer as the spectral resolving eLement is outlined. The relationships between spectral resolving power, interferometer diameter, telescope entrance stop diameter and coronal field of view as it applies to LASCO is reviewed. Performance requirements imposed on the interferometer by the coronal source and the science objectives are described. The optical, mechanical, electronic and semi-automated control designs as well as the interferometer modes of operation are summarized. The actual flight model Fabry-Perot interferometer performance allows the instrument to operate with high luminosity and with finesse values high enough to provide approximately optimal passband widths and reasonable tunable ranges aBout useful spectral features. We conclude with some early results indicative of the flight performance of the instrument.

Article: Not Available


Title: EIT images of the EUV solar atmosphere

Authors: Portier-Fozzani, F.; Moses, J.D.; Delaboudiniere, J.P.; Gurman, J.B.; Clette, F.; Maucherat, A.

Journal: Astron. Soc. Pac. Conf. Ser. (USA), Astronomical Society of the Pacific Conference Series, vol.111, p. 402-6

Publication Date: 1996

Abstract: The Extreme-ultraviolet Imaging Telescope (EIT) was one of several instruments launched on board the SOHO (Solar and Heliospheric Observatory) satellite on 1995 December 2. It was stationed in a halo orbit around the L1 Earth-Sun Lagrangian point on 1996 February 14, and has already produced thousands of wide-field images of the low corona at 4 wavelengths (171, 195, 284 and 304 Angstrom). These wavelengths correspond to different emission lines (Fe IX-X, Fe XII, Fe XV and He II), formed over a wide range of plasma temperatures, from 8*10/sup 4/ K (transition region) to 2*10/sup 6/ K (quiet corona and active regions). In this respect, the EIT experiment is fully complementary to the Yohkoh mission which studies hot active corona. The first EIT images and movies reveal how this sensitive instrument will provide unprecedented information about the dynamics of small scale phenomena in the quiet solar corona and inside coronal holes. Results of a local deconvolution method, used to correct a grid pattern present in raw EIT images, are also presented.

Article: Not Available


Title: Ultraviolet observations of the structure and dynamics of an active region at the limb

Authors: Korendyke, C.M.; Dere, K.P.; Socker, D.G.; Brueckner, G.E.; Schmieder, B.

Journal: Astrophysical Journal, vol.443, no.2, pt.1, p. 869-77

Publication Date: 20 April 1995

Abstract: The structure and dynamics of active region NOAA 7260 at the limb has been studied using ultraviolet spectra and spectroheliograms obtained during the eighth rocket flight of the Naval Research Laboratory's High Resolution Telescope and Spectrograph (HRTS). The instrument configuration included a narrow-bandpass spectroheliograph to observe the Sun in the lines of C IV lambda 1550 and a tandem-Wadsworth mount spectrograph to record the profiles of chromospheric, transition region and coronal lines in the 1850-2670 Angstrom region. The combination of high spatial resolution and high spectral purity C IV slit jaw images with ultraviolet emission-line spectra corresponding allows examination of a variety of active region phenomena. A time series of spectroheliograms show large-scale loop systems composed of fine-scale threads with some extending up to 100 Mm above the limb. The proper motion of several supersonic features, including a surge were measured. The accelerated plasmas appear in several different geometries and environments. Spectrograph exposures were taken with the slit positioned at a range of altitudes above the limb and provide a direct comparison between coronal, transition region and chromospheric emission line profiles. The spectral profiles of chromospheric and transition region emission lines show line-of-sight velocities up to 70 km/s. These lower temperature, emission-line spectra show small-scale spatial and velocity variations which are correlated with the threadlike structures seen in C IV. Coronal lines of Fe XII show much lower velocities and no fine structure.

Article: Not Available


Title: Ultraviolet Jets and Bright Points in the Solar Chromosphere. I. Search for One-to-One Relationships

Authors: Cook, J. W.; Rutten, R. J.; Hoekzema, N. M.

Journal: Astrophysical Journal v.470, p.647

Publication Date: 10/1996

Abstract: Not Available

Article: Available from ADS


Title: Comparison of solar flare emission measures from broadband soft X-ray and ultraviolet spectrograph observations

Authors: Cook, J.W.; Waljeski, K.; Moses, D.; Brueckner, G.E.

Journal: Adv. Space Res. (UK), Advances in Space Research, vol.17, no.4-5, p. 101-4

Publication Date: Feb.-March 1996

Abstract: Joint observations of a solar flare were obtained by the AS&E Imaging X-ray Telescope and the NRL High Resolution Telescope and Spectrograph (HRTS). We compare emission measures from soft X-ray and HRTS data. A small isolated X-ray loop close to the HRTS slit position has an emission measure Ne^2 Delta L of 3.5*10^29 cm^(- 5), compared to an emission measure of 2.7*10^29 cm^( -5) obtained from the intensity of flaring Fe XXI 1354 Angstrom plasma along the HRTS slit.


Title: The coronal context of transition region explosive events

Authors: Moses, D.; Cook, J.W.

Journal: Space Sci. Rev. (Netherlands), Space Science Reviews, vol.70, no.1-2, p. 81-4

Publication Date: Oct. 1994

Abstract: Transition region explosive events are observed throughout the quiet Sun and represent an interesting local heating phenomenon. The coronal counterparts of these events, if they exist, were not observed in a sounding rocket campaign dedicated to this objective. The coronal instrument complement on the SOHO spacecraft provides an opportunity to extend this search for the coronal counterparts of the transition region explosive events, as well as to explore the correspondence of explosive events with large scale coronal structures, such as coronal dark lanes.

Article: Not Available


Title: EIT: Extreme-Ultraviolet Imaging Telescope for the SOHO Mission

Authors: Delaboudiniere, J.-P., Artzner, G. E., Brunaud, J., Gabriel, A. H., Hochedez, J. F., Millier, F., Song, X. Y., Au, B., Dere, K. P., Howard, R. A., Kreplin, R., Michels, D. J., Moses, J. D., Defise,  J. M., Jamar,  C., Rochus,  P., Chauvineau,  J. P., Marioge,  J. P., Catura,  R. C., Lemen, J. R., Shing, L., Stern, R. A., Gurman, J. B., Neupert, W. M., Maucherat, A., Clette, F., Cugnon, P., Van Dessel, E. L.

Journal: Solar Physics, v. 162, p. 291-312.

Publication Date: 12/1995

Abstract: The Extreme-ultraviolet Imaging Telescope (EIT) will provide wide-field images of the corona and transition region on the solar disc and up to 1.5 R above the solar limb. Its normal incidence multilayer-coated optics will select spectral emission lines from Fe IX (171 Angstrom), Fe XII (195 Angstrom), Fe XV (284 Angstrom), and He II (304 Angstrom) to provide sensitive temperature diagnostics in the range from 6*10E4K to 3*10E6 K. The telescope has a 45*45 arcmin field of view and 2.6 arcsec pixels which will provide approximately 5-arcsec spatial resolution. The EIT will probe the coronal plasma on a global scale, as well as the underlying cooler and turbulent atmosphere, providing the basis for comparative analyses with observations from both the ground and other SOHO instruments. The paper presents details of the EIT instrumentation, its performance and operating modes.

Article: Not Available


Title: Enhancing the spatial resolution of solar coronagraph images using dynamic imaging

Authors: Karovska, M., Zaccheo, T. S., Cook, J. W., Brueckner, G. E., Howard, R. A.

Journal: Proc. SPIE Vol. 2804, p. 175-184, Missions to the Sun, David M. Rust, Ed.

Publication Date: 11/1996

Abstract: The LASCO C1 mirror coronagraph onboard the SOHO satellite (launched on 2 December 1995) was designed to observe the fine structure of the solar corona from 1.1 to 3.0 R. Even though the optical resolution is approximately 3 arc sec, the nominal achieved resolution is set by the CCD pixel size of 5.6 arc sec. A pixel size of 1.5 arc sec or less is needed to obtain diffraction limited observations according to the Nyquist criteria, and therefore the actual coronagraph images are under sampled by a factor of 4. We have explored improving the spatial resolution of the LASCO C1 images using the technique of dynamic imaging. Successive images are obtained with sub-pixel displacements of the steerable primary mirror. Typically a set of 4 images is obtained with 1/2 pixel displacements in the x and y axes. Using simulated data we have studied the improvement resulting both from simple co-addition of the multiple observations, and from a deconvolution algorithm we call Fractional Pixel Restorations (FPR). We studied the effects in numerical simulations of noise, contrast variations, modest differences in the scene observed in the multiple images, etc. WE have also applied co-addition and the FPR algorithm to laboratory pre-flight images of a wire mesh target, which significantly improved the resolution. Using dynamic imaging with 16 images and 1/4 pixel steps, it would in principle be possible to reach the diffraction limit of the telescope in some circumstances (low noise, sufficient image contrast, no temporal changes in the observed scene, a well characterized instrumental point response function). By the time of this meeting we hope to have high resolution solar images from the LASCO C1 telescope to show. LASCO is a cooperative project of an international group of scientists at the Naval Research Laboratory, Washington, DC, the Max- Planck Institute fur Aeronomie, Germany, the Laboratoire d'Astronomie Spatiale, France, and the Space Research Group at the University of Birmingham, Great Britain.

Article: Not Available


Title: Validation of the UARS solar ultraviolet irradiances: comparison with the ATLAS 1 and 2 measurements

Authors: Woods, T.N., Prinz, D.K., Rottman, G.J., London, J., Crane, P.C., Cebula, R.P., Hilsenrath, E., Brueckner, G.E., Andrews, M.D., White, O.R., VanHoosier, M.E., Floyd, L.E., Herring, L.C., Knapp, B.G., Pankratz, C.K., Reiser, P.A.

Journal: Journal of Geophysical Research, vol.101, no.D6, p. 9541-69

Publication Date: April 1996

Abstract: The measurements of the solar ultraviolet spectral irradiance made by the two Upper Atmosphere Research Satellite (UARS) solar instruments, Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) and SOLar Stellar Irradiance Comparison Experiment (SOLSTICE), are compared with same-day measurements by two solar instruments on the Shuttle ATmospheric Laboratory for Applications and Science (ATLAS) missions, ATLAS SUSIM and Shuttle Solar Backscatter UltraViolet (SSBUV) experiment. These measurements from the four instruments agree to within the 2 sigma uncertainty of any one instrument, which is 5 to 10% for all wavelengths above 160 nm and for strong emission features below 160 nm. Additionally, the long-term relative accuracy of the two UARS data sets is better than the original 2% goal, especially at wavelengths greater than 160 nm. This level of agreement is credited to accurate preflight calibrations coupled with comprehensive inflight calibrations to track instrument degradation. Two solar irradiance spectra, 119 to 410 nm, are presented, the first combines observations from UARS SUSIM and UARS SOLSTICE taken on March 29, 1992, during the ATLAS 1 mission, and the second combines spectra for April 15, 1993, during the ATLAS 2 mission. The ATLAS 1 mission coincided with the initial decline from the maximum of solar cycle 22 when solar activity was relatively high. The ATLAS 2 mission occurred somewhat later during the declining phase of the solar cycle 22 when solar activity was more moderate.

Article: Not Available


Title: Ozone variability in the upper stratosphere during the declining phase of the solar cycle 22

Authors: Chandra, S., Froidevaux, L., Waters, J.W., White, O.R., Rottman, G.J., Prinz, D.K., Brueckner, G.E.

Journal: Geophysical Research Letters, vol.23, no.21, p. 2935-8

Publication Date: Oct. 1996

Abstract: Recent studies of the solar cycle variation of ozone have shown that the response of ozone in the upper stratosphere to solar UV variation, as inferred from the SBUV (solar backscatter ultraviolet) type measurements, is about a factor of two greater than estimated from 2-D photochemical models. Because of potential errors in accounting for the long term instrument drift in the SBUV type of measurements, the significance of this discrepancy is difficult to quantify. In this paper, ozone measurements from the Microwave Limb Sounder (MLS) and the solar irradiance measurements from the Solar Stellar Irradiance Comparison Experiment (SOLSTICE) and the Solar Ultraviolet Irradiance Monitor (SUSIM) onboard the Upper Atmosphere Research Satellite (UARS) are analyzed to estimate the upper stratosphere ozone response to changes in the solar UV irradiance. During the three year period of UARS measurements, analyzed for the declining phase of the solar cycle 22, the solar irradiance in the 200-205 nm range decreased by about 5% from a near solar maximum to a near solar minimum level. During the same period, ozone mixing ratio measured from the MLS instrument decreased by about 2-4% in the 0.7-3 hPa region. In the upper stratosphere, the general characteristics of the MLS time series are similar to those inferred from the NOAA-11 SBUV/2 measurements. The SBUV/2 trends above 1.5 hPa, however, are significantly greater than those derived from the MLS data. The UARS data suggest that the long term solar UV response of ozone in the upper stratosphere is unDerestimated by 2-D photochemical models as in previous studies based on the SBUV type measurements.

Article: Not Available


Title: Solar ultraviolet spectral-irradiance observations from the SUSIM-UARS experiment

Authors: Brueckner, G.E., Floyd, L.E., Lund, P.A., Prinz, D.K., Van Hoosier, M.E.

Journal: Metrologia (France), Metrologia, vol.32, no.6, p. 661-5

Publication Date: May 1996

Abstract: The Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) instrument on board the Upper Atmosphere Research Satellite (UARS) has measured solar ultraviolet spectral-irradiance values since October 1991. The calibration and tracking methods are described. The intensity values have a precision of 1% at wavelengths longer than 200 nm. Short-term ultraviolet (UV) variability is correlated with other chromospheric indices at wavelengths shorter than 280 nm. At longer wavelengths, this correlation changes gradually into an anticorrelation. There exists a long-term solar-cycle component at all wavelengths, which seems to be independent of the rotational modulation. The variability in the integrated UV from 110 nm to 300 nm amounts to 33% of the variability in the total solar irradiance.

Article: Not Available


Title: Calibration of the solar ultraviolet spectral irradiance monitor (SUSIM) on ATLAS-2

Authors: Andrews, M.D., Van Hoosier, M.E.

Journal: Metrologia (France), Metrologia, vol.32, no.6, p. 629-31

Publication Date: May 1996

Abstract: Uncertainty in the calibration of the Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) produces an uncertainty in the measurement of solar irradiance. The three primary sources of uncertainty in the irradiance during the ATLAS-2 mission are from wavelength determination, irradiance standard, and the in-flight ageing correction. The wavelength determination leads to an uncertainty in the irradiance in both the calibration data and the solar observations. The first effect is important only at short wavelengths. The second effect is important wherever the solar spectrum is steep but can be eliminated by summing over spectral features. The uncertainty in the irradiance standard is about 2%. The ageing correction produces a wavelength-dependent uncertainty which is typically 1% to 2%. The total 1 sigma uncertainty in the ATLAS-2 SUSIM irradiance measurement (130 nm to 410 nm) is 2% to 4%. For the ATLAS-3 mission, the performance of the instrument has been enhanced by an improved wavelength determination, a new D2 lamp and power supply, and the addition of a filter wheel in place of a fixed entrance filter.

Article: Not available


Title: Solar wind research with the Large Angle Spectroscopic Coronagraph (LASCO) experiment onboard the Solar and Heliospheric Observatory (SOHO) satellite

Authors: Brueckner, G. E.

Journal: Solar Wind 8, p. 70

Publication Date: 06/1995

Abstract: The ESA-NASA satellite, to be launched in October 1995, carries three nested coronagraphs, which will image the solar corona from 1.1 R(solar radii) to 30 R(solar radii). Super polished mirrors have been developed for the design of a mirror Lyot coronagraph which has a straylight level comparable with the coronal intensity from 1.1 R, to 30 R(solar radii) Coronal details can be imaged with a spatial resolution of 6 arc seconds. A Fabry Perot interferometer with a spectral resolution of 0.7 A at the wavelength of the green coronal emission line will allow the simultaneous construction of spectra over the entire field of view of 10(exp 6) pixels. The middle coronagraph (1.5 R(solar radii) - 6 R(solar radii)) and the outer coronagraph (3 R(solar radii) - 30 R(solar radii)) are externally occulted lens Lyot coronagraphs. Their straylight level 10(exp -11) B(meansolar brightness) and 10(exp -12) B(mean solar brightness) respectively is an order of magnitude smaller than the intensity of the corona. The sensitivity of LASCO to distinguish between different solar wind acceleration mechanisms will be discussed as well as its ability to discern different CME models.

Article: Not available


Title: Comparison of CME masses and kinetic energies near the Sun and in the inner heliosphere

Authors: Webb, D. F., Howard, R. A., Jackson, B. V.

Journal: Solar Wind 8, p. 97

Publication Date: 06/1995

Abstract: Masses have now been determined for many of the CMEs observed in the inner heliosphere by the HELIOS 1 and 2 zodiacal light photometers. The speed of the brightest material of each CME has also been measured so that, for events having both mass and speed determinations, the kinetic energies of the CMEs are estimated. We compare the masses and kinetic energies of the individual CMEs measured in the inner heliosphere by HELIOS and near the Sun from observations by the SOLWIND (1979-1983) and SMM coronagraphs (1980). Where feasible we also compare the speeds of the same CMEs. We find that the HELIOS masses and energies tend to be somewhat larger by factors of 2-5 than those derived from the coronagraph data. We also compare the distribution of the masses and energies of the HELIOS and coronagraph CMEs over the solar cycle. These results provide an important baseline for observations of CMEs from coronagraphs, from the ISEE-3/ICE, WIND and Ulysses spacecraft and in the future from SOHO.

Article: Not available


Title: Ground-based observations of the corona in the visible and NIR spectral ranges

Authors: Epple, A., Schwenn, R.

Journal: Solar Wind 8, p. 60

Publication Date: 06/1995

Abstract: Since late 1993 we have been using a mirror coronagraph on Pic du Midi (PICO) to observe the solar emission corona in several spectral lines of (FE-X), (FE-XIII), and (FE-XIV). For good meteorological conditions the diffuse corona and coronal holes in between can be seen out to 1.2 solar mass for sun center. Active regions can be mapped to bond 1.5 solar mass in the green and infrared lines. Recent observations of PICO are presented.

Article: Not available


Title: Mass ejections from the sun and their interplanetary counterparts

Authors: Schwenn, R.

Journal: Solar Wind 8, p. 45

Publication Date: 06/1995

Abstract: Since the first observations of solar mass ejection events in the early seventies from OSO 7 and Skylab a few thousand of these remarkable dynamic incidents have been observed by now, covering about two full solar activity cycles. The mass ejecta include mainly hot coronal plasma, plus cold prominence material in variable amounts. The ejecta are often recognised in the form of interplanetary plasma clouds detected in the distant solar wind by appropriately located spacecraft. Clouds which have been energetic enough to drive large scale interplanetary shock waves can be identified most readily, but clouds without associated shocks do also occur. The plasma clouds are characterized by a variety of signatures indicating that they actually originate from injections of different material into the ambient solar wind. Usually only a few of the signatures are found simultaneously. Apparently the bidirectional streaming of halo electrons is a most reliable criterion, indicating a magnetic bottle or plasmoid topology of the clouds. The discussion of the most recent discoveries in this context will show that quite a few crucial problems still remain to be addressed by the upcoming SOHO mission.

Article: Not available


Title: The coronal aureole.

Authors: Fang, Y., Lamy, P.L., Llebaria, A.

Journal: Astron. Astrophys. 293, 208-214 (1995)

Publication Date: 01/1995

Abstract: We calculate the coronal aureole using the Fourier transform and we show that the outer corona significantly contributed to its value. We further propose a new, simple mathematical method which allows to derive the scattering function directly from two observational images taken successively during an eclipse. This method is successfully tested using different models of the scattering function.

Article: Available from ADS


Title: The LASCO Database at LAS

Authors: Mathieu, C., Llebaria, A., Lamy, P.

Journal: Vistas in Astronomy, v. 39, p. 109-110.

Publication Date: 00/1995

Abstract: Not Available

Article: Not Available


Title: Laboratory measurements of light scattering by dust particles

Authors: Combet, P., Lamy, P.L.

Journal: Advances in Space Research, v. 15, Issue 10, p. 65-68

Publication Date: 00/1995

Abstract: Not Available

Article: Not Available


Title: Discrimination of Point-like Objects in Astronomical Images using Surface Curvature

Authors: Llebaria, A., Lamy, P., Malburet, P.

Journal: Astronomical Data Analysis Software and Systems IV, ASP Conference Series, Vol. 77, 1995, R.A. Shaw, H.E. Payne, and J.J.E. Hayes, eds., p. 484.

Publication Date: 00/1995

Abstract: A new method for the discrimination of point-like objects in astronomical images is presented. The method makes use of the surface curvature of the image, without any a priori knowledge of the shape of the point-like objects.

Article: Available from ADS


Title: The O IV and S IV intercombination lines in solar and stellar ultraviolet spectra

Authors: Cook, J. W.; Keenan, F. P.; Dufton, P. L.; Kingston, A. E.; Pradhan, A. K.; Zhang, H. L.; Doyle, J. G.; Hayes, M. A.

Journal: Astrophysical Journal, Part 1, vol. 444, no. 2, p. 936-942

Publication Date: 05/1995

Abstract: New calculations of O IV electron density diagnostic emission-line ratios involving the 1399.8, 1401.2, 1404.8, and 14076.4 A transitions are presented. A comparison of these calculations with observational data from a quiet solar region, a sunspot, and an active region obtained with the High Resolution Telescope and Spectrograph (HRTS), two flares observed with the SO82B spectrograph on board Skylab, and Hubble Space Telescope (HST) observations by the Goddard High Resolution Spectrograph (GHRS) of Capella, gives good results using the ratio R1 = I(1407.4 A)/I(1401.2 A). However, the electron density obtained using the ratio R2 = I(1407.4 A)/I(1404.8 A) is often an order of magnitude smaller. The O IV 1404.8 A line is blended with the S IV 1404.8 A line, and we investigate whether this ratio may still be used as a density diagnostic if the S IV 1406.1 A line intensity is used to correct for the presence of S IV 1404.8 A, using previous S IV calculations by Dufton et al. We still find systematic differences compared to density determinations from line ratios that do not involve the O IV 1404.8 A line, which we suggest are due to errors in earlier theoretical calculations of the S IV atomic data, and also possibly to previously unconsiDered fluorescent pumping of the upper level of the S IV 1404.8 A transition.

Article: Available from ADS


Title: Solar UV irradiance variability during the declining phase of the solar cycle 22

Authors: Chandra, S.; Lean, J.L.; White, O.R.; Princz, D.K.; Rottman, G.J.; Brueckner, G.E.

Journal: Geophysical Research Letters, vol.22, no.18, p. 2481-4

Publication Date: 15 Sept. 1995

Abstract: The SUSIM (Solar Ultraviolet Spectral Irradiance Monitor) and the SOLSTICE (Solar Stellar Irradiance Comparison Experiment) instruments on the UARS (Upper Atmosphere Research Satellite) have been making continuous measurements of the solar UV flux in the spectral range 115-420 nm since October 1991. This period, characterized as the declining phase of solar cycle 22, shows a transition from near maximum to near minimum solar activity levels. During this period, the solar UV flux at Lyman alpha decreased by about 45% from a mean solar maximum value of about 9 mW/m^2, and the integrated solar flux between 200-205 nm decreased by about 5% from a mean value of about 47 mW/m^2. Using the MgII index as a proxy of solar UV irradiance variability, it is shown that the temporal relationship of the UARS solar Lyman alpha irradiance and the MgII index during solar cycle 22 is significantly different than during solar cycle 21, inferred from the SME (Solar Mesosphere Explorer) Lyman alpha measurements. Moreover, during solar cycle 22, the scale factor for solar Lyman alpha irradiance (% change for 1% change in MgII index) is about 1.5 times larger for long term changes than for changes over the time scale of a solar rotation. Unlike Lyman alpha , the scale factor for the UV flux in the 200-205 nm wavelength range, is close to unity both for the rotational and longer time scales.

Article: Not Available