Search Publications
Measuring the Physical Properties of the Solar Corona: Results from SUMER/SOHO and TRACE
Warren, H. P.
Using SUMER observations taken above the limb of a quiet region we derive electron temperatures, emission measures, and absolute elemental abundances. This analysis, which uses recently published ionization balance calculations and the latest solar photospheric abundances, indicates that the low-FIP elements are enriched by a factor of 2.3±0.7 in …
Do EUV Nanoflares Account for Coronal Heating?
Aschwanden, Markus J.
Recent observations with EUV imaging instruments such as SOHO/EIT and TRACE have shown evidence for flare-like processes at the bottom end of the energy scale, in the range of Eth≈1024-1027 erg. Here we compare these EUV nanoflares with soft X-ray microflares and hard X-ray flares across the entire energy range. Fr…
LASCO observations of the coronal rotation
Simnett, G. M.; Schwenn, R.; Lamy, P. L. +3 more
The near-rigid rotation of the corona above the differential rotation of the photosphere has important implications for the form of the global coronal magnetic field. The magnetic reconfiguring associated with the shear region where the rigidly-rotating coronal field lines interface with the differentially-rotating photospheric field lines could p…
Non-Uniqueness of Atmospheric Modeling
Judge, Philip G.; McIntosh, Scott W.
We focus on the deceptively simple question: how can we use the emitted photons to extract meaningful information on the transition region and corona? Using examples, we conclude that the only safe way to proceed is through forward models. In this way, inherent non-uniqueness is handled by adding information through explicit physical assumptions a…
Observations of Transition Region Plasma
Brekke, Pâl
Recent space missions have changed our view of the solar transition region. In particular the ESA/NASA Solar and Heliospheric Observatory (SOHO) and NASA's TRACE satellite have provided a unique opportunity to explore the solar atmosphere in detail. The combination of high spatial, spectral and temporal observations has made it possible to derive …
Electron density and temperature structure of two limb active regions observed by SOHO-CDS
Young, P. R.; Mason, H. E.; Landi, E. +1 more
The analysis of two active regions on the limb using observations from SOHO-CDS allows us to determine the electron density and temperature distribution of the coronal emission. We find that the active regions have hot cores (3×106 K) with larger cooler (106 K) loop structures extending above the limb. The electron number den…
SOHO Observations of the Structure and Dynamics of Sunspot Region Atmospheres
Kjeldseth-Moe, O.; Haugan, S. V. H.; Brekke, P. +2 more
We present results from a study of the spatial distributions of line emission and relative line-of-sight velocity in the atmosphere above 17 sunspot regions, from the chromosphere, through the transition region and into the corona, based on simultaneous observations of ten EUV emission lines with the Coronal Diagnostic Spectrometer - CDS on SOHO. …
Multi-wavelength observations of the onset phase of a coronal mass ejection
Thompson, B. J.; Inhester, B.; Harrison, R. A. +6 more
The structure and dynamics of the initial phases of a coronal mass ejection (CME) seen in soft X-ray, extreme ultraviolet and optical emission are described. The event occurred on the SW limb of the Sun in active region AR 8026 on 9 April 1997. Just prior to the CME there was a class C1.5 flare. Images taken with the Extreme Ultraviolet Imaging Te…
Anomalous Line Shifts From Local Intensity Gradients on the Soho/cds NIS Detector
Haugan, S. V. H.
Line shifts for some emission lines on the SOHO/CDS NIS detector appear to be strongly correlated with local intensity gradients along the slit in a way that seems impossible to explain with a physical solar model. Line widths also show a correlation with local intensity gradients. The most plausible instrumental explanation seems to be an ellipti…
Evidence for non-potential magnetic fields in the quiet Sun
Chae, Jongchul; Woodard, M. F.
A comparison of BBSO Hα centerline filtergrams and videomagnetograms was made to investigate the existence of non- potential magnetic fields in the quiet Sun near magnetic network. We use the fibril structure in the Hα images as a proxy for the horizontal chromospheric magnetic field which we compare with the horizontal field obtained by potential…