Search Publications
What is Moss?
Fletcher, L.; Schrijver, C. J.; De Pontieu, B. +3 more
TRACE observations of active regions show a peculiar extreme ultraviolet (EUV) emission over certain plage areas. Termed `moss' for its spongy, low-lying, appearance, observations and modeling imply that the phenomenon is caused by thermal conduction from 3-5 MKcoronal loops overlying the plage: moss is the upper transition region emission of hot …
Does Magnetic Flux Submerge at Flux Cancelation Sites?
Schrijver, Carolus J.; Harvey, Karen L.; Jones, Harrison P. +1 more
Simultaneous measurements of the magnetic fields in the photosphere and chromosphere were used to investigate if magnetic flux is submerging at sites between adjacent opposite polarity magnetic network elements in which the flux is observed to decrease or `cancel'. These data were compared with chromospheric and coronal intensity images to establi…
Variations of Photospheric Magnetic Field Associated with Flares and CMEs
Kosovichev, A. G.; Zharkova, V. V.
Using high-cadence magnetograms from the SOHO/MDI we have investigated variations of the photospheric magnetic field during solar flares and CMEs. In the case of a strong X-class flare of May 2, 1998, we have detected variations of magnetic field in a form of a rapidly propagating magnetic wave. During the impulsive phase of the flare we have obse…
Simulations of small-scale explosive events on the Sun
Innes, D. E.; Tóth, G.
Small-scale explosive events or microflares occur throughout the chromospheric network of the Sun. They are seen as sudden bursts of highly Doppler-shifted spectral lines of ions formed at temperatures in the range 2×104−5×105 K. They tend to occur near regions of cancelling photospheric magnetic fields and are thought to be directly associated wi…
Observation of a 3d Magnetic Null Point in the Solar Corona
Filippov, Boris
A saddle-like structure is clearly discerned in SOHO EIT images in the Fe wavebands in the active region NOAA 8113, from 6 to 10 December 1997, when the active region reached the solar limb. It appears after the emergence of a small patch of parasitic polarity near the footpoints of the loops forming the outer boundary of an arcade. There is a 3D …
On the sunspot transition region
Wilhelm, K.; Fredvik, T.; Kjeldseth-Moe, O. +2 more
The EUV line emission and relative line-of-sight velocity in the transition region between the chromosphere and corona of 36 sunspot regions are investigated, based on observations with the Coronal Diagnostic Spectrometer - CDS and the Solar Ultraviolet Measurements of Emitted Radiation - SUMER on the Solar and Heliospheric Observatory - SOHO. The…
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…