Search Publications
A Note on Saturation Seen in the MDI/SOHO Magnetograms
Liu, Y.; Scherrer, P. H.; Norton, A. A.
A type of saturation is sometimes seen in sunspot umbrae in MDI/SOHO magnetograms. In this paper, we present the underlying cause of such saturation. By using a set of MDI circular polarization filtergrams taken during an MDI line profile campaign observation, we derive the MDI magnetograms using two different approaches: the on-board data process…
Dissipation of Standing Slow Magnetoacoustic Waves in Hot Coronal Loops
Sigalotti, L. Di G.; Mendoza-Briceño, C. A.; Luna-Cardozo, M.
The damping of standing slow waves in hot (T>6 MK) coronal loops of semicircular shape is revisited in both the linear and nonlinear regimes. Dissipation by thermal conduction, compressive viscosity, radiative cooling, and heating are examined for nonstratified and stratified loops. We find that for typical conditions of hot SUMER loops, therma…
Multi-Wavelength Signatures of Magnetic Reconnection of a Flare-Associated Coronal Mass Ejection
Joshi, Bhuwan; Veronig, Astrid M.; Manoharan, P. K. +2 more
The evolution of an X2.7 solar flare, that occurred in a complex βγδ magnetic configuration region on 3 November 2003 is discussed by utilizing a multi-wavelength data set. The very first signature of pre-flare coronal activity is observed in radio wavelengths as a type III burst that occurred several minutes prior to the flare signature in Hα. Th…
Coronal Magnetic Connectivity and EUV Dimmings
Harra, Louise K.; Wang, Jingxiu; Zhang, Yuzong +3 more
Coronal dimming can be considered to be a disk signature of front-side coronal mass ejections (CMEs) (Thompson et al.: 2000, Geophys. Res. Lett.27, 1431). The study of the magnetic connectivity associated with coronal dimming can shed new light on the magnetic nature of CMEs. In this study, four major flare-CME events on 14 July 2000, 28 October 2…
Observation of Interactions and Eruptions of Two Filaments
Zhang, Hongqi; Liu, Yu; Wang, Haimin +4 more
We present new observations of the interactions of two close, but distinct, Hα filaments and their successive eruptions on 5 November 1998. The magnetic fields of the filaments are both of the sinistral type. The interactions between the two filaments were initiated mainly by an active filament of one of them. Before the filament eruptions, two da…
Comparison of Large-Scale Flows on the Sun Measured by Time-Distance Helioseismology and Local Correlation Tracking
Zhao, Junwei; Kosovichev, Alexander G.; Švanda, Michal
We present a direct comparison between two different techniques: time-distance helioseismology and a local correlation tracking method for measuring mass flows in the solar photosphere and in a near-surface layer. We applied both methods to the same dataset (MDI high-cadence Dopplergrams covering almost the entire Carrington rotation 1974) and com…
Solar Trans-equatorial Activity
Harra, Louise K.; Wang, Jingxiu; Zhang, Yuzong +3 more
We have found that solar flares in NOAA active region (AR) 10696 were often associated with large-scale trans-equatorial activities. These trans-equatorial activities appeared to be very common and manifest themselves through i) the formation and eruption of trans-equatorial loops (TELs), ii) the formation and eruption of trans-equatorial filament…
Spectral Diagnostics of the Magnetic Field Orientation in a Prominence Observed with SOHO/SUMER
Heinzel, P.; Anzer, U.; Schmieder, B. +1 more
During several campaigns focused on prominences we have obtained coordinated spectral observations from the ground and from space. The SOHO/SUMER spectrometer allows us to observe, among others, the whole Lyman series of hydrogen, while the Hα line was observed by the MSDP spectrograph at the VTT. For the Lyman lines, non-LTE radiative-transfer co…
RHESSI Microflares: I. X-Ray Properties and Multiwavelength Characteristics
Veronig, A. M.; Hanslmeier, A.; Stoiser, S. +1 more
We study the general X-ray and multiwavelength characteristics of microflares of GOES class A0.7 to B7.4 (background subtracted) detected by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) on 26 September 2003 comparing them with the properties of regular flares. All the events for which X-ray imaging was feasible originated in o…
Solar Oscillation Frequency Changes on Time Scales of Nine Days
Hill, F.; Jain, K.; Tripathy, S. C. +1 more
We establish that global solar p-mode frequencies can be measured with sufficient precision on time scales as short as nine days to detect activity-related shifts. Using ten years of GONG data, we report that mode-mass and error-weighted frequency shifts derived from nine days are significantly correlated with the strength of solar activity and ar…