Search Publications
Nonlinear Force-Free and Potential-Field Models of Active-Region and Global Coronal Fields during the Whole Heliosphere Interval
Canou, A.; Amari, T.; Petrie, G. J. D.
Between 24 March 2008 and 2 April 2008, the three active regions (ARs) NOAA 10987, 10988 and 10989 were observed daily by the Synoptic Optical Long-term Investigations of the Sun (SOLIS) Vector Spectro-Magnetograph (VSM) while they traversed the solar disk. We use these measurements and the nonlinear force-free magnetic field code XTRAPOL to recon…
Photospheric Magnetic Evolution in the WHI Active Regions
Welsch, B. T.; McTiernan, J. M.; Christe, S.
Sequences of line-of-sight (LOS) magnetograms recorded by the Michelson Doppler Imager are used to quantitatively characterize photospheric magnetic structure and evolution in three active regions that rotated across the Sun's disk during the Whole Heliosphere Interval (WHI), in an attempt to relate the photospheric magnetic properties of these ac…
Relationship between the Parameters of Coronal Holes and High-Speed Solar Wind Streams over an Activity Cycle
Obridko, V. N.; Shelting, B. D.
The comparison of the brightness and area of coronal holes (CH) to the solar wind speed, which was started by Obridko et al. (Solar Phys.260, 191, 2009a) has been continued. While the previous work was dealing with a relatively short time interval 2000 - 2006, here we have analyzed the data on coronal holes observed in the Sun throughout activity …
Location of Decimetric Pulsations in Solar Flares
Vilmer, Nicole; Benz, Arnold O.; Battaglia, Marina
This work investigates the spatial relation between coronal X-ray sources and coherent radio emissions, both generally thought to be signatures of particle acceleration. Two limb events were selected during which the radio emission was well correlated in time with hard X-rays. The radio emissions were of the type of decimetric pulsations as determ…
Comparison of Nonlinear Force-Free Field and Potential Field in the Quiet Sun
Zhang, H. Q.; Su, J. T.; Liu, S.
In this paper, a potential field extrapolation and three nonlinear force-free (NLFF) field extrapolations (optimization, direct boundary integral (DBIE), and approximate vertical integration (AVI) methods) are used to study the spatial configuration of magnetic field in the quiet Sun. It is found that differences in the computed field strengths am…
Toward Waveform Heliotomography: Observing Interactions of Helioseismic Waves with a Sunspot
Zhao, Junwei; Kosovichev, Alexander G.; Ilonidis, Stathis
We investigate how helioseismic waves that originate from effective point sources interact with a sunspot. These waves are reconstructed from observed stochastic wavefields on the Sun by cross-correlating photospheric Doppler-velocity signals. We select the wave sources at different locations relative to the sunspot, and investigate the p- and f-m…
Solar Spectral Irradiance Variations in 240 - 1600 nm During the Recent Solar Cycles 21 - 23
Weber, M.; Pagaran, J.; Floyd, L. E. +2 more
Regular solar spectral irradiance (SSI) observations from space that simultaneously cover the UV, visible (vis), and the near-IR (NIR) spectral region began with SCIAMACHY aboard ENVISAT in August 2002. Up to now, these direct observations cover less than a decade. In order for these SSI measurements to be useful in assessing the role of the Sun i…
Non-Varying Granulation and Photospheric Network During the Extended 2007 - 2009 Solar Minimum
Utz, D.; Hanslmeier, A.; Muller, R.
We have analysed the wide band images taken by Hinode/SOT, in a blue continuum window and in the G-band, more or less on a daily basis in the frame of the synoptic program, to investigate the variation of the solar granulation and of the photospheric network with the activity cycle. A particular attention has been given to disentangle solar effect…
Multiwavelength Study on Solar and Interplanetary Origins of the Strongest Geomagnetic Storm of Solar Cycle 23
Kumar, Pankaj; Uddin, Wahab; Manoharan, P. K.
We study the solar sources of an intense geomagnetic storm of solar cycle 23 that occurred on 20 November 2003, based on ground- and space-based multiwavelength observations. The coronal mass ejections (CMEs) responsible for the above geomagnetic storm originated from the super-active region NOAA 10501. We investigate the Hα observations of the fl…
The Global Context of Solar Activity During the Whole Heliosphere Interval Campaign
Plunkett, S. P.; Webb, D. F.; Mandrini, C. H. +9 more
The Whole Heliosphere Interval (WHI) was an international observing and modeling effort to characterize the 3-D interconnected "heliophysical" system during this solar minimum, centered on Carrington Rotation 2068, March 20 - April 16, 2008. During the latter half of the WHI period, the Sun presented a sunspot-free, deep solar minimum type face. B…