Search Publications
Prominence Eruptions and Coronal Mass Ejection: A Statistical Study Using Microwave Observations
Howard, R. A.; Gopalswamy, N.; Shibasaki, K. +3 more
We present the results of a statistical study of a large number of solar prominence events (PEs) observed by the Nobeyama Radioheliograph. We studied the association rate, relative timing, and spatial correspondence between PEs and coronal mass ejections (CMEs). We classified the PEs as radial and transverse, depending on whether the prominence mo…
Evidence for the Formation of a Large-Scale Current Sheet in a Solar Flare
Holman, Gordon D.; Sui, Linhui
We present X-ray evidence for the formation of a large-scale current sheet in a flare observed by the Ramaty High-Energy Solar Spectroscopic Imager on 2002 April 15. The flare occurred on the northwest limb, showing a cusp-shaped flare loop in the rise phase. When the impulsive rise in hard X-rays (>25 keV) began, the cusp part of the coronal s…
The Relationship Between X-Ray Radiance and Magnetic Flux
Johns-Krull, Christopher M.; Pevtsov, Alexei A.; Longcope, Dana W. +4 more
We use soft X-ray and magnetic field observations of the Sun (quiet Sun, X-ray bright points, active regions, and integrated solar disk) and active stars (dwarf and pre-main-sequence) to study the relationship between total unsigned magnetic flux, Φ, and X-ray spectral radiance, LX. We find that Φ and LX exhibit a very nearly…
On the Interaction between Convection and Magnetic Fields
Cattaneo, Fausto; Emonet, Thierry; Weiss, Nigel
Turbulent convection in the solar photosphere can act as a small-scale dynamo, maintaining a disordered magnetic field that is locally intense. On the other hand, convection is inhibited in the presence of a strong, externally imposed magnetic field, as for instance, in a sunspot. Large-scale, three-dimensional, numerical experiments on highly non…
Dynamical and Physical Properties of a Post-Coronal Mass Ejection Current Sheet
Lin, Jun; Raymond, John C.; Li, Jing +3 more
In the eruptive process of the Kopp-Pneuman type, the closed magnetic field is stretched by the eruption so much that it is usually believed to be ``open'' to infinity. Formation of the current sheet in such a configuration makes it possible for the energy in the coronal magnetic field to quickly convert into thermal and kinetic energies and cause…
Direct Detection of a Coronal Mass Ejection-Associated Shock in Large Angle and Spectrometric Coronagraph Experiment White-Light Images
Wu, S. T.; Howard, R. A.; Vourlidas, A. +2 more
The Large Angle and Spectrometric Coronagraph Experiment (LASCO) C2 and C3 coronagraphs recorded a unique coronal mass ejection (CME) on 1999 April 2. The event did not have the typical three-part CME structure and involved a small-filament eruption without any visible overlying streamer ejecta. The event exhibited an unusually clear signature of …
Identification of Solar Sources of Major Geomagnetic Storms between 1996 and 2000
Zhang, J.; Bothmer, V.; Howard, R. A. +1 more
This paper presents identification of solar coronal mass ejection (CME) sources for 27 major geomagnetic storms (defined by disturbance storm timeindex<=-100 nT) occurring between 1996 and 2000. Observations of CMEs and their solar surface origins are obtained from the Large Angle and Spectrometric Coronagraph (LASCO) and the EUV Imaging Telesc…
The Properties of Small Magnetic Regions on the Solar Surface and the Implications for the Solar Dynamo(s)
Title, Alan M.; Schrijver, Carolus J.; Hagenaar, Hermance J.
We find that bipolar active regions that emerge onto the Sun's surface are part of a smoothly decreasing frequency distribution that spans almost 4 orders of magnitude in flux and 8 orders of magnitude in frequency. Distributions of emergence latitude and dipole orientation narrow from nearly uniform for the smallest observed ephemeral regions (~5…
Alfvénic Turbulence in the Extended Solar Corona: Kinetic Effects and Proton Heating
Cranmer, S. R.; van Ballegooijen, A. A.
We present a model of magnetohydrodynamic (MHD) turbulence in the extended solar corona that contains the effects of collisionless dissipation and anisotropic particle heating. Recent observations have shown that preferential heating and acceleration of positive ions occur in the first few solar radii of the high-speed solar wind. Measurements mad…
Rapid Acceleration of a Coronal Mass Ejection in the Low Corona and Implications for Propagation
Gallagher, Peter T.; Dennis, Brian R.; Lawrence, Gareth R.
A high-velocity coronal mass ejection (CME) associated with the 2002 April 21 X1.5 flare is studied using a unique set of observations from the Transition Region and Coronal Explorer (TRACE), the Ultraviolet Coronagraph Spectrometer (UVCS), and the Large Angle and Spectroscopic Coronagraph (LASCO). The event is first observed as a rapid rise in GO…