Search Publications
Photospheric and heliospheric magnetic fields
Schrijver, Carolus J.; De Rosa, Marc L.
The magnetic field in the heliosphere evolves in response to the photospheric field at its base. This evolution, together with the rotation of the Sun, drives space weather through the continually changing conditions of the solar wind and the magnetic field embedded within it. We combine observations and simulations to investigate the sources of t…
Interplanetary coronal mass ejections in the near-Earth solar wind during 1996-2002
Cane, H. V.; Richardson, I. G.
We summarize the occurrence of interplanetary coronal mass ejections (ICMEs) in the near-Earth solar wind during 1996-2002, corresponding to the increasing and maximum phases of solar cycle 23. In particular, we give a detailed list of such events. This list, based on in situ observations, is not confined to subsets of ICMEs, such as "magnetic clo…
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…
CHIANTI-An Atomic Database for Emission Lines. VI. Proton Rates and Other Improvements
Young, P. R.; Mason, H. E.; Landini, M. +3 more
The CHIANTI atomic database contains atomic energy levels, wavelengths, radiative transition probabilities, and electron excitation data for a large number of ions of astrophysical interest. Version 4 has been released, and proton excitation data are now included, principally for ground configuration levels that are close in energy. The fitting pr…
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…
Reconstruction of solar irradiance variations in cycle 23: Is solar surface magnetism the cause?
Solanki, S. K.; Krivova, N. A.; Unruh, Y. C. +1 more
A model of solar irradiance variations is presented which is based on the assumption that solar surface magnetism is responsible for all total irradiance changes on time scales of days to years. A time series of daily magnetograms and empirical models of the thermal structure of magnetic features (sunspots, faculae) are combined to reconstruct tot…
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…
Active longitudes in sunspot activity: Century scale persistence
Usoskin, I. G.; Berdyugina, S. V.
A novel analysis of sunspot group data for the past 120 years reveals that sunspots in both northern and southern hemispheres are formed preferably in two persistent active longitudes separated by 180°. In the Carrington reference frame, the active longitudes continuously migrate in phase with respect to the Carrington meridian with a variable rat…