Search Publications
A Critical Assessment of Nonlinear Force-Free Field Modeling of the Solar Corona for Active Region 10953
Leka, K. D.; Cheung, Mark C. M.; Lites, Bruce W. +16 more
Nonlinear force-free field (NLFFF) models are thought to be viable tools for investigating the structure, dynamics, and evolution of the coronae of solar active regions. In a series of NLFFF modeling studies, we have found that NLFFF models are successful in application to analytic test cases, and relatively successful when applied to numerically …
The Nature of Flare Ribbons in Coronal Null-Point Topology
Aulanier, G.; Schrijver, C. J.; Masson, S. +1 more
Flare ribbons are commonly attributed to the low-altitude impact, along the footprints of separatrices or quasi-separatrix layers (QSLs), of particle beams accelerated through magnetic reconnection. If reconnection occurs at a three-dimensional coronal magnetic null point, the footprint of the dome-shaped fan surface would map a closed circular ri…
Observing the Roots of Solar Coronal Heating—in the Chromosphere
De Pontieu, Bart; McIntosh, Scott W.; Hansteen, Viggo H. +1 more
The Sun's corona is millions of degrees hotter than its 5000 K photosphere. This heating enigma is typically addressed by invoking the deposition at coronal heights of nonthermal energy generated by the interplay between convection and magnetic field near the photosphere. However, it remains unclear how and where coronal heating occurs and how the…
A New Approach to Analyzing Solar Coronal Spectra and Updated Collisional Ionization Equilibrium Calculations. II. Updated Ionization Rate Coefficients
Savin, D. W.; Landi, E.; Bryans, P.
We have re-analyzed Solar Ultraviolet Measurement of Emitted Radiation (SUMER) observations of a parcel of coronal gas using new collisional ionization equilibrium (CIE) calculations. These improved CIE fractional abundances were calculated using state-of-the-art electron-ion recombination data for K-shell, L-shell, Na-like, and Mg-like ions of al…
Automated LASCO CME Catalog for Solar Cycle 23: Are CMEs Scale Invariant?
Berghmans, D.; Robbrecht, E.; Van der Linden, R. A. M.
In this paper, we present the first automatically constructed LASCO coronal mass ejection (CME) catalog, a result of the application of the Computer Aided CME Tracking software (CACTus) on the LASCO archive during the interval 1997 September-2007 January. We have studied the CME characteristics and have compared them with similar results obtained …
Empirical Constraints on Proton and Electron Heating in the Fast Solar Wind
Cranmer, Steven R.; Kasper, Justin C.; Matthaeus, William H. +1 more
We analyze measured proton and electron temperatures in the high-speed solar wind in order to calculate the separate rates of heat deposition for protons and electrons. When comparing with other regions of the heliosphere, the fast solar wind has the lowest density and the least frequent Coulomb collisions. This makes the fast wind an optimal test…
On the Weakening of the Polar Magnetic Fields during Solar Cycle 23
Sheeley, N. R., Jr.; Wang, Y. -M.; Robbrecht, E.
The Sun's polar fields are currently ~40% weaker than they were during the previous three sunspot minima. This weakening has been accompanied by a corresponding decrease in the interplanetary magnetic field (IMF) strength, by a ~20% shrinkage in the polar coronal-hole areas, and by a reduction in the solar-wind mass flux over the poles. It has als…
Quantitative Measurements of Coronal Mass Ejection-Driven Shocks from LASCO Observations
Vourlidas, Angelos; Ontiveros, Veronica
In this paper, we demonstrate that coronal mass ejection (CME)-driven shocks can be detected in white light coronagraph images and in which properties such as the density compression ratio and shock direction can be measured. Also, their propagation direction can be deduced via simple modeling. We focused on CMEs during the ascending phase of sola…
EUV Wave Reflection from a Coronal Hole
Temmer, M.; Howard, R. A.; Gopalswamy, N. +7 more
We report on the detection of EUV wave reflection from a coronal hole, as observed by the Solar Terrestrial Relations Observatory mission. The EUV wave was associated with a coronal mass ejection (CME) erupting near the disk center. It was possible to measure the kinematics of the reflected waves for the first time. The reflected waves were genera…
A Power-Law Distribution of Solar Magnetic Fields Over More Than Five Decades in Flux
Lamb, D. A.; DeForest, C. E.; Hagenaar, H. J. +3 more
Solar flares, coronal mass ejections, and indeed phenomena on all scales observed on the Sun, are inextricably linked with the Sun's magnetic field. The solar surface is covered with magnetic features observed on many spatial scales, which evolve on differing timescales: the largest features, sunspots, follow an 11-year cycle; the smallest seem to…