Search Publications
Origins of the Ambient Solar Wind: Implications for Space Weather
Cranmer, Steven R.; Riley, Pete; Gibson, Sarah E.
The Sun's outer atmosphere is heated to temperatures of millions of degrees, and solar plasma flows out into interplanetary space at supersonic speeds. This paper reviews our current understanding of these interrelated problems: coronal heating and the acceleration of the ambient solar wind. We also discuss where the community stands in its abilit…
Statistical Studies of Solar White-light Flares and Comparisons with Superflares on Solar-type Stars
Notsu, Yuta; Maehara, Hiroyuki; Namekata, Kosuke +9 more
Recently, many superflares on solar-type stars have been discovered as white-light flares (WLFs). The statistical study found a correlation between their energies (E) and durations (τ): τ \propto {E}0.39, similar to those of solar hard/soft X-ray flares, τ \propto {E}0.2{--0.33}. This indicates a universal mechanism of energy…
Determining the Intrinsic CME Flux Rope Type Using Remote-sensing Solar Disk Observations
Palmerio, E.; Kilpua, E. K. J.; Green, L. M. +4 more
A key aim in space weather research is to be able to use remote-sensing observations of the solar atmosphere to extend the lead time of predicting the geoeffectiveness of a coronal mass ejection (CME). In order to achieve this, the magnetic structure of the CME as it leaves the Sun must be known. In this article we address this issue by developing…
High-resolution observations of flare precursors in the low solar atmosphere
Xu, Yan; Cao, Wenda; Liu, Chang +9 more
Solar flares are generally believed to be powered by free magnetic energy stored in the corona1, but the build up of coronal energy alone may be insufficient to trigger the flare to occur2. The flare onset mechanism is a critical but poorly understood problem, insights into which could be gained from small-scale energy releas…
Turbulent Kinetic Energy in the Energy Balance of a Solar Flare
Harra, L. K.; Kontar, E. P.; Perez, J. E. +5 more
The energy released in solar flares derives from a reconfiguration of magnetic fields to a lower energy state, and is manifested in several forms, including bulk kinetic energy of the coronal mass ejection, acceleration of electrons and ions, and enhanced thermal energy that is ultimately radiated away across the electromagnetic spectrum from opti…
Observational Signatures of Transverse Magnetohydrodynamic Waves and Associated Dynamic Instabilities in Coronal Flux Tubes
Yokoyama, T.; Antolin, P.; De Moortel, I. +1 more
Magnetohydrodynamic (MHD) waves permeate the solar atmosphere and constitute potential coronal heating agents. Yet, the waves detected so far may be but a small subset of the true existing wave power. Detection is limited by instrumental constraints but also by wave processes that localize the wave power in undetectable spatial scales. In this stu…
Microflare Heating of a Solar Active Region Observed with NuSTAR, Hinode/XRT, and SDO/AIA
Krucker, Säm; White, Stephen M.; Grefenstette, Brian W. +7 more
NuSTAR is a highly sensitive focusing hard X-ray (HXR) telescope and has observed several small microflares in its initial solar pointings. In this paper, we present the first joint observation of a microflare with NuSTAR and Hinode/XRT on 2015 April 29 at ∼11:29 UT. This microflare shows the heating of material to several million Kelvin, observed…
Solar Active Region Coronal Jets. II. Triggering and Evolution of Violent Jets
Panesar, Navdeep K.; Moore, Ronald L.; Sterling, Alphonse C. +2 more
We study a series of X-ray-bright, rapidly evolving active region coronal jets outside the leading sunspot of AR 12259, using Hinode/X-ray telescope, Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI), and Interface Region Imaging Spectrograph (IRIS) data. The detailed evolution of such r…
Radiative Diagnostics in the Solar Photosphere and Chromosphere
van Noort, M.; de la Cruz Rodríguez, J.
Magnetic fields on the surface of the Sun and stars in general imprint or modify the polarization state of the electromagnetic radiation that is leaving from the star. The inference of solar/stellar magnetic fields is performed by detecting, studying and modeling polarized light from the target star. In this review we present an overview of techni…
Comprehensive Analysis of the Geoeffective Solar Event of 21 June 2015: Effects on the Magnetosphere, Plasmasphere, and Ionosphere Systems
Fineschi, Silvano; Stangalini, Marco; Bruno, Roberto +34 more
A full-halo coronal mass ejection (CME) left the Sun on 21 June 2015 from active region (AR) NOAA 12371. It encountered Earth on 22 June 2015 and generated a strong geomagnetic storm whose minimum Dst value was −204 nT. The CME was associated with an M2-class flare observed at 01:42 UT, located near disk center (N12 E16). Using satellite data from…