Bastille Day event

About: Bastille Day event is a research topic. Over the lifetime, 314 publications have been published within this topic receiving 7969 citations.

Solar and interplanetary sources of major geomagnetic storms (Dst ≤ −100 nT) during 1996–2005

Abstract: [1] We present the results of an investigation of the sequence of events from the Sun to the Earth that ultimately led to the 88 major geomagnetic storms (defined by minimum Dst �� 100 nT) that occurred during 1996–2005. The results are achieved through cooperative efforts that originated at the Living with a Star (LWS) Coordinated DataAnalysis Workshop (CDAW) held at George Mason University in March 2005. On the basis of careful examination of the complete array of solar and in situ solar wind observations, we have identified and characterized, for each major geomagnetic storm, the overall solar-interplanetary (solar-IP) source type, the time, velocity, and angular width of the source coronal mass ejection (CME), the type and heliographic location of the solar source region, the structure of the transient solar wind flow with the storm-driving component specified, the arrival time of shock/disturbance, and the start and ending times of the corresponding IP CME (ICME). The storm-driving component, which possesses a prolonged and enhanced southward magnetic field (Bs), may be an ICME, the sheath of shocked plasma (SH) upstream of an ICME, a corotating interaction region (CIR), or a combination of these structures. We classify the Solar-IP sources into three broad types: (1) S-type, in which the storm is associated with a single ICME and a single CME at the Sun; (2) M-type, in which the storm is associated with a complex solar wind flow produced by multiple interacting ICMEs arising from multiple halo CMEs launched from the Sun in a short period; (3) C-type, in which the storm is associated with a CIR formed at the leading edge of a high-speed stream originating from a solar coronal hole (CH). For the 88 major storms, the S-type, M-type, and C-type events number 53 (60%), 24 (27%), and 11 (13%), respectively. For the 85 events for which the surface source regions could be investigated, 54 (63%) of the storms originated in solar active regions, 11 (13%) in quiet Sun regions associated with quiescent filaments or filament channels, and 11 (13%) were associated with coronal holes. Remarkably, nine (11%) CME-driven events showed no sign of eruptive features on the surface or in the low corona (e.g., no flare, no coronal dimming, and no loop arcade, etc.), even though all the available solar observations in a suitable time period were carefully examined. Thus while it is generally true that a major geomagnetic storm is more likely to be driven by a frontside fast halo CME associated with a major flare, our study indicates a broad distribution of source properties. The implications of the results for space weather forecasting are briefly discussed.

The extreme magnetic storm of 1–2 September 1859

Abstract: Using empirical results on the interplanetary magnetic field strengths of magnetic clouds versus velocities, we show that the 1 September 1859 Carrington solar flare most likely had an associated intense magnetic cloud ejection which led to a storm on Earth of DST ~ -1760 nT.

Evidence for the Formation of a Large-Scale Current Sheet in a Solar Flare

Abstract: 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 source separated from the underlying flare loop and remained stationary for about 2 minutes. During this time, the underlying flare loops shrank at ~9 km s-1. The temperature of the underlying loops increased toward higher altitudes, while the temperature of the coronal source increased toward lower altitudes. These results indicate that a current sheet formed between the top of the flare loops and the coronal source during the early impulsive phase. After the hard X-ray peak, the flare loops grew outward at ~8 km s-1, and the coronal source moved outward at ~300 km s-1, indicating an upward expansion of the current sheet. About 30 minutes later, postflare loops seen in the Solar and Heliospheric Observatory (SOHO) EUV Imaging Telescope 195 A passband rose at ~10 km s-1. A large coronal looplike structure, observed by the SOHO Large Angle and Spectrometric Coronagraph C2 and C3 detectors, also propagated outward at ~300 km s-1. These observations are all consistent with the continued expansion of the current sheet.

Energy partition in two solar flare/CME events

Abstract: Using coordinated observations from instruments on the Advanced Composition Explorer (ACE), the Solar and Heliospheric Observatory (SOHO), and the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), we have evaluated the energetics of two well-observed flare/CME events on 21 April 2002 and 23 July 2002. For each event, we have estimated the energy contents (and the likely uncertainties) of (1) the coronal mass ejection, (2) the thermal plasma at the Sun, (3) the hard X-ray producing accelerated electrons, (4) the gamma-ray producing ions, and (5) the solar energetic particles. The results are assimilated and discussed relative to the probable amount of nonpotential magnetic energy available in a large active region.

Explorer 12 Observations of Solar Cosmic Rays and Energetic Storm Particles after the Solar Flare of September 28, 1961

Abstract: A full description of the cosmic ray experiment on Explorer 12 is given and cosmic ray measurements made during the solar event of September 28, 1961, are reported and discussed. Galactic cosmic ray measurements are also reported. A few hours before the class 3 flare of September 28, two short counting rate increases were observed and are interpreted as electron bursts. The anisotropy of the medium- and low-energy solar protons early in the event and their intensity throughout the event are described. It is found that the history of the intensity of the solar protons is consistent, once isotropy is established, with their having diffused through interplanetary space with an effective mean free path of 0.04 AU. This result is discussed and is shown to be not obviously in disagreement with the generally accepted views regarding the configuration of the interplanetary magnetic field. An estimate of the distance from the sun at which diffusion becomes unimportant and particles escape gives 2 to 3 AU. It is pointed out that simple diffusion (where the particles are scattered from discrete scattering centers and the influence of a general magnetic field is negligible) does not account for the behavior of the anisotropy before isotropy is reached. Two days after the flare, and beginning just before the sudden commencement of a magnetic storm, there was a large increase in the intensity of protons between 2 and 15 Mev, the lower energy limit being determined by the sensitivity of the detectors. As most of these particles, which we have called ‘energetic storm particles,’ arrived after the sudden commencement occurred, we suggest that they were solar protons trapped within the plasma cloud which caused the magnetic storm. The outline of a possible trapping mechanism is given. Explorer 12 measurements of the Forbush decrease of September 30, 1961, are compared with neutron monitor measurements at Deep River. The decrease is larger at Explorer 12 by a factor of 1.7±0.3.