The Association of Solar Flares with Coronal Mass Ejections During the Extended Solar Minimum

We study the association of solar flares with coronal mass ejections (CMEs) during the deep, extended solar minimum of 2007?–?2009, using extreme-ultraviolet (EUV) and white-light (coronagraph) images from the Solar Terrestrial Relations Observatory (STEREO). Although all of the fast (v>900 km?s^?1), wide (θ>100^°) CMEs are associated with a flare that is at least identified in GOES soft X-ray light curves, a majority of flares with relatively high X-ray intensity for the deep solar minimum (e.g. ?1×10^?6 W?m^?2 or C1) are not associated with CMEs. Intense flares tend to occur in active regions with a strong and complex photospheric magnetic field, but the active regions that produce CME-associated flares tend to be small, including those that have no sunspots and therefore no NOAA active-region numbers. Other factors on scales similar to and larger than active regions seem to exist that contribute to the association of flares with CMEs. We find the possible low coronal signatures of CMEs, namely eruptions, dimmings, EUV waves, and Type III bursts, in 91 %, 74 %, 57 %, and 74 %, respectively, of the 35 flares that we associate with CMEs. None of these observables can fully replace direct observations of CMEs by coronagraphs.     

The Neupert effect: What can it tell us about the impulsive and gradual phases of solar flares?

The Neupert effect is the name given to the correlation observed in many flares between the time-integrated microwave and hard X-ray emissions and the soft X-ray emission light curve. We have used hard X-ray data from the Hard X-Ray Burst Spectrometer (HXRBS) on the Solar Maximum Mission (SMM) and soft X-ray data from the detector on GOES to determine what fraction of all events show this correlation and how the correlation changes from the impulsive to the gradual phase. We have found that of 66 HXRBS events observed in 1980 with a peak rate of > 1000 counts s^-1, 58 (80%) showed good correlations with peaks in the GOES time derivative plot corresponding to peaks in the hard X-ray (HXR) plots to within ±20 s. In 20 of these good-correlation cases (30%), the soft X-ray (SXR) time derivative stays high after the HXR emission has decreased suggesting that the later emissions result from energy release in a loop already affected by the initial energy release. In 8 of the 13 flares that showed poor correlation, the SXR time derivative shows no peak corresponding to the initial HXR impulsive peak that has structure on a time scale of 1 s. This suggests that in these events the initial impulsive energy release results primarily in electron acceleration, and that the secondary plasma heating from the accelerated electrons contributes relatively little compared to the more gradual plasma heating already taking place at the same time. The more gradually varying events, commonly referred to as type C flares, tend to show poorer correlation between the SXR time derivative and the HXR time profile. Of 26 GOES X1 or greater flares recorded between 1980 and 1989 with HXR peaks lasting over 10 rain, 13 (50%) showed poor correlation with the gradual HXR peaks either not registering at all in the SXR time derivative plots or showing up as very broad peaks. In one case, on 1981 April 26, the SXR time derivative peak was delayed by 13 rain. Only 17 (65%) of the 26 X-flares had an earlier, impulsive component and of those, 12 (71%) showed good correlation between the impulsive peaks.     

RHESSI Data Analysis Software: Rationale and Methods

The Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) performs imaging spectroscopy of the Sun with high spatial and spectral resolution from 3 keV to 17 MeV using indirect Fourier-transform techniques. We review the rationale behind the RHESSI data analysis software, and explain the underlying structure of the software tools. Our goal was to make the large data set available within weeks after the RHESSI launch, and to make it possible for any member of the scientific community to analyze it easily. This paper describes the requirements for the software and explores our decisions to use the SolarSoftWare and Interactive Data Language programming packages, to support both Windows and Unix platforms, and to use object-oriented programming. We also describe how the data are rapidly disseminated and how ancillary data sets are used to enhance the RHESSI science. Finally, we give a schematic overview of some of the data flow through the high-level analysis tools. More information on the data and analysis procedures can be found at the RHESSI Data Center website, http://hesperia.gsfc.nasa.gov/rhessidatacenter. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1022444531435     

A solar flare observed with the SMM and Einstein satellites

We present X-ray observations of the 21 July, 1980 flare which was observed both with the Einstein Observatory Imaging Proportional Counter (IPC) and the X-Ray Polychromator (XRP) and Gamma-Ray Spectrometer onboard the SMM satellite. The Einstein observations were obtained in scattered X-ray light, i.e., in X-rays scattered off the Earth's atmosphere. In this way it is possible to obtain spatially unresolved X-ray data of a solar flare with the same instrument that observed many X-ray flares on other stars. This paper juxtaposes the results and implications of the stellar interpretation to those obtained from the far more detailed SMM observations. The result of this calibration observation is that the basic properties of the flaring plasma can be reliably determined from the stellar data, however, the basic physics issues can only be studied through models.     

Energy transport and dynamics

We report findings concerning energy transport and dynamics in flares during the impulsive and gradual phases based on new ground-based and space observations (notably fromYohkoh). A preheating sometimes occurs during the impulsive phase. Caxix line shifts are confirmed to be good tracers of bulk plasma motions, although strong blue shifts are not as frequent as previously claimed. They often appear correlated with hard X-rays but, forsome events, the concept that electron beams provide the whole energy input to the thermal component seems not to apply. Theory now yields: new diagnostics of low-energy proton and electron beams; accurate hydrodynamical modeling of pulse beam heating of the atmosphere; possible diagnostics of microflares (based on X-ray line ratio or on loop variability); and simulated images of chromospheric evaporation fronts. For the gradual phase, the continual reorganization of magnetic field lines over active regions determines where and when magnetic reconnection, the mechanism favoured for energy release, will occur. Spatial and temporal fragmentation of the energy release, observed at different wavelengths, is considered to be a factor as well in energy transport and plasma dynamics.Report of Team 4, Flares 22 Workshop, Ottawa, May 25–28, 1993.