J. Jakimiec

Energy release and transport in arcade flares

Abstract This work is based on hard and soft X-ray observations from the YOHKOH satellite. We investigate an example of an arcade flare, for which the arcade channel is seen in soft X-rays as a long bright filament. We have found that: 1. (1) Energy can efficiently flow along the arcade channel from the very beginning of a flare. 2. (2) During flare evolution a few kernels of hard X-ray emission develop along the arcade channel. Clearly, they are new, additional sources of the flare energy release. A probable scheme of formation of such hard X-ray kernels is briefly discussed.

Investigations of turbulent motions and particle acceleration in solar flares

Abstract Investigations of X-ray spectra of solar flares show that intense random (turbulent) motions are present in hot flare plasma. Here we argue that the turbulent motions are of great importance for flare development. They can efficiently enhance flare energy release and accelerate particles to high energies.

DIFFERENTIAL EMISSION MEASURE ANALYSIS OF HOT-FLARE PLASMA FROM SOLAR-MAXIMUM MISSION X-RAY DATA

We have investigated differential emission measure (DEM) distribution of hot flare plasma (T>10 MK) using SMM X-ray data from Bent Crystal Spectrometer (BCS) and Hard X-ray Imaging Spectrometer (HXIS). We have found that the analysis provide a very sensitive test of consistency of observational data coming from different instruments or different channels of the same instrument. This has allowed to eliminate some systematic differences contained in the analysed data. Typical examples of the DEM distribution are discussed. It is stressed that these improvements in the multitemperature flare diagnostics are very important for the discussion of flare energetics.

Energy release in solar flares

Abstract One of the basic features of solar flares is the very fast heating of large plasma volumes. A significant fraction of the hot flare plasma is contained in X-ray kernels which are situated near the tops of flaring loops (loop-top flare kernels). In the present paper it is argued that in the flare kernels a chain (cascade) of violent reconnections develops, as a result of which the kernels are filled with many transient reconnection sites, so that the flare energy release occurs over a large plasma volume. Formation of the kernels is briefly discussed. It is suggested how such turbulent model of the flare energy release can also explain basic features of the flare impulsive phase, i.e. acceleration of a large number of electrons in very short time.

Investigation of turbulent kernels in solar flares

Abstract Observational evidence that the plasma in hot X-ray sources in solar flares is highly turbulent is presented. The turbulent flare kernels are considered to be the main source of the flare energy release. Properties of kernels in big flares are discussed.

Intercomparison of flare observations with two SMM spectrometers: BCS and HXIS

Abstract The temperature diagnostics of hot flare plasma, obtained from two Solar Maximum Mission instruments (HXIS and BCS), is compared. A good general agreement between the HXIS and BCS-Fe temperature scales has been found. However, for the growth phase of some flares a systematic difference, T HXIS >T Fe , has been found, which is not likely to be due to the typical non-thermal electron beams. Possible explanation of this effect is briefly discussed.

Investigation of the energy release in flare kernels

Abstract We have investigated the heating rate, E H , in flare kernels for a number of M-class flares. We have found that: 1) The heating rate decreases with the altitude of kernel. We explain this as a result of magnetic field decrease with the height in the corona, i.e. the decrease of the available magnetic energy H 2 /8π, per unit volume. 2) However, the temperature of the investigated kernels does not decrease with the altitude. We explain this as being the result of decreasing conductive losses from the kernel with increasing height, which compensates the decrease of E H . We have divided the investigated flares into three groups: low, intermediate and higher loops, and calculated the median values of the heating rate, E H , and of other parameters for each group. The low loops (compact flares) have high heating rates E H .

Flare diagnostics based on Prognoz 9 X-ray data

Abstract The X-ray fluxes measured aboard the Prognoz 9 satellite in the energy range 2–160 keV have been analysed for several big flares which occurred during 1983. A new method of analysis called LEBAN (Loop Energy Balance Analysis) has been applied. The LEBAN method allows us to estimate the effective length and volume of the flaring loop under the assumption of single constant-cross-section geometry. Results of the analysis provide the necessary information to investigate in detail the time behaviour of individual terms comprising the energy balance equation for the hot (T > 4MK) flaring plasma. The LEBAN method is described and the flare parameters derived for eight flares are presented.

Investigation of the energy release in long-duration flares

We investigate an example of long-duration arcade flare of 14/15 May 1993. Its spatial structure can be reliably determined from the Yohkoh X-ray images and Kitt Peak magnetograms. Temperatures, densities and heights of the loop-top flare kernels have been estimated from these data and also the kernel heating has been investigated in detail. We have found that (1) The energy release in the loop-top flare kernels occurs also during the whole flare decay phase; (2) The kernel evolution during the decay phase is quasi-steady-state, i.e. it is determined by the slow decrease of the heating rate, EH(t).

Structure and energetics of filament-like SXR flares

Abstract We investigate an example of flare having the shape of a long, bright filament in soft X-rays (SXR). Another characteristic feature of the flare and of other similar flares is that a few emission kernels, best seen in hard X-rays (HXR), develop along the filament. The kernels are new sites of the flare energy release. It is shown that the kernels develop at the crossings of perpendicular magnetic flux tubes. The flare energy release, and the flow of heat and plasma along the filament are carefully investigated.