it should be stabilized and eject downwards a flute with a field which, in its turn, should wobble with period t ~ 1 ■ 3 min and move downwards at a velocity
In this case, the amplitude of the wobbling is
1 = (dlnn/dz)-1 = 108 0^8 5cm; Av = 106^7cm/sec. (4.18.4)
After colliding at velocity vo with the low-lying shear zone or a singular point of type X, the flute should disturb the magnetic field in that region and induce an electric field sufficient to create turbulence in the sheet and trigger the flare with electric field
Such a 'flare' version of the events requires a sufficiently high degree of the shear, 9X ~n± 0.1, otherwise the prominence will appear in the quiet state with the damping of the excessive mass to the flute-column (Pustil'nik, 1973). The total number of wobblings of the flute N ~ n^jdpr = 10 20, the time of the completed descent Tact = Nt ~ (0.5 1.0) hours.
The particles accelerated in the sheet will enter the chromosphere and corona and cause the observed flare displays in all bands (Kaplan et al., 1974; Syrovatsky, 1972). The detailed structure of the flare of such type is shown in Fig. 4.18.1.
A very important property of the prominence of the flares will be noted. Since all the force lines involved in the merging through the current sheet are short-circuited to the photosphere, the direct ejection of accelerated particles from the flare to the solar wind is impossible, i.e. such flares are either of non-proton character or proton-delayed (when the particles leak from the trap due to the Bohm diffusion or an instability of the flute type within = 103"4 sec after the flare).
The relationship between the solar flares of considered type and the ascent of new magnetic fluxes to the atmosphere has been confirmed by observations (Rust, 1976). The destabilization of the filaments (prominences) within 30^60 min prior to a flare was observed for overwhelming majority of flares: >80% according to Ramsey and Smith (1965) and =100% according to Moreton (1965). The detailed pattern of filament activation also coincides with the predictions (Pustil'nik, 1976).
4.18.3. Non-evolutionary channels of triggering of the prominence type of flares
The development of the lower loop of the field should raise the X-type singular point and the shear zone, thereby decreasing the depth of the depression in the arc and, hence, increasing the thickness of the prominence. If in this case the thickness exceeds the critical value, the prominence will be automatically destabilized and a flare will be triggered within 50-60 min (in case of a favorable measure of the shear) according to Ramsey and Smith (1965). This pattern is probably observed in some cases with the pre-flare rising and thickening of filament (Martin and Ramsey, 1972). If a shock wave from a flare in one region catches up with a filament in a state near the stability threshold in another region, such filament will be excited and turn out to be abruptly unstable with subsequent triggering of a 'prominence' flare (Pustil'nik, 1976). When a fast particle flux is ejected from the outside to the force lines supporting the prominence, then such fast particles will move along the force line depression under the prominence and, creating a centrifugal acceleration g = v2/R >> gsun , should make the prominence significantly 'heavier' thereby transferring it to the unstable state. This mechanism is of great importance to the proton flares.
The observations of Zhitnik and Lifshitz (1972) are indicative of the existence of dense and hot arc-like coronal condensations (cc) over the active region with the following properties:
ncc = 1010cm"3, ncor = 108cm"3, Tcc =(4 - 6)x 106 K > Tcor = 2 X106 K . (4.18.6) These condensations appear probably owed to overheating of the closed forced tubes by the waves from under the photosphere (Kaplan et al., 1974). Such condensation hanging from the curved force lines cannot fly apart to the rarified corona due to the action of the force lines and is subjected to the balloon mode of flute instability. Such instability results in the flute soothing of the condensation surface with periods
A± = 16n(nkT)cc x(d/H)= (3 x 109 -1010) cm. (4.18.8)
Since the condensation is a source of intense radio emission, such soothing should give rise to the fluctuations of the flux and other characteristics of the radio emission (Pustil'nik and Stasyuk, 1974) with a period rn ~ Tb = 103-4 sec (4.18.9)
and an amplitude
which was observed by Gelfreikh et al. (1969), Durasova et al. (1971). The permanent heating of the condensation increases the pressure in the condensation and, hence, the flute amplitude. Within the time
such heating should wobble the flute soothing up to an amplitude
where q+ = 6 x 106 erg/(cm sec) is the power of the heating by the waves (Kaplan et al., 1974) and AhY is the distance to the Y-type singular point. In this case the radio fluctuation amplitude should increase by
This process will be accompanied by the disturbance of the Y-type singular point and the overlaying current sheet by the flutes from the condensation colliding with them
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