Структура и динамика полярных токовых систем : материалы международного симпозиума «Полярные геомагнитные явления», 25-31 мая, Суздаль, СССР / Акад. наук СССР, Кол. фил. им. С. М. Кирова, Поляр. геофиз. ин-т. – Апатиты : [б. и.], 1988.

TIME DELAY OP MAGNETIC DISTURBANCES RELATIVE TO SOLAR WIND VARIATIONS. The problem of the temporal response of the magnetosphere to changes in solar wind parameters is a key one for the identification of the mechanisms of the solar wind energy input into the magnetosphere. In the driven model (Perreault and Akasofu,19.78) magnetosphere responds directly to variations in the solar wind conditions. In this case the energy is dissipated through a convec tion process and the time lag between the energy input and the enhanced magne- tospheric activity should be equal to the time required to plasma convecting from the dayside merginal region to the inner magnetosphere. In the energy storage-release model (McPherron et al.,1973) the magnetosphere responds to the solar wind by storing energy in the tail lobes and releasing it impuls ively at- expansion onset. In this case the time delay between energy input and dissipation would be controlled by the processes which cause energy release from the tail. The first statistical analyses ehowed that the correlation for delay time Д T ~ 40 min is maximum (Arnoldy, 1971 i Meng et al.,1973). This is in accord with the view that the energy is stored in the tail before it releases in a substorm expansion phase. The process of energy storage was named as the growth phase. However the following studies (Clauer et al.,1981j Bargatze et al.,1985) carried out using the technique of linear prediction filtering show that the prediction filters are composed of two response pulses peaking at lage about 20*30 minutes during the period of strong activity and ~ 60 minutes during the period of moderate activity. A possible interpretation is that the 20-minute pulse represents magnetospheric response directly due to solar wind ' coupling and that 60-minute pulse is the response due to the release of energy from the tail. New findings were obtained by Dmitrieva and Sergeev (1983,1985) when they studied the duration of the substorm growth phase in relation to the conditions of the explosive phase triggering. In this study the moment of drastic devel opment of DPg variation on the polar cap was taken as the beginning of the growth phase and the moment of Pi2 onset in the middle latitudes was taken as the beginning of the explosive phase. The authors came to the conclusion that substorms might be forced or arise spontaneously. Forced substorma are trig gered by some external causes, for example by changes in the solar wind param eters while spontaneous substorma start under invariable solar wind condit ions. The duration of the growth phase of spontaneous substorms t is ole.arly dependent on the IMF parameters B g or B^sin 0/2 as follows (Fig.8)» B g T = 225 nT or BT sin2e/2 T = 300 nT Therefore the growth phase duration of spontaneous substorms may be 2 hours when B g = 2 nT and only 20 minutes when B B = 10 nT. The account of the solar wind velocity negligibly changes these results. In cases of forced sub storms the duration of the growth phase decreases over a wide range and may be nearly zero (Dmitrieva and Sergeev,1983). It means that the state of the magne tosphere with a lot of stored energy ia a normal one. TRIGGERING OF THE STORM EXPLOSIVE PHASE. External causes causing forcing the explosive phase may be various. The discontinuities in the solar wind plas ma velocity as trigger of substorms were pointed out by Kokubun et al.(1977) and Iyemori and Tsunomura (1983). But the most common cause is a sharp turning of the IMF B z component from the southward to northward direction. The effi ciency of such reversals in B z is shown in case studies (Caan et el., 1977; Pellinen et al.,1982| Rostoker,1983i Mishin et al.,1983) as well as in the I24