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Дата изменения: Thu Jan 27 20:04:37 2000 Дата индексирования: Tue Oct 2 01:37:05 2012 Кодировка: Поисковые слова: halloween |
North-South (Bz) component of the Interplanetary Magnetic Field (IMF) in the GSM frame of reference is the main factor controlling geomagnetic activity. Under southward directed IMF the Earth's magnetosphere is open to input from the solar wind flow. This energy is accumulated in the magnetosphere and is subsequently released and dissipated during geomagnetic storms and substorms. Other characteristics of the solar wind are less important.
Since practical importance of solar wind measurements was recognized, a number of approaches was developed for prediction of the geomagnetic activity basing on the solar wind data. Usually geomagnetic indices Kp, Dst, AE are estimated with the use of linear filters or neural networks.
In our technique simple and a bit different approach is used: As geomagnetic activity is clearly controlled by the solar wind, we assume that an appropriate function of the solar wind parameters describing input to the magnetosphere, can characterize also the geomagnetic activity. Predicted level of the geomagnetic activity is formulated qualitatively (e.g., quiet, weak, strong ...)
Such qualitative characteristics appear to be less accurate compared with results of other methods in which concrete values of Dst and Kp indices are obtained. However, at present time interpretation of these indices in terms of their practical consequencies is anyway qualitative, especially during the real-time forecast. Difference between actual and predicted indices (that is error of prediction) is also often high. Therefore, we consider that qualitative prediction of the level of geomagnetic activity is adequate, at least at the current level of our knowledge.
Typical geomagnetic storm starts after 3 hours of Bz=-10 nT [Gonsalez et al, JGR, 99, 5771-5792, 1994]. The corresponding energy input is about 1016 Joules. Typical energy accumulated during substorm growth phase is about 1015 J. [Pulkkinen et al., JGR, 103, 15-28, 1998]. Contracted-oval (small) substorms are often associated with only 1014 J input [Petrukovich et al, subm. to JGR].
Three parameters are calculated: integral of energy input during preceeding 90 min (E90), integral of energy input during preceeding 180 min (E180) and integral of energy input during interval with ε > 1010 W (Eac). The reset to Eac = 0 occurs after 30 minutes of input smaller than this threshold. E90 parameter better describes substorms-level activity, while E180 and Eac are more adequate for storm-level activity. More information can be found in Petrukovich et al., [subm. to GRL].
Author: Anatoli Petrukovich
Questions and comments are welcomed at apetruko@iki.rssi.ru