Physics of auroral phenomena : proceedings of the 39th annual seminar, Apatity, 29 February-4 March, 2016 / [ed. board: N. V. Semenova, A. G. Yahnin]. - Апатиты : Издательство Кольского научного центра РАН, 2016. - 167 с. : ил., табл.

“Physics o f Auroral P henom ena ”, Proc. XXXIX An n u al Sem inar, A patity, pp. 7-10, 2 0 1 6 © Polar Geophysical Institute, 2016 Polar Geophysical Institute COMPARISON OF THE "EXPANDED” AND “POLAR” SUBSTORMS BEHAVIOR DURING THE 23 AND 24 SOLAR CYCLES I.V. D esp irak1, A .A . L u b ch ich1, N .G . K leim enova2 1P o la r Geophysical Institute, Apatity, Russia 2Schm idt Institute o f the Physics o f the Earth RAS, Moscow , Russia e-mail: despirak@ gmail.com Abstract. We presented ihe comparative analysis of the two different types of substorm behavior during the 23-th and 24-th solar cycles. The substorms have been studied in: (a) close to the 23-th solar cycle maximum (1999- 2000, Wp> 100); (b) close to the last maximum (2012-2013, Wp~60), (c) during the 23-th and 24-th solar cycle minima (1995-1996, Wp=3-17 and 2008-2009, Wp=3). As in previous study, we divided the considered substorms into 3 types according to auroral oval dynamics. The first type - the substorms which are observed only in auroral latitudes (called “usual” substorms); the second type - the substorms which propagate from auroral latitudes (<70°) to polar geomagnetic latitudes (>70°) (called “expanded” substorms, according to an expanded oval); and the third type - the substorms which are observed only at latitudes above -70° in the absence of simultaneous geomagnetic disturbances below 70” (called “polar” substorms, according to a contracted oval). The aim of this work is the analysis of the space weather conditions before the onset of two types of substorms which observed at high geomagnetic latitudes - before “expanded” and “polar” substorms. Our analysis was based on the 10-s sampled IMAGE magnetometer data, and the 1-min sampled OMNI solar wind and Interplanetary Magnetic Field (IMF) data. The following substorm characteristics have been compared: (i) the seasonal variations of the occurrence, (ii) the solar wind parameters before the substorm onset, and (iii) the polar cap PC-index values before the substorm onset. The new interesting result of our study is the finding the different values of the PC-index before the different types of substorms. The PC-index was stronger before the "expanded" substorms than before the "polar" substorms. So, the PC-index values before the "expanded" substorm onsets were 1.5±0.7 (1995-1996, Wp~13), 1.1 ±0.8 (2008-2009, Wp~3) 1.6±0.9 (2012-2013, Wp~60), 2.0±0.8 (1999-2000, Wp -105), and they were more than twice lower before the "polar" substorm onsets - 0.7±0.4 (1995-1996), 0.4±0.3 (2008-2009), 0.52±0.5 (2012-2013), 0.8±0.6 (1999-2000. It is shown also that for the substorms which observed during the solar minima (1995-1996 and 2008-2009), the PC- index values were 1.3 times less than ones closed to the solar maxima (1999-2000 and 2012-2013). Introduction One of the factors of the space weather is the magnetetosheric substorms excitation in the night sector of the auroral latitudes. Typically, the substorm intensity is estimated by the AE, AL, and AU indices of geomagnetic activity. These indices are calculated accordingly to the observation data from 12 ground-based auroral stations located at the different longitudes. However, these indices estimate the substorm activity too roughly because they do not reflect the substorm latitudinal features. The aim of this work is the analysis of the space weather conditions before the onset of different types of substorms. Substorms were divided into different types according their latitudinal features. It is known that under the normal conditions, the auroral oval is located at the geomagnetic latitudes of about 65- 67 degrees. Under the quiet conditions, the auroral oval shrinks and shifts to higher latitudes (above 70 degrees of the geomagnetic latitudes). It is the “contracted oval”. In the disturbed conditions, the equatorward boundary of the auroral oval shifts to the lower latitudes, up to 50 degrees of latitudes, and the poleward boundary extends to the higher latitudes, it is the “expanded auroral oval” [1]. A search for the difference between the substorms occurring on the "normal", "contracted" and "extended" oval attracted the attention of the researchers [2] for a long time. In different studies, substorms were divided into “confined” and “widerspead” [3], “localized” and “normal” [4], ’’substorms on a contracted oval” and “normal” [5], “small” and “normal-size” [6], “high-latitude” and “usual” [7, 8], “polar” and “usual” [9], “polar” and “high-latitude” [10]. So, all substorms may be divided into 3 types according to the auroral dynamics: the first type - “usuall” substorms according to the normal auroral oval, the second type - the “expanded” substorms according to the expanded oval, the third type - the “polar” substorms according to the contracted oval. In our work we will consider only two types of substorms, which are observed at high latitudes. Namely, at the IMAGE profile above BJN station (71 degrees of geomagnetic latitudes). We term the first type of substorms as “expanded” substorms. Such substorm events begin at latitudes of the auroral zone and then move poleward. Namely, the substorm onset is observed at the latitudes from 54 to 66 degrees of the geomagnetic latitudes. And in the substorm maximal phase, the westward electrojet “center” is observed at 75.1 - 75.2 degrees of latitudes (IMAGE stations LYR-NAL). The second type of substorms we term as the “polar” substorms. The disturbances begin at geomagnetic latitudes above 70 degrees of 7