Physics of auroral phenomena : proceedings of the 35th Annual seminar, Apatity, 28 Februaru – 02 March, 2012 / [ed. board: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2012. - 187 с. : ил., табл.

“Physics o f Auroral Phenomena", Proc. XXXV Annual Seminar, Apatity, pp. 17 - 20, 2012 © Kola Science Centre, Russian Academy of Science, 2012 Polar Geophysical Institute SUBSTORMS ASSOCIATED WITH THE FRONTS OF STREAMS IN THE SOLAR WIND I.V. Despirak1, A.A. Lubchich1, R. Koleva2 1 Polar Geophysical Institute, RAS, Apatity, Murmansk region, 184200, Russia 2Space Research & Technologies Institute, BAS, Sofia, Bulgaria Abstract. It is well known that the various structures in the solar wind flow are either related to the solar corona structure or are created along solar wind propagation. Structures created while the solar wind propagates through the Solar system are the regions of compressed plasma at the fronts of recurrent solar wind streams (CIR) and magnetic clouds (Sheath). Auroral disturbances observed by Polar spacecraft during Sheath and CIR events had an unusual form. On one side these disturbances exhibited typical substorm signatures, but on the other side they had very large longitudinal dimensions and covered a very large area. To examine weather these disturbances represent substorms we considered data from the Geotail spacecraft in the magnetotail. Auroral bulge parameters were obtained by the UV1 onboard Polar; solar wind parameters were taken from the OMNI data base. All auroral disturbances observed by Polar during Sheaths and CIRs for the periods 1997-1998; 2000; October 2001 and December 1996 were studied. We show that some signatures of a typical substorm were observed in the magnetotail, namely: 1) fast plasma flows associated with a reconnection process (tailward/earthward flows) 2) a sharp decrease of the total pressure following the interval of a pressure increase. This enables us to consider the auroral disturbances during the fronts of high­ speed streams as substorm. Introduction Solar wind is not a uniform flow, various large-scale structures and streams exist within it (Pudovkin, 1996). The streams and structures in the solar wind could be two types: quasi-stationary and disturbed (Yermolaev et al., 2009). To the disturbed type belong the interplanetary manifestations of coronal mass ejections that can include magnetic clouds (MC) and EJECTA (or interplanetary coronal mass ejection). Disturbed structures are also structures generated in the interplanetary medium along solar wind propagation - compression regions in front of incoming fast recurrent streams (CIR) and magnetic clouds (Sheath) (e.g. Klein and Burlaga, 1983; Balong, 1999). The disturbed solar wind structures - magnetic clouds (MC) and the compression regions in front of streams (Sheath and CIR), have a noticeable in magnitude and duration south component of the magnetic field (Bz<0) and could trigger geomagnetic storms (Yermolaev et al., 2010). The relationship between storm time substorms and isolated substorms is still an open question. Many researches find no differences between storm-time and nonstorm classical substorms, while others find substantial difference between them, e.g during storm-time substorms they observe lack of bulge, lack of bifurcation of aurora (e.g. McPherron et al., 2002; Hoffmann et al., 2010). Recently we considered auroral bulge developments during 4 solar wind structures: magnetic clouds (MC), recurrent streams (RS), and regions of their interaction with undisturbed solar wind (Sheath and CIR) (Despirak et al., 2009). It was demonstrated that during the impact of compression regions Sheath and CIR peculiar auroral disturbances of large area and very large longitudinal and latitudinal dimensions are observed. Fig. 1. Examples of auroral disturbances development by Polar UVI data during Sheath, 17 September 2000 (a) and during CIR, 28 February 1997 (b). On each auroral image the blue curve delimits the bulge region. Although the auroral disturbances during Sheaths and CIRs have signatures of an auroral substorm development - localized onset and formation of the auroral bulge, a question arises if these disturbances are substorms. To answer this question we investigat magnetotail plasma dynamics in the course of the auroral bulge formation when the magnetosphere is driven by Sheaths and CIRs. In the course of a substorm fast plasma flows in the magnetotail are observed and satellites in the near or middle tail can register a reversal of a tailward plasma flow to an earthward plasma flow. The observation of fast flow ..................................................................................................................... 1 17 ГУКМурманска* государственная облзстна* универсальная научная библиотека “ “ 1 енная 1 □