Physics of auroral phenomena : proceedings of the 33rd Annual seminar, Apatity, 02 - 05 March, 2010 / [ed.: A.G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2011. - 206 с. : ил.

T.E. Val'chuk In our Institute this theme is considered in works o f V.N. Obridko about large-scale fields on the Sun [ 6 ], of K.I.Nikolskaja about CHs in a cycle [7-8], E.I.Mogilevsky and T.E.Valchuk about fractal research o f sources and qualities of SW [9]. It is known that the recurrent flows are the most expressed on a decrease branch o f solar cycles. The purpose of the present work is to study recurrent SW events in the last minimum o f SA. The solar origin o f recurrence and SW parameters in near-Earth cosmic space, especially sector structure o f IMF shows us the connection between solar and heliospheric phenomena. 2. Data and calculations For interpretation the picture of last minimum we choose the data representing a near-Earths cosmic space: plasma parameters and an interplanetary magnetic field in SW (data Wind; SOHO, University of Maryland), the data about sector structure (SS) IMF (ACE). Geomagnetic disturbance was estimated by Ap index. Solar parameters are presented as follows: coronal pictures by LASCO SOHO; MDI magnetograms and solar disc in soft X-ray EIT SOHO; solar spots on a disk in continuum (SOHO); and also synoptic charts o f photospheric magnetic field and charts of source surface field WSO; and also cards of CHs in Fe XIV line NSO Sacramento Peak for addition of a dynamic transformation o f CHs in CR 2052-2091 in 23-th minimum in years 2007-2010. Fractal calculations were made on all period o f a minimum (except for time intervals o f data absence - from hours up to several days). The Higuchi method allows us to estimate fractal dimension (FD) o f SW plasma, as the characteristic of SW plasma flow structure. FD characteristics and the synoptic analysis (based on the concrete examination of data set about sources of SW on the solar disk) can supplement each other. FD variations were calculated by means of the sliding window lasting 6 hours with the 3-sentry step; the similar technique was applied in [9]. 3. IMF polarity and SW flows The IMF sector structure transformations are valuable factors o f solar minimum. It is necessary to consider that SS is the reflection in SW a large-scale magnetic field o f the Sun. Taking into account the helio-projection o f our Earth on the solar disk making 7 degrees above and below relatively solar equator in equinoxes affects in primary polarity: S - spring equinoxes in CRs № 2054, 2068, 2081 and N - autumn equinoxes in CRs 2061, 2074 and 2088 accordingly in 2007, 2008 and 2009. In [5] four-sector structure is presented as the basic feature in the descending and minimum phase of solar cycle. The current minimum №23 reveals the following: 4 sectors o f IMF in CRs 2052- 2059 are transformed to two-sector structure in CRs 2060-2069; in beginning o f CR 2070 the occurrence o f positive SS is not positive sector display, but only variations near heliosphere plasma layer, when SW velocity is low. In 2007, from CR 2060, the two-sector structure is presented as steady phenomenon in the next Carrington rotations. The steady sector boundary (September 1, 2007, (-/+) transition) exists as the most stable up to 2009. In an autumn equinox 2008 positive SS remains only on September, 15 and 16. Positive sector IMF is steady, and up to CR 2080 it is connected with a fast stream of positive polarity. It is necessary to notice that from CR 2060 up to CR 2079 the crossing of HPL occurs on steady boundary of two fast streams - in negative and positive polarity o f IMF. In 2009 the stability of large-scale solar magnetic fields in near-equatorial belt o f the Sun decreases a little. It is visible on reduction of speed and loss of structural features o f streams. There is ample evidence that large-scale magnetic field in equatorial belt of the Sun is transformed. The line o f polarity section o f source surface field is approached to Sun equator; HPL reaches the most flattening. Geomagnetic disturbance is represented as weak geomagnetic storms and active periods. Geomagnetic activity in 2009 gets the least in minimal phase of SA. Nevertheless in 2007, when high-speed impulses o f activity are expressed distinctly, the arrival of co­ rotation regions, following after HPL crossing, causes geomagnetic activity. We will study these situations in consecutive change of CRs of the Sun for the purpose o f identification o f high-speed SW stream sources from unipolar areas of magnetic fields on the solar disk 4. Fractal dimension variations in front of fast SW streams in HPL transitions In the beginning 2007 in an explicit form data of the SW speed and plasma concentration are very like from CR 2052 up to CR 2057. It shows the saving of structure and characteristics o f long-living areas of polarity on the Sun. These areas remain in the specified CRs in the beginning o f 2007. We will consider the steady boundary o f HPL transition (from negative polarity to positive) in the beginning of CRs. After HPL transition the fast SW stream is generated from near-equatorial CH of positive polarity. Fractal dimension variations show the functions similar to each other in general features two samples are on Fig. 1. The co-rotation region (CIR) in the case of fast SW flow near HPL gives fractal dimension values 1 2< FD< 1.4, that is appreciably lower than typical FD ~ 1.5 in HPL transition. 96