2. Processing of the Data

[3]  The initial data were the observations of coronal brightness by the coronagraph SOHO/LASCO-C2 at altitudes of 2.3 R-5.5 R. Photometry of daily images was carried out at various heights with step 2^o along position angles during May 1996-May 2003. These data were used both in fits and gif formats. The final results are similar to use in both formats. However, gif format is more preferable because it uses logarithmic scale for coronal brightness.

[4]  We determined daily mean coronal intensity using daily brightness of the ( K + F ) corona at heights of 2.3 R-5.5 R and along of position angels. Distribution of coronal brightness at the latitudes for every day has been expressed in part of daily mean coronal intensity. We determined monthly mean coronal intensity using these data.

Figure 1

[5]  Figure 1 shows distribution of the ( K + F ) coronal brightness (in arbitrary units) as a function of latitude for 1996.0-2003.5. The corona at heights more than 2.5 R has maximal brightness near the equator during the minimum activity. The width of equatorial belts of the corona grows with development of solar activity and two branches of bright corona drift in a direction to the poles in 1998. The maximum of coronal brightness reached at middle and high latitudes of the northern and southern hemispheres during the polar magnetic field reversal in 1999-2001.

[6]  There is appreciable asymmetry of solar corona in the northern and southern hemispheres. The corona of the northern hemisphere was brighter particularly at high altitudes. Period of 1997-2001 corresponds to polarward migration of filament bands in the process of magnetic field reversal. The inverse branch of coronal activity from high latitudes toward the equator was also observed after magnetic field reversal in 2001. However, the total ( K + F ) solar corona was observed with smaller average brightness at heights less than 4.0 R.

Figure 2

[7]  The solar corona brightness has longitude heterogeneity. Figure 2 shows the synoptic charts of ( K + F ) coronal brightness at heights of 2.5 R and 4.0 R for 1999. Active longitudes of the northern and southern hemispheres are similar and they do not correspond to model of heliosphere current layer [Zhao and Hoeksema, 1995].

Figure 3

[8]  The nonradial direction of coronal streamers is important property of coronal structures [Koutchmy and Loucif, 1984; Loucif and Koutchmy, 1989; Makarov, 1994; Nesmianovich, 1965]. The centers of coronal streamers have been determined for measurement nonradial direction of streamers on daily coronal images from LASCO-C2 during 1996-2002. The mean number of the streamers on one coronal image has been about 20 in the minimum and 30-40 in the maximum of the solar cycle, respectively. These data was used to determine angles between the center of coronal streamers and solar radius up to height 2.3 R. Figure 3a shows latitude-time distribution of the angles nonradial direction for all coronal structures. The total number of coronal streamers has been about 80,000 during 1996-2002.

[9]  One can see the two main periods connected with solar cycle. The first period is before an epoch 1999.5 when the streamers have the slope to equator. It corresponds to the model [Zhao and Hoeksema, 1995] in that the streamers have nonradial direction during the minimum activity and sloped to heliosphere current layer under influence of the magnetic field of coronal holes. Another period is after 1999.5 when the coronal streamers were turned to the poles of the northern and southern hemispheres. Maximum slope to the poles has been observed during the polar magnetic field reversal 2000-2001.

[10]  From another hand, the nonradial direction of coronal streamers does not change with solar cycle according to [Eselevich and Eselevich, 2002]. It changes with the latitude only. The coronal streamers on the latitudes up to 60^o were sloped to the equator, but they were sloped to the poles on the latitudes more than 60^o. We verified this hypothesis. Figure 3b shows the distribution of bright coronal streamers. It is seen that direction of coronal streamers was changed during the solar cycle after 1999.5. The coronal streamers were turned at all latitudes to the poles. There is some difference between the angles of the slope at the east and west solar limb.