Zonal and meridional ionospheric currents in the Central Asian sector

Abstract

The daily and seasonal variations of all the three components <i>H</i>, <i>Y</i> and <i>Z</i> of the geomagnetic field have been described on the basis of the data from a unique network of observations within a narrow longitude belt extending from the magnetic equator to 60° dip latitude. The daily variations of the westward field (<i>Y</i>) shows remarkable changes between the summer and winter months. The amplitude of the daily variation is reduced to an insignificantly small value during the local winter months. The horizontal field (<i>H</i>) also does not show clear variation at observations north of the latitude of <i>S</i>_q focus during the local winter months. These features lead to the absence of vortex-type <i>S</i>_q current system during local winter months. The latitudinal variations of the diurnal and semi-diurnal components are discussed in detail. Seasonal variations in solar and lunar tides have been discussed and attributed to rather independent sources in the zonal and meridional currents. The tidal modes of ionospheric winds in the Central Asian sector need to the probed for explaining the drastic changes of the observed effects with season.