Day-to-day variations of geomagnetic declination in Indo-Russian longitude sector

Abstract

Day-to-day variability of the eastward component of geomagnetic field (<i>Y</i>) during a quiet period at a unique chain of thirteen geomagnetic observatories extending from 0° to 60° dip latitude within a narrow belt around 145°E geomagnetic meridian has been analyzed. The daily variations of the horizontal field (<i>H</i>) and geographic east component (<i>Y</i>) depart considerably from what is expected from the classical ionospheric current system described in literature. The correlations of DY between any two pairs of stations are higher as compared to the corresponding values for H field. The correlation for <i>Y</i>_range, <i>Y</i>_max or <i>Y</i>_min at Trivandrum with those of other stations decreases with increasing distance reaching a value of 0.5 at 40° dip latitude. At low latitudes, the <i>Y</i>_range is correlated better with <i>Y</i>_min than with <i>Y</i>_max. the differences in latitudinal variations of the correlation coefficients of both the <i>H</i>_range(<i>RH</i>) and <i>Y</i>_range (<i>RY</i>) are interpreted in terms of the superposition of the lunar semi-diurnal current system over global <i>S</i>_q current system. This develops a region between 20° and 40° dip latitudes with the zonal components of the two current systems opposing each other on some days and adding each other on other days without seriously affecting the meridional current components.