Polarisation Characteristics of Pulsations Associated with Storm Sudden Commencements.

Abstract

Polarisation properties of magnetic pulsations associated with SCs recorded at an equatorial station, Choutuppal (Gm. Lat.: 7.5°N), during the years 1970-88 have been analysed. The results show that in contrast to a well defined local time dependent sense of rotation of polarisation vector reported for high and middle latitude pulsations (Wilson and Sugiura, 1961;Lanzerotti et al., 1981), the equatorial pulsations exhibit a predominantly clockwise sense of rotation particularly from around 22 his to early afternoon hours (13 to 14 his LT) while the events occurring later in the afternoon exhibit, in addition, a counter clockwise sense as well. The results for this equatorial station are consistent with the observations reported for very low latitude stations (Yumoto, 1986), thus indicating a latitudinal factor in characterising the local time dependence of sense of rotation of polarisation vector. The results are discussed in relation to the existing models invoking the azimuthally travelling ionospheric eddy currents for the immediate source of equatorial pulsations.