Ion drifts observed at Malvern: evidence of ion drag and substorm induced electric fields

Abstract

Day-time ion drift observations, made at Malvern (52.1°N, 2.3°W) using an incoherent scatter radar in quadristatic configuration during the period October 1972 to October 1974 are analysed. Out of the seventeen days' observations considered here nine are magnetically quiet days and eight are magnetically disturbed days. A significant negative correlation was observed between v ∥ (field aligned ion drift) and v TN (crossfield drift in meridional plane) on all the days, indicating that ion drag is important even on magnetically disturbed days. Drifts along the field line v ∥ ' ( v ∥ after removing the ion drag component) showed less day-to-day variability as compared to v ⊥ N and v ⊥ E where v ⊥ E is the crossfield drift in the zonal plane. The value of v ∥ 'is ~20 ms −1 and it is found to be mostly downwards. Crossfield drifts ( v ⊥ N , v ⊥ E ) showed larger day-to-day variability indicating the same variability for their driving electric fields. Values of v ⊥ E are found to be larger than those of v ⊥ N indicating stronger north-south electric fields. The large day-to-day variability in crossfield drifts suggest that even on quiet days there is a significant contribution from electric fields of magnetospheric origin. A major substorm event on 18 September 1974 is accompanied by a substantial reduction in eastward drift ( v ⊥ e ) though change in v ⊥ N is comparatively smaller. Similar changes are noticed for other substorm events occurring in after noon hours in European longitude zone. These results confirm that substorm electric fields penetrate down to the latitude of Malvern.