Quiet time meridional (vertical) ion drifts at low and middle latitudes observed by ROCSAT‐1

Abstract

In situ ion drift observations from the ROCSAT‐1 satellite, near the 600 km altitude and for the years 1999–2003, are used to describe variations in the local time (LT) distribution of meridional E × B drifts at low and middle latitudes, for different longitudes and seasons. We derive the ion drifts in the direction perpendicular to the magnetic field during quiet times defined by Kp ≤ 3 and Dst > −100 nT. Offsets in the original data are removed by considering separately the northbound and southbound passes in a given volume and by enforcing magnetic conjugacy for the ion drift components perpendicular to the magnetic field. Three major features are identified for which the variations in latitude, longitude, and season allow the major drivers of these features to be indicated: (1) a latitude/magnetic apex height variation in the prereversal (after sunset) enhancement of the vertical drift that is attributed to similar variations in the flux tube–integrated Pedersen conductivity, (2) the daytime meridional drifts that are largely driven by the E region dynamo show significant latitude variations that are attributed to the relative importance of diurnal and semidiurnal wind fields as a function of latitude, and (3) a downward enhancement of the ion drift before sunrise is attributed to a reversal in the F region zonal wind during the nighttime.