On the variability of equatorial F-region vertical plasma drifts

We use incoherent scatter radar measurements from the Jicamarca Observatory to study the variability of equatorial F-region vertical plasma drifts. The daytime average upward drifts do not vary much with solar activity, but the evening upward and the nighttime downward drifts increase from solar minimum to solar maximum. Our data indicate that the quiet-time variability of the Jicamarca vertical drifts is local time, seasonal, and solar cycle dependent. This variability is largest in the dawn-noon sector and during March equinox solar minimum periods, when the midday average upward drift velocity from consecutive magnetically quiet days can often change by more than 10 m/s. The day-to-day variability of the vertical drifts decreases in the afternoon sector and with the increase of solar activity for all seasons. There are several possible processes responsible for the quiet-time plasma drift variability. (C) 2001 Elsevier Science Ltd. All rights reserved.