VHF and HF radar measurements of E and F region plasma drifts at the magnetic equator

Abstract

Simultaneous observations of E region horizontal irregularity drifts by VHF backscatter radar and of F region vertical plasma drifts by HF Doppler radar conducted during daytime on a few magnetically quiet days at Trivandrum (dip 0.2°N) are presented. A comparative study of the two measurements indicates broadly (1) a resemblance in the daytime changes of the E‐W component between the electric fields and (2) evidence of quasi‐periodic electric field variations with periods ranging mostly from 1 to 2 hours. The electric fields derived from HF Doppler radar observations are somewhat lower than those deduced by VHF radar observations. The correlation coefficient for the variations of the electric fields measured by the two experimental techniques is found to be in the range of about 0.5 to 0.9. The observed difference in the E and F region electric fields at the magnetic equator is discussed in terms of the measurement uncertainties and the limitations involved in deriving E‐W electric fields. The observations are suggestive of a latitudinal variation in the E‐W component of the electric field in the equatorial ionosphere.