Simultaneous radar observations of meter-scale F region irregularities at and off the magnetic equator over India

Abstract

Simultaneous observations of equatorial spread F irregularities made with an 18 MHz radar from Trivandrum, located at the geomagnetic equator, and a 53 MHz radar from Gadanki, located at a magnetic latitude of 6.5°N, corresponding to nearly the same longitude zone, are presented. The observations correspond to 8.3 and 2.8 m irregularities, respectively. The spread F irregularities at both the locations are found to occur nearly at the same time but are observed for longer duration at Gadanki than at Trivandrum. The spread F structures as observed in the intensity maps corresponding to Gadanki are characterized by multiple periodic plumes in contrast to a limited number of plumes observed over Trivandrum. The Doppler velocities associated with these irregularities corresponding to Trivandrum are in the range of -100-150 m s^-1, whereas they are in the range of -100-250 m s^-1 at Gadanki. Further, the fluctuating velocity fields are much stronger in the Gadanki observations than in the Trivandrum observations. Remarkably, the spectral widths are <100 m s^-1 in Trivandrum observations in contrast to those observed at Gadanki with values as high as 300 m s^-1. The observations are compared with those made elsewhere and are discussed in the light of current understanding of the meter-scale irregularities responsible for the radar backscatter.