Simulation study of the longitudinal variation of evening vertical ionospheric drifts at the magnetic equator during equinox

Abstract

Quiet‐time low‐latitude ionospheric electric fields and vertical drifts in the evening sector at equinox are examined as a function of longitude and solar activity, using simulations from the Magnetosphere‐Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (MTIEGCM). The model inputs are held fixed with respect to universal time, in order to evaluate the contributions to longitudinal variations of the equatorial electric fields and drifts associated with zonal variations in the geomagnetic field. The simulated upward evening drift is somewhat larger than observations. It increases with solar activity at a similar rate in all longitude sectors. This rate, about 0.32–0.37 m/s per unit of 10.7 cm solar flux, is quantitatively consistent with observations in the Peruvian sector but is considerably greater than observations in the Indian sector. The simulations agree with observations in finding larger vertical drifts in the American‐Atlantic sector than in the East Asian‐Pacific sector, generally associated with longitudinal variations in the strength of the geomagnetic field. Relations among the longitude variations of the vertical drift, the conductivity, the eastward wind velocity, the geomagnetic declination, and gradients of the wind and declination are examined, revealing few clear correlations. However, extrema of many of these quantities are noted in the American‐Atlantic sector.