Neutral wind-driven gradient drift instability in the low-latitude daytime e region

Abstract

We present strong evidence for the wind-driving, daytime E region field-aligned irregularities (FAIs) on the basis of Sanya VHF radar observations on 29 June 2009. The observed sporadic E (Es) and echoing layers show a clear diurnal tidal descending trend and a gravity-wave-scale oscillation with a period of 40-50 min, which are consistent with the diurnal tidal height evolution seen from the meteor wind observations. The most important finding is that the daytime continuous FAIs are closely related to the negative vertical zonal wind shear, which also forms the dense ion layer. Associated observations suggest that the FAIs are generated on both sides of the Es layer. The echoes form two layers with 10 km vertical distance, about half the vertical wavelength of the diurnal tide. Our results, for the first time, demonstrate that the daytime E region continuous FAIs can be formed by the wind-driven gradient drift instabilities. We suggest that the latitudinal variation of the daytime E region FAI morphologies is caused by the dip angle dependence of the instability growth rate. Continuous echoes observed elsewhere at low latitudes and midlatitudes may also be attributed to the wind effects. Copyright 2011 by the American Geophysical Union.