Inertial instability analysis of the equatorial F region zonal neutral jet

Inertial instability in the atmosphere is a fundamental packet type instability in which an imbalance in the horizontal forces leads to amplifying meridional excursions in a zonal flow and the generation of waves. The instability criterion depends on the sign of the difference between the Coriolis parameter and the meridional gradient of the mean zonal flow. Because of the small value of the Coriolis parameter near the equator, the low-latitude regions are especially susceptible to this type of instability, as has been shown in a number of analyses of equatorial flows at altitudes below the thermosphere. Recent results based on CHAMP satellite data have shown the presence of a zonal jet in the F region that follows the magnetic equator, i.e., a region close to but not generally coincident with the geographic equator. The large winds imply decreasing winds on either side of the maximum and thus significant meridional gradients in the zonal winds, which suggests that the conditions for inertial instability may exist. Here we analyze some of the wind observations to determine the stability of the flow with respect to inertial instability