Large-scale instabilities of the lower thermosphere during an active period

Abstract

[1] We have simulated the high-latitude thermosphere during active periods with a general circulation model and have examined the instability of the thermospheric polar jets spun up by ion drag. We find that the jets are unstable as a result of strong vertical shears on the bottom side (baroclinic) and strong lateral shears on the flanks (barotropic). We have analyzed the model output for evidence of structures indicative of instability and have found a disturbance in the region of strong vertical shear indicative of baroclinic instability and structures at higher altitudes indicative of barotropic instability. Our finding suggests that it may be possible to understand high-latitude structures such as density cells in the framework of instabilities. These structures are presently not included in empirical models used for density prediction in the upper atmosphere.