IONOSPHERIC RESPONSE TO TRAVELING CONVECTION TWIN VORTICES

Traveling convection twin vortices have been observed for several year s. At ionospheric altitudes, the twin vortices correspond to spatially localized, transient structures embedded in a large-scale background convection pattern. The convection vortices are typically observed in the morning and evening regions. They are aligned predominantly in the east-west direction and have a horizontal extent of from 500-1000 km. Associated with the twin vortices are enhanced electric fields, parti cle precipitation, and an upward/downward field-aligned current pair. Once formed, the twin vortex structures propagate in the tailward dire ction at speeds of several km/s, but they weaken as they propagate and only last for about 10-20 minutes. Because these convection structure s might have a significant effect on the localized ionosphere, the USU ionospheric model was used to calculate the response of the ionospher e to ''representative'' traveling convection twin vortices for a range of background conditions. The ionospheric response includes localized temperature enhancements, ion composition changes, non-Maxwellian ion distributions, and plasma upwelling events. The response is transient and the magnitude of the response depends on the background ionospher ic conditions and on the characteristics of the twin vortices.