NEUTRAL DENSITY CELLS IN THE HIGH-LATITUDE THERMOSPHERE .1. SOLAR MAXIMUM CELL MORPHOLOGY AND DATA-ANALYSIS

A new high latitude thermospheric neutral density structure has been r evealed in NCAR-TIGCM simulations at 120-350 km altitude. The structur e consists of density cells above 50 degrees latitude with radii of ap proximately 1000 km. There are between two to four cells present depen ding on the altitude and magnetic activity. For example, at 200 km und er magnetically active conditions, the density structure consists of f our cells: low density cells are located near dawn and dusk and high d ensity cells are located near noon and midnight. Density variations am ong the cells range from 5 to 50% for magnetically quiet and active co nditions respectively. The cells are present at all seasons, for a wid e range of magnetic activity levels, and at solar minimum and solar ma ximum. The density cell morphology is established for equinox solar ma ximum as a function of altitude and magnetic activity. Departures of t he cell structure from this morphology due to seasonal and solar cycle s are discussed. The cell morphology provides a new framework in which to interpret lower thermospheric density data. Data to test and confi rm the model predictions were provided by the SETA-1 satellite. Copyri ght (C) 1996 Elsevier Science Ltd