Climatology of Air Upwelling and Vertical Plasma Flow in the Terrestrial Cusp Region: Seasonal and IMF-Dependent Processes
At polar regions a continuous outflow occurs of terrestrial atmosphere into space. Thermodynamic forces are not strong enough to allow air parcels escaping the Earth’s gravity field. But due to the partial ionization of the upper atmosphere by the sun’s short-wavelength radiation electrodynamic forces can move the charged particles upward along open field lines. Already in the early space age it was recognized that considerable amounts of ionospheric ions populate the magnetosphere. In this chapter, the acceleration mechanisms of the upwelling ions at altitudes of source regions are investigated. For the first time the role of the neutral particles in the thermosphere is also included in the considerations. In our studies we make use of data from the satellites CHAMP (400 km), GRACE (500 km), and DMSP (830 km). Detailed studies are performed to analyze the conditions accompanying the upwelling of neutral and ionized particles. Here we consider average properties of field-aligned currents, thermospheric wind, and electron temperature. Also, the dependences on environmental conditions are tested. Hardly any dependence on seasons emerges either for air upwelling or for ion upflow. An important driver for the processes seems to be magnetic field reconnection between the terrestrial and interplanetary magnetic field (IMF) and with that the orientation of the IMF. Intense flows of precipitating electrons, which are caused by the merging process, play a central role for both kinds of upflow. But further drivers, different for the two species, are needed to facilitate the observed ion and neutral upwelling.
The CHAMP and GRACE missions were sponsored by the Space Agency of the German Aerospace Center (DLR) through funds of the Federal Ministry of Economics and Technology. The Center for Space Sciences at the University of Texas at Dallas and the US Air Force are gratefully acknowledged for making available the DMSP thermal plasma data. The authors gratefully acknowledge the use of NASA/GSFC’s Space Physics Data Facility’s OMNIWeb service and OMNI IMF and Solar wind data. The Deutsche Forschungsgemeinschaft (DFG) supported G. N. Kervalishvili through the Priority Programme “Planetary Magnetism” SPP 1488.
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