Thermospheric changes shortly after the onset of daytime joule heating
Abstract
In the first few tens of minutes after the onset of widespread Joule heating, the motion of the ionospheric atmosphere can be approximated by the onedimensional motion of a gas in a gravity field  a problem that is easily solved because the motion takes place at constant pressure. The solution provides an estimate of time for which the model is applicable to the physical situation. Seasonal variations of the early effects are examined by using ion profiles appropriate to each season. The results show that the atmosphere above 100 km is strongly modified within a few tens of minutes after the onset of widespread heating: the density can double, the temperature can increase several hundred degrees, and the molecular nitrogen concentration can quadruple. Vertical winds exceeding 100 m/sec at 400km altitude are possible for a brief period after the onset of electric fields of 100 mV/m  rare but observed events. In the first few tens of minutes after the onset of a given electric field, the greatest power is deposited in the thermosphere around summer solstice, while the greatest winds occur at 200 km altitude in the summer and at 400km in the winter. These differing seasonal effects show primarily that a given level of change occurs sooner for one season than another, not that long term seasonal differences exist. Once a magnetic storm is in progress, the quietday ion profiles change to the nonseasonal storm profile ; for this ion distribution, Fregion effects are minimum regardless of season. Joule heating effects in the upper thermosphere are therefore concluded to be selflimiting.
 Publication:

Planetary and Space Science
 Pub Date:
 December 1974
 DOI:
 10.1016/00320633(74)901068
 Bibcode:
 1974P&SS...22.1625B
 Keywords:

 Ionospheric Disturbances;
 Ionospheric Heating;
 Magnetic Storms;
 Resistance Heating;
 Thermosphere;
 Annual Variations;
 Atmospheric Models;
 Ionospheric Conductivity;
 Ohmic Dissipation;
 One Dimensional Flow;
 Plasma Dynamics;
 Polar Substorms;
 Wind Profiles;
 Geophysics