A nighttime temperature maximum in the thermosphere above Saint Santin in winter

摘要

The Saint Santin(45N)incoherent scatter radar data base shows a local enhancement in nighttime ion temperature that occurs in winter only. Its amplitude can exceed 100 K and averages 40 K on the basis of a conservative computation. The enhancement peaks near 4 LT and has a duration of about 4 hours. We discuss two possible explanations for this feature: (1) it is caused by the convergence of global winds at the global pressure minimum, under which Saint Santin rotates at winter solstice, and(2)it is an extension or propagation of the well-known low-latitude midnight temperature maximum to midlatitudes, perhaps to that pressure minimum.