31st Annual European Meeting on Atmospheric Studies by Optical Methods, Ambleside, Lake District, U.K., 22-28 August 2004

Effects of long-term cooling of the lower ionosphere on cosmic radio noise absorption

Th. Ulich¹, E. Turunen¹, P. Verronen², C.-F. Enell¹, A. Ranta¹

¹Sodankylä Geophysical Observatory, Sodankylä, Finland,
²Finnish Meteorological Institute, Geophysical Research Division, Helsinki, Finland.

Abstract

Model estimates of the effects of increasing greenhouse gas emissions predict cooling of the mesosphere and lower thermosphere (MLT) of typically 10K for doubled greenhouse gases. Various authors claim to observe a cooling in the MLT region by means of, among others, rocket soundings, measurements of F2-layer peak height, satellite drag, and ionospheric critical frequencies. Serafimov and Serafimova (1992) predicted that because the absorption of cosmic radio noise depends on electron-neutral collision frequency, which, in turn, is a function of temperature and neutral air density, riometer measurements reflect long-term changes of temperature. Here we use the detailed Sodankylä neutral and ion chemistry model (SIC) to estimate the effects of a cooled neutral atmosphere on chemical composition and on absorption of cosmic radio noise.