Southern hemisphere observations of a long-term decrease in F region altitude and thermospheric wind providing possible evidence for global thermospheric cooling

F region peak heights,.derived from ionospheric scaled parameters through 38-year data series from both Argentine Islands (65 degrees S, 64 degrees W) and Port Stanley (52 degrees S, 58 degrees W) have been analyzed for signatures of secular change. Long-term changes in altitude, which vary with month and time of day, were found at both sites. The results can be interpreted either as a constant decrease in altitude combined with a decreasing thermospheric wind effect or as a constant decrease in altitude which is altitude-dependent. Both interpretations leave inconsistencies when the results from the two sites are compared. The estimated long-term decrease in altitude is of a similar order of magnitude to that which has been predicted to result in the thermosphere from anthropogenic change related to greenhouse gases. Other possibilities should not, however, be ruled out.