Observations of mesospheric summer echoes at VHF in the polar cap region

VHF radar measurements have been carried out at high polar latitudes using the SOUSY-Svalbard-Radar in the summer of 1999 and spring of 2000 at Longyearbyen/Norway (78 degrees N, 16 degrees E). The vertical and temporal variabilities of polar mesospheric summer echoes and mean winds in the mesopause region have been studied for the first time at such high latitudes in the polar cap region. The typical height variation of the received signal is characterized by a pronounced double layer structure during June and July, which is much less pronounced at latitudes 10 degrees further south. Within late summer to equinox conditions, however, the two peaks merge and one layer is dominating. It is suggested that these features together with observed changes in the mesospheric wind system are related to the temperature variation in the mesopause region.