Dependence of polar mesosphere summer echoes on solar and geomagnetic activity Original Research Article

Observations of polar mesosphere summer echoes (PMSE) were carried out at Andenes (69.3°N, 16.0°E) with the ALOMAR SOUSY radar during 1994–1997 and with the ALWIN radar during 1999. These data have been used to investigate the dependence of PMSE on solar and geomagnetic activity. Mainly during night-time and the morning hours a significant correlation was found between the signal-to-noise ratio (SNR) of the radar echoes and the geomagnetic K indices of Tromsø (69.66°N, 18.94°E). This correlation is markedly smaller during afternoon. Supported by investigations with riometer observations at Andenes and Ivalo (68.55°N, 27.28°E) the diurnal variation of the correlation between SNR and geomagnetic activity can be explained by the diurnal variation of ionization due to precipitation of high energetic particles. Changes of the solar wave radiation characterized by the Lyman α radiation or the solar 10.7 cm radio flux (F10.7 index), however, do not create significant PMSE variations.