Statistical properties of Polar Mesosphere Summer Echoes as detected with the Super Dual Auroral Radar Network

Polar Mesosphere Summer Echoes (PMSE) are extremely strong radar backscatter from mesospheric heights which are frequently observed during summer months at polar latitudes. PMSE have been studied with the ground-based VHF radars in Alaska and Scandinavian sector for more than 20 years. In contrast, observations in other local time sectors and in the Southern Hemisphere are not enough and our knowledge on global distribution of PMSE is still poor. This is mainly due to the lack of VHF radar facilities suitable for the detection of PMSE in these regions. Further detailed investigations are required to estimate possible interhemispheric asymmetry and global distribution of PMSE activities. Alternative way of monitoring the occurrence of PMSE in more global sense is indispensable for more detailed analysis of PMSE. Recent investigations of near-range measurements recorded by the Super Dual Auroral Radar Network (SuperDARN) have suggested that PMSE can be detected by the oblique-sounding coherent HF radars of SuperDARN (Ogawa et al., 2002, 2003, 2004; Hosokawa et al., 2004). Very recently, Hosokawa et al. (2005) developed an algorithm for automated extraction of PMSE from near-range SuperDARN measurements. The algorithm is applied to the data obtained by the Syowa East radar in Antarctica and Pykkvibaer radar in Iceland whose fields-of-view are magnetically conjugate. The rate of PMSE occurrence in the SuperDARN data is greatly enhanced in summer months. The rate of PMSE occurrence reaches a maximum of 90% in Iceland and 60% in Syowa near the summer solstice, suggesting possible interhemispheric asymmetry of PMSE activities. In this paper, we have examined statistical characteristics of SuperDARN-PMSE as extracted from the data of more than 10 years with the algorithm introduced by Hosokawa et al. (2005). Consequently, significant frequency dependence of PMSE occurrence probability was found, in which the echoes are more prominent when the radar is operated at lower frequencies. This frequency dependence is probably due to the elevation angle dependence of the main beam on the operating frequencies. We also estimated latitudinal and longitudinal distributions of PMSE activities by using all available SuperDARN data. We will discuss derived global map of PMSE activities in terms of distributions of mesospheric temperature and winds.