Mesosphere summer echoes observed with VHF and MF radars at Wakkanai, Japan (45.4°N)

Mesosphere summer echoes (MSE) were observed during 2000-2001 and in 2009 with a 46.5-MHz VHF radar at Wakkanai, Japan (45.4 degrees N). MSE at VHF (VHF-MSE) are active at 80-90 km altitudes in the daytime mainly during June-July. Echo layer thickness ranges from a few to about 5 km, and layer altitude and echo intensity are often modulated by short-period atmospheric gravity waves while the layer descends gradually at 0.2-0.8 m/s with time, maybe due to tides. Detailed analyses of three VHF-MSE events show that meridional winds at the MSE altitudes over Wakkanai observed with a collocated 1.96-MHz MF radar are equatorward, indicating that cold ice particles and/or irregularities are advected southward from higher latitudes. It is found that VHF-MSE are often accompanied by simultaneous MSE at MF (MF-MSE) from a common volume, suggesting that plasma turbulence and/or short-scale electron density structures are responsible for the generation of VHF- and MF-MSE. (C) 2011 Elsevier Ltd. All rights reserved.