Medium frequency radars in Japan and Alaska for upper atmosphere observations

MF (medium frequency) radars (MFR) are powerful tools for understanding the upper atmosphere, by measuring horizontal wind velocity and electron densi ty. This article introduces three MFR systems, two in Japan, Yamagawa (31.2 0 degrees N, 130.62 degrees E) and Wakkanai (45.36 degrees N, 141.81 degree s E) radars, and one at Poker Flat, Alaska (85.1 degrees N, 147.5 degrees W ). Experimental techniques, and their observed results are briefly shown. H orizontal wind velocity was observed by those MFRs, in height ranges of 60- 100 km (day) and 80-100 km (night) at Yamagawa and Wakkanai, while the data coverage is unusually low, > 54 km (day) and > 68 km (night), at Poker Fla t. Comparison of MFR winds with temperature observed by a collocated Raylei gh lidar at Poker Flat shows consistency of those two instrument results in terms of atmospheric wave theory, implying validity of MFR data at such lo w altitudes. Electron density results at Poker Flat agree reasonably with I nternational Reference Ionosphere model values at 74-84 km, and agree well with variation of cosmic noise absorption by the Poker Flat imaging riomete r, suggesting valid electron density estimation by MFR at least below 80-85 km.