Fig. 5
From: Occurrence of F region echoes for the polar cap SuperDARN radars
Line plots of the echo occurrence rate averaged between 12 and 18 LT (smoothed by applying a running 60-day boxcar filter) versus time of the year for a the northern hemisphere INV, CLY, and RKN radars and c the southern hemisphere MCM, SPS, and CLY radars. Dashed lines in a and c are the ground scatter occurrence rate for the INV and MCM radars, respectively. b and d are the average F region peak electron density between 12 and 18 LT (smoothed by applying a running 60-day boxcar filter), purple line, and the E × B magnitude (smoothed by applying a running 60-day boxcar filter, gray line in b only), both versus time of the year. Arrows in a and c point at local, minor echo occurrence minima in winter. Arrows in b indicate time equinoctial E × B plasma flow magnitude enhancements for some years of observations