Occurrence rates of SuperDARN ground scatter echoes and electron density in the ionosphere

Ground scatter (GS) echoes in Super Dual Auroral Radar Network (SuperDARN) observations have been always expected to occur under high-enough electron density in the ionosphere providing sufficient bending of high frequency radio wave paths toward the ground. In this study, we provide direct evidence statistically supporting this notion by comparing the GS occurrence rate for the Rankin Inlet SuperDARN radar and the F region peak electron density N
m
F
2
measured at Resolute Bay by the Canadian Advanced Digital Ionosonde and incoherent scatter radars RISR-N/C. We show that the occurrence rate increases with N
m
F
2
roughly linearly up to about ∼4 · 10
¹¹
m
⁻³
and the trend saturates at larger N
m
F
2
. One expected consequence of this relationship is correlation in seasonal and solar cycle variations of the GS echo occurrence ratte and N
m
F
2
. GS occurrence rates for a number of SuperDARN radars at middle latitudes, in the auroral zone and in the polar cap are considered separately for daytime and nighttime. The data indicate that the daytime occurrence rates are maximized in winter and nighttime occurrence rates are maximized in summer for middle latitude and auroral zone radars in the Northern Hemisphere, consistent with the winter anomaly (WA) phenomenon. The effect is most evident in the North American and Japanese sectors, and the quality of WA signatures deteriorates in the European and, especially, in the Australian sectors. The effect does not exist in the South American sector and in the polar caps of both hemispheres.