Abstract
Abstract. The occurrence of F region ionospheric echoes observed by a number of SuperDARN HF radars is analyzed statistically in order to infer solar cycle, seasonal, and diurnal trends. The major focus is on Saskatoon radar data for 1994–2012. The distribution of the echo occurrence rate is presented in terms of month of observation and magnetic local time. Clear repetitive patterns are identified during periods of solar maximum and solar minimum. For years near solar maximum, echoes are most frequent near midnight during winter. For years near solar minimum, echoes occur more frequently near noon during winter, near dusk and dawn during equinoxes and near midnight during summer. Similar features are identified for the Hankasalmi and Prince George radars in the northern hemisphere and the Bruny Island TIGER radar in the southern hemisphere. Echo occurrence for the entire SuperDARN network demonstrates patterns similar to patterns in the echo occurrence for the Saskatoon radar and for other radars considered individually. In terms of the solar cycle, the occurrence rate of nightside echoes is shown to increase by a factor of at least 3 toward solar maximum while occurrence of the near-noon echoes does not significantly change with the exception of a clear depression during the declining phase of the solar cycle.
Highlights
The SuperDARN HF radars monitor global-scale plasma convection patterns by measuring the Doppler velocity of coherent echoes received from the F region ionosphere
It has been established that the rate of echo detection with the SuperDARN radars varies with radar location, time of day, season and solar cycle (e.g., Milan et al, 1997; Ruohoniemi and Greenwald, 1997; Koustov et al, 2004; Kane et al, 2012)
Since the inferred pattern of seasonal and MLT/local time (LT) variations in echo occurrence seems to be similar for at least several northern hemisphere and one southern hemisphere SuperDARN radars, we hypothesized that it might be seen in data for the entire network
Summary
The SuperDARN HF radars monitor global-scale plasma convection patterns by measuring the Doppler velocity of coherent echoes received from the F region ionosphere. An abundance of such echoes is a critical factor for producing reliable convection maps. Changes in propagation conditions for radio waves to reach ionospheric irregularities and irregularity production factors have been discussed as reasons for variations in echo occurrence. This study performs a more detailed investigation of the diurnal (magnetic local time, MLT), seasonal and solar cycle variations in the occurrence of F region echoes detected by the SuperDARN radars than previous studies mentioned in the above paragraph.
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