2011 SuperDARN Workshop
Observations of an evening enhancement in ground backscatter from mid-latitude SuperDARN radars
S. de Larquier, J.M. Ruohoniemi, J.B.H. Baker, N. Ravindran-Varrier
Bradley Department of Electrical and Computer Engineering, Virginia Tech, Blacksburg, Virginia, USA
abstract. Under geomagnetically quiet conditions, the daytime mid-latitude ionosphere is mainly influenced by solar radiation: typically, electron densities in the ionosphere peak around solar noon. Previous observations from the Millstone Hill Incoherent Scatter Radar (ISR) have evidenced the presence of evening electron densities higher than daytime densities during the summer. The recent development of mid-latitude Super Dual Auroral Radar Network (SuperDARN) radars over North America and Japan has revealed an evening enhancement in ground backscatter during the summer. SuperDARN observations are compared to data from the Millstone Hill ISR, confirming a direct relation between the observed evening enhancements in electron densities and ground backscatter. Statistics over a year of data from the Blackstone radar show that the enhancement occurs during sunset for a few hours from April to September. The evening enhancement observed by both SuperDARN and the Millstone Hill ISR is shown to be related to recent satellite observations reporting an enhancement in electron densities over a wide range of longitudes in the Northern hemisphere mid-latitude sector during summer time. Finally, global results from the International Reference Ionosphere (IRI) and the Horizontal Wind Model (HWM07) are presented in relation with previously published experimental results and proposed mechanisms of the evening enhancement, namely thermospheric horizontal winds and geomagnetic field configuration. It is shown that the IRI captures the features of the evening enhancement as observed by SuperDARN radars and satellites.