2011 SuperDARN Workshop
Sub-auroral flow shear observed by King Salmon HF radar and RapidMAG
T. Hori (1), T. Kikuchi (1), Y. Tsuji (1), A. Shinbori (2), K. Ohtaka (3), M. Kunitake (3), S. Watari (3), T. Nagatsuma (3) and O. Troshichev (4)
(1) Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Japan
(2) Research Institute of Sustainable Humanosphere, Japan
(3) National Institute of Polar Research, Japan
(4) Arctic and Antarctic Research Institute, Russia
abstract. We examine in detail the evolution of ionospheric flow shears found in the sub-auroral region. Flow shear structures are often observed in the dusk sector by the SuperDARN King Salmon (KSR) HF radar. Interestingly, some of those show the eastward (westward) flow on the lower (higher) latitude side, respectively, opposite to the typical polarity of the dusk convection cell. In some of those flow shear events, the IMF has a weak but persistent southward component (~ -1 to -3 nT) before onset of flow shears and following decreases of the southward IMF or even northward turning appear to cause the flow shears. The radar observations also show that those changes of convection structure take place rather quickly (~several min). The ground magnetograms provided by the Russian Auroral and Polar Ionospheric Disturbance Magnetometers (RapidMAG) show gradual increases (abrupt declines) of the H-component in association with the increases (decreases) of the merging electric field, respectively, derived from the simultaneous solar wind-IMF observations. The fairly coherent increases (decreases) of the H-component over the wide range of local time (afternoon to evening) indicate development (decay) of the large-scale DP2 current system. We also made ostatistical studies on this kind of flow shear events. It is found that some of flow shears are formed upon changes of the DP2 current system, while more flow shears occur during substorms and do not necessarily show clear temporal correlation with DP2 variations. Comparison of flow shear positions with simultaneous satellite observations revealed that flow shears are formed in the region of the trapped ring current or plasma sheet ions. This fact suggests that the diverging electric field at a flow shear is brought in the ionosphere by a field-aligned current from the ring current and/or the plasma sheet.