A Study of the Afternoon Convection Cell's Response to an IMF Southward Turning

Nozomu NISHITANI and Tadahiko OGAWA
Nagoya University, Japan
Natsuo SATO and Hisao YAMAGISHI
National Institute of Polar Research, Japan
Mike PINNOCK
British Antarctic Survey, UK
Jean-Paul VILLAIN
LPCE/CNRS, France
George SOFKO
University of Saskatchewan, Canada

There has been a lot of controversy over the topic of ionospheric response to an IMF southward turning. [1] and [2] reported that the ionospheric responses are immediate, and that they are probably due to the propagation of disturbances with a fast magnetosonic mode. On the other hand [3] and other papers concluded that there should be an expansion of the convection cell with a time scale of 10 to 20 minutes, which they actually observed with EISCAT and other instrument. In this paper we deal with an event where the IMF turns from northward (+6 nT) to southward (-19 nT) within 30 minutes and discuss the response of the ionospheric convection to the IMF southward turning. In fact we observe both (1) sudden response of the convection change from the noon to the midnight sector, and (2) equatorward expansion of the afternoon convection cell with the time delay of up to 20 min. These results are consistent with both immediate response and expanding convection cell theories.

[1] Ridley et al., J. Geophys. Res., 103, 4023-4039, 1998.
[2] Ruohoniemi and Greenwald, J. Geophys. Res., 101, 21743-21763, 1996.
[3] Lockwood et al., Geophys. Res. Let., 13, 72-75, 1986

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