2011 SuperDARN Workshop       

SuperDARN and reversed flow events in the cusp

K. Oksavik (1), J. Moen (1,2), E.H. Rekaa (2), H.C. Carlson (3) and M. Lester (4)
(1) The University Centre in Svalbard, Longyearbyen, Norway
(2) Department of Physics, University of Oslo, Oslo, Norway
(3) Center for Atmospheric & Space Sciences, Utah State University, Logan, Utah, USA
(4) Department of Physics & Astronomy, University of Leicester, Leicester, U.K.

abstract. We present several examples of reversed flow events (RFEs) from the cusp ionosphere. RFEs are 100-200 km wide flow channels opposing the background plasma convection. RFEs were discovered a few years ago by the EISCAT Svalbard Radar. In this paper we show that SuperDARN can also see RFEs. We use the location of distinct auroral signatures to test the standard range finding algorithm, and we find that it overestimated the ground range of the SuperDARN echoes by 140 km. We report a close relationship between RFEs and the development of HF backscatter power and spectral width. Wide spectra were seen near the edges of the RFEs (i.e. associated with the flow shear), and there was a significant increase in SuperDARN HF backscatter power when the RFE expanded, much faster than anticipated from the gradient drift (GD) instability alone, suggesting that RFE flow shears may foster rapid growth of Kelvin-Helmholtz (KH) instabilities. However, the cusp ionosphere is a complex region and other modes of instability growth may also be relevant.

Sakaguchi KaoriNICT Japan