The ionospheric signature of transient dayside reconnection and the associated pulsed convection return flow

S E Milan,M Lester,G Sofko,R A Greenwald

doi:10.1007/s005850050841

Abstract

Three SuperDARN coherent HF radars are employed to investigate the excitation of convection in the dayside high-latitude ionosphere in response to transient reconnection occurring in the cusp region. This study demonstrates the existence of transient antisunward-propagating backscatter features at the expected location of the ionospheric footprint of the cusp region, which have a repetition rate near 10 min. These are interpreted as the ionospheric signature of flux transfer events. Moreover, transient sunward-propagating regions of backscatter are observed in the convection return flow regions of both the pre- and post-noon sectors. These patches are observed to propagate towards the noon sector from at least as far around the auroral zone as 07 MLT in the pre-noon sector and 17 MLT in the post-noon sector, travelling with a velocity of approximately 1.5 to 2 km s-1. These return flow patches have a repetition rate similar to that of the transient features observed at local noon. While providing supporting evidence for the impulsive nature of convection flow, the observation of sunward-propagating features in the return flow region is not consistent with current conceptual models of the excitation of convection.Key words. Ionosphere (plasma convection) Â· Magnetospheric physics (magnetopause Â· cusp Â· and boundary layers; magnetosphere-ionosphere interactions)

Highlights

Ionospheric convection is generally accepted to be excited, at least in part, by magnetic reconnection occurring on the dayside at or near the subsolarCorrespondence to: S
The present study reports on measurements of the plasma drift over a signi®cant proportion of the dayside high-latitude ionosphere, made by three of the SuperDARN coherent HF radars
Between 76° and 80° magnetic latitude, a region of backscatter with plasma drift away from the radar is observed; this region is thought to correspond to the ionospheric footprint of the cusp, as will be discussed later

Summary

Introduction

Ionospheric convection is generally accepted to be excited, at least in part, by magnetic reconnection occurring on the dayside at or near the subsolarCorrespondence to: S. That within this conceptual framework the excitation of convection is a consequence of the displacement of the pre-existing openux of the polar cap by the much smaller region of newly openedux created by reconnection; as the ratio of areas of the new and old openux regions is of the order of 0.03 (Lockwood et al, 1990), the plasma displacement in response to an individual FTE should be small, especially away from the ionospheric footprint of the cusp.

Results

Conclusion