A numerical model of the ionospheric signatures of time-varying magnetic reconnection: II. Measuring expansions in the ionospheric flow response

S K Morley,M Lockwood

doi:10.5194/angeo-23-2501-2005

Abstract

Abstract. A numerical model embodying the concepts of the Cowley-Lockwood (Cowley and Lockwood, 1992, 1997) paradigm has been used to produce a simple Cowley-Lockwood type expanding flow pattern and to calculate the resulting change in ion temperature. Cross-correlation, fixed threshold analysis and threshold relative to peak are used to determine the phase speed of the change in convection pattern, in response to a change in applied reconnection. Each of these methods fails to fully recover the expansion of the onset of the convection response that is inherent in the simulations. The results of this study indicate that any expansion of the convection pattern will be best observed in time-series data using a threshold which is a fixed fraction of the peak response. We show that these methods used to determine the expansion velocity can be used to discriminate between the two main models for the convection response to a change in reconnection. Keywords. Magnetospheric physics (Magnetosphereionosphere interactions) – Ionosphere (Plasma convection; Modeling and forecasting)

Highlights

The nature of the ionospheric convection response to a change in the IMF is the subject of much discussion, with evidence for two apparently conflicting viewpoints
Freeman uses a variant of the CL model since the polar cap maintains circularity at all times and the CL paradigm necessarily requires an anisotropic expansion of the polar cap followed by a progressive return to equilibrium by means of the resultant convection
Freeman did not model the effects of an expanding perturbation to equilibrium, introduced to the CL paradigm in later papers (Cowley and Lockwood, 1997; Lockwood and Cowley, 1999), but acknowledged that the instantaneous response at all local times was due to their adoption of a circular polar cap boundary

Summary

Introduction

The nature of the ionospheric convection response to a change in the IMF is the subject of much discussion, with evidence for two apparently conflicting viewpoints. Some recent papers have reported a two-stage ionospheric convection response (Murr and Hughes, 2001; Lu et al, 2002; Nishitani et al, 2002) to a change in the magnetopause reconnection rate These papers present observations that show that both quasi-instantaneous and expanding responses can occur concurrently, no consensus has yet been reached on a mechanism that incorporates both responses within a single framework. A recent paper by Freeman (2003) described both the CL and REA models within a single mathematical framework of the expanding-contracting polar cap (ECPC) model. Freeman did not model the effects of an expanding perturbation to equilibrium, introduced to the CL paradigm in later papers (Cowley and Lockwood, 1997; Lockwood and Cowley, 1999), but acknowledged that the instantaneous response at all local times was due to their adoption of a circular polar cap boundary

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