Modeling the observed proton aurora and ionospheric convection responses to changes in the IMF clock angle: 2. Persistence of ionospheric convection

Lockwood, M., Throp, K., Lanchester, B.S., Morley, S.K., Milan, S.E., Lester, M. and Frey, H.U. (2006) Modeling the observed proton aurora and ionospheric convection responses to changes in the IMF clock angle: 2. Persistence of ionospheric convection. Journal of Geophysical Research, 111 (A02306), 1-13. (doi:10.1029/2003JA010307).

Abstract

[1] We apply a numerical model of time-dependent ionospheric convection to two directly driven reconnection pulses during a 15-min interval of southward IMF on 26 November 2000. The model requires an input magnetopause reconnection rate variation, which is here derived from the observed variation in the upstream IMF clockangle, θ. The reconnection rate is mapped to an ionospheric merging gap, the MLT extent of which is inferred from the Doppler-shifted Lyman-α emission on newly opened field lines, as observed by the FUV instrument on the IMAGE spacecraft. The model is used to reproduce a variety of features observed during this event: SuperDARN observations of the ionospheric convection pattern and transpolar voltage; FUV observations of the growth of patches of newly opened flux; FUV and in situ observations of the location of the Open-Closed field line Boundary (OCB) and a cusp ion step. We adopt a clock angle dependence of the magnetopause reconnection electric field, mapped to the ionosphere, of the form E_nosin⁴(θ/2) and estimate the peak value, E_no, by matching observed and modeled variations of both the latitude, Λ_OCB, of the dayside OCB (as inferred from the equatorward edge of cusp proton emissions seen by FUV) and the transpolar voltage Φ_PC (as derived using the mapped potential technique from SuperDARN HF radar data). This analysis also yields the time constant t_OCB with which the open-closed boundary relaxes back toward its equilibrium configuration. For thecase studied here, we find t_OCB = 9.7 ± 1.3 min, consistent with previous inferences from the observed response of ionospheric flow to southward turnings of the IMF. The analysis confirms quantitatively the concepts of ionospheric flow excitation on which the model is based and explains some otherwise anomalous features of the cusp precipitation morphology.

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