Model/data comparisons of ionospheric outflow as a function of invariant latitude and magnetic local time

Abstract

Globally quantifying ionospheric outflows as a function of local time, invariant latitude and solar wind conditions is the key to determining the mass loading of the magnetosphere, and it subsequent dynamics. This paper provides a first comparison of model predicted outflows with Polar and Akebono outflow measurements for a quiet period that occurred on 18 March 1997. It is shown that that the model is able to account for the H+ fluxes observed on the dayside by Akebono with fluxes of the order of several times 109 ions/cm2/s. H+ fluxes observed by Polar in the midnight auroral zone are lower by an order of magnitude than the model fluxes. The difference is attributed to the presence of a lower energy component below the low energy cutoff of TIMAS. During the geomagnetically quiet conditions considered here, the model underestimates the O+ flux seen by Akebono on the dayside. The model correctly predicts the energetic fluxes of O + seen on the nightside by Polar at several 107 ions/cm2/s. This calibration of the outflow model predicts the following magnetospheric features: (1) the dayside ionospheric -3) densities of cold plasma in the vicinity of the magnetopause, particularly on the dusk side during periods of enhanced convection; (2) the composition of the magnetosphere can change over the course of very small IMF changes (±1-2 nT in the present study) with northerly turnings allowing solar wind entry via the low latitude boundary layer, while pressure pulses aid high latitude entry across a magnetopause that is otherwise dominated by ionospheric plasma on the earthward side of the magnetopause; and (3) the calculated changes in the ionospheric outflow rate are sufficiently large that composition of the magnetosphere can change from one that is predominantly ionospheric in origin to one that is primarily of solar wind origin for changes in the IMF as small as ±1 nT. Copyright 2008 by the American Geophysical Union.