Showing papers by "Arthur D. Richmond published in 2002"

Modes of high-latitude electric field variability derived from DE-2 measurements: Empirical orthogonal function (EOF) analysis

Abstract: [1] In this study we characterize dominant modes of high-latitude electric field variability as a set of two-dimensional empirical orthogonal functions (EOFs), based on a sequential non-linear regression analysis of the electric field derived from plasma drift measurements during the Dynamics Explorer-2 (DE-2) satellite mission (1981–1983). Together with the mean fields, 11 EOFs are capable of representing 68% of the squared electric field in the original data, leaving only a fairly random component as a residual. While such mathematically independent EOFs do not necessarily represent physically independent modes of variability, each of the first two EOFs is actually related to a widely known physically prominent effect on the convection patterns. Variability associated with the interplanetary magnetic field (IMF) BY component emerges as the primary mode, and variability associated with the IMF BZ effect emerges as the secondary mode. The tertiary mode reflects variability in the cusp region, but is not significantly correlated with the IMF.

Neutral wind influence on the electrodynamic coupling between the ionosphere and the magnetosphere

Abstract: [1] The influence of the ionospheric wind dynamo on the steady state electrodynamic interaction between the ionosphere and the inner magnetosphere is evaluated with the Magnetosphere-Thermosphere-Ionosphere Electrodynamics General Circulation Model (MTIE-GCM) of Peymirat et al [1998] Two types of interaction between the solar wind–magnetosphere (SWM) dynamo and the ionospheric dynamo are considered: either the SWM dynamo is a voltage generator imposing a fixed electric potential in the polar cap or it is a hybrid current/voltage generator such that the electric potential in the polar cap results from the combined action of the SWM and ionospheric dynamos The following results are found (1) The dynamo effect of winds that are accelerated by the high-latitude ion convection increases the meridional electric field in the auroral zone but reduces the potential variation around the Auroral Zone Equatorial boundary (AZEQ) and the plasma pressure in the nightside magnetosphere close to the Earth, corresponding to an enhancement of the shielding effect produced by Region 2 field-aligned currents The magnitudes of the wind-induced effects are on the order of 10% for the shielding potential and 20% for the plasma pressure reduction (2) The wind-induced reduction of magnetospheric plasma pressure near the Earth is ∼4 times larger for a doubling of the plasma source density in the tail (3) The relative influence of winds on shielding is similar for polar cap potential drops of 30 kV and 70 kV (4) When the wind is allowed to influence the polar cap potential, it increases the potential drop along the polar cap boundary by ∼10% but does not modify the net influence on the shielding potential along AZEQ (5) The influence of the neutral winds set up by the high-latitude convection is restricted to the auroral zone