GEM: Model of the Low-Latitude Boundary Layer

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It is proposed to develop a numerical model of the low- latitude boundary layer (LLBL), located in the equatorial region of the Earth's magnetoshpere adjacent to its outer boundary, the magnetopause, and the coupling of that layer to the dayside auroral ionosphere via field-aligned currents. The model is intended as a building block in the construction of a global geospace circulation model (GGCM) with predictive capability. Two versions of the LLBL model will be developed. First, a relatively sophisticated self-consistent model of steady plasma flow, magnetic fields and currents will be completed and its parameters constrained by comparison with observations. In this model, partial differential equations are solved numerically in the boundary layer approximation. On the basis of results and experience gained from this model a simpler version, based on ordinary differential equations, will be developed for use in parallel with, and coupled to, existing models, or models under development as part of the GEM program, of internal magnetospheric convection on one side of the layer and external solar-wind plasma flow on its other side. This simpler version of the boundary-layer model will have as its basic theoretical elements: (i) the equation of momentum conservation in the flow direction integrated over the thickness of the boundary layer and (ii) polynomial (or other parametric) representations of variations across the boundary layer, with free parameters that will allow the model to accommodate, perhaps iteratively, boundary conditions provided by an internal circulation model and an external flow model. The simpler model which is expected to be numerically fast will be benchmarked by comparison w ith the self-consistent boundary layer code (which is computationally too slow to be used in a GGCM), as well as with observed ionospheric and equatorial signatures of the layer.