Global magnetosphere modeling with empirical ring current pressure

As the ring current builds up due to plasma sheet convection and injections of hot plasma, the resulting increased pressure drives strong field-aligned currents into the ionosphere, and modifies the global configuration of the magnetosphere and the magnetotail, thus altering the ring current source regions. This feedback loop presents a compelling challenge for first-principles modeling: MHD and energy-dependent drifts may be appropriate descriptions in the outer and inner magnetosphere, respectively, while both of these descriptions are potentially important in the transition region. One way to tackle this problem is to couple global MHD models with dedicated first-principles models of the ring current. Another, complementary, approach is to derive the ring current pressure from empirical models. The TS07d model utilizes millions of historical spaceborne magnetometer measurements and sophisticated data mining techniques to reconstruct globally the geomagnetic field and electrical currents. Using the quasi-static force balance, they can be used to derive plasma pressure which can be ingested directly into a global magnetosphere model. Here, we take this novel approach and ingest the isotropic component of the instantaneous ring current pressure derived from TS07d into our global magnetosphere MHD model, Gamera, which is a reinvention of the high-heritage LFM code. The empirical pressure modifies the MHD energy equation via a source heating term with an adjustable heating rate. The pressure is assumed to be constant along the magnetic field lines and is spread over the field line by using our new interpolation and field-line tracing algorithm on the native curvilinear non-orthogonal MHD grid. Our results demonstrate the formation of a strong ring current pressure in the global model and the corresponding rearrangement of the entire magnetosphere, accompanied by an intensification of the R2 field aligned current and the equatorward shift of the R1/R2 currents in the ionosphere. Both the ring current pressure and the ionospheric field aligned current patterns are in agreement with the corresponding observations, including the Van Allen Probes and AMPERE.