Effects of inner magnetospheric convection on ring current dynamics: March 10–12, 1998

Abstract

A stream‐stream interaction region observed by the Wind spacecraft from ∼1200 UT to ∼2400 UT, March 10, 1998, triggered a major geomagnetic storm which peaked within a few hours at Dst≈−130 nT and Kp=7+. During the main phase of this storm the north–south component of the interplanetary magnetic field (IMF) was large and negative (Bz≈−l5 nT), the solar wind velocity was ∼550 km/s, and the solar wind dynamic pressure increased to ∼10 nPa. We simulated the storm time injection and trapping of H+, O+, and He+ ring current ions using our global drift‐loss model with initial and boundary conditions as specified by measurements from the Equator‐S ion composition (ESIC) instrument, the HYDRA instrument on Polar, and the hot plasma instruments on geosynchronous spacecraft. We demonstrated effects of magnetospheric convection, comparing results derived from two inner magnetospheric convection models: (1) the 3 hour averaged Kp‐dependent Volland‐Stern model and (2) the Weimer [1996] IMF‐driven model, where we input interplanetary data from the Magnetic Field Investigation (MFI) and Solar Wind Experiment (SWE) instruments on Wind at 30 min resolution. During the main phase of the storm the Volland‐Stern model predicted a large‐scale electric field of ∼1 mV/m at L=2 to L=5, whereas the Weimer model predicted a maximum electric field of ∼3.5 mV/m localized near dusk at L≈3. We found that both ring current simulations show reasonable agreement with ESIC and HYDRA data at larger L shells and on the nightside. However, the simulation using a Volland‐Stern model predicted wider dips in the ion energy spectra than observed at low L shells in the postnoon local time sector. Ions followed paths at larger distances from Earth and experienced less collisional losses in the Weimer convection model. As a result, the agreement between model and data was significantly improved on the dayside when the IMF‐driven convection model of Weimer was used.