HR: 17:00h
AN: SM54A-05    [Abstracts]
TI: The Calm before the Storm in CIR/Magnetosphere Interactions
AU: * Borovsky, J E
EM: jborovsky@lanl.gov
AF: Los Alamos National Laboratory, Mail Stop D466, Los Alamos, NM 87545 United States
AU: Steinberg, J T
EM: jsteinberg@lanl.gov
AF: Los Alamos National Laboratory, Mail Stop D466, Los Alamos, NM 87545 United States
AB: Intervals of extreme geomagnetic calm tend to occur just prior to recurring high-speed-stream-driven storms. Because of the growth of the outer plasmasphere and the entry of cool dense plasma sheet, these calm intervals may be important for preconditioning the magnetosphere for the ensuing storms. It is argued that this preconditioning causes (1) a decay of the number density of relativistic electrons in the outer radiation belt owing to plasmaspheric plasma waves, (2) a mass loading of the convection of the middle magnetosphere during the early phase of the storms, (3) dumping of the outer electron radiation belt by the formation of a plasmaspheric drainage plume, and (4) a contribution to the inner plasma sheet and ring current by the convection of cool dense plasma into the dipole. Calm intervals are driven by the uncompressed slow wind that passes the Earth immediately prior to the CIR. Using 73 years of geomagnetic data it is shown that the occurrence rate of calms before recurring storms is substantially greater than random-occurrence probability would predict, even though the properties of the wind that produce calms before storms are statistically similar to the properties of the wind that produce quiet intervals during solar minimum. The recurrence of storms and calms are studied and it is found that both tend to recur with a 27-day period (strongest during declining phase) and that the persistence of calm recurrence (~3 solar rotations) is greater than the persistence of storm recurrence (~2 solar rotations). An argument based on the Russell-McPherron effect is given as to why there is a tendency for calms to occur just prior to high-speed-stream-driven storms.
DE: 2102 Corotating streams
DE: 2740 Magnetospheric configuration and dynamics
DE: 2774 Radiation belts
DE: 2788 Magnetic storms and substorms (7954)
DE: 7954 Magnetic storms (2788)
SC: SPA-Magnetospheric Physics [SM]
MN: Fall Meeting 2005