Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsa44a..01f&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #SA44A-01
Physics
0545 Modeling (4255), 2411 Electric Fields (2712), 2427 Ionosphere/Atmosphere Interactions (0335), 3369 Thermospheric Dynamics (0358), 7954 Magnetic Storms (2788)
Scientific paper
Quantifying the storm-time electrodynamic response requires a baseline from which to measure the changes. Day-to-day changes in quiet-time electric fields at mid and low latitudes are a consequence of leakage of magnetospheric fields from high latitudes, variability in the thermospheric wind system, and solar-induced conductivity changes. On the dayside, E-region winds tends to dominate the wind-driven electrodynamic variability due to the high conductivities; on the nightside, F-region winds become significant as E-region plasma decays. The quiet-time day-to-day changes in equatorial vertical plasma drift on the dayside are of order of 50% and exhibit multi-day periodicities, indicative of a lower atmosphere source. On the nightside, fluctuating F-region winds from geomagnetic activity are a likely source of variability. During extreme events the storm changes are dramatic, so deviation from quiet conditions is more easily identified. In the storm case, electrodynamic changes arise from penetrating magnetospheric fields and the disturbance dynamo. The penetration electric fields are immediate but tend to recover quickly. The disturbance dynamo is slower to develop but also longer-lived. The fastest disturbance dynamo effect in numerical simulation is apparent within an hour or two of onset of geomagnetic activity, which could become confused with apparent long-lived penetration on the nightside. Understanding the physics of the dynamo, during both quiet and disturbed times, is necessary to determine the source of the storm-time changes, and to correctly partition the variability to the different sources.
Fuller-Rowell Tim
Maruyama Naomi
Richmond Arthur
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