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Sep 24, 2013 – “Magnetic Field Topology at Earth During Northward IMF Near Solstice”


Speaker:Frederick Wilder (LASP)
Date:Sep 24, 2013
Time:4:00 PM
Location:LASP Space Science Building, room N248 upstairs. Map

Seminar Abstract:

When the interplanetary magnetic field (IMF) is northward, reconnection between the IMF and the geomagnetic field occurs at high latitudes on lobe/tail field lines poleward of the cusp. This reconnection leads to “reverse” convection in the polar ionosphere, with sunward flow at high latitudes. Over the past several decades, there has been significant debate regarding the magnetic field topology, as well as the transport of magnetic flux between hemispheres, during northward IMF. We present an overview of the models developed as a result of these debates, with particular focus on the “interchange cycle,” whereby open magnetic flux draped over the dayside can reconnect with lobe field lines in the opposite hemisphere. Using simultaneous observations of reverse convection in each hemisphere from the Super Dual Auroral Radar Network (SuperDARN), as well as precipitating particle data from the Defense Meteorological Satellite Program (DMSP) spacecraft, we show evidence of convection and open-closed boundary (OCB) characteristics associated with this interchange cycle during a northern hemisphere winter event. Additionally, we use the Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) magnetohydrodynamic (MHD) model to reproduce these observations, as well as to separate out conductivity and dipole tilt effects on hemispheric asymmetries in the reverse convection potential. We find that an effect of the interchange cycle, whereby lobe flux is in constant motion in the summer hemisphere and stagnant in the winter hemisphere, can explain hemispheric asymmetries in the reverse convection potential, regardless of whether or not there is an asymmetry in ionospheric conductivity.