Modeling the relative contribution of magnetospheric currents to the stormtime ground dawn-dusk asymmetric H perturbation during solar wind dynamic pressure enhancements

Details Modeling the relative contribution of magnetospheric currents to the stormtime ground dawn-dusk asymmetric H perturbation during solar wind dynamic pressure enhancements Modeling the relative contribution of magnetospheric currents to the stormtime ground dawn-dusk asymmetric H perturbation during solar wind dynamic pressure enhancements

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsm53a1443s&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #SM53A-1443

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7954 Magnetic Storms (2788), 7959 Models

Scientific paper

Our recent studies have found that solar wind dynamic pressure enhancements can cause clear dawn-dusk asymmetric H perturbations in low-latitude ground magnetometers, particularly when the IMF Bz has been southward for some time before the compression occurs. The asymmetry consists of negative H perturbations on the dusk side and positive H perturbations on the dawn side, a response that is uncharacteristic of what is expected from a typical magnetospheric compression. This response was qualitatively interpreted as the result of the intensification of the existing partial ring current by the pressure enhancement. The assumption is that the intensified partial ring current creates the negative perturbations on the dusk side, overwhelming the effect of all other magnetospheric (Chapman-Ferraro and R1 and R2) currents. The present study quantitatively investigates the contribution of all the different magnetospheric current systems to the asymmetric ground H perturbations. We use Tsyganenko magnetic field models, which include separate modules for each magnetospheric current, thus being able to also separate their individual contributions. We first focus on the pressure enhancement event that occurred during the main phase of the September 25, 1998 storm. We use the TS04 model to simulate the ground H variations during our pressure enhancement event. We find that the original TS04 model does not reproduce the observed dawn-dusk asymmetric H perturbations. However, the TS04 includes the effect of the current solar wind dynamic pressure only in the magnetopause and tail current modules. We thus have modified the model by adding the current state of dynamic pressure and IMF Bz to the parameterization scheme to the modules for the R1 and R2 field-aligned currents and for the symmetric and asymmetric ring currents. We then fit the model to the low- and mid-latitude ground magnetometer observations. Preliminary results show that the major contributor to the ground asymmetric H perturbation is the intensified partial ring current and its closure current. None of the other magnetospheric current systems can reproduce the observations on the ground, even when the current pressure is added to their modules.

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