Abstract
AbstractWe utilize 17 years of combined Van Allen Probes and Arase data to statistically analyze the response of the inner magnetosphere to the orientation of the interplanetary magnetic field (IMF) By component. Past studies have demonstrated that the IMF By component introduces a similarly oriented By component into the magnetosphere. However, these studies have tended to focus on field lines in the magnetotail only reaching as close to the Earth as the geosynchronous orbit. By exploiting data from these inner magnetospheric spacecraft, we have been able to investigate the response at radial distances of <7RE. When subtracting the background magnetic field values, provided by the T01 and IGRF magnetic field models, we find that the IMF By component does affect the configuration of the magnetic field lines in the inner magnetosphere. This control is observed throughout the inner magnetosphere, across both hemispheres, all radial distances, and all magnetic local time sectors. The ratio of IMF By to the observed By residual, also known as the “penetration efficiency,” is found to be ∼0.33. The IMF Bz component is found to increase, or inhibit, this control depending upon its orientation.
Highlights
The presence of a nonzero y-component in the interplanetary magnetic field (IMF By) has been shown to modify the topology of the magnetic field in the Earth's magnetosphere
When subtracting the background magnetic field values, provided by the T01 and IGRF magnetic field models, we find that the IMF By component does affect the configuration of the magnetic field lines in the inner magnetosphere
We find a similar response in the Southern Hemisphere as in the Northern Hemisphere, with a clear dependence of the observed By component on the IMF By component
Summary
The presence of a nonzero y-component in the interplanetary magnetic field (IMF By) has been shown to modify the topology of the magnetic field in the Earth's magnetosphere. The exact amount by which a nonzero IMF By component contributes to the local magnetic field in the magnetosphere has been shown to vary by location, dipole tilt, and the sign of IMF Bz. For example, Fairfield (1979) found an average “penetration efficiency” of the IMF By component of 0.13, using data from the IMP-6 spacecraft recorded between −20RE and −33RE downtail. From different regions of the magnetosphere, have been undertaken showing a broadly similar result but with different penetration efficiencies. Both Cowley and Hughes (1983) and Nagai (1987) used data from geostationary satellites (ATS 6 and GOES 6) and found penetration efficiencies of 0.28 and 0.3, respectively. Studies from the plasma sheet region of the magnetosphere have observed penetration efficiencies of around 0.50–0.60 (e.g., Lui, 1984; Petrukovich, 2009)
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