Inner Magnetospheric Response to the IMF By Component:Van Allen Probes and Arase Observations

We utilise 17 years of combined Van Allen Probes and Arase data to statistically analyse the response of the inner magnetosphere to the orientation of the 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 Earth as geosynchronous orbit. By exploiting data from these inner magnetospheric spacecraft, we have been able to investigate the response at radial distances of < 7 RE. 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 MLT sectors. The ratio of IMF By to 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.