Understanding the explicit IMF By dependence on solar wind - magnetosphere coupling
Abstract
Recently, an explicit dependence of the dawn-dusk component (By) of the Interplanetary Magnetic Field (IMF) on ionospheric electrodynamics has received significant attention. Although first noted in the 1970's, we now know that the sign of IMF By can modulate the strength of the auroral electrojet and Birkeland currents, energetic electron particle precipitation fluxes, and also the average size of the polar cap, the latter being the topic for this presentation. These signatures are seen from both hemispheres, and exhibit a seasonal dependence. However, the underlying mechanisms responsible for this behavior are poorly understood. We here present observations strongly suggesting an explicit IMF By effect on the solar wind - magnetosphere coupling. When the Earth's dipole is tilted in the direction corresponding to northern winter, positive IMF By is found to on average lead to a larger polar cap than when IMF By is negative during otherwise similar conditions. This explicit IMF By effect is found to reverse when the Earth's dipole is inclined in the opposite direction (northern summer), and is consistently observed from both hemispheres using the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) to infer the size of the region 1/2 current system. Two possible interpretations are presented: 1) The dayside reconnection rate is affected by the combination of dipole tilt and IMF By sign in a manner explaining the observations; 2) The combination of dipole tilt and IMF By sign affect the global conditions for maintaining a given nightside reconnection rate. The observations as well as idealized magnetohydrodynamic (MHD) model runs are analyzed and discussed in light of the two different interpretations in order to enhance our understanding of this explicit IMF By effect.
- Publication:
-
43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E.634R