In this research, we investigate the electrodynamic coupling between the solar wind, the magnetosphere, and the ionosphere.   The moving solar wind produces and electric field that can couple to the Earth's magnetic field lines to couple the electric field to the high latitude ionosphere.  The coupling is primarily controlled by the relative orientation between the solar wind magnetic field and the geomagnetic field.  Anti-parallel conditions produce the best coupling.  The coupling of the solar wind electric field to the geomagnetic field drives electrical currents though the magnetosphere and ionosphere and sets up and electric field in the ionosphere that also drives Hall currents (the ionosphere has an anisotropic conductivity tensor) and produces plasma convection.   A variety of methods have been developed to measure the high latitude ionospheric electric field and it has been found to develop linearly with the strength of the solar wind electric field up to a point, at which point it becomes nonlinear, with less increase as the solar wind electric field increases.   Under extreme driving conditions (very large solar wind electric field) the development of the ionospheric electric field is very small, and this is called cross polar electric field saturation, though it does not seem to really be limited to a specific value.  The cause of the nonlinear development of the ionospheric electric field during extreme solar wind driving is not understood and this research is directed to develop our understanding of this phenomena.
Utilizing the NSF incoherent scatter radar facility in Resolute Canada, we have conducted measurements of this high latitude ionospheric electric field during a period of extreme solar wind driving.   Unlike laboratory experiments we must make many observations and attempt to control the variables through statistical examination.  In the case of one of our measurement periods, we encountered some extremely rare solar wind conditions.  In the period 2010 - 2015, these conditions occurred only 0.035% of the time, most of it during our set of observations.   This rare occurrence was remarkable because it did not produce the expected non-linear development of the ionospheric electric field.  We had excellent coupling conditions, the Resolute radar was in the perfect position to measure the resulting ionospheric electric field and the unique set of conditions produced a linear development of the ionospheric electric field, thus enabling us to determine that solar wind conditions are important to regulate the non-linear development of the ionospheric electric field.  While we were looking for an ionospheric source for the non-linear behavior, we were able to determine that high plasma beta (a measure of the partition between the particle kinetic energy and the magnetic energy within a plasma) is a controlling factor in the coupling process.  Low beta (high magnetic energy) tends to limit the coupling process and leads to the ionospheric electric field saturation,  The high beta conditions that occurred during our experiment enabled more efficient coupling during the strong driving and let to a linear ionospheric electric field development that produced an unusual and extremely large ionospheric electric field measured by the Resolute ionospheric radar.   
The results of this research have eliminated some of the theoretical proposals to explain the saturation phenomena and have been very significant in developing our understanding of the coupling phenomena between the solar wind and the Earth’s magnetosphere and ionosphere.  While this is only one set of observations, they are very significant and have focused attention to the importance of solar wind Mach number and plasma beta as important parameters to control the magnetic reconnection process that is responsible for the coupling of energy between the solar wind and ionosphere.

Last Modified: 01/16/2018
Modified by: Calvin Robert Clauer