Two-dimensional Turbulence and its Role in Solar Wind-Magnetosphere-Ionosphere Coupling

Abstract:

A number of papers have discussed the role of two-dimensional (2-D) turbulence in geospace coupling processes. There has also been evidence that the Mesosphere and Lower Thermosphere (MLT) is 2-D turbulent. In this talk we will review high latitude velocity and electric field data from a variety of satellites, and show that the measured electric field structures are consistent with this hypothesis, particularly when B_z is northward. These fields will mix the ubiquitous plasma density gradients at high latitudes and create the structured ionosphere we observe for any direction of the IMF. If this interpretation is correct, then it is unnecessary to invoke ExB instabilities to explain high latitude ionospheric plasma density and velocity structures. Anisotropy in the auroral plasma is produced by the strong geomagnetic field, which sets up the conditions for 2-D turbulence in the medium. The physics of 2-D turbulence is such that the energy in the system cascades to large scales and eventually fills the available system. This explains the fact that the polar cap occasionally exhibits large-scale vortices when B_z is northward. The spectrum of electric field fluctuations at high k numbers in the system follows the predictions of 2-D turbulence theory, consistent with satellite and rocket observations.