Solar Wind Coupling to Ground Magnetic Fields and Their Time Derivatives

Dr. Robert Weigel
NRC, NASA Goddard Space Flight Center

Nonlinear basis functions are used to determine data--derived coupling functions that map solar wind measurements to high--latitude ground magnetic fields and their time derivatives. The coupling functions are used to determine, as a function of spatial location, the functional form of the driver, the relative importance of solar wind inputs, and the level of nonlinearity. It is shown that the coupling function that maps solar wind information to ground magnetic fields (and their time derivatives) depends strongly on the local time and latitude of the observation point. We show that most of the nonlinearity in the coupling function occurs in the midnights sector, for both SW-Bx and SW-|dB_x/dt| mappings. The form of the optimal coupling function between Bx and dBx/dt are found to differ substantially. The relative contribution to the prediction error of each of the solar wind input variables is considered. It is shown that some locations may be inherently unpredictable, while others are highly predictable; these results are discussed in the context of improving real time models of the high--latitude ionosphere.