State-Dependent Response of the Polar Cap Index and High Latitude Ground Magnetic Fields to Solar Wind Coupling

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Funds are provided to quantify the dependence of the polar cap index (PC) on solar wind parameters, and thereby to determine the best functional form for PC, by calculating response filters based on singular value decomposition theory. At present, PC values are derived by using a scheme that aims to force agreement, on average, between PC and the solar wind motional electric field. Preliminary examination of the derivation scheme has revealed problems in how PC is defined. These problems may actually degrade the usefulness of the index in research studies and in an operational sense as a space weather forecasting or nowcasting tool. In addition, PC will be used to estimate the level of solar wind driving force that leads to polar cap potential drop saturation and determine the relative contributions of Hall and field-aligned currents to polar magnetic field disturbance. An improved and consistent definition of PC, as is sought in this research, should allow improved nowcasting and short-term forecasting of space weather events known to interfere with radio communication, radars, and low-orbiting and geostationary satellites.