APPLICATION OF THE EMPIRICALLY DERIVED POLYTROPIC INDEX FOR THE SOLAR-WIND TO MODELS OF SOLAR-WIND PROPAGATION

An empirically derived polytropic index for the solar wind is applied to two magnetohydrodynamic models of solar wind propagation. The first of these models is time-independent and can be used to define an init ial solar wind state for the second, time-dependent model. The time-de pendent model simulates the propagation of disturbances, such as shock s that originate at the Sun, through the interplanetary medium to Eart h as a space weather forecasting tool. Both models assume adiabatic fl ow of the solar wind. Changes are made to these models to include the effects of heating of the solar wind by applying the empirically deriv ed polytropic index. The adjustments made to the time-independent mode l produce a moderate solar wind state that compares well with Hellos 1 data. Data concerning several shocks observed at the Sun and correspo nding storm sudden commencements at Earth are used to investigate the predictions for shock arrival times made by the time-dependent model. Changes in the predictions for shock arrival times resulting from the application of the empirically derived polytropic index for the solar wind are discussed.