Authors: N.S.M. Subashchandar (Department of Space Science and Center for Space Plasma and Aeronomic Research (CSPAR), The University of Alabama in Huntsville), Bingbing Wang (Department of Space Science and Center for Space Plasma and Aeronomic Research (CSPAR), The University of Alabama in Huntsville), Lingling Zhao (Department of Space Science and Center for Space Plasma and Aeronomic Research (CSPAR), The University of Alabama in Huntsville)

When galactic cosmic rays propagate in the heliosphere, the interaction with the solar wind and embedded magnetic field causes long term variations of cosmic ray flux, this is called solar modulation of cosmic rays. The classic Force-Field model is most widely used to study solar modulation due to its simplicity and the ability to reproduce some observations. However, the model is derived by treating the diffusion coefficient and cosmic rays intensity as only a function of radial distance from the Sun which cannot be realistic. We proposed a new model by assuming that the radial streaming flux is zero the same as the classic Force-Field model but the cosmic ray intensity is a function of both radial distance and polar angle. The improved Force-Field model can describe the latitudinal dependence of the solar modulation at the expense of solving the equations numerically. We also find a simple analytic expression connecting the modulation potential with the solar wind speed and heliospheric magnetic field at the Earth. By comparison, this relationship works well for low and intermediate solar activity epoches and is better than a more complex model [2].