Latitudinal dependence of solar wind speed

We study the solar-cycle evolution of solar wind bulk speed as a function of source magnetic field strength on the basis of the data sets provided by King and Hoeksema et al. Effects of solar transient events are removed by considering the lower envelope of scatter diagrams of solar wind speed, as a function of normalized source surface magnetic field strength. The background solar wind speed follows a function of the form upsilonsub(SW) = upsilon0 + upsilon1 (1 - cossup(n) lambdasub(m)), where lambdasub(m) is the magnetic latitude, set equal to the arc sine of the normalized field strength. We find the value of n is largest at solar minimum, and smallest at solar maximum, while upsilon0 and upsilon1 remain fairly constant throughout the solar cycle. This implies the latitudinal gradient in background solar wind speed is steepest at solar minimum and most broad at solar maximum. The lowest and highest background speeds remain fairly constant throughout the solar cycle. Our new function is inserted into the improved kinematic code of Hakamada and Akasofu, and solar wind speed and IMF are simulated for two periods in the solar cycle. We are able to reproduce observed parameters for specific coronal hole passages. (author)