NASA's Cosmos

Distributions of solar wind speeds at solar minimum and maximum

Distributions of
solar wind speeds at solar minimum and maximum

. Plots of the solar wind speed as a function of solar latitude, obtained from two orbits of the Ulysses spacecraft (top panel). The north and south poles of the Sun are at the top and bottom of each plot, the solar equator is located along the middle, and the velocities are in units of kilometers per second, abbreviated km s^-1. The sunspot numbers (bottom panel) indicated that the first orbit (top left) occurred through the declining phase and minimum of the 11-year solar activity cycle, and that the second orbit (top right) spanned a maximum in activity. Ultraviolet images of the solar disk and white-light images of the inner solar corona form a central backdrop for the wind speed data, and indicate the probable sources of the winds. Near solar minimum (top left), polar coronal holes, with open magnetic fields, give rise to the fast, low-density wind streams, whereas equatorial streamer regions of closed magnetic field yielded the slow, gusty, dense winds. At solar maximum (top right), small, low-latitude coronal holes gave rise to fast winds, and a variety of slow-wind and fast-wind sources resulted in little average latitudinal variation. (Courtesy of David J. McComas and Richard G. Marsden. The Ulysses mission is a project of international collaboration between ESA and NASA. The central images are from the Extreme ultraviolet Imaging Telescope and the Large Angle Spectrometric Coronagraph aboard the SOlar and Heliospheric Observatory, abbreviated SOHO, as well as the Mauna Loa K-coronameter.)