Velocity Profiles in the Solar Corona from Multi‐Instrument Observations

Abstract

We present a method to derive outflow velocities in the solar corona using different data sets, including solar wind mass flux coming from the SWAN SOHO instrument, electron density values from LASCO-C2, and interplanetary solar wind velocities derived from ground-based interplanetary scintillation observations (IPS). In a first step, we combine the LASCO electron densities at 6 R☉ and the IPS velocities and compare the product to the SWAN mass fluxes. It is found that this product represents the actual mass flux at 6 R☉ for the fast wind, but not for the slow wind. In regions dominated by the slow wind, the fluxes derived from SWAN are systematically smaller. This is interpreted as proof that the fast solar wind has reached its terminal velocity at ~6 R☉ and expands with constant velocity beyond this distance. On the contrary, the slow solar wind has reached only half of its terminal value and is thus accelerated farther out. In a second step, we combine the LASCO-C2 density profiles and the SWAN flux data to derive velocity profiles in the corona between 2.5 and 6 R☉. Such profiles can be used to test models of the acceleration mechanism of the fast solar wind.