Latitudinal dependence of outflow velocities from O VI Doppler dimming observations during the Whole Sun Month

Abstract

Empirical determinations of outflow velocities in the solar corona provide a much needed constraint, along with density and temperature determinations, of the acceleration and heating mechanisms in the extended corona. Much progress has been made on density determinations from white light polarized brightness observations but outflow velocities have been more difficult to determine. We present the first determinations of outflow velocities versus height and latitude based on a three‐dimensional (3‐D) reconstruction of the O VI 1032 and 1037 À emissivities. The Doppler dimming (and pumping) of the local emissivities give true localized outflow velocities at the selected locations in the extended corona from ∼1.75 to 2.75 solar radii. The velocities are based on an empirical model of the corona which is constrained by the reconstructed O VI emissivities derived from the SOHO Ultraviolet Coronagraph Spectrometer (UVCS) synoptic observations and by electron density determinations based on white light measurements from the SOHO Large Angle Spectroscopic Coronagraph (LASCO) and Mauna Loa Solar Observatory (MLSO) Mk III coronameter.