Solar Wind Speed And Temperature Relationship

Abstract

Previous studies of solar wind proton temperature and speed have found a break in the curve between 400 and 550 km/s. Examining all the OMNI 2 data from 1965 to 2009, we create plots binned in both temperature and speed in order to identify where the majority of the points lie. Using yearly color plots to evaluate the curve shape we find most of the data is well represented by a single linear fit even though the slope varies significantly from year to year. A clear break in the temperature speed curve occurs in 2003 coincident with a large polar coronal hole extension which produced faster wind speeds than expected at low latitudes based on the Ulysses speed-latitude polar coronal hole relationship. Although the slope does not change in a systematic way for each individual solar cycle, there seems to be an overall decrease in the slope since 1972.