Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm24b..02e&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SM24B-02
Physics
[2164] Interplanetary Physics / Solar Wind Plasma, [2784] Magnetospheric Physics / Solar Wind/Magnetosphere Interactions
Scientific paper
Often equatorial holes emit wind with speeds between 500 and 650 km/s, but on rare occasions they can emit wind as fast as polar coronal holes (~700-830 km/s). The best example of this was a large outward polarity coronal hole that lasted from January to December of 2003. Solar wind speed estimates for this hole based on photospheric expansion factors and the travel times of waves in the chromosphere both under-predicted the wind speed. These methods rely on empirical relationships that may not include enough such atypically fast measurements in order to predict them well. Alternatively, the photospheric and chromospheric properties could be the same for all holes, and the atypically fast wind may develop in the corona. The solar wind speed and temperature are highly correlated except in Interplanetary Coronal Mass Ejections. The relationship temperature-speed (T-V) relationship can usually be characterized by a single linear fit although in 2003 there is a distinct break at high speeds associated with this atypically fast wind in 2003. The solar wind speed and the Kp magnetic index are also well correlated quantities; however, a plot of Kp versus speed (V) for a years worth of data shows a broad distribution. Using the solar wind measurements from 2003 we demonstrate that changing solar wind properties associated with coronal holes can broaden the Kp-V distribution. In compressions a rising solar wind speed is associated with increased magnetic field strength, density, and temperature. Using the speed-time slope criteria we can define separate compressions and rarefactions for both the T-V and Kp-V relationships. The compression and rarefaction categories are overlapping, but there is a clear average separation that reflects the dynamic evolution in route from the Sun to Earth. Although we can separate compressions and rarefactions in the Kp-V relationship using a pressure, density or a running speed-time slope criterion, the advantage of a running speed-time slope criterion is that the solar wind speed has a long autocorrelation time, much longer than any other solar wind parameter, or field quantity. The solar wind speed is often predicted using empirical relationships between solar measurements and solar wind observations (e.g., expansion factor predictions). It is easier to predict the solar wind speed than the solar wind density or pressure; therefore, we put forth the idea that a running speed-time slope could be coupled with such an empirical solar-heliospheric relationship to improve neural network and empirical based magnetospheric predictions.
Elliott Heather Alison
Henney Carl John
Jahn J.-
McComas David John
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