Date of Award

Spring 2009

Project Type

Dissertation

Program or Major

Physics

Degree Name

Doctor of Philosophy

First Advisor

Lynn M Kistler

Abstract

Using data from the Plasma and Suprathermal Ion Composition (PLASTIC) instruments onboard the Solar Terrestrial Relations Observatory (STEREO), I have studied the evolution of solar wind stream interfaces in the ecliptic plane near 1 AU over time scales of hours to a few days. STEREO consists of two nearly identical satellites in orbits similar to the Earth's orbit about the Sun. One observatory leads the Earth (STEREO/A), and the other lags behind (STEREO/B). The PLASTIC instruments, build by a team lead by A.B. Galvin of the University of New Hampshire, measure solar wind and suprathermal ion composition. In this work, the instruments were used to determine the bulk properties of solar wind protons. The PLASTIC instruments functioned somewhat differently than anticipated pre-launch, so it was necessary to carry out an in-flight calibration for the bulk solar wind proton data. The proton data were then used to identify transitions between slow and fast solar wind for thirteen Carrington rotations covering March 2007 through February 2008. During this interval the heliographic longitude separation between the two observatories grew from about 2 degrees to 45 degrees. After a solar wind transition was observed at STEREO/B, the expected time-of-arrival at STEREO/A was calculated assuming ideal corotation with the Sun and negligible source evolution. The difference between expected and actual arrival times was generally less than ten hours when heliographic longitude separation between the observatories was less than 20 degrees, and time separation was less than a day. Discrepancies of more than 40 hours occurred when heliographic latitude separation between the observatories exceeded 5 degrees. By propagating the solar wind data back to the sun, the source regions were identified for particular cases, and the sources were examined for both latitudinal differences and for source evolution. Both latitude differences and source evolution were reflected in the in situ solar wind proton data. In 32 of 41 cases the stream interface between slow and fast solar wind arrived earlier than predicted. This result is important to forecasting the arrival of high-speed streams at Earth, which are known to cause recurrent geomagnetic storms.

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