IGPP Seminar Series

Anisotropies Observed Magnetic Field Fluctuations Measured in the Solar Wind and Foreshock

by James Weygand
UCLA, IGPP

Abstract

For this study we use eleven different solar wind spacecraft to determine two fundamental turbulence scale lengths in the solar wind: the correlation scale and the Taylor microscale. By subsetting our solar wind data into slow, intermediate, and fast speed ranges we observe a systematic change in these turbulence scale lengths, which indicates the transition from one dominant type of solar wind turbulence at slow speeds, quasi two dimensional turbulence, to another dominant type, Alfvenic turbulence, at high speeds. We also find that a third scale length smaller than the correlation scale and larger than the Taylor microscale is observed within all three solar wind types and we offer a possible interpretation. By further restricting the data into subsets within the Earth’s foreshock and outside the foreshock, we have been able to compare the characteristic scale lengths in the two regions. The third scale length markedly decreases in the foreshock region where it decreases from tens of thousands of kilometers to less than ten thousand kilometers in most angular bins. Measurements of the correlation scale and Taylor microscale and their variation with solar wind speed and location are important because these two scale lengths can also be used to determine the effective magnetic Reynolds number, which is critical for magnetohydrodynamic modeling of the solar wind, and cosmic ray modulation with in the solar system.
Tuesday, 06 April 2010
3853 Slichter Hall
Refreshments at 3:45 PM
Lecture at 4:00 PM