Entropy Generation across Earth's Collisionless Bow Shock

Entropy Generation across Earth’s Collisionless Bow Shock

G. K. Parks, E. Lee, M. McCarthy, M. Goldstein, S. Y. Fu, J. B. Cao, P. Canu, N. Lin, M. Wilber, I. Dandouras, H. Réme, and A. Fazakerley

Phys. Rev. Lett. 108, 061102 – Published 9 February 2012

Abstract

Earth’s bow shock is a collisionless shock wave but entropy has never been directly measured across it. The plasma experiments on Cluster and Double Star measure 3D plasma distributions upstream and downstream of the bow shock allowing calculation of Boltzmann’s entropy function $H$ and his famous $H$ theorem, $d H / d t \leq 0$ . The collisionless Boltzmann (Vlasov) equation predicts that the total entropy does not change if the distribution function across the shock becomes nonthermal, but it allows changes in the entropy density. Here, we present the first direct measurements of entropy density changes across Earth’s bow shock and show that the results generally support the model of the Vlasov analysis. These observations are a starting point for a more sophisticated analysis that includes 3D computer modeling of collisionless shocks with input from observed particles, waves, and turbulences.

Received 7 October 2011

DOI:https://doi.org/10.1103/PhysRevLett.108.061102

Authors & Affiliations

G. K. Parks^1,*, E. Lee², M. McCarthy³, M. Goldstein⁴, S. Y. Fu⁵, J. B. Cao⁶, P. Canu⁷, N. Lin¹, M. Wilber¹, I. Dandouras⁸, H. Réme⁹, and A. Fazakerley¹⁰

¹Space Sciences Laboratory, University of California, Berkeley, California, USA
²School of Space Research, Kyung Hee University, Yongin, Korea
³Planetary and Space Sciences, University of Washington, Seattle, Washington, USA
⁴Goddard Space Flight Center, NASA, Greenbelt, Maryland, USA
⁵Institute for Space Physics and Applied Technology, Peking University, Beijing, China
⁶Space Science Institute, School of Aeronautics, Beihang University, Beijing, China
⁷Laboratory for Plasma Physics, Ecole Polytechnique, Paris, France
⁸University of Toulouse, UPS-OMP, IRAP, Toulouse, France
⁹CNRS, IRAP, BP44346,Toulouse cedex 4, France
¹⁰MSSL, University College London, London, England