Entropy Generation across Earth’s Collisionless Bow Shock
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Author/Creator ORCID
Date
2012-02-09
Type of Work
Department
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Citation of Original Publication
Parks, G. K., E. Lee, M. McCarthy, M. Goldstein, S. Y. Fu, J. B. Cao, P. Canu, et al. “Entropy Generation across Earth’s Collisionless Bow Shock.” Physical Review Letters 108, no. 6 (February 9, 2012): 061102. https://doi.org/10.1103/PhysRevLett.108.061102.
Rights
This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
Public Domain Mark 1.0
Public Domain Mark 1.0
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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, dH / dt ≤ 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.