Entropy distribution in the plasma sheet

[1] Geotail data were used to study the long‐term averaged spatial and flow speed dependencies of the ion entropy per unit volume and per unit flux tube and the average entropy per ion. It was concluded that some process associated with the production of fast flows substantially increased the entropy of an average ion. Entropy in the fastest flows exhibited little y dependence, showing that the process generating these flows near midnight was similar to the process acting near the flanks. It also was found that the irreversible aspect of reconnection does not change the entropy per ion significantly when two closed flux tubes are involved but can be significant during reconnection at the magnetopause or of two lobe flux tubes. The entropy per unit flux tube and PV were compared. Both of these parameters provided useful information when there were gradients in the flux tube particle content. The difference between the average observed entropy per ion and the value that would be expected if the single particle distribution function f (v) had evolved to an equilibrium Maxwellian was evaluated. After examining the effects of a non‐Maxwellian equilibrium and of a generalized entropy, it was concluded that most of the observed deviation from standard equilibrium thermodynamics was produced by statistical fluctuations in the number of ion counts within the energy angle boxes used to evaluate f (v) and that the remainder was attributable primarily to real plasma fluctuations.