Strong electron heating at the earth's bow shock

The paper reports on two sets of bow shock crossings observed by the ISEE 1 and ISEE 2 spacecraft, in which very large electron temperature increases were found. When the two sets of shocks with the large electron heating were compared with the rest of the 52 bow shock crossings of the compiled series, these sets were found to correlate with an unusually high upstream solar wind flow speed. The highest correlation was found between the amount of electron heating, expressed by the difference in temperature between the downstream and upstream electrons (rather than their ratio), and the total change in the bulk flow energy per particle across the shock. The results suggest that the appropriate quantity to consider in studies of electron heating at shocks is the temperature difference rather than the temperature ratio. The latter can be artificially elevated by low upstream temperatures.