Update on a proposed mechanism for the regulation of minimum mid-tropospheric and surface temperature in the Arctic and Antarctic

This paper is an update from our earlier paper to include data through July 2008. In our earlier paper, which included data through 1998, a mechanism which generally limits Arctic minimum 500 mb temperatures to the -40째C to -45째C range was presented. The current paper is in agreement with those earlier findings and also shows some evidence of later autumn onset dates of the initial appearance of these temperatures, in agreement with the recent reduction of Arctic sea ice cover in the summer and fall. In the southern hemisphere, little change can be seen for the seasonal onset and end of the temperatures reaching -40째C area, while the appearance of temperatures reaching -44째C area seems to show a later onset date beginning about 1998, but this time period is too small to define a clear trend. The limiting of the minimum of these midtropospheric temperatures has important implications for minimum surface temperatures that can occur over land during the Arctic winter.