Chase TN, Herman BM and Pielke Sr RA
We examine mid-tropospheric temperatures in the Northern Hemisphere using the 500 mb pressure surface from reanalysis data as a representative level. This standard analysis level is significant meteorologically (i.e. for frontal identification and jet stream dynamics) and climatologically (e.g. changes in long term front and jet structures would be expected to extend throughout the troposphere as would tropospheric warming). We find that 500 mb temperatures are bracketed between about ?42°C and ?3°C with very few excursions beyond these brackets suggesting a limiting physical process or processes. In this paper we update the data for the ?42°C limit which we have proposed in previous papers, document the ?3°C limit for the first time, and briefly discuss the possible physical mechanisms responsible for this observed temperature bracketing concluding that the limits on both maximum and minimum temperatures are due to convective processes. This self-regulation of tropospheric temperatures constrains changes in jet stream and baroclinic storm dynamics and therefore constrains changes in climate variability.
