Atmospheric circulation and poleward sensible heat flux variations associated with the recent Northern Hemisphere warming

This dissertation is based on the premise that the Northern Hemisphere has been warming since about 1975. The focus has been on (1) identifying the nature and extent of the warming at the surface and 700mb constant pressure level, and (2) the relationship between temperature changes and those of the atmospheric circulation and the meridional flux of kinematic sensible heat at the 700mb constant pressure level.; The data used are grid-averaged 700mb geopotential heights and temperatures and land-based surface station temperatures. Seasonal mean values for each variable were obtained for long-term (1948-1987) averages; for the 1976/87 (warm) and 1963/75 (cool) periods. Regression analysis of the long-term seasonal averages of temperature was used to give an estimate of the overall trend of the 700mb temperatures. Rotated principal components used to obtain the dominant mode of circulation in the winter season.; The results indicate that in general, the mean temperatures over the oceans appear to be lower (at 700mb) in 1976/87 compared to 1963/75, while mean temperatures over the continents are higher (at the surface and 700mb). The spatial pattern of temperature differences between the winter subperiods exhibits a close correspondence with the upper air Pacific North American (PNA) teleconnection pattern in its positive mode. Regions which appeared to be warming were influenced by increased southerly geostrophic flow and the dominant mode of circulation for winter was the PNA in its positive phase.; The meridional, kinematic eddy sensible heat flux was calculated as the product of the v-component of the geostrophic wind and the temperature deviation from the latitudinal mean. The zonal averages of each eddy flux and the zonal divergence of the fluxes were computed by season. The seasonal mean flux differences between the warm and cool periods are largest during winter. Changes in the total eddy flux are due chiefly to changes in the transient eddy flux and the latter is generally weaker in the warm period than in the cool. This suggests that a key difference between the periods 1963/75 and 1976/87 is the occurrence of fewer or weaker storms or at the least, a modification of the storm tracks.