A Study of the General Circulation over the Northern Hemisphere during the Winters of 1976–77 and 1977–78

Abstract

This paper shows the horizontal and vertical structure of the atmosphere during the winters of 1976?77 and 1977?78 (W77 and W78, respectively) over the Northern Hemisphere. The data source for this study is the NMC octagonal grid analyses. One objective of this study is to document the atmospheric conditions during two winters that W record-cold temperatures in the eastern United States and yet had very different precipitation patterns, especially over the western United States. The second objective is to see if individual winters show the same relationships between mean and eddy fluxes and other circulation statistics as the 11-year mean winter reported on in a series of papers by Ngar-Cheung Lau. The 11-year mean winter is an average of the winters of 1965?66 through 1975?76. The results show large anomalies in the time-mean flow for both winters. The transient eddy activity is for the most part not significantly anomalous. The geopotential height and temperature anomalies have little, if any, westward tilt with height and the height and temperature anomalies are in phase; thus the anomalies have the structure of equivalent barotropic waves. These anomalies are also similar to patterns shown in several articles on teleconnections. The heat fluxes show anomalies on the order of 4 K day?1 in the time-mean flow, with a few smaller anomalies in the transient eddy flux. Deviations of the jet stream from its normal position help to explain observed precipitation patterns during the two winters. A good correspondence is also noted between divergence anomalies calculated from upper tropospheric vorticity advection and precipitation anomalies. The relationships noted by Lau for the ll-year average winter transient eddy heat flux and potential vorticity fluxes are also reproduced in these two winters.