Mean upper contour patterns of the northern hemisphere — the thermal‐synoptic view‐point

The mean 500 mb contour patterns and 1,000‐500 mb thickness patterns for the northern hemisphere in January and July are examined. The orographic‐dynamical hypothesis advocated by Bolin (1950) is considered. A thermal‐synoptic explanation, resting mainly on the direct thermal effects of land and sea modified by baroclinic synoptic processes, is regarded as satisfactory.