The Weather and Circulation of September 1966Large-Amplitude Flow Over North America and Heavy

• Main Author: Raymond A. Green
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Arctic; Barents Sea; Pacific
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.395.3001; http://docs.lib.noaa.gov/rescue/mwr/094/mwr-094-12-0715.pdf

Outstanding features of the average 700-mb. circulation in September were the large-amplitude ridges and troughs over the continents (fig. 1). Positive height anomalies prevailed the full length of the ridge axis over western North America from the Canadian Arctic to the tropical eastern Pacific (fig. 2). By comparison, the Asiatic ridge was much stronger at middle latitudes but did not extend as far northward. The trough over western Russia was extremely deep with height anomalies decreasing from near zero near the Black Sea to 500 ft. below normal in the polar Low over the Barents Sea. Height changes (fig. 3) indicate considerable amplification of the circulation from August to September. Over the continents there were rises in the September ridges and falls in the troughs; over the oceans there were sizable falls in the principal troughs. Coastal troughs in the western Atlantic and Pacific amplified and storminess increased in these areas with consequences ranging from disastrous to beneficial. In the western Pacific a typhoon recurving northward through the deeper trough crossed Japan with great cost, of life and property. Along the east coast of North America three wave cyclones brought widespread rainfall to dry areas. In the eastern Pacific the distribution of 1000-700-mb. thickness and sea-surface temperature favored cyclonic development. Two storms intensified there to remarkable sea level pressures of 950 and 955 mb. Barotropic response to this deepening was no doubt a factor in support of the North American ridge. Abnormal storminess across the northern Pacific was reflected in the 700-mb. wind field with average speeds of more than 15 m.p.s. (5-8 m.p.s. above normal) from near Japan to 140 ' W. along the mean jet axis (fig. 4). The jet axis there was near its normal location. It was farthest from its average September location over Asia where the largest height departures occurred. Zonal westerlies at 700 mb. were 8.2 m.p.s. in the western sector of the hemisphere. This was slightly faster than ...