THE WEATHER AND CIRCULATION OF SEPTEMBER 1969 Persistence of the August Regime in the United States
The mean trough-ridge pattern over the United States was very similar to that of August, but elsewhere in the middle and high latitudes of the Northern Hemisphere fairly large changes occurred. The strong upper level ridge extending over the Arctic Basin from North America (fig. 1) replaced a deep L...
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.395.3770 http://docs.lib.noaa.gov/rescue/mwr/097/mwr-097-12-0910.pdf |
| Summary: | The mean trough-ridge pattern over the United States was very similar to that of August, but elsewhere in the middle and high latitudes of the Northern Hemisphere fairly large changes occurred. The strong upper level ridge extending over the Arctic Basin from North America (fig. 1) replaced a deep Low that had persisted over the Beaufort Sea most of the summer. The 700-mb surface rose 160 m in that area (fig. 2). East of this strong ridge, a long fetch of brisk northwesterly flow over eastern Canada resulted in a deep complex Low over the Greenland area with two major negative anomaly centers (fig. 3). The 80-m center between Greenland and Scandinavia represented a drop of 180 m in the 700-mb height from the previous month for that locality. In the Pacific area, the formation of a Low over the Bering Sea during September with an intense trough extending into the Gulf of Alaska caused increased westerlies in the middle latitudes which reversed a long period retrogression of the Pacific ridge (Dickson, 1969). Downstream changes in the monthly mean pattern resulting from these increased Pacific westerlies were minor; however, weekly changes across the United States were quite striking. These changes will be discussed in detail under section 4. Progression at the higher latitudes across Eurasia was predominant in September with August’s trough near Novaya Zemlya moving to eastern Asia and being replaced by a ridge that moved eastward from Scandinavia. In the European area, the formation of a new monthly mean trough over Spain was associated with rising 700mb heights over central Europe as the cutoff Low over Europe during August rejoined the westerlies to form a full latitude trough from east of the Black Sea to the Arctic Basin. 2. TEMPERATURE The temperature anomalies over the United States, like the 700-mb heights, changed very little from August. Above-normal temperatures prevailed over most of the western part of the Nation (fig. 4). A strip of near- to above-normal temperature extended eastward along the ... |
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