THE WEATHER AND CIRCULATION OF JANUARY 1970 UDC 651.w6.1:551.513.1:551.624.~6(74+77):551.577.37~79)"1970.01" Record Cold in the Eastern Third of the Nation and Record Rainfall in she Pacific Northwest
prevailed over the western part of the Northern Hemisphere during January 1970, with the strongest westerlies averaging 17 m sec-1 at 35O N., which was nearly 10 m sec-I above the normal for that latitude. Troughs and ridges at middle latitudes were characterized by moderate amplitude. There were th...
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.395.2378 http://docs.lib.noaa.gov/rescue/mwr/098/mwr-098-04-0328.pdf |
| Summary: | prevailed over the western part of the Northern Hemisphere during January 1970, with the strongest westerlies averaging 17 m sec-1 at 35O N., which was nearly 10 m sec-I above the normal for that latitude. Troughs and ridges at middle latitudes were characterized by moderate amplitude. There were three principal cyclonic centers of action in the Northern Hemisphere, located near Novaya Zemlya, between Kamchatka and the Aleutians, and over eastern Canada (fig. 1). The latter was split into two cells. A pronounced high-latitude blocking center with heights 180 m above normal was located over the Arctic Ocean north of the Bering Strait, while a blocking ridge just west of Norway produced heights 110 m above normal (figs. 1 and 2). The broad cyclonic flow over the oceans at midlatitudes was associated with anomaly centers of 100 and 170 m below normal over the Pacific and Atlantic, respectively (fig. 2). The Atlantic center was over two and one-half standard deviations below normal. Frequent and relatively deep surface cyclones crossed these oceanic areas on tracks south of normal. Episodes of damaging surf in the Hawaiian Islands, which had begun in December, continued into January. The mean 700-mb jet stream was displaced south of the normal January position, particularly over the two oceans (fig. 3). Peak mean speeds were more than 10 m sec- ' above normal over the Pacific and in excess of 15 m sec- ' above normal over the eastern Atlantic. Monthly mean wind speeds were below normal over the northern sectors of the oceans. The greatest change in circulation between December and January occurred over the central Atlantic where an unusually strong ridge (Posey 1970) gave way to fast westerlies and broad cyclonic flow. The departures from the respective normals of the 700-mb height fell by as much as 320 m between the 2 mo (fig. 4). Heights increased with respect to normal at high latitudes, particularly over |
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