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HOME > Expert Assessments > Climate Diagnostics Bulletin > Extratropical Highlights
Extratropical Highlights - February 2003

1. Northern Hemisphere

The 500-hPa circulation during February featured a persistent pattern of positive height anomalies over the Gulf of Alaska, the low latitudes of the North Atlantic, Scandinavia, and eastern China, and negative height anomalies over Canada, southern Europe, and north-central Siberia (Figs. E10, E12). These conditions partly reflected the negative phases of the Pacific/ North American (PNA) and the East Atlantic (EA) teleconnection patterns, which is a reversal from the positive phases of these modes recorded during the past four months (Tables E1, E2, Figs. E7, E8).

The prominent temperature anomalies during February included warmer-than-normal conditions across southern and central Alaska, Scandinavia, and most of Asia, and cooler than normal conditions across North America and southern Europe (Fig. E1). Prominent precipitation departures during the month included above-average precipitation over the southwestern and southeastern United States, and below-average precipitation over the northwestern United States, Central America, the Caribbean Sea, and most of Europe (Fig. E3).

a. Pacific/North America

Over the Pacific/ North American sector the circulation during February featured an upper-level ridge over the Gulf of Alaska, and a very strong upper-level trough over eastern Canada (Figs. E10, E11). This circulation was associated with anomalous northerly flow extending from northwestern Canada to the Northern Plains States, which contributed to considerably below-average temperatures over much of the continent with the magnitude of the largest negative temperature departures exceeding 3°C over the central and northern Plains States (Fig. E1).

The circulation also featured an eastward extension of the East Asian jet stream and an eastward shift of the associated jet exit region toward the eastern Pacific (Figs. E11, T21). Farther east a highly confluent flow and enhanced jet stream winds were observed across the southern United States. These conditions reflect an ongoing southward shift of the mean jet axis across the eastern North Pacific and North America, with the mean jet core entering the continent over northern Mexico instead of in its climatological position over the Pacific Northwest. They also reflect a strong coupling of the East Asian and subtropical jet streams, with essentially a single jet core extending from Japan to the southeastern United States. Similar conditions were also evident in January, consistent with the typical atmospheric response to mature El Niņo conditions.

A strong flow of marine air continued into Alaska during February, increasing surface temperatures to 6°-8°C above average across the southern part of the state (Fig. E1). This anomalous warmth is also consistent with El NiZo.

b. North Atlantic and Europe

Below-average heights covered the high latitudes of the North Atlantic and southern Europe during February, and above-average heights spanned the low latitudes of the North Atlantic and Scandinavia (Fig. E10). This 4-celled anomaly pattern was associated with enhanced jet stream winds over the western North Atlantic, and reduced jet stream winds and below-average precipitation across central Europe. It was also associated with a pronounced split-flow configuration over the eastern North Atlantic, with the southern branch of the jet stream contributing to above-average precipitation across the Mediterranean Sea (Fig. E3).

2. Southern Hemisphere

Above-average 500-hPa heights were evident over the central South Pacific, in the area south of Australia, and throughout the polar region during February, and below-average heights covered the high latitudes of the South Pacific and portions of the east-central South Atlantic (Fig. E16). The dominant temperature anomalies during the month reflected above-average temperatures over most of South America, southern Africa, the Indian Ocean, and southeastern Australia. The prominent precipitation anomalies included above-average rainfall over northeastern Brazil and below-average rainfall over southeastern Brazil. Above-average rainfall was also recorded across southern Australia and portions of northwestern Australia.

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Page last modified: January 15, 2002
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