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HOME > Expert Assessments > Climate Diagnostics Bulletin > Extratropical Highlights
Extratropical Highlights - March 2004

1. Northern Hemisphere

The 500-hPa circulation during March 2004 featured above-average heights in the lower and middle latitudes (Figs. E10, E12), and below-average heights over northern Canada and central Siberia. Over the eastern North Pacific anomalous cyclonic streamfunction anomalies were observed in the subtropics of both hemispheres (Fig. T22). This inter-hemispheric symmetry is consistent with the enhanced convection over the western Pacific and lack of convection over the eastern Pacific. In contrast during February anticyclonic circulation anomalies were observed across nearly the entire subtropics in both hemispheres. These month-to-month fluctuations in the subtropical circulation are consistent with the ongoing MJO activity.

Prominent temperature departures during March included warmer than average conditions across Alaska and Canada, nearly all of Europe, Asia, and China, and a continuation of warmer than average SSTs over large portions of the North Atlantic (Fig. E1).

a. Pacific/North America

The upper-level circulation during March featured a persistent north-south dipole of streamfunction anomalies over the eastern North Pacific and western North America. This pattern reflected anticyclonic streamfunction anomalies in the middle latitudes and cyclonic streamfunction anomalies in the subtropics. These anomalies projected onto the strong positive phase (+2.2) of the East Pacific teleconnection pattern (Table E1, Figs. E7, E8). This anomalous circulation was associated with a complete disappearance of the East Asian jet core east of the date line, and with a northward shift of the jet axis into southwestern Canada (Fig. T21). The resulting enhanced westerlies across western and central Canada (Fig. E11) contributed to above-average surface temperatures across the region, and also brought enhanced precipitation to western Canada and the Inter-Mountain region of the United States (Fig. E3).

The Inter-Mountain region has experienced above-average precipitation in four of the last five months (Fig. E5) and also recorded above-average totals during the 2002-03 winter. This region had previously experienced large precipitation deficits during the prolonged 1998-2001 Pacific cold episode. Southern California also experienced above-average precipitation during March, and has received rainfall surpluses in three of the last four months. Farther east below-average precipitation was observed during March from the mid-western U.S. to New England. Monthly totals were generally below the 30th percentile of occurrences in these areas, with isolated regions reporting totals below the 10th percentile.

b. Asia

The circulation across Asia featured a zonally-elongated pattern of 500-hPa height anomalies, with above-average heights in the subtropics and middle latitudes, and below-average heights at high latitudes. This anomalous circulation was associated with enhanced upper-level westerlies north of the Tibetan Plateau, and reduced westerlies south of the Plateau (Fig. T21).This circulation contributed to significantly above-average surface temperatures (+3 to +5 C) from the Caspian Sea to eastern China and Mongolia, with temperatures in most places exceeding the 90th percentile of occurrences. Much of central Russia and China also experienced well above-average surface temperatures during February.

2. Southern Hemisphere

In the Southern Hemisphere the 500-hPa circulation during Maech featured an anomalous zonal wave-3 pattern, with below-average heights south of the three continents and above-average heights over the central ocean basins (Fig. E16). This circulation was associated with enhanced rainfall across southern Australia and southern Africa (Fig. E3).

In southern Africa the rainy season normally lasts from October to March. Area-averaged rainfall during March was well above-average, with totals generally above the 90th percentile of occurrences (Fig. E3). The enhanced rainfall and associated axis of upper-level divergence (Fig. T23) was situated in the area of ascending motion between the anomalous upper-level trough and ridge axes (Figs. T21, T22). Overall, the 2003-2004 rainy season featured below-average rains during November and December, and above-average rains during January-March.

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