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HOME > Expert Assessments > Climate Diagnostics Bulletin > Extratropical Highlights
 
Extratropical Highlights - November 2002
 

The 500-hPa circulation during November featured a north-south dipole pattern of height anomalies over the North Pacific and North Atlantic, with above-average heights at high latitudes and below-average heights in the middle latitudes (Fig. E10). Above average heights and anticyclonic streamfunction anomalies were also evident in the subtropics over both ocean basins (Fig. T22). In the extratropics these anomalies reflect the negative phase of the Arctic Oscillation (Fig. A2.1)

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Over the Pacific Ocean these anomaly patterns reflected the positive phase of the Pacific/ North American (PNA) pattern and negative phase of the East Pacific (EP) pattern. Over the Atlantic Ocean they reflected the negative phase of the North Atlantic Oscillation (NAO) and positive phase of the East Atlantic (EA) pattern (Table E1, Figs. E7, E8). Similar phases for each of these teleconnection patterns were also observed in October. These circulation anomalies were associated with an eastward extension of the main Pacific jet stream to well east of the date line, and with a southward shift of the North Atlantic jet stream to southern Europe (Figs. E11, T21). Similar anomaly patterns were also evident in the Southern Hemisphere.

In both hemispheres the anticyclonic streamfunction anomalies over the central subtropical Pacific Ocean are seen to flank the region of enhanced equatorial convection, and are consistent with the atmospheric response to mature El Niņo conditions (Fig. T25). The eastward extended Pacific jet streams in both hemispheres are centered along the poleward flanks of these circulation anomalies, and are also consistent with ongoing El Niņo conditions.

In the Northern Hemisphere the prominent temperature anomalies during November included warmer than normal conditions over western Canada, Alaska, southern Europe, and most of central Asia, and cooler than normal conditions over eastern North America and northern Europe (Fig. E1). Prominent precipitation departures during the month included a continuation of drier than normal conditions in the Pacific Northwest region of the United States (Figs. E3, E5, E6), and above-average precipitation across the southeastern states and most of central Europe (Figs. E3, E4).

a. Pacific/North America

The strong positive PNA pattern (+1.6, Table E1) during November was associated with amplified troughs across the central North Pacific and over eastern North America, and an amplified ridge over western North America (Fig. E10). These conditions contributed to a strong southwesterly flow and above-average surface temperatures across Alaska and western Canada, with departures exceeding +5°C (above the 90th percentile) in southeastern Alaska (Fig. E1).

The amplified trough across the eastern U.S. was also associated with a large-scale pattern of negative height anomalies that extended to central Europe. This overall circulation brought anomalous northerly flow from northern Canada to the south-central United States (Fig. E11), and resulted in below-average surface temperatures across eastern North America.

Over the U.S. the primary region of above-average precipitation during November was observed in the southeast (Figs. E3, E6). This area was situated immediately downstream of the mean upper-level trough axis along the right-entrance region of the enhanced North Atlantic jet stream (Figs. E11, T21). The Gulf Coast and Southeast regions have recorded above-average precipitation in each of the last three months (Fig. E5).

Below-average precipitation was observed in the Pacific Northwest and Midwest during November. The Pacific Northwest has recorded precipitation deficits in every month since February 2002 (Fig. E5). This combination of decreased precipitation in the Northwest, and above-average precipitation and increased storminess and across the Gulf Coast and Southeast (Fig. E14), is consistent with the atmospheric response to El Niņo.

b. North Atlantic and Europe

The circulation over the North Atlantic and Europe featured above-average heights at high latitudes and in the subtropics, and below-average heights in the middle latitudes (Fig. E10). Enhanced jet stream winds were also observed across the central Atlantic in association with a southward shift of the mean jet axis to southern Europe (Figs. E11, T21). These conditions brought cooler and drier than normal conditions to Scandinavia, and warmer and wetter than normal conditions to central and southern Europe (Figs. E1, E3).

2. Southern Hemisphere

The upper-level circulation during November featured a north-south dipole pattern of height anomalies over the three oceans, with above-average heights at lower latitudes and below-average heights at higher latitudes. Above average heights were also observed over the high latitudes of the eastern South Pacific and across southern Australia (Fig. E16). This overall circulation was associated with an eastward extension of the Pacific jet stream to well east of the date line, and with strengthening of the jet stream winds across the central South Atlantic (Figs. T21, E17).

In Brazil prominent precipitation anomalies during November reflected the continuation of suppressed convection in northern and central sections and enhanced convection in the South (Figs. E3, E4, T25). Below-average precipitation was also again observed across eastern Australia, with monthly totals generally below the 10th percentile. Thee rainfall patterns are consistent with the ongoing El Niņo conditions. Much of Brazil and Australia were also considerably warmer than normal during the month, with temperatures exceeding the 90th percentile in parts of both countries (Fig. E1).


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