1. Northern Hemisphere
During January the 500-hPa
height pattern featured positive anomalies over the eastern North Pacific,
the southeastern
U.S.
, the
Mediterranean Sea
, and eastern
Siberia
, and negative anomalies over
Alaska
and
Scandinavia
(Figs. E9, E11).
In the subtropics, the 200-hPa streamfunction pattern featured cyclonic
anomalies in both hemispheres across the tropical Pacific, indicating no
discernible El Niņo signal (i.e., anticyclonic anomalies) on the
upper-level circulation (Fig. T22).
The main surface temperature
departures during January reflected warmer-than-average conditions across
Canada
, the eastern half of the
U.S.
, and nearly all of
Eurasia
(Fig. E1). For the entire Northern
Hemisphere, monthly mean land surface temperatures were ~1.4°C above the
1971-2000 mean, reflecting a continuation of the exceptional warmth observed
in December. The main precipitation anomalies during January included
above-average totals in the south-central and central
U.S.
, southern
Scandinavia
, northeastern
Europe
, and western
Russia
, and below-average totals extending from the
Mediterranean Sea
eastward to
Pakistan
(Fig. E3).
a. Pacific/
North America
Despite ongoing weak El Niņo
conditions, the upper-level circulation during January featured cyclonic
anomalies across the eastern subtropical North Pacific (Fig. T22).
The presence of strong and persistent positive height anomalies at 500-hPa
over the eastern North Pacific is also inconsistent with El Niņo (Fig. E9).
Therefore, the continued anomalous warmth across
Canada
and the eastern
U.S.
during January cannot easily be attributed to El Niņo.
Instead, enhanced westerlies
and strong onshore flow north of the anomalous ridge resulted in
exceptionally warm surface temperatures across
Canada
, with much of the country experiencing temperatures in the upper 70th
percentile of occurrences (Fig. E1). The
eastern
U.S.
also experienced above-average temperatures during the month, with
departures of 2°-3°C recorded throughout the northeast and
Great Lakes
region. This anomalous warmth reflected the combination of a persistent
upper-level ridge in the southeast, and reduced cold-air advection from
Canada
.
The 500-hPa circulation
pattern also featured a strong confluent flow over the south-central
United States
. Large-scale ascending motion in this region contributed to above-average
precipitation from eastern
Texas
northeastward to the southern
Great Lakes
(Fig. E3). The most significant departures
were observed in eastern
Texas
, where totals were in the highest 90th percentile of
occurrences.
b.
North Atlantic
/
Europe
The 500-hPa circulation
pattern during January featured below-average heights over
Scandinavia
and above-average heights across southern
Europe
and the
Mediterranean Sea
(Fig. E9). This pattern reflected a strong
negative phase (-2.9) of the
Scandinavia
teleconnection pattern. This
anomaly pattern was associated with an extensive onshore flow of marine air
across northern
Europe
and southern
Scandinavia
, which contributed to exceptionally warm surface temperatures and
above-average precipitation throughout the region. Farther east,
above-average heights and surface temperatures were also observed across
central and northern
Asia
. As a result, temperatures were generally 3°-5°C above average from
central
Europe
to
Mongolia
, with the largest departures (6°-8°C) recorded in central
Russia
.
2. Southern Hemisphere
The anomalous 500-hPa circulation pattern during January
was fairly weak, with the main features being negative height anomalies over
the high latitudes of both the central South Pacific and
South
Atlantic
Oceans
(Fig. E15). In the subtropics, cyclonic
anomalies were observed across the eastern half of the South Pacific, which
is opposite to what is typically found during El Niņo episodes (Fig. T22).
The southern African rainy season extends from October to
April. Precipitation during January was well above average, with
area-averaged totals in the upper 80th percentile of occurrences
(Fig. E4). However, there was a pronounced
north-south dipole to the anomaly pattern, with above average totals in
northern
Mozambique
and
Tanzania
, and below average totals in southern
Mozambique
and southeastern
South Africa
(Fig. E3). So far in the 2006-07 rainy
season for southern
Africa
, area-averaged totals were below-normal in October, near-normal in both
November and December, and above normal in January (Fig.
E4).
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