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.
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.
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