1. Northern Hemisphere
The 500-hPa circulation during November 2003 featured above-average
heights across the North Pacific, over the southeastern U.S., and over
Scandinavia/ eastern Europe, and below-average heights over western North
America, the high latitudes of the North Atlantic, and central Russia (Figs.
E10, E12). These
anomalies were associated with significant changes in the mid-latitude jet
streams, including a westward retraction of the East Asian jet core to well
west of the date line, and the development of a strong jet stream across
the north-central United States (Fig. T21).
Above-average surface temperatures were observed in the eastern U.S.,
and most of Alaska and Europe during November (Fig.
E1), while below-average temperatures were observed in the western
United States and portions of central Siberia. Prominent precipitation
anomalies during the month included below-average totals along the eastern
seaboard of the United States, the eastern Mediterranean Sea, and eastern
Europe (Fig. E3).
a. Pacific/North America
The mean upper-level circulation during November featured a broad ridge
south of the Aleutian Islands and a trough across North America (Fig.
E10). This represents a significant westward shift of the mean
ridge and trough axes from their climatological mean locations over western
and eastern North America, respectively. This circulation was associated
with a three-celled pattern of height anomalies, with positive anomalies
over the high latitudes of the North Pacific and the southeastern U.S., and
negative anomalies over western North America. This anomaly pattern
reflected a strong negative phase (-1.8) of the Pacific/ North American (PNA)
teleconnection pattern (Table E1, Figs. E7,
The negative PNA pattern during November was also associated with a
pronounced westward retraction of the East Asian jet core to well west of
the date line (Fig. T21), and with a
northward shift of the mean westerlies to Alaska. This circulation
contributed to above-average temperatures in Alaska.
A well-defined jet stream was also evident across the north-central and
northeastern United States (Fig. E11). The
pronounced westward shift of this jet stream, which is normally located
over the North Atlantic, is consistent with the westward shift of the mean
upper-level ridge and trough axes during the month. This circulation
contributed to below-average temperatures in the northwestern U.S. and to
above-average temperatures in the eastern part of the country (Fig.
E1). It also contributed to above-average precipitation in the
Inter-Mountain and Great Lakes regions (Fig. E5),
and to below-average precipitation in the Southeast, Mid-Atlantic, and
Northeast regions. These latter areas were situated along the mean
upper-level ridge axis and south of the mean jet core (Fig.
A large-amplitude ridge extended southward from Scandinavia to the
Mediterranean Sea during November, while upper-level troughs covered the
high latitudes of the North Atlantic and central Russia (Fig.
E10). This blocking pattern projected very strongly onto the
positive phase (+1.9) of the Scandinavia teleconnection pattern (Table
E1, Figs. E7, E8).
Over the eastern North Atlantic this circulation was associated with a
pronounced split flow configuration, with the northern branch of the jet
stream entering the continent near Great Britain and the southern branch
entering near southern Portugal (Fig. T21).
This circulation was consistent with above-average temperatures over most
of Europe (Fig. E1). Farther downstream the
blocking pattern brought below-average temperatures to central Russia, and
also contributed to below-average precipitation in areas such as eastern
Europe and the eastern Mediterranean Sea, regions that were situated
beneath the mean upper-level ridge axis.
2. Southern Hemisphere
In the Southern Hemisphere the 500-hPa circulation during November
featured above-average heights south of Australia and over the high
latitudes of the eastern North Pacific, and below-average heights over the
Indian Ocean, the central South Pacific, and southern South America (Fig.
E16). This overall circulation was associated with enhanced
upper-level westerlies across the central South Pacific, and with warmer (Fig.
E1) and wetter (Fig. E3) than
average conditions over southern South America. Over Australia
significantly above-average temperatures were observed in the southeast,
and above-average precipitation was recorded in the south-central portion
of the continent.