1. Northern Hemisphere
The 500-hPa height field during
June 2009 featured large areas of negative anomalies in the middle latitudes and
generally positive anomalies at high latitudes (Fig. E9). This pattern was associated with
large amplitude troughs over the central North Pacific, the western
, the eastern
, and with ridges over the high latitudes of the
, near the
, and over eastern
The 200-hPa streamfunction field
indicated near average conditions in the subtropics across the eastern half of
, in association with the demise of La Niņa and the onset of weak El Niņo
conditions (Fig. T22).
Also, the combination of negative streamfunction anomalies from north-central
and positive anomalies across the subtropical
reflected weaker subtropical ridges that were contracted equatorward in both
The main temperature signals
during June included above average temperatures in the southeastern
, and below average temperatures in the northern
The main precipitation signals included above average totals across the central
U.S., eastern Europe, and Mongolia, and below average totals in southwestern
Russia, India, and southeastern Asia (Fig. E3).
a. North Pacific/
This is the first time in almost a
year that no La Niņa signal was evident in the NH extratropical circulation.
During June, strong 500-hPa troughs were evident over the central North Pacific,
, and the extreme western
Between the trough axes, enhanced anticyclonic curvature was evident in the
Gulf of Alaska
and over the southern
Also, a confluent flow
configuration was present in the Intermountain region in response to the
combination of an anomalous zonal flow over the northern
and the trough in the southwest.
This overall circulation
contributed to above average precipitation from
to the northeastern
, with the most significant surpluses observed in the Inter-Mountain,
, Mid-Atlantic, and Northeast regions of the
(Figs. E5, E6).
In contrast, anomalously dry (and warm) conditions were observed in the
region. Rainfall totals from eastern
were less than 25% of normal and in the lowest 10th percentile of
The 500-hPa circulation during
June featured a dipole pattern of 500-hPa height anomalies over the
, with above average heights in the north and below average heights in the
middle latitudes (Fig. E9).
This pattern reflected the negative phases of both the NAO and EA teleconnection
pattern (Table E1).
The trough over the eastern
North Atlantic Ocean
, combined with a strong ridge over the
contributed to above average temperatures across southern
and portions of the
, with some areas recording values in the upper 90th percentile of
occurrences (Fig. E1).
The circulation during June featured a reduced strength of the Indian
monsoon ridge at 200-hPa, and a confinement of the subtropical ridge to central
This pattern was associated with a slow start to the Indian monsoon season, with
area-averaged monsoon rainfall in the lowest 10th percentile of
occurrences (Fig. E4).
2. Southern Hemisphere
The circulation during June reflected a zonal wave-2
pattern of 500-hPa height anomalies in the middle latitudes, and wave-1 pattern
at high latitudes (Fig. E15).
Aspects of this pattern included above average heights over the southern
, and below average heights over southern
and the east-central South Pacific.
In the subtropics, the 200-hPa streamfunction pattern
featured positive anomalies from southern
, in association with a reduced strength of the subtropical ridge. Consistent
with this pattern, anomalous upper-level westerly winds and above average
rainfall extended across the subtropical