| The Northern Hemisphere 500-hPa
circulation during June featured a wave-four pattern of anomalies within the latitude band
40°-50°N, and a dominance of positive anomalies in the lower mid-latitudes throughout
the hemisphere (Fig. E10). In the subtropics and lower
mid-latitudes, these height anomalies were accompanied by a large-scale pattern of 200-hPa
anticyclonic circulation anomalies (Fig. T22, bottom),
which were especially strong from the Caribbean Islands eastward to the northern flank of
the Asian monsoon ridge. This entire region experienced surface temperatures in the upper
90th percentile during the month. A corresponding region of anticyclonic
circulation anomalies was also evident in the Southern Hemisphere from the western South
Atlantic eastward to southeastern Australia. In both hemispheres, these anomalies were
situated along the poleward flanks of the mean subtropical ridge axes, consistent with an
overall poleward expansion of the subtropical ridges.
a. North America
The mean 500-hPa circulation over North America featured above-average heights across
the southwestern United States and eastern Canada, and below-average heights over
southwestern Canada (Fig. E10). These areas coincided with
above-normal and below-normal mean surface temperatures, respectively (Fig.
E1).
Above-average rainfall (Fig. E3) was recorded during the
month across the Gulf Coast states, the Southeast, the Ohio Valley (Fig.
E5) and along the eastern seaboard of the United States northward to eastern
Canada. The Gulf Coast states and the Southeast region have experienced lower-than-average
rainfall for the past two years. The Ohio Valley region has recorded generally
below-average precipitation since October 2000 (Fig. E5).
b. China
Above-average rainfall covered eastern and east-central China during June (Fig. E3), with area-averaged totals reaching the 95th
percentile (Fig. E4). Above-average rainfall was also
observed during May over large portions China. Climatologically, June represents the onset
of the peak in this area’s rainy season. Last year above-average precipitation
prevailed throughout the entire June-August peak in the rainy season.
2. Southern Hemisphere
The Southern Hemispheric circulation during
June featured anticyclonic streamfunction anomalies at 200-hPa from the western South
Atlantic eastward to southeastern Australia (Fig. T22, bottom).
These anomalies are located along the poleward flanks of the mean subtropical ridge axes,
and are consistent with an overall poleward expansion of the subtropical ridges. As
discussed above, similar anomalies were also evident along the poleward flanks of the mean
subtropical ridge axes in the Northern Hemisphere.
In Australia, this overall anomaly pattern was accompanied by above-average 500-hPa
heights across the southern part of the continent. (Fig. E9).
The largest positive height anomalies were observed in the east and southwest, and were
accompanied by below-average rainfall in both regions (Fig. E3).
Extreme warmth was also observed across eastern Australia during the month, with surface
temperatures exceeding the 90th percentile throughout the region (Fig. E1, bottom). |
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