- August 2014
1. Northern Hemisphere
The 500-hPa circulation during August
featured above-average heights across Canada, Greenland, and central Russia, and
below-average heights over southern Alaska, the central North Atlantic, and central
Europe (Fig. E9).
This pattern projected onto the strong negative phase of both the North
Atlantic Oscillation (NAO, -2.28) and the east Atlantic/ West Russia (-1.69)
teleconnection pattern (Table E1, Fig. E7).
The main land-surface temperature signals
included well above-average temperatures in northeastern Canada, southern
Greenland, and western Russia, and below-average temperatures in the
west-central U.S., the eastern U.S., and northern Europe (Fig. E1). The main precipitation signals included
above-average totals in eastern Alaska, the north-central U.S., and northern
Europe, and below-average totals in western Alaska, the northwestern U.S., and south-central
Russia (Fig. E3).
a. North Pacific/ North America
The mean 500-hPa circulation during
August featured troughs over southern Alaska and California, and an anomalous
ridge across eastern Canada and Greenland (Fig.
E9). This pattern was associated above-average
precipitation in eastern Alaska and the north-central U.S., and with
below-average precipitation in the extreme northwestern U.S. (Fig. E3).
Area-averaged totals in both the Inter-Mountain and Great Plains regions
reached the 80th percentile of occurrences (Fig. E5), with many locations recording more than 175% of normal
precipitation (Fig. E6).
According to the U.S. Drought
above-average precipitation helped to lessen drought conditions in central
Plains states, with the most significant improvements observed in Nebraska and
eastern Kansas. In contrast, a massive area of exceptional drought continued in
central/ southern California and western Nevada, and severe or extreme drought
extended across the U.S. Southwest, California, southern Oregon, central
Washington, and southern Idaho.
The 500-hPa circulation during
August featured above-average heights over Greenland and below-average heights
across the central North Atlantic and Europe (Fig. E9). This pattern projected strongly
onto the negative phase of both the North Atlantic Oscillation (NAO, -2.28) and
the east Atlantic/ West Russia (-1.69) teleconnection pattern (Table E1, Fig. E7).
This anomaly pattern was associated
with well above-average precipitation in central and northern Europe, and with
below-average precipitation in southwestern Russia (Figs. E3, E4).
It was also associated with well above-average temperatures in southern
Greenland and western Russia, with many locations recording departures in the
upper 90th percentile of occurrences (Fig. E1).
c. Northern Africa
The West African monsoon, which
lasts from June-September, has been well below average so far this year. Area-averaged
totals during August were near average, following well below-average totals
during June and July (Figs. E3, E4). Overall, the suppressed
west African monsoon has likely contributed to exceptionally non-conducive
conditions for hurricane formation across the tropical North Atlantic,
including enhanced vertical wind shear, sinking motion, and atmospheric
stability, and a southward shift of the African Easterly Jet (AEJ). Another contributing factor has been an
amplified Tropical Upper-Tropospheric trough (TUTT) over the western North
Atlantic and Caribbean Sea (Fig. T22).
2. Southern Hemisphere
The mean 500-hPa circulation during
August featured above average heights south of Australia and Africa, and
below-average heights over the central ocean basins (Fig. E15). In southeastern Australia
downstream of the mean ridge axis, exceptionally dry conditions continued
during the month with regional precipitation totals in the lowest 10th
percentile of occurrences (Figs. E3, E4). Exceptionally
cool conditions were recorded in north-central Australia, where monthly
departures were in the lowest 10th percentile of occurrences.
The Antarctic ozone hole typically develops during August
and reaches its peak aerial extent in September and October. By the end of
August 2014, the ozone hole (Fig. S6) spanned 10 million square kilometers, which is
less than the 2004-2013 mean of 15 million square kilometers (Fig. S8, top).
The aerial coverage of polar stratospheric cloud (Fig. S8, bottom) and the SH polar vortex
(Fig. S8, middle) were near average
during August 2014, while polar stratospheric temperatures were below average (Fig. S4).