Extratropical Highlights

  Table of Indices  (Table 3)

  Global Surface Temperature  E1

  Temperature Anomalies (Land Only)  E2

  Global Precipitation  E3

  Regional Precip Estimates (a)  E4

  Regional Precip Estimates (b)  E5

  U.S. Precipitation  E6

  Northern Hemisphere

  Southern Hemisphere

  Stratosphere

  Appendix 2: Additional Figures

Extratropical Highlights

AUGUST 2009

1. Northern Hemisphere

The 500-hPa height field during August 2009 featured positive anomalies in the polar region and across both the central North Pacific and North Atlantic Oceans , and negative anomalies in the Gulf of Alaska , over the high latitudes of the North Atlantic , and over south-central Russia (Fig. E9). Aspects of The circulation reflected a strong negative phase (-2.3) of the East Pacific (EP) teleconnection pattern, and a strong positive phase (+2.6) of the East Atlantic (EA) teleconnection pattern (Table E1, Fig. E7).

The main temperature signals during August included above average temperatures in the Europe and southern China , and below average temperatures in the central U.S. and in the vicinity of the Caspian Sea (Fig. E1). The main precipitation signals included above average totals in the central and northeastern U.S. , and below average totals in western Alaska , the southwestern U.S. , central Europe , and southwestern Russia (Fig. E3).

a. North Pacific/ North America

The 200-hPa circulation during August featured persistent troughs over the extreme eastern North Pacific and eastern North America , and a suppressed ridge over the southwestern U.S. (Fig. T22). This circulation contributed to below average temperatures across the central U.S. It also contributed to above average precipitation across the middle portion of the country, and to a continuation of below average precipitation along the Gulf Coast . Below average precipitation was also recorded in association with a suppressed southwestern U.S. monsoon.

The Midwestern U.S. has recorded above average precipitation for the last six months (Fig. E5), while the mid-Atlantic and Northeast regions have recorded above average totals in each of the last three months. Conversely, rainfall deficits in the Gulf Coast states extend back to November 2008.

b. North Atlantic and Europe

The 500-hPa circulation during August featured a dipole pattern of height anomalies over the North Atlantic , with above average heights in the middle latitudes and below average heights at high latitudes (Fig. E9). This pattern reflected a strong positive phase of the East Atlantic (EA) teleconnection pattern (Table E1). This circulation was associated with enhanced upper-level westerly winds and increased storminess in northern Europe , and with below average precipitation in portions of southern Europe (Fig. E3). It was also associated with above average temperatures across central and southern Europe , where departures in some areas exceeded the 90^th percentile of occurrences (Fig. E1).

  2. Southern Hemisphere

The 200-hPa streamfunction field during August indicates El Niño was impacting the upper-level circulation in both the SH subtropics and extratropics (Fig. T22). The subtropical ridge was stronger than average across the central South Pacific and weaker then average over the Indian Ocean . There was also an overall eastward extension/ shift of the mean subtropical ridge, which is consistent with El Niño. Another El Niño impact is indicated by cyclonic streamfunction anomalies across much of the SH extratropics (Fig. T22).

The 500-circulation during August featured an anomalous zonal wave-3 pattern, with above average heights at high latitudes centered over the three ocean basins and below average heights located generally poleward of the three continents (Fig. E15). The main temperature signals during August included significantly warmer than normal conditions across Australia and southern South America (Fig. E1). Precipitation was well above average in southeastern Brazil , and was well below average in eastern Australia for a second month (Figs. E3, E4).