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

OCTOBER 2009

1. Northern Hemisphere

The 500-hPa height field during October featured above-average heights in the polar region and below average heights in the middle latitudes (Fig. E9). This pattern reflected one of the strongest negative phases of the Arctic Oscillation on record dating back to 1950. Regional aspects of the circulation included ridges in the Gulf of Alaska and the eastern North Atlantic, and amplified troughs across the central North Pacific, western North America, and the central North Atlantic . These anomalies projected onto several regional teleconnection patterns (Table E1, Fig. E7), including exceptionally strong negative phases of the West Pacific (-2.4) and Polar/ Eurasia (-2.6) patterns, a modest negative phase of the NAO (-1.0), and a positive phase of the East Atlantic (+1.4) pattern.

The main temperature signals during October included above average temperatures in China , and below average temperatures in central Canada and the central United States (Fig. E1). The main precipitation signals during October included above-average totals across much of North America and eastern Europe, and below-average totals in eastern China (Fig. E3).

a. North Pacific/ North America

The 500-hPa circulation during October featured a ridge over the Gulf of Alaska and a strong trough in western North America (Fig. E9). This pattern was associated with exceptionally cool temperatures across central Canada and the central U.S. , with departures in many regions (-2^o to -4^oC) falling into the lowest 10^th percentile of occurrences (Fig. E1). In contrast, much of Alaska recorded above average temperatures during the month, with departures in many regions exceeding +3^oC.

Much of North America recorded well above average precipitation during October (Fig. E3). Precipitation in the central and northwestern U.S. and southwestern Canada generally exceeded 175% of normal (Fig. E6), with departures in the upper 90^th percentile of occurrences. In the U.S. , the Great Plains, Midwest , Ohio Valley, Mid-Atlantic, and Northeast have recorded above average precipitation for much of the last five months (Fig. E5).

b. China

The strength of the mean upper-level ridge was below average west of the Tibetan Plateau, which allowed for the mean ridge axis to be centered over western China (Fig. T22). This pattern contributed a continuation of drier than average conditions across eastern China , where totals were generally in the lowest 30^th percentile of occurrences. This marks the second straight month with significant precipitation deficits in China .

  2. Southern Hemisphere

The 500-hPa circulation during October reflected an anomalous zonal wave-3 pattern, with above average heights over the central South Pacific and in the areas south of Australia and South Africa and, and below average heights located south of South America and near New Zealand (Fig. E15).

The main temperature anomalies during October reflected cooler than average temperatures in extreme southern South America (Fig. E1). For the entire South African monsoon region the start to the 2009-10 monsoon season, which runs from October through April, featured near-average rainfall totals (Fig. E4). Below average precipitation was observed throughout eastern Australia during the month, with northeastern Australia recording deficits for the fourth straight month.

The Antarctic ozone hole typically reaches its peak aerial extent during September and October. During 2009 the size of the ozone hole was approximately equal to the 1999-2008 mean. The 2009 ozone hole reached a peak extent of 24 million square kilometers in late September, and still covered 13.5 million square kilometers in late October (Fig. S8).