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

JUNE 2009

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 U.S. , the eastern North Atlantic , and Mongolia , and with ridges over the high latitudes of the North Atlantic , near the Caspian Sea , and over eastern Siberia .

The 200-hPa streamfunction field indicated near average conditions in the subtropics across the eastern half of the Pacific Ocean , in association with the demise of La Niña and the onset of weak El Niño conditions (Fig. T22). Also, the combination of negative streamfunction anomalies from north-central Africa to Pakistan and positive anomalies across the subtropical Indian Ocean reflected weaker subtropical ridges that were contracted equatorward in both hemispheres.

The main temperature signals during June included above average temperatures in the southeastern U.S. , southern Europe , and China , and below average temperatures in the northern Plains States and central Canada (Fig. E1). 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/ North America

This is the first time in almost a year that no La Niña signal was evident in the NH extratropical circulation. During June, strong 500-hPa troughs were evident over the central North Pacific, the southwestern U.S. , and the extreme western North Atlantic (Fig. E9). Between the trough axes, enhanced anticyclonic curvature was evident in the Gulf of Alaska and over the southern U.S. (Fig. T22). Also, a confluent flow configuration was present in the Intermountain region in response to the combination of an anomalous zonal flow over the northern U.S. and the trough in the southwest.

This overall circulation contributed to above average precipitation from Oregon to the northeastern U.S. , with the most significant surpluses observed in the Inter-Mountain, Great Plains , Mid-Atlantic, and Northeast regions of the U.S. (Figs. E5, E6). In contrast, anomalously dry (and warm) conditions were observed in the Gulf Coast region. Rainfall totals from eastern Texas to western Mississippi were less than 25% of normal and in the lowest 10^th percentile of occurrences.

b. North Atlantic and Europe

The 500-hPa circulation during June featured a dipole pattern of 500-hPa height anomalies over the North Atlantic , 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 Caspian Sea contributed to above average temperatures across southern Europe and portions of the Middle East , with some areas recording values in the upper 90^th percentile of occurrences (Fig. E1).

c. India

            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 China (Fig. T22). This pattern was associated with a slow start to the Indian monsoon season, with area-averaged monsoon rainfall in the lowest 10^th 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 Indian Ocean , and below average heights over southern Australia and the east-central South Pacific.

In the subtropics, the 200-hPa streamfunction pattern featured positive anomalies from southern Africa to Australia , 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 Indian Ocean and southern Australia (Fig. E3).