Monthly Highlights

1.Climate in China

During September 2006，monthly mean surface air temperatures were near or above normal in most of China, with temperatures about 1ºC above normal in middle Northeast China, eastern Inner Mongolia, regions from eastern Northwest China through eastern Tibet to western Sichuan and mid-lower reaches of the Yangtze River.

For the month, precipitations were observed less than normal in most of China. Precipitations were observed 30~80% below average in the western Northwest, the southeastern Northeast, most of the North, eastern part of the regions between the Yellow River and the Huaihe River, northwest of the regions south to the Yangtze River, the western South and most of Guizhou and Yunnan and the western Tibet, with no precipitation in parts of above regions. Precipitations were 30~50% above normal in central Inner Mongolia, parts of eastern and middle Northwest China and middle reaches of the Yellow River, with maximums over 100% above normal.

2.Climate in the world  

During September 2006，monthly mean surface air temperatures were above normal in most Europe, the mid-high latitudes of Asia, most of South America and most of Australia, with temperatures 2~4ºC above normal in most of Europe, northern Russia and central Australia, and more than 4ºC above normal in locations.

For the month, precipitations were observed more than 50% below average in central Europe, most of China, Mongolia, southern Russia, most of Australia, southern Africa, northern and most of southern South America, with no precipitation in Northwest China, central Australia, parts of southern South America. Meanwhile, precipitations were more than 50% above average in southern Europe, northern Russia, most of the Indian Peninsula, western Africa and southern Brazil.

3.General Circulation Features

Northern Hemisphere: During September 2006, the mean 500hPa geopotential height field exhibited mainly a 4-wave pattern at the mid-high latitudes. Abnormal ridges developed over northern Europe and northern North America. In the 500hPa height anomaly field, positive anomalies above 4 dam covered areas from northern North America to the polar region, regions from the northeastern North Atlantic Ocean to most of Europe and regions from the northwestern Pacific Ocean to the Baikal Lake with maximum above 12 dam over regions from northern North America to the polar region. Negative anomalies below –4 dam were over regions from northern Russia to the polar region, the eastern North Atlantic Ocean and parts of North America with minimums below –12 dam over regions from northern Russia to the polar region. For the month, the Northwest Pacific subtropical high was larger and slightly stronger than normal, and it was located in slightly farther south and extended farther west than normal.

Southern Hemisphere: For the month, zonal circulation mainly dominated the eastern Hemisphere and meridional circulation prevailed in the western hemisphere in the mean 500hPa geopotential height field at the mid-high latitudes. The 500hPa height anomaly field exhibited a “+ - +” pattern with the absolute values of the anomaly centers all above 8 dam at the mid-high latitudes of the South Pacific. Heights were generally near normal in other regions.

4.Tropical Features

Sea Surface Temperatures (SSTs): During September 2006, positive SST anomalies above 0.5ºC were observed in the equatorial Pacific east to 160ºE with two maximum centers above 1.5ºC, which located at around 180º and 110ºW. SSTA indices all increased compared with last month and NINO Z、NINO 3.4 、NINO 3、NINO 4 and NINO 1+2 indices were 0.9ºC, 0.7ºC, 0.9ºC, 0.9ºC and 0.9ºC respectively. Meanwhile, negative SST anomalies below -0.5ºC were observed in the eastern Indian Ocean south to the equator.

Subsurface Temperatures: During September 2006, abnormal subsurface warm water persisted in the equatorial Pacific Ocean, with its centers enhancing slightly and its location shifting eastward and upward. Meanwhile, cold water in offshore of South America shrank but its intensity enhanced.

Warm Pools: During September 2006, areas of the western Pacific and Indian Ocean warm pools were near normal and their intensities were both stronger than normal.

 Wind Field：During September 2006, at the lower troposphere (850hPa), weak westerly anomalies covered the equatorial western Pacific Ocean, while easterly anomalies were over the eastern equatorial Indian Ocean. At the upper troposphere (200hPa), zonal winds were near normal over the equatorial Pacific and the equatorial Indian Ocean.

Southern Oscillation: In the month, Southern Oscillation Index (SOI) was –0.4, with an increase of 0.9 from last month.

Convection over the Tropics: During September 2006, the anomalous outgoing longwave radiation (OLR) showed that convections were suppressed over regions from the eastern equatorial Indian Ocean to western Indonesia and enhanced slightly over the regions from the equatorial western Pacific to the date line. In the lower troposphere (850hPa) divergent wind field, a convergent center was over 145ºE, 15ºN, and a divergent center located around 107.5ºW, 15ºS. Correspondingly, at the upper troposphere (200hPa), the divergent center was found over 115ºE, 12.5ºN, and the convergent center was observed over 90ºW, 17.5ºS.

5.ENSO Monitoring and Prediction

(1) During September 2006, positive SST anomalies above 0.5ºC covered the equatorial Pacific Ocean east to160ºE. The index of NINO Z was 0.9 ºC.  

(2) Compared with last month, abnormal warm subsurface water persisted in the equatorial Pacific Ocean with center shifting eastward and enhancing slightly.

(3) Southern Oscillation Index (SOI) was -0.4.

(4) Weak westerly anomalies covered the equatorial western Pacific Ocean.

(5) The anomalous outgoing longwave radiation (OLR) showed that convections were suppressed over the western part of Indonesia and enhanced over the equatorial western Pacific..

(6) Most of models predicted that SSTs would be abnormally above normal during following six months.

In conclusion, tropical oceanic and atmospheric conditions showed obvious features of ENSO warm phase, and these features are expected to persist in the following 2~3 months.