Monthly Highlights

1． Climate in China

During September 2009, whole country monthly mean surface air temperature was 17.1℃, with 1.1℃ above normal and being the third highest since 1951. Monthly mean temperature anomalies were generally above or near normal in most of China. Positive anomalies of 1-4℃ were observed in the Jiangnan Region, most of South China，most of Southwest China, Qinghai, eastern Xinjiang, central Inner Mongolia and northern Hebei.

For the month, precipitations were observed 30-100% more than normal in most of North China, central Northwest China, northern and western Xinjiang, western Tibet, western and northeastern Inner Mongolia, western Guangxi, northeastern Guangdong and Hainan, with over 100% in parts of above regions. Meanwhile, precipitations were observed 30-80% less than normal in most of southwestern China, eastern South China, most of the Jiangnan Region, the western Jianhuai Region, the Jianghan Region, south-central Northeast China, northeastern Inner Mongolia, northern Hebei, the Shandong Peninsula, southern Henan and Ningxia, with over 80% in locations of above regions. Precipitations were near normal in the rest regions of China.

In September, daily maximum temperature extremes occurred in eastern Southwest China and western Guangxi province. The maximum temperatures were higher than 40℃ in Yuanyang (40.2 ℃) of Yunnan , Gulin (40.6℃) of Sichuan. Daily precipitation extremes occurred in the coast of Zhejiang and western Gansu. The maximums of daily precipitations set new records in following 3 stations, i.e. Wenling (347.6mm), Yuhuang (281.0mm) and Dongtou (346.0mm) of Zhejiang.

2． Climate in the World

During September 2009, temperatures in the world were mainly above normal. Positive anomalies above 1℃ were observed in most of Europe, west-central Russia, most of East Asia, northwestern South Asia, eastern Africa, northeastern West Africa, northern South Africa, northern and central North America, parts of northeastern South America and east-central Australia, with anomalies 4-6℃ in central Canada. Meanwhile, temperatures were 1-2℃ below normal in northern West Asia, eastern Mongolia, northwestern Africa, central America, northern Argentina and southwestern Australia , with temperatures over 2℃ below normal in parts of above regions.

For the month, precipitations were at least 50% more than normal in central Russia, most seacoast of the Mediterranean Sea, northern West Asia, most of Central Asia, most of northwestern China, northwestern Africa, parts of northwestern Canada, southeastern North America, southeastern South America, with precipitations over 200% more than normal in parts of above regions. Precipitations were observed over 50% less than normal in most of Europe, western Russia and the Far East of Russia, west-central Mongolia, parts of southern China, eastern Africa and South Africa, southern West Africa, southern Canada, western America and most of Alaska, northeastern and southwestern South America, northern Australia, with no precipitation in locations of above regions.

3．General Circulation Features

Northern Hemisphere: During September 2009, the mean 500hPa geopotential height field exhibited a 3-wave pattern at the mid-high latitudes. In the anomaly field, negative anomalies below -4 dam were over the northeastern North Pacific, regions from the Baffin Island eastward to the Barents Sea via the Greenland Island. Meanwhile, positive anomalies above 4 dam were over northern North America, regions from the northeastern North Atlantic Ocean to western Russia, with central values above 12 dam over northern North America. For the month, the subtropical high over the Northwest Pacific was obviously larger and stronger, and its location was more westward than normal.

Southern Hemisphere: In the mean 500hPa geopotential height anomaly field in September, while negative anomalies below -4 dam were observed over the southeastern Indian Ocean and the sea south to Australia, positive anomalies above 4 dam covered the rest regions of the middle-high latitude, with central values above 28 dam.

4. Tropical Features

Sea Surface Temperatures (SSTs): During September, equatorial SSTs were at least 0.5℃ above average across the central and eastern Pacific Ocean, with maximum positive departure above 1.0℃. In September, indices of NINO 3, NINO 4, NINO 3.4 and NINO Z were 0.8℃ except index of NINO 1+2 being 0.3℃, with drops of 0.6℃, 0.2℃ and 0.1℃ from last month for the indices of NINO 1+2, NINO 3 and NINO Z, respectively, and with the same values as last month for the indices of NINO 4 and NINO 3.4.

Subsurface Temperatures: During September, the anomalously warm subsurface water prevailed over most of the equatorial Pacific, with the maximnm at 150m depth near the Date Line, shifting eastward and rising obviously in the central and eastern Pacific. Meanwhile, small scope of anomalously cold subsurface water emerged near the coasts of South America.

Warm Pools: During September, the areas of the western Pacific and Indian Ocean warm pools were slightly larger and the intensities were above normal.

Wind Field：For the month, at lower troposphere (850hPa), equatorial winds were near normal over the central and eastern Pacific and westerly anomalies were observed in the western Pacific. At upper troposphere (200hPa), westerly wind anomalies were observed over the equatorial Pacific east of 110ºW and easterly anomalies covered the equatorial Pacific west of 160ºE.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 0.3, with a rise of 0.6 from last month.

Convections over the Tropics: During September, the anomalous outgoing longwave radiation (OLR) showed that enhanced convection was present over the equatorial Pacific west of the Date Line except for suppressed convection over Indonesia and convection was near normal over the equatorial Pacific east of the Date Line. In the lower troposphere (850hPa) divergent wind field, a convergent center was near 140ºE, 10ºN and a divergent center was near 115ºW, 10ºS over the tropical Pacific. At upper troposphere (200hPa), the corresponding divergent and convergent center was near 140ºE, 12.5ºN and 115ºW, 20ºS.

5. ENSO Monitoring and Outlook

During September 2009, the monitoring results showed that El Niño conditions persist in the equatorial Pacific, with the features such as warmer sea surface over the central and eastern equatorial Pacific, NINO Z index being 0.8℃, anomalously warm subsurface water across most of the equatorial Pacific, low-level westerly wind anomalies and upper-level easterly anomalies over the western equatorial Pacific. However, we should still pay more attentions to generally enhanced convections over the western Pacific, cold water appearing in the far eastern equatorial Pacific and the fluctuation of SOI. Most statistical and dynamic climate models predict that equatorial SST anomalies will keep above 0.5℃ in the central and eastern Pacific till winter 2009-2010.

Based on the aforementioned analysis, El Niño conditions are supposed to remain during the coming 3 months. We will continue to monitor the further development of the El Niño conditions and to update the monitoring, diagnosis and prediction information in time.