Monthly Highlights

1.Climate in China

The average temperature of China in September 2010 was 17.1℃ with 1.1℃ above normal, which was ranking the 4^th warmest September since 1961. The mean surface air temperatures were at least 1.0℃-2.0℃ above normal in most Northeast China, central-eastern Northwest China, southern Jianghuai area, the Jianghan area, most of Jiangnan, most of Southwest China, central-eastern Inner Mongolia, northern Xinjiang, with at least 2℃ above normal in locations of above regions. The temperatures were near normal in the rest areas of China.

In September, the average precipitations of China were 85.1 mm and 30.1% more than normal, which was the wettest September since 1961. The mean precipitations were at least 30-100% more than normal in western Northwest China, most of North China, the Huanghuai area, the Jianghuai area, central and western Jiangnan area, most of South China, central-western Inner Mongolia, and precipitations 200% more than normal in southern Xinjiang, northern Gansu, northern Qinghai, western Inner Mongolia. Meanwhile, precipitations were observed 30-80% less than normal in most of Northeast China, northeast Inner Mongolia and northern Xinjiang, with precipitations at least 80% less than normal in locations. The precipitations were near normal in the rest area of China.

In September, daily maximum temperature extremes mainly occurred in Yunnan, Guangxi, Guizhou, Chongqing, Hunan, Zhejiang, Jiangsu, Ningxia etc., furthermore, the maximum temperature of one station reached or prompted new records. Meanwhile, the consecutive days with maximum temperature were reached maximum temperature extremes in 2 stations, which were located in Guizhou and Xinjiang. Daily precipitation extremes of 38 stations occurred in Guangdong, Xinjiang, Anhui, Jiangsu, Hebei etc.. New records of daily maximum precipitation were reported in 6 stations, i.e. Suyu, Sihong of Jiangsu; Xiaoxian of Anhui, Huadu of Guangdong, etc. The consecutive days of precipitation extremes occurred in 40 stations, which were located in Xinjiang, Xizang, Gansu etc., and new records were broken in 7 stations. Moreover, durative precipitation extremes of 26 stations occurred in Xinjiang, Henan, Shanxi, Hebei etc.. New records of extreme durative precipitation were reported in 6 stations.

2.World Climate

During September 2010, temperatures were 1-4℃ above normal in eastern Europe, central-western West Asia, most of East Asia, parts of northeastern Russia, southeastern Ice Land, parts of North Africa, southwestern North America and central South America. Meanwhile, temperatures were 1-4℃ below normal in southwestern Europe, north Asia, parts of West Africa, northern North America and Australia.

For the month, precipitations were at least 50% above normal in parts of central-western Europe, most of northern and eastern East Asia, most of South Asia, parts of central and northeastern Russia, central-eastern Africa, central-eastern and parts of northwestern North America, parts of northern South America and most of Australia, with at least 200% above normal in locations of above regions. Meanwhile, precipitations were at least 50% less than normal in northwestern Europe, most of West Asia and Central Asia, parts of northeastern East Asia, parts of Northeast Asia, parts of North Africa, southeastern North America and central South America, with no precipitation in locations of above regions.

3.General Circulation Features

Northern Hemisphere: During September of 2010, the mean 500hPa height field exhibited a 4-wave pattern at the mid-high latitudes. The positive anomalies above 4 dam covered the regions from mosts of the Arctic Ocean, central of Northeast Pacific Basin, to northeastern North America, areas form Iceland, northern and central-eastern Europe to central Asria, with central values above 12 dam over eastern Iceland. Meanwhile, negative anomalies below -4 dam covered the regions from central North Asia to northeastern North Pacific, northwestern North Pacific to northwestern North America. For the month, the Northwest Pacific subtropical high (NWPSH) was larger and stronger, and it extended northward and abnormaly westward.

Southern Hemisphere: For the month, in the 500hPa geopotential height anomaly field, positive anomalies above 4 dam covered the region from the Antarctica to Southeast Indian Ocean, and the areas over central-western South Pacific, with central values above 12 dam over the central South Pacific. Meanwhile, negative anomalies below -4 dam covered the Antarctica-Pacifc Ridge, with central values below -12 dam.

4. Tropical Features

Sea Surface Temperatures (SSTs): During September 2010, SSTs were 1.0-2.0℃ below normal in the most equatorial central and eastern Pacific with the minimum below -2.5℃. NINO 1+2, NINO 3, NINO 4, NINO 3.4 and NINO Z indices were -1.5℃, -1.3℃, -1.4℃, -1.6℃and -1.3℃, respectively, with drops of 0.2℃, 0.3℃, 0.4℃ and 0.2℃ for NINO 3, NINO 4, NINO 3.4 and NINO Z from last month, and with same value for NINO 1+2. Meanwhile, equatorial SSTs were 0.5℃ above normal with maximum above 1.5℃ in the western Pacific and most Indian Ocean.

Subsurface Temperatures: During September 2010, anomalous cold subsurface water controlled most of the central and eastern equatorial Pacific. Meanwhile, negative anomaly strengthened with central intensity below -6℃.

Warm Pools: During September 2010, both the area and intensity of the Indian Ocean warm pool were above normal. The area of the western Pacific warm pool was close to normal, and its intensity was still above normal.

Wind Field: For the month, at lower troposphere (850hPa), westerly anomalies covered the equatorial Pacific east of 160ºW, and easterly anomalies prevailed over the equatorial Pacific west of 160ºW, which were favorable for a tendency to keep cooling of the SST in the central and eastern equatorial Pacific. At upper troposphere (200hPa), westerly anomalies covered the most equatorial Pacific.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 2.4, with a rise of 0.6 from last month.

Convections over the Tropics: During September 2010, the anomalous Outgoing Longwave Radiation (OLR) showed that enhanced convection was observed between Hainan and Taiwan, the northwestern Pacific near the southeast of Taiwan, and Indonesia, whereas suppressed convection controlled the western equatorial Pacific. In the lower troposphere (850hPa) divergent wind field, a convergent center was around 115ºE, 10ºN, and a divergent center was near 115ºW, 15ºS. At the upper troposphere (200hPa), the corresponding divergent and convergent centers were near 115ºE, 10ºN and 85ºW, 5ºS, respectively.

5.ENSO Monitoring and Outlook

Monitoring showed that during September 2010, sea surface temperature continued to go down very quickly and La Niña conditions persisted across the equatorial Pacific. Analysis showed that the tropical Pacific featured a rapid transition from warm event to cold condition. Anomalous cold subsurface water controlled most of the central and eastern equatorial Pacific with central intensity below -6℃, and the sum of NINO Z index from July to September was -3.3℃ ranking first at the first three months of the cold events since 1951, indicating the fast SST decline and the strongest intensity at an early stage. And supporting the cold phase features, SOI was continuously positive in recent half year, implying a swift adjustment of tropical atmosphere to La Niña conditions and a well coupled pattern of tropical ocean-atmosphere. SOI from July to September, respectively, ranked first, too. Compared with SOI peak value of cold events, SOI of September 2010 was only second to SOI of November 1973. Most statistical and dynamic climate models predicted that La Niña conditions were likely to last till the spring 2011.

Aforementioned analysis indicates that La Niña conditions are likely to continue and develop to a La Niña event in the future 6 months at least. Therefore, we will closely monitor the development of ENSO conditions and update our ENSO wrap-up in time.