Monthly Highlights

Climate in China

During May 2010, monthly mean surface air temperatures were 1-2℃ below normal in northeastern and central-southern Xinjiang. Meanwhile, temperatures were observed 1-4℃ above normal in northeastern Inner Mongolia, eastern Northeast China, central North China, southwestern Tibet, southeastern Northwest China and most of Yunnan.

For the month, above-normal precipitations were observed in most China, with precipitations 50% more than normal in most of Northeast China, northern North China, Inner Mongolia, eastern Northwest China, southwestern Xinjiang, eastern Tibet and northern Jiangnan, and precipitations 200% more than normal in locations of above regions. Meanwhile, precipitations were observed 30-80% less than normal in parts of northwestern Xinjiang, western Tibet, parts of Jianghuai, Huanghuai, parts of western Southwest China and parts of western Southeast China.

In May, daily maximum temperature extremes occurred in Yunnan, Guizhou, Sichuan, Guangxi and Hainan. The maximum temperatures set new records in Zhengyuan (38.2℃) , Guangnan（37.6 ℃）、Yanshan（34.9 ℃）、Shilin（34.4 ℃） of Yunnan, Xilin（41.0 ℃）of Guangxi, Qinglong（34.6 ℃）of Guizhou, Jinyang（40.4 ℃）of Sichuan and so on. Daily precipitation extremes occurred in Hunan, Guangdong, Fujian, Jiangxi, Chongqing, Qinghai and Xinjiang. New records of daily precipitation were reported in following 5 stations, i.e. Lianyuan(172.0mm), Liling（168.8 mm）of Hunan, Wengyuan（240.1 mm）、Jiaoling（196.8mm） of Guangdong, Tuoli（34.0mm）of Xinjiang.

Climate in the World

During May 2010, temperatures were 1℃ below normal in parts of western Europe, central Siberia, eastern Australia, parts of North America and parts of central South America. Meanwhile, temperatures were 2℃ above normal in the regions from eastern Europe to Ural, eastern Russia, western South Asia, northern Alaska, parts of eastern North America and parts of northern Africa, with temperatures 4-6℃ above normal in locations.

For the month, precipitations were observed at least 50% more than normal in western Europe, parts of West Asia, parts of Central Asia, northern Siberia, northern East Asia, northern Australia, parts of North America and central South America, with precipitations at least 200% more than normal in locations. Meanwhile, precipitations were at least 50% less than normal in western Siberia, parts of Central Asia, northern South Asia, the Far East, southern North America, parts of northern South America, northern and eastern Africa and parts of Australia, with no precipitation in parts of above regions.

General Circulation Features

Northern Hemisphere: During May 2010, the mean 500hPa geopotential height field exhibited obviously meridional circulation at the mid-high latitudes. In the 500hPa geopotential height anomaly field, positive anomalies above 4 dam covered oceans from eastern North America to the polar regions, the northeastern Northern Atlantic Ocean and the regions from the Ural Mountains to east of 120ºE in Asia, with central values above 12 dam in the polar regions. Meanwhile, negative anomalies below -4 dam covered the regions east to Japan, western North America and the western North Atlantic Ocean，with central values below -8 dam in the regions east to Japan and the western North Atlantic Ocean. For the month, the Northwest Pacific subtropical high (NWPSH) was larger, stronger than normal and it extended more westward than normal.

Southern Hemisphere: During May 2010, in the 500hPa geopotential height anomaly field, positive anomalies above 4 dam covered parts of Antarctica, most of the southern Pacific Ocean, the southwestern South Atlantic Ocean, southern South America and parts of the southern South-Indian Ocean. Meanwhile, negative anomalies below -4 dam covered the polar regions of the southeastern Pacific and the regions south to Africa.

Tropical Features

Sea Surface Temperatures (SSTs): During May 2010, SSTs were generally near normal in the equatorial central and eastern Pacific, but SSTs were observed less than -0.5℃ below normal in part between 120-140 ºW. Meanwhile, SSTs were above normal in oceans west of the equatorial Date Line. NINO 1+2, NINO 3, NINO 4, NINO 3.4 and NINO Z indices were 0.0℃, -0.1℃, 0.4℃, -0.1℃ and 0.1℃, with drops of 0.6℃, 0.7℃, 0.4℃, 0.8℃ and 0.6℃ from last month, respectively.

Subsurface Temperatures: During May 2010, anomalously cold subsurface water controlled most of the equatorial central and eastern Pacific. Meanwhile, it enhanced significantly, expanded eastward and uplift obviously, with central values below -3℃.

Warm Pools: During May 2010, both the area and intensity of the western Pacific and the Indian Ocean warm pools were above normal.

Wind Field：For the month, at lower troposphere (850hPa), weak westerly anomalies covered the equatorial Pacific east of 160 ºW, and easterly anomalies prevailed over the Pacific west of 160ºW. At upper troposphere (200hPa), zonal winds were near normal.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 0.8, with a drop of 0.6 from last month.

Convections over the Tropics: During May 2010, the anomalous Outgoing Longwave Radiation (OLR) showed that enhanced convection was observed over Indonesia, while suppressed convection was observed near the Date Line. In the lower troposphere (850hPa) divergent wind field, a convergent center was around 115ºE, 0º, and a divergent center was near 105ºW, 25^oS. At the upper troposphere (200hPa), the corresponding divergent and convergent centers were near 130ºE, 0º and 105ºW, 25ºS, respectively.

ENSO Monitoring and Outlook

 2009/2010 El Nino ended finally in May 2010 and its intensity is moderate. Monitoring showed that during May 2010, SSTs were near normal in the equatorial central and eastern Pacific, but SSTs were observed -0.5℃ below normal between 120-140ºW. Anomalously cold subsurface water controlled most of the equatorial central and eastern Pacific. Meanwhile, it enhanced significantly, expanded eastward and uplift obviously, with central values below -3℃. SOI was positive for past two consecutive months. All above showed that tropical atmosphere and ocean were favorable for a quick transition to La Nina conditions. Meanwhile, most statistical and dynamic climate models predicted that a quick transition to La Nina conditions was expected to occur during this summer.

Aforementioned analysis indicates that a transition to cold conditions will continue over the equatorial central and eastern Pacific in the next 2-3 months, and La Nina conditions are possibly to be true in summer 2010. Therefore, we will closely monitor the development of ENSO conditions and update our ENSO wrap-up in time.