Monthly Highlights

Climate in China

During August 2008, monthly mean surface air temperatures were observed at least 1℃ above normal in western and eastern Xinjiang, northeastern Inner Mongolia, most Heilongjiang, parts of central North China and parts of the southern Yangtze River Valley, with 2-4℃ above normal in parts of Xinjiang and Inner Mongolia. Meanwhile, temperatures were at least 1℃ below normal in central Qinghai and eastern Southwest China, with temperatures 2-4℃ below normal in southeastern Sichuan and Chongqing. Temperatures were near normal in other regions of China.

For the month, precipitations were observed 30-100% more than normal in mid-eastern Xinjiang, western Inner Mongolia, regions from mid-eastern Xizang to western Sichuan, and regions from eastern Southeast China to the middle and lower reaches of the Yangtze River Valley, with over 200% more than normal in locations. Meanwhile, precipitations were observed 30-80% less than normal in southern and northern Xinjiang, central Qinghai, most of Gansu, most Northeast China, eastern and southern North China and the southeastern coast, with no precipitations in parts of southern Xinjiang.

Climate in the World

During August 2008, temperatures were at least 1℃ above normal in regions from eastern Europe to Mid-Asia, West Asia, eastern Russia, eastern Canada, western America, most of northern and central South America, northern Africa and parts of South Africa, with temperatures at least 4℃ above normal in northeastern Russia and parts of eastern Canada. Meanwhile, temperatures were at least 1℃ below normal in northern Europe, eastern Mongolia, parts of Pakistan, and most Australia, with temperatures at least 2℃ below normal in locations.

For the month, precipitations were at least 50% less than normal in most Eurasia in 40-50^oN belt, most Far East Russia, eastern North America, most South America, South Africa, and eastern Australia, with no precipitation in parts of above regions. Meanwhile, precipitations were observed at least 50% more than normal in most Eurasia around 60^oN latitude, parts of South Asia, Northwest China and the middle reaches of the Yangtze River Valley, western Canada, central-southern part of America, the eastern coast of Brazil, most West Africa, and western Australia, with precipitations at least 200% more than normal in locations.

General Circulation Features

Northern Hemisphere: During August 2008, in the 500hPa geopotential height anomaly field, positive anomalies above 4 dam covered most Europe in 40-50^oN belt, and regions from Far East Russia to northeastern North America across polar regions, with central values above 8 dam over eastern Arctic Ocean and northeastern North America. Meanwhile, negative anomalies below -4 dam covered most Europe around 60^oN latitude, regions from the northeastern North Pacific to Alaska, and the northeastern coast of America, with central values below -8 dam over the northeastern North Pacific. For the month, the subtropical high over the Northwest Pacific was larger and stronger than normal, and its position was more southward and westward than normal.

Southern Hemisphere: For the month, in the 500hPa geopotential height anomaly field, positive anomalies above 4 dam covered regions from the southeastern South Indian Ocean to western Antarctica, regions from the southern South Pacific to eastern Antarctica, and the southern South Atlantic Ocean, with central values above 12 dam over the southern South Indian Ocean, and around 20 dam over eastern Antarctica. Meanwhile, negative anomalies below -4 dam covered the southwestern South Indian Ocean, southern South America, New Zealand and the sea area east to it.

Tropical Features

Sea Surface Temperatures (SSTs): During August, the positive SST anomalies dominated the eastern and western equatorial Pacific, especially in the first location where central values were above 2.0℃. The area of negative SST anomalies appeared in regions around the dateline with central values below -0.5℃. In August, indices of NINO 1+2, NINO 3, NINO 4, NINO 3.4 and NINO Z were 1.0℃, 0.7℃, -0.3℃, 0.1℃ and 0.3℃, with rises of 0.2℃, 0.2℃, 0.0℃, 0.0℃and 0.1℃ from last month, respectively.

Subsurface Temperatures: During August，subsurface anomalously cold water strengthened significantly in the central equatorial Pacific and broke the anomalously warm water in the equatorial Pacific along thermocline depth, which resulted in the decline of subsurface anomalously warm water in the eastern Pacific.

Warm Pools: During August, areas of both the western Pacific warm pool and the Indian Ocean warm pool were near or just below the normal, while their intensities were above normal.

Wind Field：For the month, at lower troposphere (850hPa), easterly anomalies covered the western and central equatorial Pacific, with central values below -4m/s, while weak westerly anomalies prevailed over the eastern equatorial Pacific. At upper troposphere (200hPa), weak westerly anomalies dominated the western and central equatorial Pacific, while easterly anomalies covered the eastern equatorial Pacific, with central values below -8m/s.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 0.9, with a rise of 0.7 from last month.

Convections over the Tropics: During August, the anomalous outgoing longwave radiation (OLR) showed that convection was enhanced over the central Indonesia, and suppressed over the equatorial Pacific between 140ºE-170ºW. In the lower troposphere (850hPa) divergent wind field, a convergent center and a divergent center were observed over 125ºE, 20ºN and 100ºW, 20ºS, respectively. At upper troposphere (200hPa), the corresponding divergent center was over 125ºE, 15ºN, and the convergent center was over 90ºW, 20ºS.

ENSO Monitoring and Prediction

(1) During August, the status of SST anomalies showed a pattern in the central and eastern equatorial Pacific that the obviously positive anomalies dominated the eastern part while the negative ones dominated the western part.

(2) During August，subsurface anomalously cold water strengthened significantly in the central equatorial Pacific and broke the anomalously warm water in the equatorial Pacific along thermocline depth, which resulted in the decline of subsurface anomalously warm water in the eastern Pacific.

(3) Southern Oscillation Index (SOI) was 0.9.

(4) At lower troposphere (850hPa), the easterly anomalies covered the central and western equatorial Pacific, while weak westerly anomalies prevailed over the eastern equatorial Pacific.

(5) Convection was enhanced over the central Indonesia and suppressed over the equatorial Pacific between 140ºE-170ºW.

(6) The predictions of most statistical and dynamic models indicated ENSO-neutral conditions in the subsequent 3 months.

During August, the current status indicated that the tropical Pacific was still in the ENSO-neutral condition although significant warming had occurred in the eastern equatorial Pacific. Based on monitoring of recent atmospheric and oceanic conditions in the tropical Pacific and predictions of statistical and dynamic models, the ENSO-neutral conditions are expected to continue for the subsequent 3 months.