Monthly Highlights

Climate in China

During July 2009, except for temperatures 1-2℃ below normal in eastern Northeast China, monthly mean surface air temperatures were near or above normal in most China, with 1-2℃ above normal the Qinghai-Xizang Plateau, central western Inner Mongolia, northern Shanxi, central Gansu, southwestern Shanxi and Yunnan, with temperatures at least 2℃ above normal in parts of the Tibetan Plateau.

For the month, precipitations were observed 30-100% more than normal in the most Jiangnan area, the southern Jianghuai area, eastern Shandong, northeastern Heilongjiang, Qinghai, northwestern Sichuan, northeastern Guangxi, with precipitations at least 100% more than normal in locations. Meanwhile, precipitations were observed 30-80% less than normal in western Northwest China and most Inner Mongolia, central southern Northeast China, most Gansu, western and southern Xizang, Chongqing and Hubei.

In July, daily maximum temperature extremes occurred in the middle-lower reaches of the Yangtze River, central South China, eastern Southwest China, eastern Gansu and southern Tibet. The maximum temperatures prompted new records in 23 stations including Yinxian station of Zhejiang, Xujiahui station of Shanghai, Alashan-Zuo-Qi station of Inner Mongolia, Jingzhou station of Hubei, Fugong station of Yunnan, Lhasa station of Tibet etc. Daily precipitation extremes occurred in parts of central and northern Shanxi, Shandong Peninsula, Anhui, Jiangsu, southern Hunan, southern Jiangxi and Guangxi. New records of daily precipitation were reported in 15 stations including Penglai station of Shandong, Dayu station of Jiangxi, Tiandeng station of Guangxi, Miyi station of Sichuan, Maqu station of Gansu etc. Both daily maximum temperature and precipitation extremes were observed in Zitong station of Sichuan and Jinshan station of Shanghai.

Climate in the World

During July 2009, temperatures were at least 1-2℃ above normal in central southern Europe, parts of Central Siberia, most Mongolia, central western China, partly northern South Asia, western North Africa and partly East Africa, western and partly northeastern North America, parts of central northern South America and partly Australia, with temperatures at least 4℃ above normal in partly East Africa and locations in northeastern North America. Meanwhile, temperatures were 1-2℃ below normal in regions from most West Siberia to northern Central Asia, eastern Northeast Asia, most central eastern America, partly southern South America, with temperatures at least 3℃ below normal in locations.

For the month, precipitations were at least 50% more than normal in parts of western and southeastern Europe, western Siberia and locations in central Siberia, partly Central Asia, partly West Africa, partly Northwest Africa and partly South Africa, parts of central western America, parts of southern South America, with precipitations at least 200% more than normal in parts. Meanwhile, precipitations were 50% less than normal in northwestern Europe and the southwestern coastal areas, Central Siberia, Mongolia, most southwestern and partly northern China, eastern Central Asia, southern South Asia and partly West Asia, partly North Africa and most East Africa, western and partly northeastern North America, parts of southern South America and most central northern Australia, with no precipitations in parts.

General Circulation Features

Northern Hemisphere: During July 2009, the mean 500hPa geopotential height field mainly exhibited a 4-wave pattern at the mid-high latitudes. In the anomaly field, positive anomalies above 4 dam covered regions from the Arctic to parts of northern Canada, regions from Alaska to locations of the northern North Pacific Ocean, with central values above 12 dam over the central Arctic and parts of northern Canada. Meanwhile, negative anomalies below -4 dam covered regions from northwestern Europe to the northern North Atlantic Ocean, regions from southeastern Canada to parts of northern America, regions from locations in eastern Russia to locations in the northern Pacific Ocean, eastern East Asia and north Central Asia, with central values below -12 dam over regions from northwestern Europe to the northern North Atlantic Ocean. For the month, the subtropical high over the Northwest Pacific was larger and stronger, and its location was slightly further Northward and eastward than normal.

Southern Hemisphere: In July, the mean 500hPa geopotential height field exhibited a 3-wave pattern at the mid-high latitudes. In the anomaly field, positive anomalies above 4 dam covered the Antarctic and most high latitude sea areas and the most Southeast Pacific Ocean near 20 ºS, with central values above 28 dam over the high latitude around the South Polar. Meanwhile, negative anomalies below -4 dam covered parts of the Southwest Pacific Ocean and the South India Ocean between 40 ºS -60 ºS, with central values below -12 dam over the Southwest Pacific Ocean.

Tropical Features

Sea Surface Temperatures (SSTs): During June, the SSTs were above normal in most of the central and eastern equatorial Pacific, with maximum positive departures above 1.5℃. In July, indices of NINO 1+2, NINO 3, NINO 4, NINO 3.4 and NINO Z were 0.8℃, 1.0℃, 0.6℃, 0.9℃ and 0.8℃, with a rise of 0.2℃, 0.3℃, 0.0℃, 0.3℃ and 0.1℃ from last month, respectively.

Wind Field：For the month, at lower troposphere (850hPa), except easterly anomalies controlled around the dateline, strong westerly anomalies prevailed over the west equatorial Pacific and weak westerly anomalies prevailed over the east equatorial Pacific. At upper troposphere (200hPa), except westerly anomalies covered the west equatorial Pacific, easterly anomalies covered the most equatorial Pacific.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 0.1, with a rise of 0.1 from last month.

Convections over the Tropics: During July, the anomalous outgoing longwave radiation (OLR) showed that the convection was enhanced over regions from the western equatorial Pacific to near the dateline. The remainder was near normal in the equatorial Pacific. In the lower troposphere (850hPa) divergent wind field, a convergent center was near 130ºE, 15ºN and a divergent center was near 90ºW, 25ºS in the tropical Pacific. Correspondingly, at upper troposphere (200hPa), the convergent center was near 130ºE, 15ºS and the divergent center was near 90ºW, 25ºS.

ENSO Monitoring and outlook

During July 2009, the SSTs and the anomalously warm subsurface water kept increasing and continued to be in El Nino status. El Nino Z was up to 0.8℃. At 850 hPa, weak eastlies prevailed over the most equatorial Pacific. Most statistical and dynamic models indicated that the SST anomalies could keep above 0.5℃ in the central and eastern equatorial Pacific until early 2010.

Based on aforementioned analysis, El Nino conditions will keep in 1-3 months in the central and eastern equatorial Pacific. We will closely monitor and update ENSO conditions and provide information of ENSO in time.