Monthly Highlights

Climate in China

The average temperature of China was 22.8℃ in July 2010, which was the warmest July since 1961. Temperatures were at least 1℃ above normal in most Southwest China, western South China, the southwestern Jiangnan area, the eastern Huanghuai area, most North China, most Northwest China and Inner Mongolia, with 2-4℃above normal in northwestern Hebei, northern Shanxi, central and western Inner Mongolia, eastern Xinjiang, the Hexi area of Gansu, Qinghai, central-northern Tibet and northwestern Sichuan.

In July, precipitations were at least 30-100% more than normal in the middle and lower reaches of the Yangtze river, eastern Sichuan, central and southern Shaanxi, western and southern Henan, western Qinghai, western part of south Xinjiang, northern and southern Northeast China, with 100% more than normal in parts of above regions. Precipitations were 30-80% less than normal in eastern and northern South China, the southwestern Jiangnan area, most North China, most Inner Mongolia, most Gansu, central-southern and northeastern Xinjiang, with at least 80% below normal in parts of above regions. Precipitations were near normal in rest of regions.

In July, daily maximum temperature extremes occurred in most North China，central Inner Mongolia，Northern Ningxia, most Gansu, central Sichuan, partly Xinjiang and Qinghai, coast of Fujian, partly Guangxi and Hainan(Fig.1). The maximum temperature of 74 stations reached or prompted new records. These stations were located in Inner Mongolia, Shanxi, Hebei, Gansu, Xinjiang, Beijing, etc. Meanwhile, consecutive maximum temperature day extremes were reached by 65 stations, which were located in Hebei, Shandong, Guangdong, Guangxi and Hainan where new records were broken in 7 stations. Daily precipitation extremes of 114 stations occurred in Jilin, Liaoning, Shandong, Henan, Shaanxi, Sichuan, Jiangsu, Anhui, Hubei and Zhejiang. New records of daily maximum precipitation were reported in 39 stations, i.e. Tieling, Taian of Liaoning; Binxian of Shaanxi; Guangshui of Hubei; Wenling of Zhejing; Renshou of Sichuan, etc.. Besides, consecutive precipitation day extremes occurred in 70 stations, which were located in Liaoning, Jilin, Qinghai, Guangxi, Hubei et al. and new records were broken in 15stations.

Climate in the World

During July 2010, temperatures were 1-4℃ above normal in most Europe, partly eastern Siberia, most East Asia, the northern Arabia Peninsula, northeastern and southwestern South Asia, most North America, eastern and northwestern South America, parts of western and northern Africa and northern Australia, with 4-6℃ above normal in central and northern Europe. Meanwhile, temperatures were 1-2℃ below normal in western Siberia, locations of northwestern and southeastern South Asia, Alaska, southwest and west coast of United States, southwestern South America and southwestern Australia.

For the month, precipitations were at least 50% above normal in locations of southern Europe, northwestern South Asia, southern Central Asia, eastern West Siberia, southeastern Central Siberia, the northern Jiangnan area of China, most Australia, partly West Africa, central United States, parts of central and northern South America, with at least 200% above normal in locations. Precipitations were at least 50% below normal in eastern Europe, western West Siberia, most Central Asia, most northern China, northwestern West Asia, northwestern North America, partly east and west coast of South America and locations of western Australia.

General Circulation Features

Northern Hemisphere: During July 2010, the mean 500hPa geopotential height field exhibited a 4-wave pattern at the mid-high latitudes. In the 500hPa geopotential height anomaly field, positive anomalies above 4 dam covered regions near the Bavkal Lake to the Okhotsk Sea, the northeastern Pacific, northeastern North America and Europe, with central values above 16 dam over Europe. Meanwhile, negative anomalies below -4 dam covered the northeastern Atlantic and the partly polar region, with central values below -8 dam over the polar region. For the month, the Northwest Pacific subtropical high (NWPSH) was larger and obviously stronger than normal. It extended abnormaly westward.

Southern Hemisphere: For the month, in the 500hPa geopotential height anomaly field, positive anomalies above 4 dam covered the eastern South Pacific Ocean and the southeastern South Indian Ocean, the southwestern South Atlantic Ocean, with central values above 12 dam over the southeastern South Pacific Ocean. Meanwhile, negative anomalies covered the polar region, with central values below -20 dam over the Antarctica.

Tropical Features

Sea Surface Temperatures (SSTs): During July 2010, SSTs were at least -0.5℃ below normal in the most equatorial central and eastern Pacific. The negative anomaly center was located in the further equatorial eastern Pacific, with the minimum below -2.0℃. Negative SST anomalies got stronger. For the month, NINO 1+2, NINO 3, NINO 4, NINO 3.4 and NINO Z indices were -1.6℃，-1.0℃，-0.5℃，-1.0℃ and -0.9℃, with drops of 1.2℃, 0.4℃, 0.5℃, 0.5℃ and 0.5℃ from last month, respectively.

Subsurface Temperatures: During July 2010, anomalously cold subsurface water controlled most of the equatorial central and eastern Pacific. Meanwhile, negative anomalies enhanced slightly, with central values below -6℃.

Warm Pools: During July 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), westerly anomalies covered the equatorial Pacific east of 160ºW, and easterly anomalies prevailed over the equatorial Pacific west of it. At upper troposphere (200hPa), westerly anomalies covered the most equatorial Pacific.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 1.8, with an increase of 1.5 from last month.

Convections over the Tropics: During July 2010, the anomalous Outgoing Longwave Radiation (OLR) showed that enhanced convection was observed over the Maritime Continent, whereas suppressed convection was observed over the equatorial Pacific between 140ºE-150ºW. In the lower troposphere (850hPa) divergent wind field, a convergent center was around 120ºE, 15ºN, and a divergent center was near 80ºW, 25ºS. At the upper troposphere (200hPa), the corresponding divergent and convergent centers were near 115ºE, 10ºN and 80ºW, 25ºS, respectively.

ENSO Monitoring and Outlook

Monitoring showed that during July 2010, La Nina conditions were present across the equatorial Pacific. Compared with last month, anomalously cold subsurface water enhanced in the equatorial central and eastern Pacific, and SOI also increased significantly. Most statistical and dynamic climate models predicted that La Niña conditions were likely to continue till early 2011.

Aforementioned analysis indicates that La Niña conditions are likely to continue and develop to a La Niña event at least in the future 5-6 months. Therefore, we will closely monitor the development of ENSO conditions and update our ENSO wrap-up in time.