Monthly Highlights
1. Climate in China
During August 2012, the mean surface air temperature over China was 21.4℃, which was 0.6℃ higher than normal（20.8℃）. Monthly mean surface air temperatures were 1-2℃ above normal in central-eastern and southwestern Xinjiang, northeastern and southern Northwest China, western Inner Mongolia, central Xizang and northeastern Southwest China. While temperatures were 1℃ below normal in most Northeast China, northeastern Inner Mongolia, central-southern North China, central-northern Huanghuai, southwestern Jianghuai, western Jiangnan and part of southern South China, with 1-2℃ below normal in locations.
In the month, average precipitation over China was 92.1 mm, which was 12.4% less than normal (105.1mm). Precipitations were observed generally 30-100% above normal in northern and southwestern Xinjiang, western Xizang, northern and eastern Qinghai, part of southwestern Gansu, southern Northeast China, southeastern North China, southern Huanghai, central-northern Jiangnan and part of southwestern South China, with over 100% above normal in locations. Meanwhile, precipitations were observed 30-50% below normal in central Xinjiang, northeastern Northwest China, most Inner Mongolia, North China, central-western North China, central Xizang, most Southwest China, western Jiangnan and central-eastern South China, with over 80% below normal in locations.
In August, extremes of High Temperature (HT), Consecutive High Temperature Days (CHTD), Daily Precipitation (DP), and Consecutive Precipitation (CP) were observed in China. HT extreme events occurred in 18 stations in eastern Southwestern China and coasts of the southeast, with new records in Tongcheng station, Hubei province. Extremes of CHTD occurred in 66 stations in the western Jianghuai area, the eastern Jianghan, Sicuan and Chongqing. Meanwhile, extreme of daily precipitation mainly occurred in 24 stations, with Jingdezhen station, Jiangxi province setting a new record. CP extremes occurred in 48 stations in Liaoning, Hebei and Shandong, etc. with 17 stations setting new record.
2. World Climate
During August 2012, monthly mean temperatures were 1-4℃ above normal in central and southeastern Europe, mostly Central Asia, local Northwest China, most North America, western Australia, southern South America. Meanwhile, monthly mean temperatures were 1-2℃ below normal in central Siberia, local North America, central and northern South America, most west Africa, local South Africa, central and eastern Australia, with temperatures at least 2℃below normal in locations.
For the month, precipitations were at least 50% above normal in northeastern Europe, northern Central Asia, most Siberia, central and northern Indian, coasts of eastern China, northern South Asia, southwestern North America and southeastern South America, central and southern West Africa. Meanwhile, precipitations were at least 50% below normal in southern North Europe, northern Russia, southern Central Asia, local Northeast China, most North America, western South America, southern Africa and most Australia, with no precipitation in locations.
3. General Circulation Features
Northern Hemisphere: During August 2012, the field of mean 500hPa geopotential height exhibited a five-wave pattern over mid-high latitudes. In the field of height anomaly, positive anomalies above 4 dam covered the Mediterranean Sea, northern Central Asia, regions from the Sea of Okhotsk to Southwestern the Bering Strait and the Greenland. Meanwhile, negative anomalies below -4 dam covered locations of the northeastern North Atlantic Ocean, regions from central-northern Siberian to the eastern Barents Sea, the northern Bering Sea, locations of northeastern America, with central values below -12 dam over locations of the northeastern North Atlantic Ocean. During the month, the northwestern Pacific subtropical high was weaker than normal, with a smaller area and more northward high ridge, and the west end of its ridge shifted more eastward than normal.
Southern Hemisphere: For the month, the field of mean 500hPa geopotential height exhibited a three-wave pattern over mid-high latitudes. In the field of height anomaly, positive anomalies above 4 dam covered the southwestern South Atlantic Ocean, the southwestern and southeastern South Pacific Ocean, parts of the southern South Indian Ocean, with central values above 12 dam over the southwestern South Atlantic Ocean and the southwestern South Pacific Ocean. Meanwhile, negative anomalies below -4 dam covered the central and southeastern South Pacific Ocean, regions from southeastern South Atlantic Ocean to the southwestern South Indian Ocean, with central values below -16 dam over the southeastern South Pacific Ocean.
4. Tropical Features
Sea Surface Temperatures (SSTs): During August 2012, SSTs were 0.5℃ above normal in the central and eastern equatorial Pacific with maximum above 1.0℃. NINO 1+2, NINO 3 index was 0.4℃ and 0.7℃, with a drop of 0.5℃ and 0.2℃, while NINO 4 and NINO 3.4 indices were 0.4℃ and 0.7℃, with rises of 0.3℃ and 0.2℃, respectively. NINO Z indices were 0.6℃, was roughly the same as in July.
Subsurface Temperatures: During August 2012, anomalously warm subsurface water enhanced and uplift in the eastern equatorial Pacific, with central values above 2.0℃ at about 50m depth.
Warm Pools: During August 2012, the area of the western Pacific Ocean warm pool was near normal, while its intensity was slightly below normal. The area of the Indian warm pool was below normal, but its intensity was above normal.
Wind Field: During August 2012, at lower troposphere (850hPa), westerly anomalies dominated the central and eastern equatorial Pacific, while easterly anomalies dominated the western equatorial Pacific. At upper troposphere (200hPa), westerly anomalies covered the eastern equatorial Pacific, while easterly anomalies covered the remainder of the equatorial Pacific。
Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was -0.4, with a decrease of 0.3 from last month.
Convections over the Tropics: During August 2012, the anomalous outgoing long wave radiation (OLRa) showed that convections were enhanced over the western equatorial Pacific, while convections were near normal across the remainder of the equatorial Pacific. At lower troposphere (850hPa) divergent wind field, a convergent center was around 90ºE, 25ºN, and a divergent center was near 90ºW, 25ºS. At upper troposphere (200hPa), the corresponding divergent center and convergent center were near 130ºE，15ºN and around 90ºW, 25ºS, respectively.
5. ENSO monitoring and outlook
The atmospheric conditions are not in favor of the warming of equatorial Pacific in the Autumn and the Winter compared with the Summer. In the equatorial Pacific, the thermocline keeps increasing slowly and the subsurface heat content anomaly remains positive. Since July sea surface temperatures in the east-central equatorial Pacific remains 0.5℃ warmer than average. A weak El Niño event is expected with the development of warm condition in the end of this year.
Therefore, we will closely monitor the development of ENSO conditions and update our ENSO wrap-up in time.