Monthly Highlights
1. Climate in China
During July 2012, the surface air temperature averaged over China was 22.1℃, which was 0.4℃ higher than normal. Monthly mean surface air temperatures were 0-1℃ below normal in western Xinjiang, central Inner Mongolia, northwestern North China, parts of eastern Southwest China and central-southern South China, while temperatures were above normal in the remainder of China, with 1-2℃ higher than normal in northwestern Northeast China, northeastern Inner Mongolia, regions from south of the lower reaches of the Yellow River to the Yangtze River Valley, and western and locations of eastern Tibet.
In July, average precipitation over China was 135.2 mm, which was 14.4% more than normal and the fourth largest since 1951. Precipitations were observed generally 30-100% above normal in western Xinjiang, central Tibet, central and northeastern Northwest China, most Inner Mongolia, northwestern Northeast China, most North China, southeastern Huanghuai, and parts of eastern Southwest China, with over 100% above normal in locations. Meanwhile, precipitations were observed 30-50% below normal in southern Xinjiang, western Tibet, parts of middle and lower reaches of the Yangtze River, the southeastern coast and northern South China, with over 50% below normal in locations.
In July, extreme events of High Temperature (HT), Daily Precipitation (DP), Consecutive Precipitation (CP) and Consecutive Precipitation Days (CPD) were observed in China. HT extreme events occurred in 108 stations in Shandong, Anhui, Jiangsu, Henan, Hubei, Hunan, Jiangxi, Zhejiang and Fujian, with new records in 6 stations. Meanwhile, extreme precipitation events mainly occurred in Beijing, Tianjin, Hebei, Shanxi, Inner Mongolia, Heilongjiang and Sichuan: 122 stations experienced DP extreme events with 30 stations setting new records；CP extreme events occurred in 102 stations, with 17 stations setting new record; CPD extreme events occurred in 52 stations, with 16 stations setting new records.
2. World Climate
During July 2012, monthly mean temperatures were 1-4℃ above normal in mid-eastern Europe, most Asia, parts of northern Africa, most North America, with temperatures 4-6℃ above normal in locations of mid-north America and central Southern Europe. Meanwhile, monthly mean surface air temperatures were observed 1-2℃ below normal in western and northwestern Europe, northeastern Asia, most Australia, parts of mid-western Africa, Alaska and most southern South America, with temperatures 2-4℃ below normal in the Russian Far East, central Australia, locations of southeastern South America.
For the month, precipitations were at least 50% more than normal in eastern Europe, central and northwestern Asia, western Africa, northeastern Australia, locations of southwestern America, central and southeastern South America, with precipitations at least 200% above normal in locations. Meanwhile, precipitations were at least 50% less than normal in mid-northern Russia, most West Asia, western South Asia, northern and southeastern Africa, mid-western Australia, mid-northern and northeastern North America, southern South America, with no precipitation in locations.
3. General Circulation Features
Northern Hemisphere: During July 2012, the field of mean 500hPa geopotential height exhibited a 4-wave pattern over the mid-high latitudes. In the anomaly field, negative anomalies below -40 gpm covered the northeastern North Atlantic Ocean, while positive anomalies dominated the remainder of the mid-high latitudes, with central values above 40 gpm over the regions from the northern Eurasia to the Sea of Okhotsk, the northwestern North Atlantic Ocean, and parts of the northern North America. During the month, the magnitude of Arctic Ocean Index was negative in the first dekad, and presented positive in the remaining days. Blocking highs occurred over the Sea of Okhotsk in the second dekad and the Lake Baikal in the third dekad. For the month, the occurrence of Northeast Cold Vortex was more frequent than normal, but its intensity was weaker than normal. The area and intensity of Northwest Pacific Subtropical High were smaller and weaker than normal, and its western ridge point and ridge line were more eastward and northward, respectively.
Southern Hemisphere: During July 2012, in the field of 500hPa geopotential height anomaly, negative anomalies below -40 gpm mainly covered the regions from southwestern South Atlantic Ocean southward to most of the Antarctic region, while positive anomalies dominated most of the remainder of the mid-high latitudes surrounding the Antarctica, with central values above 120 gpm over the southeastern South Pacific and parts of the southern South Indian Ocean.
4. Tropical Features
Sea Surface Temperatures (SSTs): During July 2012, SSTs were near normal in the western equatorial Pacific, while SST anomalies were above 0.5℃ over most of the central and eastern equatorial Pacific with central values above 1.5℃. NINO 1+2 index was 1.1℃, with a drop of 0.5℃, while NINO 3, NINO 4, NINO 3.4 and NINO Z indices were 1.0℃, 0.0℃, 0.5℃ and 0.6℃, with rises of 0.3℃, 0.1℃, 0.2℃ and 0.2℃, respectively. SSTs were near normal or slightly above normal in the equatorial Indian Ocean.
Subsurface Temperatures: During July 2012, anomalous warm subsurface water enhanced and uplift in the eastern equatorial Pacific, with central values above 3.0℃ at about 50 m depth.
Warm Pools: During July 2012, the area and intensity of the warm pools were slightly above normal in both the western Pacific and the Indian Ocean.
Wind Field: During July 2012, at lower troposphere (850hPa), westerly anomalies dominated the central and eastern equatorial Pacific, while zonal winds were near normal in the western equatorial Pacific. At upper troposphere (200hPa), westerly anomalies covered the eastern equatorial Pacific east of 100 ºW, while zonal winds were near normal over the rest of the equatorial Pacific.
Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was -0.1, with an increase of 0.7 from last month.
Convections over the Tropics: During July 2012, the anomalous outgoing long wave radiation (OLR) showed that convections were enhanced over the equatorial Pacific between 160 ºE -180º, while convections were near normal across the remainder of the equatorial Pacific. At lower troposphere (850hPa) divergent wind field, a convergent center was around 120ºE, 20ºN, and a divergent center was near 120ºW, 12.5ºS. At upper troposphere (200hPa), the corresponding divergent center and convergent center were near 130ºE, 10ºN and around 115ºW, 20ºS, respectively.
5. ENSO Monitoring and Outlook
At present, large positive sea surface temperature anomalies maintained in the central and eastern equatorial Pacific, and anomalous warm subsurface water enhanced and uplift in the eastern equatorial Pacific. Based on the monitoring and diagnostics of the tropical ocean and atmosphere, and the predictions of dynamic and statistical models, a weak-moderate El Niño event is expected to develop in the rest part of this year.
We will closely monitor the development of ENSO conditions and update the ENSO wrap-up in time.