Monthly Highlights
1. Climate in China
During February 2012, the surface air temperature averaged over China was -3.2℃ which was 1.2℃ lower than normal. While monthly mean surface air temperatures were 1~2℃ above normal in most of Southwest China and most of Qinghai, temperatures were 1~2℃ below normal in the remainder of China, with 2-4℃less than normal in most of Northeast China, northeastern North China, northeastern Northwest China, western Jiangnan, Inner Mongolia, northwestern Xinjiang, most of Guizhou and guangxi, northern Hunan.
In February, average precipitation over China was 14.5 mm, which was 17.6% less than normal. Precipitations were observed generally more than 30-80% below normal in most of China, except Southern Jianghuai, Eastern Jiangnan, eastern South China, western Jilin, northwestern Liaoning, Qinghai, western and northern Xinjiang, southwest Tibet, where precipitations were 50-100% more than normal and more than 200% above normal in locations. North China’s average annual precipitation l was only 1 mm which is 87.5% below normal. Meanwhile, Yunnan’s average annual precipitation was 5.9 mm which was 75.46% below normal being the 3th consecutive year with average annual precipitation less than normal.
In February, extremes of Daily Temperature Drop (DTD) and Consecutive No Measurable Precipitation Days (CNMPD) were observed in China. DTD extremes occurred in 9 stations, which were located in Liaoning, Hebei, Shandong, Shaanxi and Sichuan etc., with widespread DTDs of 10-16℃ and new records in Tangshan(12.9℃) and Ningshan(11.0℃). Meanwhile, CNMPDs occurred in 103 stations in Northeast China, North China, Sourthwest China etc., reached or exceeded the extreme thresholds, with CNMPDs of 32-126 days and new records in 13 satations, i.e. Ning-an(87 days), Linkou(82 days), Dongning(79 days), A-cheng(72 days), Huichun(90 days), Wangqing(87 days), Wuhouqi(126 days), Guyang(85 days), Fucheng(85 days), Shangyi(84 days), Zhangbei(84 days), Suchuan(66 days) and Litang (96 days) etc.
2. World Climate
During February 2012, temperatures in most places of the world were colder than normal. Temperatures were 1-4℃ below normal in most Europe and Asia, northern Africa, middle Australia and northern South America, with temperatures 4-8℃ below normal in central and eastern Europe, western North Asia and Central Asia. Meanwhile, temperatures were 1-4℃ above normal in central-north Russia, most North America, central-southern South America, northern Southeast Asia, with temperatures at least 4℃ above normal in northwestern Canada, north-central America and parts of north-central Russia.
For the month, precipitations were at least 50% less than normal in western Russia, India, eastern China, western Africa, parts of northern Canada, with no precipitation in parts of above regions. Meanwhile, precipitations were observed above 50% more than normal in southeastern Europe, West Asia, central America, southern Mexico, southern and northern South America, central-north Russia, with precipitations at least 200% above normal in locations.
3. General Circulation Features
Northern Hemisphere: During February 2012, 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 regions over the northern North Atlantic Ocean, the Ural of western Russia, the eastern North Pacific and part of northern United States, with central values above 12 dam over the Ural. Meanwhile, negative anomalies below -4 dam covered the Mediterranean Sea, part of northern Africa, Central Asia, the central and eastern Mongolia, and the western North Pacific. During the month, the northwestern Pacific subtropical high was not visible.
Southern Hemisphere: For the month, zonal circulation mainly dominated over mid-high latitudes in the mean 500hPa geopotential height field. In the field of height anomaly, negative anomalies below -4 dam covered the regions from the southern South Pacific to the southwestern South Atlantic Ocean, and the southwestern South Indian Ocean, with central values below -8 dam.
Meanwhile, positive anomalies above 4 dam covered the regions from the South Pole to the high latitude of the South Pacific Ocean, with central values above 8 dam over parts of the regions.
4. Tropical Features
Sea Surface Temperatures (SSTs): SST anomalies in most of the central and eastern equatorial Pacific increased obviously during February 2012, and SSTs were near or above normal in most of the eastern equatorial Pacific. Meanwhile, negative SST anomalies below --0.5℃ maintained in the central equatorial Pacific and western part of the eastern equatorial Pacific. SSTA indices of NINO regions increased obviously and NINO1+2, NINO 3, Nino4, NINO 3.4 and NINO Z indices were 0.2℃, -0.2℃, -0.9℃,-0.7℃ and -0.5℃ in February. Meanwhile, SSTs were close to normal in the equatorial Indian Ocean.
Subsurface Temperatures: During February, anomalously cold subsurface water in the equatorial central and eastern Pacific weakened while the anomalously warm subsurface water in equatorial western Pacific maintained.
Warm Pools: During February, areas of the Indian Ocean warm pool and the western Pacific warm pool were both normal, while the intensities of the two warm pools were both slightly greater than normal.
Wind Field: During February, at lower troposphere (850hPa), easterly anomalies dominated over the central equatorial Pacific while westerly anomalies enhanced in the eastern equatorial Pacific. At upper troposphere (200hPa), westerly anomalies weakened over most of the equatorial Pacific compared with last month.
Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 0.3, with a drop of 0.7 from last month.
Convections over the Tropics: During February, the anomalous outgoing long-wave radiation (OLR) showed that enhanced convection was over sea regions from the eastern Indian Ocean to eastern Bay of Bengal and the South China Sea. Meanwhile, suppressed convection was over the sea regions north to Australia and the most central equatorial Pacific.
In the divergent wind field at lower troposphere (850hPa), a convergent center was around 135°E 10ºS and a divergent center was around 117.5ºW，15ºN. At upper troposphere (200hPa), the corresponding divergent and convergent centers were near 155ºE，10ºS and 85ºW，20ºS, respectively.
5. ENSO monitoring and outlook
During February, negative SSTAs remained in the central equatorial Pacific while SST in the eastern equatorial Pacific rose obviously. Anomalously cold subsurface water in the equatorial central and eastern Pacific weakened. SST indices in NINO regions all rose. Westerly enhanced at lower troposphere over the eastern equatorial Pacific. SOI increase obviously. Above oceanic and atmospheric features indicated that La Nina was decaying rapidly in February 2012.
Based on dynamical and statistical model predictions and current monitoring of the ocean and atmosphere features, we predict the return of ENSO-neutral during the period from March to April 2012 and continuing through the summer.