Monthly Highlights

1. Climate in China

In February 2011, monthly mean surface air temperature of China was -1.2℃, being 1.7℃ above normal. Temperatures were near or above normal in most of China, except southwestern Hainan, where temperatures were over 1℃ below normal. Temperatures were observed 2~4℃ higher than normal in most of Northwest China, central-western Inner Mongolia, southeastern Northeast China, southwestern Jiangnan area, and northeastern Yunnan.

In the month, average precipitation over China was 11.4 mm, being 4.9 mm less than normal. Precipitations were 30-100% more than normal in North China, most of Huang-Huai areas, northern and western Xinjiang, central and eastern Northwest China, and southwestern Tibet, with over 100% more than normal in most of above regions. Precipitations were 30-80% less than normal in most of the rest of China, with over 80% less than normal in parts of western Northwest China, central-northern Tibet, most of Yunnan and southern Sichuan.

In February, daily minimum temperatures of 6 stations in Heilongjiang, Chongqing, Gansu, Sichuan and Hainan reached the thresholds of extreme low temperature, and new records were broken in Yuci(-24.0℃), Lingshui(-16.5℃), Baoting(2.1℃) and Fengdu(-5.5℃). Consecutive days of no precipitation surpassed the 95th percentile thresholds at 116 stations in North China and Huang-Huai areas, with values reaching records or setting new records of extreme consecutive days in 25 stations.

2. World Climate

During February 2011, monthly mean surface temperatures were observed 1~2℃ higher than normal in central-southern Russia, eastern Central Asia, most of East and West Asia, parts of North Africa, parts of eastern North America, western Alaska, and locations of South America, with over 4℃ above normal in parts of above regions. Meanwhile, temperatures were 1~2℃ below normal in most Europe, northern Russia in Asia, Afghanistan, Pakistan, western West Africa, central-western North America, and northern and western Australia, with more than 4℃ below normal in northern Europe and central North America.

For the month, precipitations were over 50% less than normal in most of the subtropical land in the Northern Hemisphere, parts of Europe, parts of Russia, parts of eastern North America, locations of northern South America, and parts of central and southern Africa, with no precipitation in locations. Meanwhile, precipitations were observed over 50% more than normal in most of Central Asia, Mongolia, parts of the Far East of Russia, North China, central-western Australia, parts of West Africa, central North America, Alaska and central-northern South America, with over 200% more than normal in locations.

3. General Circulation Features

Northern Hemisphere: During February 2011, the Arctic Oscillation was in positive phase. The field of mean 500hPa geopotential height exhibited a 3-wave pattern over the mid-high latitudes, and zonal circulations dominated Asia. In the field of 500hPa geopotential height anomaly, positive anomalies above 4 dam covered regions from northern East Asia to the northern North Pacific, and parts of the Arctic Ocean north of North Europe, with central values above 24 dam over the northern North Pacific. Meanwhile, negative anomalies below -4 dam covered the Far East of Russia, eastern Europe, Kazakhstan, regions from northern North America to the northern North Atlantic Ocean, and parts of the central North Pacific, with central values below -12 dam over western Kazakhstan and the northern North Atlantic Ocean. For the month, the Northwest Pacific Subtropical High was smaller and weaker than normal, with its ridge locating more southward and extending more eastward than normal.

Southern Hemisphere: For the month, in the field of 500hPa geopotential height anomaly, positive anomalies above 4 dam covered the southern South Indian Ocean and the southern South Atlantic Ocean between 40^oS-60^oS, and the central-southern South Pacific, with central values above 12 dam over the southeastern South Indian Ocean. Meanwhile, negative anomalies below -4 dam mainly covered the southeastern and western South Pacific between 50^oS-80^oS, with central values below -12 dam over the southeastern South Pacific.

4. Tropical Features

ace water enhanced slightly andSea Surface Temperatures (SSTs): During February 2011, SSTs were 1.0℃ below normal in the central and eastern equatorial Pacific with minimum below -1.5℃. Meanwhile, SSTs were around 0.5℃ above normal in the equatorial western Pacific. It was also worth noting that the positive SST anomalies around 0.5～1.0℃ were observed in the eastern equatorial Pacific off the coast of South America. NINO 1+2, NINO 3, NINO 4, NINO 3.4 and NINO Z indices were 0.2℃, -0.9℃, -1.1℃, -1.3℃ and -0.9℃, with rises of 0.6℃, 0.4℃, 0.4℃, 0.3℃ and 0.4℃ from last month, respectively.

Subsurface Temperatures: During February 2011(24days), the intensity and extent of anomalous cold subsurface water weakened and shrunk significantly, with central values still below -5℃. On the other hand, anomalous warm subsurface water extended eastward to the area near 160ºW.

Warm Pools: During February 2011, the area and intensity of the Indian Ocean warm pool were near normal. The area of the western Pacific warm pool was below normal, but its intensity was above normal.

Wind Field: For the month, at lower troposphere (850hPa), easterly anomalies prevailed over most of the western and central equatorial Pacific, while westerly anomalies were observed in the eastern equatorial Pacific east of 140ºW. At upper troposphere (200hPa), westerly anomalies covered the equatorial Pacific.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 2.0, with a rise of 0.1 from last month.

Convections over the Tropics: For the month, the anomalous Outgoing Longwave Radiation (OLR) showed that enhanced convection was observed over the South China Sea and vicinity of Philippines, while suppressed convection was observed from eastern part of the western equatorial Pacific to the area near the dateline. In the lower troposphere (850hPa) divergent wind field, a convergent center was around 140ºE, 10ºS, and a divergent center was near 80ºW, 10ºS. At the upper troposphere (200hPa), the corresponding divergent center was near 140ºE, 10ºS, and a convergent center was around 80ºW, 5ºS.

5. ENSO Monitoring and Outlook

Monitoring showed that during February 2011, amplitude of the negative SSTA decreased in the central and eastern equatorial Pacific. NINO Z index was -0.9℃, with a increasing of 0.4℃. Since July 2010, the La Nina has persisted for eight months, and the sum of Nino Z index over the period was -10.1℃, indicating being a moderate La Niña event.

Most statistical and dynamic climate models predicted that La Niña conditions would persist within next 3～4 months.

La Nina conditions had persisted for eight months. It was expected to last within next 3～4 months, and NESO-neutral conditions with slightly colder than normal SSTs in the central-eastern equatorial Pacific would occur during summer 2011. Therefore, we will closely monitor the development of ENSO conditions and update our ENSO wrap-up in time.