Monthly Highlights

1. Climate in China

During February 2006, monthly mean surface air temperatures were 1~3℃ below normal in northwestern Heilongjiang, northeastern and central Inner Mongolia. In the rest areas, temperatures were near or above normal. 1℃ above normal were observed in western China, coast of South China, parts of Jilin and Liaoning, with 4~5℃ above normal in parts of the Qingzang Plateau and Xinjiang. For the month, precipitations were 30% below normal in northwestern Jilin, parts of North China, southern Yunnan, southwestern Tibet, parts of Xinjiang and Qinghai. Meanwhile, precipitations were near or above normal in the rest areas, with about 30~200% above normal in western Heilongjiang, parts of Inner Mongolia, southern Northeast China, parts of central and western China.

2. Climate in the world

During February 2006, monthly mean surface air temperatures were 2~4℃ above normal in central Asia, western China, northern India, northern North Asia, Far East of Russia, Alaska, northwestern Canada, northern Argentina, Niger and eastern Australia, with 6~7℃ above normal in Alaska, eastern Kazakhstan and southern Tibet. Meanwhile, temperatures were 2~4℃ below normal in parts of Europe, southern North Asia, parts of USA and Canada, western Australia, with 6~7℃ below normal in western Russia.

During the month, precipitations were observed more than 50% below normal in northeastern Europe, central North Asia, most of Mongolia, India, most of USA, central Mexico, parts of West Africa, eastern Australia, eastern Brazil, northern Argentina, and no rainfall in locations of above regions. Meanwhile, in the rest areas, precipitations were observed more than 50% above normal in parts of Europe, central Asia, parts of China, Far East and southern Russia, parts of Alaskan, western Australia and littoral of southern Australia, parts of South Africa, eastern Venezuela and central Argentina.

3. General Circulation Features

Northern Hemisphere: During February 2006, the mean 500hPa geopotential height field exhibited a 3-wave pattern at the mid-high latitudes, and the polar vortex was weaker than normal. In the 500hPa height anomaly field, negative anomalies below -4 dam were observed over northeastern Asia, northeastern North America, central and southern Europe, and negative anomalies were below -12 dam over Far East of Russia. Meanwhile, positive anomalies above 8 dam dominated in western Asia, the northern North Pacific, northern North America and the northern North Atlantic, with central values above 16 dam. For the month, the Northwest Pacific Subtropical high was stronger than normal and extended westward compared with normal position.

Southern Hemisphere: For the month, zonal circulation prevailed over the mid-high latitudes in the mean 500hPa geopotential height field. Negative anomalies below -4 dam were observed over the southeastern South Pacific, the southern South Atlantic and the southern South Indian Ocean. Meanwhile, heights were near normal over the rest of the mid-high latitudes.

4. Tropical Features

Sea Surface Temperatures (SSTs): During February, SST anomalies increased in the eastern equatorial Pacific and offshore of South America. Negative SST anomalies below -0.5℃ in the central equatorial Pacific expended westward and reached the region nearby 160ºE. Positive SST anomalies near 0.5℃ were observed in the western equatorial Pacific and the eastern equatorial Indian Ocean. The indices of NINO1+2, NINO 3, NINO3.4, and NINO Z were 0.4℃, -0.3℃, -0.6℃, -0.4℃, with rises of 0.6℃, 0.3℃, 0.3℃ and 0.1℃ from last month, respectively. The index of NINO 4 was -0.6℃, and with drop of 0.1℃.

Subsurface Temperatures: During February, the intensity of the abnormal subsurface cold water in the eastern equatorial Pacific extended eastward and upward, and strengthened slightly. Meanwhile, the warm water strengthened slightly in the western equatorial Pacific compared with last month.

Warm Pools: During February, the area and the intensity of the western Pacific and Indian Ocean warm pool were larger and stronger than normal, respectively.

Wind Field：During February, at the lower troposphere (850hPa), weak easterly anomalies were over most of the central and western equatorial Pacific, while about 4m/s westerly anomalies were found over the eastern equatorial Pacific. Zonal winds over the equatorial Indian Ocean were near normal. At the upper troposphere (200hPa), westerly anomalies dominated over most of the equatorial Pacific west to 120ºW, and zonal winds were near normal over the eastern equatorial Pacific.

Southern Oscillation: For the month, Southern Oscillation Index (SOI) was 0.1, with a drop of 1.2 from last month.

Convection over the Tropics: During February, the anomalous outgoing longwave radiation (OLR) showed that convections were near normal over the equatorial Pacific, and suppressed in north of Australia, and enhanced over the southern tropical Pacific around the date line. In the lower troposphere (850hPa) divergent wind field, a convergent center was over 150ºE, 8ºS, and a divergent center located around 110ºW, 5ºS. Correspondingly, at the upper troposphere (200hPa), the divergent center was found over 170ºE, 5ºS, and the convergent center was observed over nearby 110ºW, 5ºS.

5. ENSO Monitoring and Prediction

① During February, SST anomalies rose in the eastern equatorial Pacific and dropped in the western equatorial Pacific. Indices of NINO 1+2 and NINO 3 were 0.4℃, -0.3℃, with rises of 0.6℃ and 0.3℃ from last month, respectively. Index of NINO 4 dropped 0.1℃ compared with last month.

② For the month, the distribution of subsurface SST anomalies of the equatorial Pacific still exhibits a framework of warm in the west and cold in the east.

③ For the month, SOI was 0.1, with drop of 1.2 from last month.

④ At the lower troposphere, weak easterly anomalies were over most of the central and western equatorial Pacific, while weak westerly anomalies covered the eastern equatorial Pacific.

⑤ Most of ENSO models showed that weak negative SST anomalies will persist in the eastern equatorial Pacific in the following 1~3 months.

In conclusion, tropical oceanic and atmospheric conditions reflected characteristics of weak cold phase, and these conditions were predicted to persist in the following 1~2 months. The air-sea development in the tropical Pacific will continue to be carefully monitored.