Monthly Highlights

Climate in China

During February 2007, monthly mean surface air temperature was the highest over China for February in record. Temperatures were observed near or slightly below normal in most of the Tibet Plateau and central and western Yunnan, while temperatures were 2-6℃ above normal in the remainder of China, with temperatures above 6℃ in northeastern Xinjiang, central Inner Mongolia and central Northeast China.

For the month, precipitations were observed 30-200% above normal in most of Northeast China, most of the Tibet Plateau, central-western Inner Mongolia, Yunnan and Central China, with precipitations over 200% more than normal in parts of above regions. Precipitations were 30-80% less than normal in western Northeast China, eastern North China, most of Xinjiang, Sichuan Basin and southern South China, with no precipitation in most of Xinjiang.

Climate in the World

During February 2007, monthly mean temperatures were 2-6℃ below normal in most of Russia north to 50°N, the East Europe Plain and the regions north to it, central and southern North America and north-western Canada, with temperatures 6-10℃ below normal in parts of above regions, while temperatures were near or above normal in the rest areas of the world. Temperatures were observed 2℃ above normal in Central and East Asia, most of Europe, the Bering Strait and its neighbouring areas, Algeria and most of Australia, with temperatures 4-9℃ above normal in parts of East Asia and regions around the Bering Strait.

For the month, monthly precipitations were observed 30-100% above normal in a band between 45-60°N of the Eurasia, parts of China, the north-western Indian Peninsula, eastern Brazil, north-eastern Argentina, central and western America, with precipitations 100-400% above normal in parts of above regions. Meanwhile, precipitations were near or below normal in the rest areas of the world. Precipitations were observed 50-80% below normal in most of the bands of northern coasts and regions between 35-45°N of the Eurasia, the southern Indian Peninsula, most of West Africa, most of Australia, Alaska, southern America and parts of South America, with no precipitation in parts of them.

General Circulation Features

Northern Hemisphere: During February 2007, the mean 500hPa geopotential height field exhibited mainly a 3-wave pattern at the mid-high latitudes, and polar vortex was weaker than normal and divided into two parts, with centers above Central Siberia and eastern Canada. In the 500hPa height anomaly field, negative anomalies below -4 dam covered regions from the mid-eastern North America to the northern North Atlantic and most of Russia with central values below -16 and -12 dam, respectively. Meanwhile, positive anomalies above 4 dam covered regions from most of the Arctic regions to the ocean south to the Aleutian Islands, a band region from Central Asia to the ocean east to Japan and the mid-latitude Atlantic Ocean, with central values above 16 and 8 dam in the northern North America and eastern Asia, respectively. Heights were near normal in the rest regions. For the month, the Northwest Pacific subtropical high was larger, stronger and extended farther west than normal, while the ridge line located slightly farther south than normal.

Southern Hemisphere: For the month, zonal circulation prevailed in the southern Hemisphere in the mean 500hPa geopotential height field at the mid-high latitudes. In the 500hPa height anomaly field, weak negative anomalies were found over the polar regions. Meanwhile, positive anomalies above 4 dam were observed over the southeastern South Pacific and the ocean south to Australia, with central values both above 8 dam. Heights were near normal in other regions.

Tropical Features

Sea Surface Temperatures (SSTs): During February 2007, SST anomalies in the eastern equatorial Pacific decreased obviously. Positive SST anomalies above 0.5℃ maintained around the Date Line of the equatorial Pacific, with central values above 1.0℃, while SSTs in other regions of the equatorial Pacific were near or below normal, with anomalies below -0.5℃ covering the regions between 120-140 ºW of the equatorial Pacific and the central values below -1.5℃. NINO Z, NINO 3.4, NINO 3, NINO 4 and NINO 1+2 SST anomaly indices were 0.3℃, 0.1℃, 0.1℃, 0.6℃ and 0.2℃, with drops of 0.5℃, 0.7℃, 0.8℃, 0.2℃ and 0.3℃ from last month, respectively. Meanwhile, positive SST anomalies above 0.5℃covered the eastern and western equatorial Indian Ocean.

Warm Pools: During February 2007, areas of the western Pacific and Indian Ocean warm pools were slightly above normal and their intensities were both stronger than normal.

Subsurface Temperatures: During February 2007, the anomalously cold subsurface waters in the equatorial Pacific Ocean enhanced, extended eastward and rose obviously compared with last month. Meanwhile, the anomalously warm waters in the central equatorial Pacific Ocean enhanced slightly compared with last month.

Wind Field：During February 2007, at the lower troposphere (850hPa), weak easterly anomalies were observed around the Date Line of the equatorial Pacific, zonal winds were near normal over other areas of the equatorial Pacific and the equatorial Indian Ocean. At the upper troposphere (200hPa), easterly anomalies covered the equatorial Pacific east to 140 ºW with the central value above 12m/s, while near normal winds or weak easterly anomalies were over other parts of the equatorial Pacific.

Southern Oscillation: For the month, Southern Oscillation Index (SOI) was -0.1, with a increase of 0.7 from last month.

Convection over the Tropics: During February 2007, the anomalous outgoing longwave radiation (OLR) showed that convections enhanced over the areas west to the Date Line of the equatorial Pacific and were near normal or slightly suppressed over other areas of the equatorial Pacific. In the lower troposphere (850hPa) divergent wind field, a convergent center was observed over 150ºE, 10ºS, and a divergent center was located in 100ºW, 5ºS. Correspondingly, at the upper troposphere (200hPa), the divergent center was found over 155ºE, 5ºS, and the convergent center was over 100ºW, 5ºS.

ENSO Monitoring and Prediction

(1) In February, 2007, negative SST anomalies below -0.5℃ occurred in the equatorial eastern Pacific between 120-140°W, while positive SST anomalies above 0.5℃ maintained in the central equatorial Pacific. NINO Z index was 0.3℃

(2) The anomalously subsurface cold waters in the equatorial Pacific Ocean enhanced, rose and extended eastward, while the anomalously subsurface warm waters in the equatorial central Pacific Ocean maintained this month.

(3) Southern Oscillation Index (SOI) was -0.1.

(4) Weak easterly anomalies were observed around the Date Line of the equatorial Pacific.

(5) Convections enhanced over the regions west to the Date Line of the equatorial Pacific.

(6) Most of models predicted that the ocean and atmosphere would mainly maintain in normal conditions in the following 3-6 months.

In conclusion, ①The El Nino event, which started in August, 2006, ended in February, 2007. ② The anomalously SST in the central and eastern equatorial Pacific showed “ warm in west and cold in east” structure, and the cold conditions are expected to maintain or strengthen in the following 1~2 months.