Monthly Highlights

Climate in China

During February 2009, surface air temperature averaged over China was the third highest since 1951. Monthly mean surface air temperatures were observed over 2℃ above normal in most China, with over 4℃ above normal in most regions south to the Yangtze river, the Hetao area, western and parts of northeastern Xinjiang and over 6℃ above normal in most South China. Meanwhile, temperatures were below normal in northern Northeast China, northeastern Inner Mongolia and northern Xinjiang.

For the month, precipitations were observed 30%~200% more than average in most Northeast China, northeastern Inner Mongolia, most North China, the Huanghuai valley, the Jianghuai valley, the Jianghan valley, northern Jiangnan, northern and parts of eastern and southern Northwest China, northern and parts of southern Xinjiang, southeastern Tibet, with above 200% more than average in southeastern Northeast China and northeastern North China. Meanwhile, precipitations were observed below or near normal in other regions of China, with 30~80% less than average in parts of central Northeast China, most Inner Mongolia, central-western Northwest China, western and central Xinjiang, central Tibet, eastern and northern Southwest China and South China, with no precipitations in parts of above regions.

Climate in the World

During the month, temperatures were over 1℃ below normal in northern Asia, parts of North Europe, northwestern and parts of central North America, parts of northwestern South America, parts of West Africa and northern Australia, with 4-6℃ below normal in central-northern and parts of northeastern Russia. Meanwhile, temperatures were over 1℃ above normal in central and southern Asia, central-eastern Europe, northern and most western Africa and southern Australia, with 4-6℃ above normal in parts of above regions.

For the month, precipitations were observed over 50% more than average in parts of central-eastern Europe, southern and parts of northeastern Russia, most northeastern China, parts of Northwest China and Southwest China, parts of Central Asia, parts of West Asia, parts of West Africa and central-southern Africa, parts of northwestern and northeastern North America, northwestern and parts of central-western South America and parts of northeastern Australia, with at least 200% above normal in locations. Meanwhile, precipitations were at least 50% less than average in western and parts of central-eastern Russia, northern and parts of western East Asia, the Indochina Peninsula, South Asia, most West Asia, most North Africa and West Africa, parts of North America, northern and parts of southern South America and central-southern Australia, with no precipitations in parts of above regions.

General Circulation Features

Northern Hemisphere: During February 2009, the mean 500hPa geopotential height field exhibited a 4-wave pattern at the mid-high latitudes. In the 500hPa geopotential height anomaly field, positive anomalies above 4 dam covered most the North Pacific, most mid-latitude regions (20-40^oN) of Euro-Asia, the regions from the northern North Atlantic to the Polar region, southwestern North America and its nearby sea areas, with central values above 28 dam over the North Pacific. Meanwhile, negative anomalies below -4 dam covered northern Asia, vicinity of the Mediterranean Sea, parts of the northeastern North Atlantic Ocean, parts of the Northeast Pacific, with central values below -12 dam over northeastern Russia. For the month, the subtropical high over the West Pacific was slightly smaller, slightly weaker and its position was northward than normal.

Southern Hemisphere: For the month, in the 500hPa geopotential height anomaly field, negative anomalies below -4 dam covered the most South Pacific south to 40°S and the southwestern South Indian Ocean, with central values below -16 dam over the southern South Pacific. Meanwhile, positive anomalies above 4 dam covered the southwestern South Pacific north to 40°S, the southeastern South Indian Ocean and parts of the South Atlantic Ocean between 40°S and 50°S.

Tropical Features

Sea Surface Temperatures (SSTs): During February, negative SST anomalies dominated most of the central and eastern equatorial Pacific, with central values below -1.0℃. Furthermore, in February, indices of NINO 1+2，NINO 3, NINO 4，NINO 3.4 and NINO Z were 0.0℃, -0.5℃，-0.7℃, -0.7℃, and -0.5℃, with a rise of 0.1℃, 0.1℃, 0.1℃,0.3℃and 0.1℃ from last month, respectively.

Subsurface Temperatures: During February，comparing with last month, anomalously cold subsurface water weakened in the eastern equatorial Pacific, and the cold center shifted eastward and upward. Meanwhile, anomalously warm subsurface water in the western equatorial Pacific strengthened slightly.

Warm Pools: During February, both areas of the western Pacific and the Indian Ocean warm pool were above normal. In addition, the intensities of the two warm pools were also above normal.

Wind Field：For the month, at lower troposphere (850hPa), easterly anomalies prevailed over the regions between 140ºE-150ºW, with central values over 8m/s, westerly anomalies prevailed over the regions west of 130ºE in the western equatorial Pacific and the eastern equatorial Pacific. At upper troposphere (200hPa), westerly anomalies covered most of the central and eastern equatorial Pacific, with central values over 16m/s, and easterly anomalies developed in the western equatorial Pacific.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 1.4, with a rise of 0.5 from last month.

Convections over the Tropics: During February, the anomalous outgoing longwave radiation (OLR) in the equatorial Pacific showed that the convection was enhanced over the regions between 110ºE-150ºE, and suppressed over the regions between 160ºE-150ºW . In the lower troposphere (850hPa) divergent wind field, a convergent center was near 150ºE, 10ºS, and a divergent center was near 110ºW, 10ºS. At upper troposphere (200hPa), the corresponding divergent center was near 160ºE, 15ºS, and the convergent center was near 90ºW, 5ºS.

During February, atmospheric and oceanic conditions in the tropical Pacific still maintained La Nina status, with NINO Z index being -0.5℃ and SOI index being 1.4. However, recent monitoring showed that anomalously cold subsurface water weakened in the eastern equatorial Pacific and anomalously warm subsurface water in the western equatorial Pacific strengthened slightly, the negative SST anomalies in the central and eastern equatorial Pacific weakened correspondingly. In addition, based on a majority of the model forecasts, La Nina conditions are expected to gradually weaken in the subsequent 1-3 months.

Based on monitoring of recent atmospheric and oceanic conditions in the tropical Pacific and predictions of statistical and dynamic models, La Nina conditions are expected to gradually weaken through the following 1-3 months .