Monthly Highlights

1. Climate in China

In March 2011, the monthly mean surface air temperature was 2.4℃, with 0.8℃ below normal (3.2℃), the lowest in the latest 23 years. The temperatures were below normal in most of China. Temperatures were observed 2~4℃ below normal in most of Northwest China, western Inner Mongolia, central-southern Southwest China and western South China, with over 4℃ lower than normal in locations, except northwestern Heilongjiang, central-southern North China, most of Huanghuai area, and western Xizang, where with 1~2℃ above normal.

In the month, average precipitation over China was 20.4 mm, with 27.4% less than normal (28.1 mm) and the least in the latest 10 years. Precipitations were 30-100% more than normal in northern and eastern Xinjiang, western Gansu, eastern Xizang, western and eastern Sichuan, southern Yunnan, western Guangxi and parts of northern Heilongjiang, with over 200% above normal in parts of above regions. Precipitations were 30-80% less than normal in most of the rest of China, with over 80% less than normal in central-eastern Inner Mongolia, central and southern Northeast China, North China, northern Huanghuai area, central and southern Xinjiang, western Qinghai-Tibet Plateau and parts of western Qinghai.

In March, daily temperature drop extremes occurred in 57 stations, which were mainly located in Fujian, Qinghai, Yunnan, Sichuan, Guizhou, and new records were broken in 5 stations. Meanwhile, long durations of temperature drop of 7 stations in Yunnan, Shaanxi and Henan were reached the threshold of temperature drop extreme, and new records were broken in Lantian (21.1℃) and Gejiu (15.1℃).The consecutive days of no precipitation extremes occurred in 32 stations, which were mainly located in Yunnan and Liaoning, and new records were broken in 4 stations. Meanwhile the consecutive days of precipitation extremes occurred in 6 stations in Guangxi.

2. World Climate

During March 2011, monthly mean surface temperatures were observed 1~2℃ higher than normal in northern and southern Europe, most of Russia in Asia, Central Asia, West Asia, North China, most of North Africa, Alaska and locations of northeastern and southern North America, with over 6~10℃ above normal in northern and Far East Russia. Meanwhile, temperatures were 1~2℃ below normal in central-eastern Europe, Inner Mongolia, Northwest China to the southwest and western South China, Indochina, most of Australia and northern North America, locations of northern South America, with over 4℃ below normal in locations of northern North America.

In March 2011, precipitations were over 50% less than normal in most of the subtropical land in the Northern Hemisphere, central Europe, central North America, parts of Alaska, and parts of central-northern Africa, with no precipitation in locations. Meanwhile, precipitations were observed over 50% more than normal in western, southern and parts of northern Russia, southeastern China, central-northern Indo-China Peninsular, parts of central-western and parts of eastern North America, central-eastern Australia, parts of West Africa, Somali Peninsular, central and northern South America, with over 200% more than normal in locations.

3. General Circulation Features

Northern Hemisphere: During March 2011, the Arctic Oscillation was in positive phase. The field of mean 500hPa geopotential height exhibited a 4-wave pattern over the mid-high latitudes, and meridional circulations dominated Asia. In the field of 500hPa geopotential height anomaly, positive anomalies above 4 dam covered regions from northern North Atlantic Ocean to Europe, regions from Central Asia to southern Russia through Mongolia, central North Pacific Ocean, regions from eastern North Pacific Ocean to southern North America, and also regions from Aleutian Islands to northern North America, with central values above 8 dam over regions from northern North Pacific to Europe and Aleutian Islands. Meanwhile, negative anomalies below -4 dam covered regions from western Russia to Arctic Ocean, northwestern and northeastern North Pacific Ocean, and parts of eastern North Atlantic Ocean, with central values below -12 dam over Arctic Ocean and northeastern North Pacific Ocean. For the month, the Northwest Pacific Subtropical High was smaller and weaker than normal, with its high ridge extending more eastward but more northward than normal.

Southern Hemisphere: In March 2011, in the field of 500hPa geopotential height anomaly, positive anomalies above 4 dam covered regions from South Atlantic Ocean in high latitudes to Antarctic, and South Pacific Ocean in mid-high latitudes, with central values above 12 dam over South Atlantic Ocean in high latitudes. Meanwhile, negative anomalies below -4 dam mainly covered South Indian Ocean in high latitudes within 40^oE-70^oE, South Atlantic Ocean in middle latitudes within 0^o-20^oW, and also southeastern South Pacific Ocean, with central values below -12 dam over the southeastern South Pacific.

4. Tropical Features

ace water enhanced slightly andSea Surface Temperatures (SSTs): During March 2011, SSTs were 1.0℃ below normal in the central and eastern equatorial Pacific. Meanwhile, SSTs were around 0.5℃ above normal in the equatorial western Pacific with maximum above 1.0℃. NINO 1+2, NINO 3, NINO 4, NINO 3.4 and NINO Z indices were -0.3℃, -0.7℃, -0.7℃, -0.9℃ and -0.7℃, with a drop of -0.5℃ for Nino 1+2 and rises of 0.1℃, 0.4℃, 0.3℃,and 0.1℃ for others from last month, respectively.

Subsurface Temperatures: During March 2011, the intensity and extent of anomalous cold subsurface water weakened and shrunk significantly, with negative central values above -1.5℃. On the other hand, the anomalous warm subsurface water extended eastward to the area near 100ºW.

Warm Pools: During March 2011, the area of the Indian Ocean warm pool was near normal, while its intensity was slightly above 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 over the regions from the equatorial Indian Ocean to west part of the western equatorial Pacific, and the eastern equatorial Pacific east of 140ºW. At upper troposphere (200hPa), westerly anomalies covered the equatorial Pacific, while easterly anomalies covered the equatorial Indian ocean and west part of the western equatorial Pacific。

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 2.1, with a rise of 0.1 from last month.

Convections over the Tropics: During March, the anomalous outgoing longwave radiation (OLR) showed that enhanced convection was observed over the equatorial eastern Indian Ocean, South China Sea and around of Philippines, while suppressed convection was observed from eastern part of the western equatorial Pacific to the area near the dateline. At lower troposphere (850hPa) divergent wind field, a convergent center was around 140ºE, 10ºS, and a divergent center was near 80ºW, 10ºN. At upper troposphere (200hPa), the corresponding divergent center was near 140ºE, 10ºS, and a convergent center was around 70ºW, 15ºN.

5. ENSO Monitoring and Outlook

Monitoring showed that during March 2011, amplitude of the negative SSTA decreased in the central and eastern equatorial Pacific. NINO Z index was -0.7℃, with a increasing of 0.1℃. The intensity and extent of anomalous cold subsurface water weakened and shrunk significantly. And, the anomalous warm subsurface water extended eastward to the area near 100ºW, which would sustain further decaying of La Nina event.

Most statistical and dynamic climate models predicted that La Niña conditions would terminate around May-June 2011.

Monitoring on recent tropical atmospheric and oceanic conditions indicated that La Niña was still persisted, but continued to weaken. And, based on the predictions of most statistical and dynamic models and diagnostic analysis, it was expected that the La Nina event would terminate around May 2011. Therefore, we will continue to concern ENSO closely and update our ENSO wrap-up in time.