Monthly Highlights

Climate in China

During March 2008, the monthly mean surface air temperatures in China were generally above normal and the averaged temperature for China is the maximum since 1951. Temperatures were observed below or near normal in most Hainan, most Yunnan, western Sichuan, southern Qinghai, central and northeastern the Tibetan Plateau. Meanwhile, temperatures were 1-4℃ above normal in most other regions of China, with 4-6℃ above normal in most Heilongjiang, most Jilin, eastern Inner Mongolia, northern and western Xinjiang and over 6℃ above normal in northern Heilongjiang, northeastern Inner Mongolia and northern Xinjiang.

For the month, precipitations were observed 30-200% above normal in most Northeast China, northern North China, central and eastern Inner Mongolia, northeastern Xinjiang and most Southwest China, with at least 200% above normal in parts of the above regions. Meanwhile, precipitations were observed below or near normal in other regions of China, with 30-80% below normal in the Huaihuai area, the Jianghuai area, the eastern Jiangnan area, most South China, southern North China, most Northwest China, southwestern Liaoning, western Inner Mongolia and western Yunnan, with at least 80% below normal in Inner Mongolia, Qinghai, Xinjiang and Xizang.

Climate in the World

During the month, temperatures were 1-2℃ above normal in most of Eurasia, parts of southwestern North America and parts of Alaska, southern South America, northwestern Africa and southern Australia, with temperatures 4-8℃ above normal in central and northern Asia and southeastern Europe. Meanwhile, temperatures were over 1℃ below normal in northwestern Russia, central-northern North America and eastern Australia.

For the month, precipitations were observed 50-100% more than average in eastern Europe, most Russia, northeastern China, most Inner Mongolia, central-southern India, eastern North America, most central-northern South America and parts of eastern Africa, with precipitations at least 200% above normal in locations. Meanwhile, precipitations were at least 50% less than average in Far East Russia, northern South Asia, most of Central Asia and most of West Asia, central-western North America, northern and southeastern South America, northern Africa and parts of eastern Africa and most Australia, with no precipitations in parts of above regions.

General Circulation Features

Northern Hemisphere: During March 2008, 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 the regions from most Asia to the northwestern North Pacific, the northeastern Pacific and the northern Atlantic, with central values above 16 dam over the Sea of Okhotsk. Meanwhile, negative anomalies below -4 dam covered western and southern Europe and parts of northern North America, with central values below -12 dam over western Europe. For the month, the subtropical high over the West Pacific was smaller and weaker and its position was more eastward and northward than normal.

Southern Hemisphere: For the month, zonal circulation prevailed at most of the mid-high latitudes. In the 500hPa geopotential height anomaly field, negative anomalies below -4 dam covered the South Pacific south to 50°S, with central values below -12 dam. Meanwhile, positive anomalies above 4 dam covered the southwestern Pacific near 40°S, parts of the southern South Indian Ocean, southern South America and the Queen Maud Land.

Tropical features

Sea Surface Temperatures (SSTs): During March 2008, La Nina conditions remained but its intensity weakened obviously. Compared with last month, SST anomalies in the central and eastern equatorial Pacific east of 170ºW increased remarkably with the biggest rise being 2℃. During March, negative SST anomalies covered the equatorial pacific between 150ºE-120ºW, with central values about -1.5℃, and positive SST anomalies dominated the equatorial Pacific near South America, with central values about 1.5℃. In March, indices of NINO 1+2, NINO 3, NINO 4, NINO 3.4, and NINO Z were 0.9℃, -0.5℃, –1.3℃, -1.1℃, and -0.7℃, with rises of 0.6℃, 0.8℃, 0.3℃, 0.8℃ and 0.6℃ from last month, respectively. Meanwhile, SSTs in most of the equatorial Indian Ocean were near normal.

Subsurface Temperatures: Compared with last month, the anomalously cold subsurface water in the central and eastern equatorial Pacific weakened obviously, and split into two parts, while the anomalously warm subsurface water still sustained in the western equatorial Pacific with its intensity strengthening.

Warm Pools: During March 2008, the area of the western Pacific warm pool was smaller but the intensity was stronger than normal, with its eastern boundary shrinking strictly and its northern boundary expanding obviously. Meanwhile, the area of the Indian Ocean warm pool was smaller and its intensity was weaker than normal.

Wind Field：For the month, at lower troposphere (850hPa), easterly anomalies prevailed over the equatorial Pacific between 135ºE-150ºW, with the maxima over 8m/s, and weak westerly anomalies covered the equatorial Pacific east of 150ºW. Meanwhile, at upper troposphere (200hPa), westerly anomalies dominated the central and western equatorial Pacific, with center values about 16m/s, and weak easterly anomalies covered the equatorial Pacific east of 130 ºW.

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

Convections over the Tropics: During March 2008, the anomalous outgoing long wave radiation (OLR) showed that convections were suppressed over the equatorial Pacific between 135ºE-160ºW, while convections were enhanced over the northern Indian Ocean and the western equatorial Pacific. For the tropical Pacific, in the divergent wind field at lower troposphere (850hPa), a divergent center and a convergent center were observed over 105ºW，20ºS, and 130ºE, 5ºS, respectively. Correspondingly, at the upper troposphere (200hPa), the convergent center was over 110ºW, 15ºS, and two divergent centers were over 115ºE, 5ºS and 160ºE，20ºS, respectively.

ENSO Monitoring and Prediction

(1) During March 2008, anomalously cold surface water weakened obviously in the central and eastern equatorial Pacific, and NINO Z index was 0.7℃ with a drop of 0.6℃ from last month.

(2) For the month, the anomalously cold subsurface water in the central and eastern equatorial Pacific weakened obviously, and split into two parts.

(3) Southern Oscillation Index (SOI) was 1.4 during this month, with a drop of 0.5 from last month.

(4) At lower troposphere (850hPa), strongly easterly anomalies still covered the equatorial Pacific between 135ºE-150ºW.

(5) Convections were suppressed over the equatorial Pacific between 135ºE-160ºW.

(6) Most ENSO models predicted that current La Niña event is likely to end before the coming midsummer.

In conclusion, the present La Niña is likely to continue to weaken during the following months, and is expected to end before midsummer 2008.