Monthly Highlights

1. Climate in China

During March 2006, monthly mean surface air temperatures were near or above normal in most of China, with temperatures 1～2℃ above normal in most of the mid-east, northern Xinjiang and parts of Yunnan, and 4℃ above normal in locations of them. Exceptions were temperatures around 1℃ below normal in northern Heilongjiang. For the month, precipitations were observed 30~100% more than average in regions from Heilongjiang to northeastern Inner Mongolia, southern South China and parts of Southwest China. Meanwhile, precipitations in most of China were 30 ~ 90% less than average, with no precipitation in parts of it.

2. Climate in the world

During March 2006, monthly mean surface air temperatures were 2~4℃ above normal from central Asia to western Mongolia, most of mid-east China, the Far East of Russia，northwestern Africa and northeastern North America, with temperatures 4～7℃ above normal in Kazakhstan. Meanwhile temperatures were 2～4℃ below normal in most of Europe, parts of central North Asia, western coast of America and Alaska, with temperatures 4～6℃ below normal in most of North Europe. They were near or slightly above normal in the other regions over the world.

During the month, precipitations were observed over 50% less than average in East Asia, eastern central Asia, the Arab Peninsula, most of North Europe, North Africa, West Africa, South Africa, central and southwestern Australia, eastern and southwestern America, Alaska, southern South America, with no precipitations in parts of above regions. Precipitations were 50% more than average in India, most of Europe, eastern and western Siberia, most of coasts of Australia and northern America.

3. General Circulation Features

Northern Hemisphere: During March 2006, the mean 500hPa geopotential height field exhibited a 4-wave pattern at the mid-high latitudes, and the areas of the polar vortexes were near normal. In the 500hPa height anomaly field, negative anomalies below -4 dam were observed over regions from the Atlantic Ocean to Europe, eastern Asia and western North America. Heights in the other regions were found near or above normal. Positive anomalies were found more than 8 dam over the North Pacific Ocean and regions from northern North America to the Polar regions, with central values more than 24 dam. For the month, the Northwest Pacific subtropical high was weaker than normal and it withdrew eastward compared with normal.

Southern Hemisphere: For the month, zonal circulation prevailed over mid-high latitudes in the mean 500hPa geopotential height field. Negative anomalies below -4 dam were observed with a band along the southern South Pacific Ocean to the southwestern South Atlantic Ocean, with central values lower than -12 dam. Meanwhile, heights were near normal over the rest of the mid-high latitudes.

4. Tropical Features

Sea Surface Temperatures (SSTs): During March 2006, negative SST anomalies enhanced in the eastern equatorial Pacific but weakened near the dateline. Negative SST anomalies below -0.5℃ covered the equatorial Pacific from the dateline to the coast of South America, with central values below -1.5℃. Positive SST anomalies near 0.5℃ were observed in parts of the western equatorial Pacific. SSTs were near normal in the equatorial Indian Ocean. The indices of NINO1+2 and NINO 3 were 0.3℃ and -0.6℃, respectively, with drop of 0.1℃ and 0.3℃ compared with last month. The index of NINO 4 was -0.3℃, with rise of 0.3℃. The indices of NINO Z and NINO3.4 were -0.4℃, -0.6℃, respectively, with both being the same as last month.

Subsurface Temperatures: During March 2006, compared with last month, the area of the abnormal subsurface cold water in the central and eastern equatorial Pacific shrank eastward apparently, with its centers shifted eastward and upward and its intensity enhanced. Meanwhile, the abnormal subsurface warm water extended eastward and its central values decreased slightly in the western equatorial Pacific.

Warm Pools: During March 2006, the areas of the western Pacific and Indian Ocean warm pool were larger than normal and their intensities were stronger than normal.

Wind Field：During March 2006, at the lower troposphere (850hPa), easterly anomalies covered most of the equatorial Pacific Ocean, while weak westerly anomalies controlled the eastern equatorial Indian Ocean. At the upper troposphere (200hPa), westerly anomalies dominated most of the equatorial Pacific, while zonal winds over the rest equatorial Pacific were near normal.

Southern Oscillation: For the month, Southern Oscillation Index (SOI) was 1.3, with rise of 1.2 from last month.

Convection over the Tropics: During March 2006, the anomalous outgoing longwave radiation (OLR) showed that convections enhanced in the western tropical Pacific but suppressed over east of the dateline in the equatorial Pacific (Fig.8). In the lower troposphere (850hPa) divergent wind field, a convergent center was over 150ºE, 5ºS, and a divergent center located around 105ºW, 5ºS. Correspondingly, at the upper troposphere (200hPa), the divergent center was found over 140ºE, 5ºS, and the convergent center was observed over 95ºW, 30ºS.

5. ENSO Monitoring and Forecasting

① During March 2006, negative SST anomalies enhanced in the eastern equatorial Pacific but weakened near the dateline. The indices of NINO Z and NINO3.4 were -0.4℃, -0.6℃,respectively, with both being the same as last month.

② During March 2006, compared with last month, the area of the subsurface cold water in the mid-eastern equatorial Pacific shrank eastward apparently, with its centers shifted eastward and upward and its intensity enhanced.

③ For the month, Southern Oscillation Index (SOI) was 1.3, with rise of 1.2 from last month.

④ At the lower troposphere, easterly anomalies covered most of the equatorial Pacific Ocean

⑤The anomalous outgoing longwave radiation (OLR) showed that convections enhanced in the western tropical Pacific but suppressed over east of the dateline in the equatorial Pacific.

⑥ Most of ENSO models showed that weak negative SST anomalies could persist in the eastern equatorial Pacific in the following 1~3 months.

In conclusion, tropical oceanic and atmospheric conditions appeared to show features of weak cold phase, and these conditions were estimated to persist in the following 1~2 months.