Monthly Highlights

Climate in China

During March 2007, monthly mean surface air temperatures were observed above normal in most of China except for parts of Northeast China, with temperatures 2-4℃ above normal in northern Xinjiang, most of Jiangnan and Jianghuai.

For the month, precipitations were observed 50-200% above normal in most of Northeast China, North China, Huanghuai, eastern Northwest China, southwestern Xinjiang and western Tibet, with precipitations over 400% more than normal in locations. Precipitations were 30-50% less than normal in most of Xinjiang, most of Southwest China and inshore region of southeastern China, with no precipitation in locations.

Climate in the World

During March 2007, monthly mean surface air temperatures were above normal in most of the world. Temperatures were 2℃ above normal in East China, Mongolia, the Far East, eastern and northern Europe, northwestern Siberia, most of USA and eastern Australia, with temperatures 6-7℃ above normal in most of Mongolia, parts of eastern Europe and parts of the Far East. Meanwhile, temperatures were observed more than 2℃ below normal in southeastern Siberia, western Canada and Alaska, with temperatures 6-10℃ below normal in Alaska.

For the month, monthly precipitations were observed 50-100% above normal in southwestern East Europe, most of central Asia, northern India, central and southern Siberia, Northeast China and North China, most of the Far East, northern and mid-southern USA, western Canada, northwestern Australia, parts of northern South America and central Argentina, with precipitations over 200% more than normal in locations. Meanwhile, precipitations were over 50% less than normal in northern Europe, western and eastern Siberia, most of Mongolia, southwestern and most of northwestern China, mid-southern India, western Indochina, southeastern and western USA, most of Alaska, northern Mexico, eastern Brazil, northern Argentina, western Australia, western West Africa, most of Egypt and South Africa, with no precipitation in parts of above regions.

General Circulation Features

Northern Hemisphere: During March, the mean 500hPa geopotential height field exhibited a 4-wave pattern at the mid-high latitudes, with the polar vortex being mainly over the western hemisphere in the mean 500hPa geopotential height field. In the 500hPa height anomaly field, positive anomalies above 4 dam covered regions from mid-southern North America to the eastern Pacific, the northeastern North Atlantic Ocean, northern and eastern Europe, the Far East and the oceans south to it, with central values above 16 dam over the Bering Sea. Meanwhile, negative anomalies below -4 dam covered Alaska and the Arctic Ocean close to it, with central values below -12 dam. Heights were near normal in other regions. For the month, the Northwest Pacific subtropical high was larger and extended farther west than normal.

Southern Hemisphere: For the month, zonal circulation prevailed at the mid-high latitudes. In the 500hPa height anomaly field, positive anomalies above 4 dam covered southeastern South Pacific and most of the polar regions, with central value above 8 dam. Meanwhile, negative anomalies covered most regions between 50-60ºS latitude. Heights were near normal in other regions.

Tropical Features

Sea Surface Temperatures (SSTs): During March 2007, SST anomalies in the central and eastern equatorial Pacific decreased obviously. Positive SST anomalies above 0.5℃ shrunk westward and maintained in the equatorial Pacific west to the Date Line, while negative SST anomalies below -0.5℃ appeared in most of eastern equatorial Pacific, with central values below -2.0℃ in the offshore of South America. NINO Z, NINO 3.4, NINO 3, NINO 4 and NINO 1+2 SST anomaly indices were 0℃, -0.1℃, -0.2℃, 0.5℃ and -0.6℃, with drops of 0.3℃, 0.2℃, 0.3℃, 0.1℃ and 0.8℃ from last month, respectively. Meanwhile, SSTs were near normal in most of the equatorial Indian Ocean.

Subsurface Temperatures: During March 2007, the anomalously cold subsurface waters in the eastern equatorial Pacific lifted, and enhanced obviously near the offshore of South America compared with last month. Meanwhile, the anomalously warm waters in the central equatorial Pacific Ocean weakened and shifted westward.

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

Wind Field：During March 2007, at the lower troposphere (850hPa), easterly anomalies covered most of the central and western equatorial Pacific, and zonal winds were near normal over the equatorial Indian Ocean. At the upper troposphere (200hPa), weak easterly anomalies were over the equatorial Pacific around the Date line, while weak westerly anomalies covered parts of the eastern equatorial Pacific.

Southern Oscillation: For the month, Southern Oscillation Index (SOI) was 0.1, with a increase of 0.2 from last month.

Convection over the Tropics: During March 2007, the anomalous outgoing longwave radiation (OLR) showed that convections enhanced over the equatorial Pacific between 140-160ºE 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 the equator near 110ºW, and a divergent center was located in 170ºW, 10ºN. Correspondingly, at the upper troposphere (200hPa), the divergent center was found over the equator near 120ºW, and the convergent center was over 160ºW, 10ºN.

ENSO Monitoring and Prediction

① In March 2007, negative SST anomalies below -0.5℃ occurred in most of the equatorial eastern Pacific, while positive SST anomalies above 0.5℃ shifted westward and maintained in the equatorial Pacific west to the Date Line. Nino Z index was 0℃.

② The anomalously cold subsurface waters in the eastern equatorial Pacific lifted, and enhanced obviously near the offshore of South America compared, while the anomalously warm waters in the central equatorial Pacific weakened and shifted westward in the month.

③ Southern Oscillation Index (SOI) was 0.1.

④ Easterly anomalies were observed over most of central and western equatorial Pacific at the lower troposphere (850hPa).

⑤ Convections enhanced over the western tropical Pacific.

⑥ Most of models predicted that SST anomaly in the eastern Pacific will decrease during the following 1-3 months.

In conclusion, the anomalously SST in the central and eastern equatorial Pacific showed a pattern of “ warm in west and cold in east”, and the cold conditions in the eastern Pacific are expected to strengthen in the following 1-3 months.