Monthly Highlights

Climate in China

During August 2006，the monthly mean surface air temperature was the highest over China for August since 1951. Monthly mean surface air temperatures were near or above normal in most of China, with temperatures 1-4ºC above normal in Northeast China, Northwest China, mid-eastern Southwest China and the middle and lower reaches of the Yangtze River.

For the month, precipitations were observed 30 - 60% more than average in parts of regions along the Huanghe River and central South China. Meanwhile, precipitations were near or less than average in the rest areas of China, with above 50% less than normal in northern Northeast China, most of Northwest China, the eastern Jiangnan area and mid-eastern Southwest China.

Climate in the world

During August 2006，monthly mean surface air temperatures were observed 1-3 ºC above normal in northern and southeastern Europe, most of East Asia, the northern Arab Peninsula, parts of Central Asia, southwestern Australia and southeastern America, with temperatures above 3-4ºC in locations. Meanwhile, temperatures were below or near normal in the remainder of the world, with temperatures 1-3ºC below normal in parts of Europe, the West Siberia Plain and Alaska. For the month, precipitations were observed more than 30% below average in northern and southeastern Europe, the West Siberia Plain, Central Asia, most of East Asia, central and southeastern India, Australia, western, southeastern and northeastern America and central South America, with no precipitation in parts of them. Meanwhile, precipitations were more than 50 % above average in most of Europe, mid-eastern Siberia, western and northern South Asia, most of Southeast Asia, South Africa, central America and southern Argentina.

General Circulation Features

Northern Hemisphere: During August 2006, the mean 500hPa geopotential height field exhibited mainly a 4-wave pattern at the mid-high latitudes. Abnormal ridges developed over the North Atlantic Ocean and the northwest Pacific Ocean. In the 500hPa height anomaly field, positive anomalies above 4 dam covered areas from northeastern North America through the North Atlantic Ocean to northern Europe, northwestern Pacific, and areas near the Ural Mountains, with maximum above 12 dam. The rest areas were covered by near or below normal heights with anomalies below -16 dam over regions around the North Pole. For the month, the Northwest Pacific subtropical high was larger but slightly weaker than normal. It was located in farther north and extended farther west than normal.

Southern Hemisphere: For the month, the mean 500hPa geopotential height field exhibited a 3-wave pattern at the mid-high latitudes. In the 500hPa height anomaly field, negative height anomalies below -8 dam covered the southeastern South Pacific Ocean and the southeastern South Indian Ocean. Heights were near normal in the rest regions.

Tropical Features

Sea Surface Temperatures (SSTs): During August 2006, SSTa increased apparently in the equatorial mid-eastern Pacific from last month where positive SST anomalies above 0.5ºC were observed with central values above 1ºC. Meanwhile, SSTs were near normal in the equatorial western Pacific. The NINO indices all increased by 0.2-0.4ºC since last month, with values being or above 0.5ºC. Meanwhile, positive SST anomalies above 0.5ºC were also observed in the equatorial mid-eastern Indian Ocean.

Subsurface Temperatures: During August 2006, abnormal subsurface warm water persisted in the equatorial Pacific Ocean, with centers shifting eastward to east of the dateline. It rose in regions around the dateline and the offshore of South America, while the abnormal cold water shrank obviously in the offshore of South America and tended to disappear.

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

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

Southern Oscillation: For the month, Southern Oscillation Index (SOI) was -1.3, with a drop of 0.5 from last month.

Convection over the Tropics: During August 2006, the anomalous outgoing longwave radiation (OLR) showed that convections were suppressed over the western part of the equatorial Western Pacific but enhanced in the eastern part of the equatorial Western Pacific. In the lower troposphere (850hPa) divergent wind field, a convergent center was over 145ºE, 25ºN, and a divergent center located around 110ºW, 15ºS. Correspondingly, at the upper troposphere (200hPa), the divergent center was found over 120ºE, 15ºN, and the convergent center was observed over 95ºW, 25ºS.

ENSO Monitoring and Prediction

① During August 2006, positive SST anomalies above 0.5ºC covered the equatorial Pacific Ocean east of 160ºE. The index of NINO Z was up to 0.6 ºC.

② During August 2006, abnormal subsurface warm water persisted in the equatorial Pacific Ocean, with centers shifting eastward to east of the dateline. It rose in regions around the dateline and the offshore of South America, while the abnormal cold water shrank obviously in the offshore of South America and tended to disappear.

③ Southern Oscillation Index (SOI) was -1.3, with a drop of 0.5 from last month.

④ Westerly anomalies covered the equatorial western Pacific Ocean and parts of the equatorial eastern Pacific Ocean.

⑤ The anomalous outgoing longwave radiation (OLR) showed that convections were suppressed over the western part of the equatorial Western Pacific.

⑥ Most of models predicted that SSTs could be above normal during following six months.

In conclusion, tropical oceanic and atmospheric conditions showed features of ENSO warm phase, and these features are expected to persist or developed in the following 2-3 months. It is most likely that a new El Nino event will come into being.