Highlights

    General Circulation Features

    Northern Hemisphere

During August, the mean 500hPa geopotential height fields exhibited a 4-wave pattern in the mid-high latitudes. Ridges covered Western Europe, Canada and the region north to Balkhash Lake, which positive anomalies were above 4 and 8 dam, respectively. Meanwhile, troughs dominated Eastern Europe and northeastern Asia, with the center values below ? dam. The rest areas of Northern Hemisphere were near normal. The Northwest Pacific subtropical high was obviously stronger than normal and extended westward remarkably.

    Southern Hemisphere

During the month, the mean 500hPa geopotential height fields exhibited a 3-wave pattern in the mid-high latitudes. Positive anomalies were above 16 dam over the Polar region and above 8 dam over the southwestern Pacific and the central-southern Indian Ocean. Meanwhile, three troughs were over the southeastern Pacific, the southeastern Atlantic and the southeastern Indian Ocean, with the center values below ? dam.

Climate for China

In August, monthly mean surface air temperatures were near or above normal in most of China, with 1~2C above normal in the Tibetan Plateau and most of region south to the Yangtze River. Temperatures were 1~2℃ below normal in western region between the Yellow River and the Huaihe River, eastern Northwest China and northern Northeast China. At the first ten-day period of this month, the heat wave persisted in most of the area south to the Yangtze River.

As to precipitation, rainfall totals with 50~80% less than normal were in central-northern Hunan and Guizhou, northern Hebei, eastern Jilin, northwestern Qinghai and southeastern Xinjiang. Meanwhile, rainfall totals of 50~150% more than normal were observed in most of regions between the Yellow River and the Huaihe River, eastern Northwest China, northern Southwest China, central-northern Heilongjiang and northeastern Xinjiang. At the last ten-day period of this month, serious floods occurred in the region between the Yellow River and the Huaihe River.

 

Tropical Features

    Sea Surface Temperatures (SSTs)

During August, SSTs were near normal over the central and eastern equatorial Pacific. Negative SST anomalies weakened continuously in the offshore of South America. Positive SST anomalies above 0.5℃ remained the eastern part of equatorial western Pacific. Correspondingly, the SST indices of NINO 4， NINO 3 and NINO 1+2 were 0.6℃，0.1℃ and ?.6℃, respectively. In addition, positive SST anomalies about 0.5C were observed in most of the equatorial Indian Ocean.

    Circulation

    Wind Field

In this month, at the lower troposphere (850hPa), weak westerly anomalies of 2 m/s covered most of the equatorial Pacific and the equatorial Indian Ocean. At the upper troposphere (200hPa), easterly anomalies about 4 m/s controlled the equatorial Pacific east to 150E. Meanwhile, westerly anomalies of 4～6 m/s were over the equatorial Pacific west to 150E.

    Southern Oscillation

The Southern Oscillation Index (SOI) was ?.5.

 

    Convection over the Tropics

During August, the anomalous outgoing longwave radiation (OLR) distribution displayed that the enhanced convections were found over the central-northern tropical Pacific and the Philippines. In the lower troposphere (850hPa) divergent wind field over the tropical Pacific, there were a convergent center near the Philippines and a weak divergent center around 110W, 10S. At the upper troposphere (200hPa), two divergent centers were around the Philippines and 90W, 10N, respectively. The convergent center was around 120W, 15S.