Monthly Highlights

Climate in China

During August 2007, monthly mean surface air temperatures for China was observed the second highest for August in record. Temperatures were 1-2℃ above normal in central and northern Northeast, northern North China, most Northwest, western and northeastern Southwest, Inner Mongolia, most Jiangsu, eastern Anhui and northern Zhejiang, with 2-4℃ above normal in northwest Heilongjiang, central and northeastern Inner Mongolia, southeastern and northwestern Qinghai. Temperatures were observed near normal in the remainder of China. For the month, precipitations were observed 30-100% above normal in eastern South China, most Jiangnan, most of the regions between Huanghe River and Huaihe River, southeastern Northeast, northern Xinjiang, northeastern and southwestern Qinghai, central Tibet, southwestern Shaanxi and northwestern Shanxi, with more than 100% above normal in parts of Jiangxi, Tibet, Shandong and Xinjiang. Meanwhile, precipitations were near or below normal in the rest areas, with 30-50% below normal in eastern North China, northeastern Jiangnan, most Inner Mongolia, western Heilongjiang, southern Xinjiang, eastern Sichuan, most Chongqing, with more than 50% below normal in locations of above regions.

Climate in the World

During August 2007, monthly mean surface temperatures were observed above normal in most of the Northern Hemisphere. Temperatures were 1-2℃ above normal in central-eastern Europe, northeastern Asia, northeastern Africa, most America, eastern South America and southern Australia, with more than 4℃ above normal in parts of above areas. Meanwhile, temperatures were about 1-2℃ below normal in most Canada, northeastern West Siberian Plain, central and southern South America and western Africa.

For the month, precipitations were observed 50-100% more than normal in northern Siberia, southeastern China, southwestern South Asia, western Africa, central America, most Central America, northeastern South America and parts of eastern Australia, with above 200% more than normal in locations. Meanwhile, precipitations were above 50% less than normal in eastern Europe, northwestern China, most Central Asia, southern and parts of northern Africa, western and southeastern America, central and southern South America and central and western Australia, with no precipitation in parts of above regions.

General Circulation Features

Northern Hemisphere: During August 2007, the mean 500hPa geopotential height field exhibited a 4-wave pattern at the mid-high latitudes, with the troughs over eastern North America, western Europe, West Siberian Plain and northeastern Asia. In the 500hPa height anomaly field, positive anomalies above 4 dam covered regions from the northern North Atlantic Ocean northward to the Greenland and from polar region to Bering Strait, with center above 16 dam over polar region. Meanwhile, negative anomalies below -4 dam covered regions from Central Siberian Plateau northward to the eastern-hemisphere part of polar region and northern North America. For the month, the Northwest Pacific subtropical high was larger and stronger than normal, and extended slightly westward and its ridge line position was more northward than normal.

Southern Hemisphere: For the month, meridional circulation prevailed at most of the mid-high latitudes. In the 500hPa height anomaly field, positive anomalies above 4 dam covered Antarctica and the seas nearby, the areas from the South Pacific Ocean westward through southern Australia to the southeastern Indian Ocean, with center above 16 dam over West Antarctica. Meanwhile, negative anomalies below -4 dam covered the eastern South Atlantic Ocean, the South Indian Ocean and the western South Pacific Ocean and southmost South America along 50°S, with center value below -12 dam over the western South Indian Ocean.

Tropical Features

Sea Surface Temperatures (SSTs): During August 2007, SSTs maintained the pattern “the cold in the east and the warm in the west” in the equatorial Pacific. The negative SST anomalies enhanced and expanded to dateline with minimum below -2.0℃. Positive SST anomalies above 0.5℃ remained in part of the western equatorial Pacific. NINO Z, NINO 3.4, NINO 4, NINO 3 and NINO 1+2 were -0.6℃, -0.5℃, 0.1℃, -1.1℃ and -1.6℃, with drops of 0.2℃, 0.2℃, 0.1℃, 0.3℃ and 0.1℃ from last month, respectively. Meanwhile, SST anomalies were about 0.5℃ above normal in most of the equatorial Indian Ocean.

Subsurface Temperatures: Comparing with last month, anomalously cold subsurface waters of the eastern equatorial Pacific extended westward to the west of Date Line with below -4℃ in center and the warm subsurface waters maintained in the western equatorial Pacific during August 2007.　

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

Wind Field：For the month, at the lower troposphere (850hPa), easterly anomalies covered the east part of the western equatorial Pacific and weak westerly anomalies controlled the west part, while zonal winds were near normal over rest of the equatorial Pacific. Easterly anomalies were over the eastern equatorial Indian Ocean. At the upper troposphere (200hPa), the zonal winds were near normal over most portions of the western equatorial Pacific, while easterly anomalies covered the east-central equatorial Pacific between 110-140ºW. Zonal winds were near normal in most of the equatorial Indian Ocean.

Southern Oscillation: For the month, Southern Oscillation Index (SOI) was 0.3, with an increase of 0.8 from last month.

Convection over the Tropics: During August 2007, the anomalous outgoing longwave radiation (OLR) showed that convections were suppressed over the region between 140-160ºE in the western equatorial Pacific and stronger than normal in the eastern Indonesia. In the divergent wind field of lower troposphere (850hPa), a divergent center located at about 85ºW, 30ºS. Correspondingly, at the upper troposphere (200hPa), the convergent center was at about 90ºW, 25ºS. Meanwhile a strongly divergent center located at about 120ºE, 17.5ºN.

ENSO Monitoring and Prediction during August 2007

(1) Comparing with last month, negative SST anomalies in the east-central equatorial Pacific enhanced in intensity and enlarged in area, and the index NINO Z dropped to -0.6℃.

(2) Anomalously cold subsurface waters of the equatorial east-central Pacific extended westward nearby the west of Date Line, however the warm subsurface waters maintained in the western equatorial Pacific.

(3) Southern Oscillation Index (SOI) increased to 0.3.

(4) At the lower troposphere (850hPa), easterly anomalies covered the east part of the western equatorial Pacific.

(5) Convections were suppressed over the region between 140-160ºE in the western equatorial Pacific and stronger than normal in the eastern Indonesia.

(6) Most NCC model forecasts indicate below-average SSTs in the Niño 3 region during the remainder of the year and oceanic and atmospheric conditions in the equatorial Pacific are likely to remain in La Nina state for the following 1-3 months.

In a word, the current oceanic and atmospheric states already turned into La Nina conditions in the east-central equatorial Pacific, and such conditions are likely to continue in following months with a weak La Nina event forming probably.