Monthly Highlights

1. Climate in China

During August 2013, the mean precipitation of China was 101.0 mm, which was 4.1% less than normal (105.3mm). Percentages of precipitation anomalies were 30-80% less than normal in most Northwest China, western Inner Mongolia, southwestern North China, the eastern Huang-Huai, most of the Jiang-Huai, the central Jiangnan, most Chongqing, most Sichuan and mid-northern Xizang, with over 80% less than normal in parts of Xinjiang and Qinghai. Meanwhile, Precipitation anomalies were 30-100% more than normal in central and northern Northeast China, northeastern Inner Mongolia, northwestern Qinghai, western and northeastern Xinjiang, western Xizang, southwestern and northeastern Yunnan and most South China, with 100% more than normal in parts of the above regions. Precipitations for the rest of the regions in China were near normal.

For the month, the surface air temperature averaged over China was 22.0°C, which was 1.2℃ above normal (20.8℃), ranking the 1^st highest since 1961 same as 2006. Monthly mean surface air temperatures were near or above normal in most China. Air temperature anomalies were 2-4℃ above normal in most regions from southern North China to the northern Jiangnan, most Qinghai, and central Shaanxi. Meanwhile, negative anomalies were 1-2℃ in locations of eastern Inner Mongolia.

In August 2013, extreme events of High Temperature (HT), Consecutive HT Day (CHTD), Daily Precipitation (DP), Consecutive Precipitation (CP) and Consecutive Precipitation Day (CPD) were observed in China. Daily maximum temperatures of 452 stations in the area from the southern Huanghuai to the Jiangnan, eastern Southwest China, etc., reached the threshold of extreme HT event, with 176 stations reaching or exceeding records, such as Xinchang (44.1℃) and Fenghua (43.5℃) in Zhejiang, Cili (43.2℃) in Hunan, Jingxian (42.7℃) in Anhui, Tanghe (42.7℃) in Henan and Yangxin (42.2℃) in Hubei. Extreme CHTD events were observed in 422 stations in 18 provinces (cities, municipality), such as Jiangsu, Zhejiang, Anhui, Henan, Hunan, Hubei, and etc., with 141 stations reaching or exceeding records, such as Changsha (48 days) , Hengshan (48 days) and Anren (45 days) in Hunan. Meanwhile, extreme DP events occurred in 52 stations of Inner Mongolia, Liaoning, Jilin, Guangdong, Guangxi, and etc., with the daily precipitation of 14 stations breaking historical records, including Chaoyang (475.1 mm) and Jiexi (336.0 mm) in Guangdong, Heishan (236.0 mm) in Liaoning, and etc. Extreme CP events occurred in 47 stations of Heilongjiang, Jilin, Guangdong, Guangxi, and etc., with 7 stations reaching or exceeding historical records, such as Ruyuan (670.7 mm) in Guangdong, Jinxiu (625.2 mm) in Guangxi, Heishan (236.4mm) in Liaoning, and etc. Additionally, extreme CPD events occurred in 34 stations of Hebei, Heilongjiang, Inner Mongolia, and etc., with 5 stations setting new records in Wudalianchi (17 days) and Qingan (15 days) in Heilongjiang, Shangyi (10 days) and Wanquan (10 days) in Hebei, Eerguna (10 days) in Inner Mongolia.

2. Climate in the World

During August 2013, monthly mean air temperatures were 1-2℃ above normal in central and northeastern Europe, mid-western North Asia, mid-eastern East Asia, most Australia, the western North America, with temperatures 2-4℃ above normal in locations of northern Europe and northwestern North America. Meanwhile, monthly mean air temperatures were 1-2℃ below normal in western Central Asia, mid-northern and southern Africa, northeastern North America and central South America, with negative anomalies below -4℃ in locations of southeastern South America.

For the month, precipitations were at least 50% more than normal in northeastern Russian, eastern West Asia, most Central Asia, northwestern South Asia, northern East Asia, central and southeastern Africa, parts of northeastern North America, and northern South America, with precipitations at least 200% above normal in locations. Meanwhile, precipitations were 50%～80% less than normal in parts of northern and western Europe, mid-northern Russia, western West Asia, northern Africa, mid-northern South Africa, most Australia, parts of central North America, mid-southern South America, with no precipitation in locations.

3. General Circulation Features

Northern Hemisphere: During August 2013, a four-wave pattern was observed in mid-high latitudes of the field of mean 500 hPa geopotential height. In the field of height anomaly, negative anomalies below -40 gpm covered areas from the northern North Atlantic Ocean to the Arctic region, the northwestern and northeastern North Pacific. Meanwhile, the positive anomalies covered northeastern Europe and parts of north Russia, parts of northwestern Canada and locations of the North Atlantic Ocean. The heights were found near normal in the rest areas. For the month, the ridge of the western North Pacific subtropical high extended further northward and westward than average, with its area smaller than normal and its intensity weaker than normal.

Southern Hemisphere: For the month, a three-wave pattern was observed in mid-high latitudes of the field of mean 500 hPa geopotential height. In the field of height anomaly, positive anomalies above 40 gpm covered areas from the Antarctic to near datelines of the southern South Pacific and locations of the southeastern South Pacific, with central values above 160 gpm over locations of the southeastern South Pacific. Meanwhile, negative anomalies below 40 gpm covered seas south of Australia, oceans from the southern South Atlantic Ocean to the southeastern South Pacific.

4. Tropical Features

  Sea Surface Temperatures (SSTs): During August 2013, weak negative SST anomalies (SSTA) dominated over most of the eastern and central equatorial Pacific, with central value below -1.5℃. Niño 1+2, Niño 3, Niño 4, Niño 3.4 and Niño Z indices were -0.9℃、-0.5℃、0.0℃、-0.3℃ and -0.3℃,with rises of 0.4℃、0.1℃、0.1℃and 0.2℃ for Niño 1+2、Niño3、Niño4 and Niño Z index, and no change for Niño 3.4 from last month.

Subsurface Temperatures: During August 2013, positive subsurface sea temperature persisted anomalies remained across most of the western and central equatorial Pacific Ocean, while negative anomalies were in the eastern equatorial Pacific.

Warm Pools: During August 2013, the area of the Indian Ocean warm pool was smaller than normal and its intensity was below normal. The area and intensity of the western Pacific warm pool were both above normal.

Wind Field: During August 2013, at lower troposphere (850hPa), the westerly anomalies covered the most equatorial central-eastern Pacific, and easterly anomalies appeared in the western equatorial Pacific. At upper troposphere (200hPa), westerly anomalies covered over the most equatorial western and eastern Pacific, and easterly anomalies appeared in the central region.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 0.0, with a drop of 0.7 from last month.

Convections over the Tropics: During August 2013, the anomalous outgoing long wave radiation (OLR) showed that convection enhanced in the maritime continent, while convections were suppressed in the western equatorial Pacific. At lower troposphere (850hPa) divergent wind field, a convergent center was around 120ºE, 15ºN, and a divergent center was over 70ºW, 30ºS. At upper troposphere (200hPa), a divergent center was near 120ºE, 15ºN, and a convergent center was around 80ºW, 25ºS.

5. ENSO Monitoring and Outlook

At present, sea surface temperatures are below normal across the eastern equatorial Pacific. Positive anomalies of subsurface temperatures persisted across the most of the western and central equatorial Pacific while negative anomalies were in the eastern equatorial Pacific. Based on models prediction and diagnoses of the oceanic variations, the ENSO-neutral conditions are expected to persist through the coming autumn. 

Therefore, we will closely monitor the development of ENSO conditions and update our ENSO wrap-up in time.