Monthly Highlights
1. Climate in China
During July 2013, the mean precipitation of China was 138.9 mm, which was 15.2% more than normal(120.6mm), ranking the 4th most since 1951 and being less than those in 1996(148.0 mm), 1998 (146.8mm) and 2012(139.7mm). Percentages of precipitation anomalies were above normal in most regions north of the Huaihe River and below normal in most regions to the south. Precipitation anomalies were 30-200% above normal in eastern Northwest China, most Northeast China, most North China, northern of Huanghuai, northwestern and southwestern Xinjiang, northwestern Gansu, northeastern Inner Mongolia, northern Sichuan and Hainan, with 200% above normal in central Shannxi. Meanwhile, precipitations were 30-80% below normal in southwestern Huanghuai, southeastern Jianghuai, most Jianghan, Jiangnan, northwestern South China and eastern Southwest China, with 80% below normal in central eastern Guizhou, central South China and central western Zhejiang.
For the month, the surface air temperature averaged over China was 22.4°C, which was 0.5℃warmer than normal (21.9℃). It was observed much warmer than normal in the southern part of China. Monthly mean surface air temperatures were 1-2℃ above normal in southern Huanghuai, Jianghuai, Jianghan, most Jiangnan, western and northeastern Southwest China and southern Qinghai, with temperatures at least 2℃ above normal in parts of these regions. Meanwhile, temperatures 1-2℃ below normal were observed in locations of Xinjiang, Shannxi, Guangdong and Hainan.
In July, 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 100 stations in 16 provinces (cities, municipality), such as Jiangsu, Shanghai, Zhejiang, Hunan, Hubei, Chongqing, Xinjiang, and etc., reached the threshold of extreme HT event, with 39 stations reaching or exceeding records, such as Zhejiang’s Fenghua (42.7℃) and Xiaoshan (42.2℃), Hunan’s Cili (42.2℃), Chongqing’s Shizhu (42.0℃), and Xinjiang’s Cele (42.0℃). Extreme CHTD events were observed in 108 stations in 14 provinces (cities, municipality), such as Jiangsu, Shanghai, Zhejiang, Hunan, Hubei, and etc., with 24 stations reaching or exceeding records, such as Hunan’s Hengshan (33 days), Changsha (32 days), Anren (32 days), and etc. Meanwhile, extreme DP events occurred in 109 stations of 23 provinces (cities, municipality) like Shanxi, Shaanxi, Hebei, Gansu, Sichuan, and etc., with the daily precipitation of 30 stations breaking historical records, including Sichuan’s Dujiangyan (416.0 mm), Wangcang (363.7 mm), Jiangxi’s Ji’an county (248.0 mm), Hebei’s Ningjin (213.1 mm), Gansu’s Lingtai (198.8 mm), and Shandong’s Laizhou (188.6 mm), and etc. Extreme CP events occurred in 173 stations of 20 provinces (cities, municipality), such as Shandong, Hebei, Shanxi, Shaanxi, Sichuan, and etc., with 44 stations reaching or exceeding historical records, such as Sichuan’s Dujiangyan (754.5 mm), Wangcang (524.5 mm), Shaanxi’s Yanchuan (400.6 mm), Yan’an (320.3mm), Shandong’s Laizhou (393.2 mm), Guangrao (318.7 mm), and etc. Additionally, extreme CPD events occurred in 113 stations of 16 provinces (municipality), such as Shandong, Hebei, Shanxi, Shaanxi, Sichuan, Jilin, and etc., with 8 stations setting new records in Xizang’s Dangxiong (25 days), Inner Mongolia’s Guchayouhouqi (11 days), Xinjiang’s Emin (9 days), Hebei’s Wuqiang (8 days), Jing county (8 days), Guantao (8 days), Qiu county (8 days), and Henan’s Taiqian (8 days).
2. Climate in the World
During July 2013, monthly mean air temperatures were 1-4℃ above normal in western Europe, northwestern Russia, southeastern East Asia, central West Asia, locations of West Africa and South Africa, eastern Australia, parts of western and eastern North America (NA) and locations of northwestern NA, and locations of eastern and southern South America (SA), with temperatures 4-6℃ above normal in parts of northern Russia. Meanwhile, monthly mean air temperatures were 1-2℃ below normal in locations of southeastern Europe, northeastern Central Asia, parts of central Russia, locations of northeastern and southern Africa, locations of northern NA, and locations of central SA, with 2-4℃ below normal in locations.
For the month, precipitation was at least 50% more than normal in regions from southeastern Europe to northern Central Asia and from northern East Asia to most Russian Far East, southwestern and parts of central East Asia, most of Southeast Asia, locations of western and central Africa, and central-southern Australia, southern and parts of northern NA, and northern and locations of southern SA, with precipitation at least 200% above normal in locations. Meanwhile, precipitation was at least 50% less than normal in the locations of northwestern Europe, parts of northern Russia, most of West Asia, parts of northern and central-southern Africa, northern Australia, parts of northwestern NA and locations of northeastern NA, and western SA, with precipitation at least 80% less than normal in locations.
3. General Circulation Features
Northern Hemisphere: During July 2013, a four-wave pattern over mid-high latitudes was observed on the field of mean 500 hPa geopotential height. In the field of height anomaly, positive anomalies above 40 gpm covered the northwestern Europe, northwestern Siberia, the northern North Pacific Ocean and regions from northeastern North America to the northwestern North Atlantic Ocean, with central values above 80 gpm in parts of northwestern Europe, northwestern Siberia and the northern North Pacific Ocean. Meanwhile, negative anomalies below -40 gpm covered locations of the northern North Pacific Ocean and northern Eurasia. For the month, the extent of the western North Pacific subtropical high was small than normal, with its intensity below normal and the high ridge extending more northward.
Southern Hemisphere: For the month, zonal circulation dominated over mid-high latitudes in the mean 500hPa geopotential height field. In the field of height anomaly, positive anomalies above 40 gpm covered the southwestern and southeastern South Pacific Ocean, locations of the southern South India Ocean and the southern South Atlantic Ocean, with central values above 120 gpm over locations of the southeastern South Pacific Ocean. Meanwhile, negative anomalies below -40 gpm covered the regions from the southern South Pacific basin to the West Antarctica, with central values below -120 gpm over locations of these regions.
4. Tropical Features
Sea Surface Temperatures (SSTs): During July 2013, weak negative SST anomalies (SSTA) dominated over most equatorial eastern and central Pacific, with the central value below -2.0℃. Niño 1+2, Niño 3, Niño 4, Niño 3.4 and Niño Z indices were -1.3℃, -0.6℃, -0.1℃, -0.3℃ and -0.5℃,with rises of 0.2℃ and 0.1℃ for Niño 1+2 and Niño 3 indices, no change for Niño 4 and Niño Z indices, and a drop of 0.1℃ for Niño 3.4 index from last month.
Subsurface Temperatures: During July 2013, anomalously warm subsurface water in the equatorial western Pacific extended eastward further. Meanwhile, anomalously cold subsurface water in the equatorial eastern-central Pacific still maintained.
Warm Pools: During July 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 July 2013, at lower troposphere (850hPa), the weak westerly anomalies covered most equatorial Pacific. At upper troposphere (200hPa), westerly anomalies covered most equatorial Pacific, with center value exceeding 8m/s.
Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 1.2, with a rise of 0.5 from last month.
Convections over the Tropics: During July 2013, the anomalous outgoing long wave radiation (OLR) showed that convection enhanced in the maritime continent and the northern Indian Ocean, while convections were suppressed in the central-eastern equatorial Pacific. At lower troposphere (850hPa) divergent wind field, a convergent center was around 90ºE, 15ºN, and a divergent center was over 85ºW, 25ºS. At upper troposphere (200hPa), a divergent center was near 100ºE, 10ºN, and a convergent center was around 0ºW, 15ºS.
5. ENSO Monitoring and Outlook
At present, the trade wind is strengthened. The MJO is not active and the convection is weak across much of the equatorial Pacific. The thermocline depth in the western Pacific is lift and deepens in the east. 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.