Monthly Highlights
1. Climate in China
During May 2013, the surface air temperature averaged over China was 16.9°C, which was warmer than normal (16.2℃) by 0.7℃. Monthly mean surface air temperatures were 1-2℃ above normal in Northeast China, Inner Mongolia, western North China, eastern Northwest China, Jianghuai and Jianghan, with 2-4℃ above normal in central and eastern inner Mongolia and northern Northeast China. Meanwhile, negative anomalies were around 0-1℃ in western and northern Xinjiang, with 1°C below normal in locations .
For the month, the mean precipitation of China was 85.5 mm, which was 23.0% less than normal (69.5mm). Percentages of precipitation anomalies were near or above normal in most China. Precipitation anomalies were 50-100% above normal in eastern Inner Mongolia, northern Northeast China, southern Northwestern China to Huanghuai, northeastern Southwest China and southeastern South China, with 100% above normal in locations. Meanwhile, precipitations were 50-80% below normal in northern Northwest China, central and western Inner Mongolia， southern Northeast China，northern North China and southwestern Tibet with 80% below normal in locations.
In May, extreme events of high temperatures (HT) and daily precipitation (DP) were observed in China. Daily maximum temperatures reached threshold of HT extreme events in 12 stations in Yunnan, Sichuan, Qinghai and Guangxi. Meanwhile, DP extreme events occurred in 19 stations, which were located in Hunan, Hubei, Fujian, Guangdong, Guangxi, Gansu, Guizhou and Xinjiang provinces, with DP setting new record in 3 station as Yongding of Fujian (170 mm), Danzhai of Guizhou (181.8 mm) and Yecheng of Xinjiang(49 mm). 601 Stations DPs were observed above 50 mm.
2. Climate in the World
During May 2013, temperatures were 2-4℃ above normal in northern North Europe, southern East Europe, northern and eastern Siberia, northeastern China, partly northern North America, partly North Africa and mid-southern Australia, with temperatures at least 4℃ above normal in part. Meanwhile, temperatures were 2-3℃ below normal in southern West Siberia，Southwest Europe and Alaska, with temperatures at least 3℃ below normal in locations.
For the month, precipitations were observed 50-100% more than normal in central Europe and its partly east, southern and eastern Siberia, eastern Central Asia and northeastern South Asia, northeastern America and Alaska, northern South and partly central America, western Australia. Meanwhile, precipitations were observed 50% less than normal in parts of northern West Siberia, parts of north China, northwestern South Asia, northwestern and southwestern North America, parts of West Africa, North Africa and East Africa, and central Australia, with no precipitation in parts of above regions.
3. General Circulation Features
Northern Hemisphere: During May 2013, a four-wave pattern over mid-high latitudes was observed on the field of mean 500hPa geopotential height. In the field of height anomaly, positive anomalies above 4 dam covered over regions from Central Siberia to northeastern East Asia and northern North Pacific, northern North Atlantic Ocean and regions from Barents Sea to East Europe plain, with central values above 8 dam. Meanwhile, negative anomalies below -4 dam were observed over West Siberia, some parts of Northwest Pacific, some parts of central North Atlantic Ocean and the region from western Arctic Ocean to Western Europe, with central values below -8 dam over some parts of above regions. For the month, the extent and intensity of western North Pacific subtropical high were near normal, with the west ridge point was eastward than normal.
Southern Hemisphere: For the month, the zonal circulation features the field of mean 500hPa geopotential height. In the field of height anomaly, positive anomalies above 4 dam covered regions over southern South Atlantic Ocean, southeastern and mid-southern South Pacific, West Antarctica and eastern South Indian Basin, with central values above 8 dam over the southern South Atlantic Ocean. Meanwhile, negative anomalies below -4 dam covered over the region from Drake Passage to southern South Pacific and the region from East Antarctica to southern South Indian Ocean, with central values below -16 dam over southern South Pacific.
4. Tropical Features
Sea Surface Temperatures (SSTs): During May 2013, weak negative SST anomalies (SSTA) dominated over most equatorial eastern and central Pacific, with the central value below -1.0℃. Niño 1+2, Niño 3, Niño 4, Niño 3.4 and Niño Z indices were -1.5,-0.7,-0.1,-0.3 and -0.5℃ respectively, with evident drop for all indices from last month. During May, SSTs in the most equatorial India Ocean were near or slightly below normal.
Subsurface Temperatures: During May 2013, anomalously warm subsurface water in the equatorial western Pacific intensified and moved eastward slightly, with the central value above 3℃. Meanwhile, anomalously cold subsurface water in the equatorial eastern Pacific also enhanced slightly from last month.
Warm Pools: During May 2013, the area of the Indian Ocean warm pool was smaller than normal and the intensity was below normal slightly. The area and intensity of the western Pacific warm pool were both above normal.
Wind Field: During May 2013, at lower troposphere (850hPa), the weak westerly anomalies covered most equatorial eastern and central Pacific, indicating decreased equatorial easterly winds, while easterly anomalies dominated the equatorial western Pacific. At upper troposphere (200hPa), westerly anomalies controlled most of the equatorial Pacific.
Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 0.7, with a rise of 0.4 from last month.
Convections over the Tropics: During May 2013, the anomalous outgoing long wave radiation (OLR) showed that convections enhanced in the equatorial western Pacific north to Indonesia, while convections were suppressed in the equatorial Pacific around date line. At lower troposphere (850hPa) divergent wind field, a convergent center was around 120ºE, 10ºN, and a divergent center was over 100ºW, 15ºS. At upper troposphere (200hPa), the corresponding divergent center was near 120ºE,5ºN, and a convergent center was around 100ºW,25ºS.
5. ENSO Monitoring and Outlook
At present, sea surface temperatures are near average across much of the equatorial Pacific, except for below average SSTs in the eastern Pacific Ocean. During the recent period, the below average subsurface temperatures remain in the eastern Pacific Ocean. Based on models prediction and diagnoses of the oceanic variations, the ENSO-neutral conditions are expected to persist through the coming summer.
Therefore, we will closely monitor the development of ENSO conditions and update our ENSO wrap-up in time.