Monthly Highlights

1. Climate in China

In May 2012, the monthly mean surface air temperature for the whole China was 16.9℃, with 0.9℃ above normal (16.0℃) being the 3^nd highest since 1951. The temperatures were near or above normal in most China, with temperatures 1~2℃ above normal in northern Xinjiang, most Gansu, most Inner Mongolia, most Northeast China, North China, Huanghuai, Jianghuai, most South China, eastern Southwest China and 2～4℃ above normal in central and southeastern North China, northern Huanghuai, parts of eastern Southwest China. Meanwhile, monthly mean surface air temperatures were near and below normal in western Xinjiang and Tibet, northwestern Jiangnan with temperatures at least 1℃ below normal in locations.

For the month, average precipitation over China was 68.4 mm, with 2% more than normal (67.0 mm). Precipitations were 30%-100% more than normal in most central and eastern Northwest China, locations of western Xinjiang, central and eastern Inner Mongolia, most Jiangnan, northeastern Southwest China, and western and southern South China, with precipitation at least 100% above normal in locations. Meanwhile, precipitations were observed 30%-80% less than normal in most Xinjiang, western Inner Mongolia, most Southwest China, parts of Northeast China, North China and Huanghuai, with precipitations at least 80% less than normal in southern North China, Huanghuai, western Southwest China and parts of Xinjiang.

In May 2012, extremes of High Temperature (HT), Consecutive High Temperature Days (CHTD) and Daily Precipitation (DP) were observed in China. Daily maximum temperatures of 93 stations in Sichuan, Yunnan, Guizhou and Guangxi reached the threshold of HT extreme, with 25 stations setting new records, and extreme of CHTD occurred in 10 stations. Meanwhile, DP extreme occurred in 7 stations, which located in Gansu, Hunan, Fujian, Guangxi, Guizhou and Yunnan.

2. World Climate

During May 2012, monthly mean temperatures were 1-4℃ above normal in most Europe, parts of northern Africa, most North America, mid-south South America and locations of western Australia, with temperatures 4-6℃ above normal in locations of the Russia’s Far East, parts of southeastern Europe and West Asia. Monthly mean surface air temperatures were observed 1-2℃ below normal in locations of Russia west to the Baykal, part of mid-east Africa, parts of northwestern North America, parts of mid-north South America and mid-north Australia, with temperatures 2-4℃ below normal in locations of northern South America and parts of mid-north Australia.

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

3. General Circulation Features

Northern Hemisphere: During May 2012, the field of mean 500hPa geopotential height exhibited a four-wave pattern over mid-high latitudes. In the field of height anomaly, positive anomalies above 4 dam covered regions from eastern Europe to Central Asia, regions from Northeast China to southeastern Russia and the Sea of Okhotsk, the eastern coast of North America as well as the northwestern North Atlantic Ocean, with central values above 12 dam over the Sea of Okhotsk. Meanwhile, negative anomalies below -4 dam covered the southeastern North Atlantic Ocean, Alaska, and parts of the Arctic polar region. During the month, the northwestern Pacific subtropical high was weaker than normal, with a smaller area and a little more northward high ridge, and the west end of its ridge shifted more eastward than normal.

Southern Hemisphere: For the month, zonal circulation mainly dominated over mid-high latitudes in the mean 500hPa geopotential height. In the field of height anomaly, positive anomalies above 4 dam covered the regions from the Polar region to the southwestern South Atlantic Ocean, southeastern South Indian Ocean, and the regions around the date line in the high latitudes over South Pacific, with central values above 8 dam over the Polar region. Meanwhile, negative anomalies below -4 dam covered the ocean south to Africa, the southeastern South Pacific, and the regions around the date line in the middle latitudes over South Pacific, with central values below -8 dam over the ocean south to Africa and the southeastern South Pacific.

4. Tropical Features

Sea Surface Temperatures (SSTs): During May 2012, SSTs were near normal in most of   the equatorial Pacific, while SST anomalies were above 0.5℃ over east of the eastern equatorial Pacific with central value about 2.0℃. NINO 1+2, NINO 3, NINO 4, NINO 3.4 and NINO Z indices were 1.1℃, 0.2℃, -0.3℃, -0.1℃ and 0.1℃. All the indices increase slightly from last month with exception Nino1+2 decreasing.

Subsurface Temperatures: During May 2012, negative anomalies of subsurface temperatures in the central equatorial Pacific weakened and shrank. Positive anomalies of subsurface temperatures in the eastern equatorial Pacific extended eastward and those in the western equatorial Pacific persisted.

Warm Pools: During May 2012, the area and intensity of warm pool in the Indian Ocean and the western Pacific were both slightly above normal.

Wind Field: During May 2012, at lower troposphere (850hPa), weak easterly anomalies were    over the western equatorial Pacific and zonal winds were near normal in the central equatorial Pacific and westerly anomalies were over the eastern equatorial Pacific. At upper troposphere (200hPa), westerly anomalies above 4m/s covered  most of the central and eastern equatorial Pacific.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was -0.3, with a sharp decrease of 0.2 from last month.

Convections over the Tropics: During May 2012, the anomalous outgoing longwave radiation (OLR) showed that enhanced convection was observed over the Pacific from Philippines to north of Australia, while convections were near normal over the central and eastern equatorial Pacific.

At lower troposphere (850hPa) divergent wind field, a convergent center was around 135ºE, 2.5ºS, and a divergent center was near 115ºW, 10ºN. At upper troposphere (200hPa), the corresponding divergent center was near 140ºE, 5ºS, and the convergent center was around 95ºW, 20ºS.

5. ENSO monitoring and outlook

At present, sea surface temperatures are near normal across much of the equatorial Pacific, except for above average SSTs in the eastern Pacific. During the recent period, the subsurface temperature anomalies remain nearly unchanged. Based on models’ prediction and trend 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.