Monthly Highlights

1. Climate in China

During December 2010, monthly mean surface air temperatures were 1-4℃ below normal in most of Northeast China, eastern Inner Mongolia, parts of northern and eastern Northwest China. Temperatures were near or above normal in the rest regions of China, with temperatures 1-4℃ above normal in western North China, the central and western Huanghuai area, most of the Jianghuai area and the Jianhan area, the northeastern and northwestern Jiangnan area, most of Yunnan, northern and central Shanxi, western Inner Mongolia, western Xinjiang and northestern Tibet.

For the month, precipitations were 50-200% more than normal in Northeast China, most of the Jiangnan area, central and northern South China, southeastern Southwest China, eastern and western Inner Mongolia, northern Xinjiang and most Gansu, with precipitations above 200% in locations of above regions. Meanwhile, precipitations were near or less than normal in the rest of China. Precipitations were at least 80% less than normal in southwestern and northeastern North China, the central and western Huanghuai area, northeastern Shanxi, southern Qinhai, with no precipitation in parts of above regions.

In December, daily minimum temperatures of 22 stations in Jilin, Liaoning, Fujian, Guangdong, Sichuan, Chongqing, Qinghai of China surpassed the 95th percentile thresholds. Daily temperature drop of 152 stations surpassed the 95th percentile thresholds in Northeast China, North China, the Huanghuai area, eastern Northwest China, eastern Southwest China, South China, and new records of daily temperature drop were reported in 38 stations. Meanwhile, long durations of temperature drop of 38 stations reached temperature drop extreme in Yunnan, Sichuan, Zhejiang, Fujian, Guangdong and Jilin. New records of extreme long durations of temperature drop were reported in 3 stations. The consecutive days of precipitation extremes occurred in 14 stations, which were located in Xinjiang, Tianjin, Heilongjiang, Guizhou, and new records were broken in 4 stations.

2. World Climate

During December 2010, monthly mean temperatures were 1-4℃ below normal in most Europe, mid-western and southeastern Siberia, northern Central Asia, northwestern and northeastern China, western South Asia, southeastern and northwestern North America, costal regions of southwestern South America and eastern Australia, with temperatures 4-9℃ below normal in mid-western and northern Europe, the central and western Siberia, eastern America and Alaska. Monthly mean surface air temperatures were observed 1-4℃ above normal in eastern Siberia, eastern and southwestern China, the northwestern Indo-China Peninsula, northern West Asia, southeastern Europe, parts of North Africa and West Africa, northeastern and southwestern North America, and parts of southeastern and northern South America, with temperatures at least 10℃ above normal in northeastern North America.

For the month, precipitations were at least 50% more than normal in regions from southwestern and mid-eastern Europe east to southern Siberia via northern Central Asia, northwestern and northeastern China, regions south of the Yangtze River in China, the west Indo-China Peninsula, most Australia, northwestern North America, northern and eastern South America, with precipitations at least 200% above normal in locations. Meanwhile, precipitations were 50-100% less than normal in most northern Europe, central Siberia, regions from North China to the Yangtze River in China, most of the Tibetan Plateau, most West Asia, the central Indo-China Peninsula, southeastern North America, southeastern South America, with precipitations 200% above normal in locations.

3. General Circulation Features

Northern Hemisphere: During December 2010, mean 500hPa geopotential height field exhibited a 4-wave pattern at the mid-high latitudes. In the 500hPa height anomaly field, positive anomalies above 4 dam dominated the northern North Atlantic, the northwestern North Pacific, with central values above 24 and 28 dam over the southern Greenland and near the Aleutian Islands respectively. Meanwhile, negative anomalies below -4 dam covered the regions from southeastern America east to most Europe via the central North Atlantic, the northeastern North Pacific, regions from northern East Asia east to the central North Pacific, with central values below -16 dam over the northeastern North Pacific. For the month, the area and intensity of the Northwest subtropical high were below normal. Its ridge line position moved further southward than normal and extended further eastward than normal.

Southern Hemisphere: In the 500hPa height anomaly field, negative anomalies below -4 dam covered the sea from south of South America to the Southeast Pacific Basin, the seas southeast of Australia, with central values below -8 dam over the Southeast Pacific Basin. Meanwhile, positive anomalies above 4 dam were over the southern South Atlantic, the southeastern South Indian Ocean, the southern South Pacific, with central values above 16 dam over the southern South Atlantic and the southeastern South Indian Oceans.

4. Tropical Features

Sea Surface Temperatures (SSTs): During December 2010, SSTs were at least 1.0℃ below normal in the central and eastern equatorial Pacific with minimum below -2.0℃. NINO 1+2 index was -1.4℃, with increase of 0.2℃from last month. NINO 4 index was -1.4℃, with a drop 0.1℃. NINO 3, NINO 3.4and NINO Z indices were -1.6℃, -1.5℃ and -1.5℃, with the same values as last month. Meanwhile, SSTs were around 0.5℃ above normal in the equatorial western Pacific and the western Indian Ocean.

Subsurface Temperatures: During December 2010, anomalous cold subsurface water area and intensity almost kept unchanged, with central values below -6℃. Anomalous warm subsurface water enhanced slightly.

Warm Pools: During December 2010, the area and intensity of the Indian Ocean warm pool were above normal. The area of the western Pacific warm pool was slightly below normal, but its intensity was still above normal.

Wind Field：For the month, at lower troposphere (850hPa), easterly anomalies prevailed over most of the equatorial Pacific. At upper troposphere (200hPa), westerly anomalies covered most of the equatorial Pacific.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 2.6, with an increase of 1.0 from last month.

Convections over the Tropics: During December 2010, the anomalous Outgoing Longwave Radiation (OLR) showed that enhanced convection was observed in the South China Sea, while suppressed convection was observed from the western equatorial Pacific to near the dateline. In the lower troposphere (850hPa) divergent wind field, a convergent center was around 135ºE, 5ºS, and a divergent center was near 90ºW, 20ºS. At the upper troposphere (200hPa), the corresponding divergent center was near 125ºE, 5ºS, and a convergent center was around 90ºW, 30ºS.

ENSO Monitoring and Outlook

 Monitoring showed that during December 2010, the intensity of the negative SSTa generally kept unchanged in the central and eastern equatorial Pacific. The centers trended toward the central equatorial Pacific. The La Nina event was in mature phase. From July to December, SSTA continuously kept above -0.5℃ for six months, while the sum of five months’SSTA was -7.8℃, which could be up to threshold of moderate or strong La Niña event in the future.

SOI was 2.6, which was the second peak in history. Anomalous cold subsurface water controlled most of the central and eastern equatorial Pacific with central values below -6℃. The low-level enhanced easterly anomalies prevailed over most of the equatorial Pacific. All these atmosphere and ocean conditions were favorable for maintenance of La Niña conditions. Most statistical and dynamic climate models predicted that La Niña conditions at least lasted till the spring 2011.

La Nina conditions persisted for six months. It is expected to last till 2011 spring at least. Therefore, we will closely monitor the development of ENSO conditions and update our ENSO wrap-up in time.