Monthly Highlights

1. Climate in China

In December 2011, China monthly mean surface air temperature was -3.8℃, which was near normal (-3.9℃). Temperatures were observed 1-4℃ above normal in most of the Tibetan Plateau, western Sichuan, western Yunnan and parts of northern Xinjiang, with more than 4℃ above normal in parts of northwestern Tibet. Meanwhile, temperatures were near or below normal in the rest of China, with temperatures 1-4℃ below normal in central-southern Northeast China, most of central and eastern Inner Mongolia, southwestern Xinjiang, the western Jianghuai area, the southwestern Jiangnan area, northeastern and western South China and parts of southeastern Southwest China, with more than 4℃ below normal in parts of eastern Inner Mongolia.

For the month, the mean precipitation over China was 7.5 mm, with precipitation 23.5% less than normal (9.8 mm). Precipitations were 30%-100% more than normal in the eastern Huanghuai area, the eastern Jianghuai area, parts of northeastern Southwest China, southeastern Qinghai, southwestern Xinjiang and northwestern Tibet, with precipitation at least 100% more than normal in locations of above regions. Meanwhile, precipitations were observed 30-80% less than normal in most Northeast China, eastern and western Inner Mongolia, central-eastern Xinjiang, most North China, the eastern Jianghan area, the western Jiangnan area, most South China, most of the Tibetan Plateau, southwestern Sichuan and northwestern Yunnan, with at least 80% less than normal in southwestern Northeast China, southeastern Xinjiang, western Qinghai, central-eastern Tibet and southeastern South China.

In December, daily temperature drop extremes, consecutive temperature drop extremes and consecutive rainy days extremes were observed in China. Daily temperature drop extremes occurred in 14 stations, which were located in Heilongjiang, Jilin, Liaoning, Fujian and Sichuan provinces, with daily temperature drops of 7-19℃. Additionally, consecutive temperature drop extremes were observed in 15 stations，distributed in Hunan, Sichuan, Guizhou, Chongqing and other 3 provinces (municipality), with consecutive temperature drops of 12-18℃. During the month, consecutive rainy day extremes occurred in 7 stations of Xinjiang, Guizhou and Yunnan provinces (districts), and precipitation in above stations generally lasted 4-7 days, with consecutive precipitation of 26 days in Zhijin of Guizhou Province and 31 days in Zhenxiong Yunnan.

2. World Climate

During December 2011, monthly mean temperatures were 2-4℃ above normal in most Europe, northern Central and western West Siberia, southwestern East Asia, northwestern Southeast Asia, northern North America, locations of southern South America, with temperatures 4-12℃ above normal in regions from northeastern Europe to northern Central Siberia, central and northern North America. Monthly mean surface air temperatures were observed 1-4℃ below normal in regions from most Central Asia to northeastern West Asia, regions from northern East Asia to southern Siberia, the eastern Far east, parts of southwestern North America, most central and eastern Australia, with temperatures 4-6℃ below normal in parts of Central Asia.

For the month, precipitations were at least 50% more than normal in western and northeastern Europe, parts of northern and southern Siberia, southeastern Central Asia, locations of southeastern Africa, southeastern North America and the Alaska, northwestern and locations of eastern South America, central Australia, with precipitations at least 100% above normal in parts. Meanwhile, precipitations were at least 50% less than normal in parts of eastern and western Siberia, regions from West Asia to southwestern East Asia through most South Asia, northeastern East Asia, western and parts of northern Africa, parts of northwestern North America, southern South America, with no precipitation in parts of above regions.

3. General Circulation Features

Northern Hemisphere: During December 2011, the field of mean 500hPa geopotential height exhibited a three-wave pattern over the mid-high latitudes. In the field of height anomaly, positive anomalies above 4 dam were located in eastern Europe, most Russia, eastern and northwestern North America, the middle and eastern North Pacific Ocean as well as the northern Atlantic Ocean respectively, with central values above 16 dam over locations of western Russia. Meanwhile, negative anomalies below -4 dam covered zonal areas north of 60^oN except high latitudes over Eurasia, with central values below -16 dam over the northeastern Atlantic Ocean. For the month, the area and the intensity of West Pacific Subtropical High were near normal while the ridge line was a bit more northern and the ridge point was obviously more eastern than normal, respectively.

Southern Hemisphere:  For the month, the field of mean 500hPa geopotential height exhibited a 3-wave pattern over the mid-high latitudes. In the field of height anomaly, positive anomalies above 4 dam covered the southwestern South Atlantic Ocean, the southwestern South Pacific Ocean and southwestern South Indian Ocean, with central values above 12 dam over southwestern South Indian Ocean and locations of southwestern South Atlantic Ocean. Meanwhile, negative anomalies below -4 dam mainly covered the polar areas and most of high latitudes, with the central values below -12 dam over the southeastern South Pacific Ocean.

4. Tropical Features

Sea Surface Temperatures (SSTs): During December 2011, SSTs were 0.5~1.0℃ below normal in the central and eastern equatorial Pacific, with central values below -1.5℃. NINO 1+2, NINO 4, NINO 3.4 and NINO Z indices were -1.1℃, -0.9℃, -1.0℃ and -0.9℃, with drops of 0.2℃, 0.4℃ 0.1℃ and 0.1℃ from last month, respectively. Meanwhile, NINO 3 index was -0.9℃, increased by 0.2 ℃ from last month. Meanwhile, SSTs were 0.5~1.0℃ above normal in the equatorial Indian Ocean.

Subsurface Temperatures: During December 2011, anomalously cold subsurface water controlled the central and eastern equatorial Pacific. Negative anomalies weakened and shifted westward. Meanwhile, the intensity and extent of anomalously warm subsurface water in equatorial western Pacific maintained.

Warm Pools: During December 2011, the area of the Indian Ocean warm pool was slightly larger than normal, and that of the western Pacific warm pool was near normal. Their intensities were both above normal.

Wind Field: In December 2011, at lower troposphere (850hPa), easterly anomalies dominated over the central and western equatorial Pacific, and weak easterly anomalies appeared in the eastern equatorial Pacific. At upper troposphere (200hPa), westerly anomalies were observed over the most equatorial Pacific.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 2.2, with a rise of 0.9 from last month.

Convections over the Tropics: During December, the anomalous outgoing long-wave radiation (OLR) showed that enhanced convection was over regions from Bay of Bengal to the South China Sea. Meanwhile, suppressed convection was over the central equatorial Pacific.

In the divergent wind field at lower troposphere (850hPa), the convergent center was around 135°E, 5°S and divergent center was around 110°W, 5°S. At upper troposphere (200hPa), the corresponding divergent and convergent centers were near 140°E, 5°S and 65°W, 30°S, respectively.

5. ENSO monitoring and outlook

Current monitoring results showed that during December 2011, atmospheric and oceanic conditions in the tropical Pacific still maintained La Niña status. Negative SST anomalies continued to stay in the central-eastern Pacific, but enhanced slowly. The index NINO Z was at -0.9℃ in December with drops of 0.1℃ from last month. Southern Oscillation Index (SOI) was at 2.2 with increased 0.9 from last month.

Based on model predictions and current monitoring of the ocean and atmosphere features, the La Niña conditions will enter its mature phase in the central and eastern equatorial Pacific. It is predicted that the La Niña conditions may decrease after February 2012 and terminate in late spring 2012.