Monthly Highlights

1.    Climate in China

During December 2012, mean surface air temperature averaged over China was -4.4℃, which was 1.2℃ lower than normal (-3.2℃). Monthly mean surface air temperatures were generally below normal except for most of Southwest China and central Northwest China. Air temperatures were generally 2-4℃ below normal in northern Northeast China, most of North China, the northern Huanghuai Region, and central-northern Xinjiang. Anomalies were below -4℃ in most of Northeast China, central-eastern Inner-Mongolia, and northern Xinjiang. Meanwhile, temperatures were 1~2℃ above normal in southern Qinghai, most of Tibet, southern Yunnan, and Hainan, with above 2℃ greater than normal in locations of the above regions.

In December, average precipitation over China was 17.6 mm, which was 67.6% more than normal (10.5 mm). Percentages of precipitation anomalies were observed 50-200% in most of Northeast China, central-eastern Inner-Mongolia, most of the central-western Northwest China, most of North China, the eastern Huanghuai Region, the Jianghuai Region, the eastern Jianghan Region, the most regions south of the Yangtze River, and most of South China, and were above 200% in eastern North China, the northeastern Huanghuai Region, and parts of central-eastern and southwestern Xinjiang. Meanwhile, precipitation amounts were generally 30~80% less than normal in southeastern Northwest China, the western Huanghuai Region, and most of Southwest China, with values more than 80% below normal in parts of southeastern Northwest China, southern Tibet, southwestern Sichuan, and most of Yunnan.

In December, extremes of Daily Minimum Temperatures (DMT), Daily Temperature Drop (DTD) and Consecutive Temperature Drop (CTD) were observed in China impacted by active cold air masses. DMT extremes occurred in 74 stations, which located in central-western Northwest China, North China, Northeast China, southern Shanxi and eastern Sichuan, and new records were recorded in Subei station (-25.5℃) of Gansu province, Weichang station (-32.3℃) and Chicheng station (-29.0℃) of Hebei province, Wulan station (-28.3℃) of Qinghai province. DTD extremes occurred in 91 stations, which located in northern China, coastal Southeast China, eastern Yunan and Hainan, with widespread DTDs of 10 ~21℃ and new records in Xinlin station of Heilongjiang province (21.2℃), Huadian of Jilin province (21.1℃) and other 9 stations. At the same time, CTD extremes occurred in 21 stations, which were located in Qinghai, Gansu, Xizang and Jilin province.

2. Climate in the World

During December 2012, mean temperatures were significantly below normal in most Eurasian between 30º-60ºN and northwestern North America, with temperatures between 8-12℃ below normal in central and western Siberia and northwestern North America and more than 12℃ below normal in locations. Meanwhile, mean temperatures were 1-4℃ below normal in parts of southern South America and parts of central and southern Africa. For the month, mean temperatures were 1-4℃ above normal in southeastern Europe, most West Asia, South Asia, the Indo-China Peninsula, most East Siberia, central and southeastern North America, parts of southeastern South America, parts of Eastern Africa, central and southern Australia, with temperatures 4-6℃ above normal in parts of northern West Asia and parts of the Far East of Russia.

For the month, precipitations were at least 50% above normal in parts of northwestern and southeastern Europe, northern West Asia, northwestern South Asia, most Central Asia, northern and eastern East Asia, western parts of the Far East of Russia, parts of northwestern and northeastern North America, parts of southern South America, parts of central-eastern and southern Africa, parts of northwestern Australia, with precipitations at least 200% above normal in locations. Meanwhile, precipitations were at least 50% below normal in locations of northern Europe, central and parts of northwestern Russia, most South Asia, the Indo-China Peninsula, western China, southern North America, northern and parts of central South America, most northern Africa and southeastern Australia, with no precipitation in locations of above regions.

3. General Circulation Features

Northern Hemisphere: During December 2012, the field of mean 500hPa geopotential height exhibited obviously meridional circulation over the mid and high latitudes of Eurasia. In the field of height anomaly, positive anomalies above 4 dam were observed over northeastern North America, parts of the northern North Atlantic Ocean, northern Eurasia continent and the northern North Pacific, with central values above 12 dam over parts of northeastern North America and eastern Europe. Meanwhile, negative anomalies below -4 dam covered western North America, Western Europe and regions from the Baikal Lake to Japan, with central values below -8 dam in locations. For the month, the area and intensity of West Pacific Subtropical High were smaller and weaker than normal, and the location of its ridge line was near normal and the western end of its ridge shifted more eastward than normal.

Southern Hemisphere:  For the month, the field of mean 500hPa geopotential height exhibited obviously meridional circulation over the mid and high latitudes of South Pacific. In the field of height anomaly, positive anomalies mainly covered the polar region, with above 4 dam over parts of the regions. Meanwhile, negative anomalies below -4 dam mainly covered most of the mid and high latitudes north to 60^oS, with central values below -8 dam over much of the southern South Atlantic Ocean.

4. Tropical Features

Sea Surface Temperatures (SSTs): During December 2012, SSTs were near normal over most of the equatorial Pacific, with central anomaly value above 0.5℃ near 160 º E and negative SST anomalies below -0.5℃in the coastal sea of South America. Niño 1+2, Niño 3, Niño 4, Niño 3.4 and Niño Z indices were -0.9℃, -0.3℃, 0.2℃, -0.1℃ and -0.1℃, with drops of 0.5℃, 0.4℃, 0.3℃, 0.4℃ and 0.3℃from last month, respectively.

Subsurface Temperatures: During December 2012, anomalously cold subsurface water in the equatorial eastern Pacific enhanced obviously, extending eastward and uplifting obviously, with central anomaly value below -2℃.

Warm Pools: During December 2012, the areas of the Indian Ocean warm pool and the western Pacific warm pool were slightly larger than normal, and their intensities were both above normal.

Wind Field: During December 2012, at lower troposphere (850hPa), weak easterly anomalies covered the western equatorial Pacific, while weak westerly anomalies covered the equatorial Indian Ocean and the central-eastern equatorial Pacific. At upper troposphere (200hPa), easterly anomalies were observed over the eastern equatorial Indian Ocean, most of the equatorial Pacific, while zonal winds were near normal over the eastern equatorial Pacific.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was -0.4, with a drop of 0.9 from last month.

Convections over the Tropics: During December 2012, the anomalous outgoing long wave radiation (OLR) showed that convection was weaker than normal near the regions of dateline, while convection was near normal over remainder of the equatorial Pacific.

At lower troposphere (850hPa) divergent wind field, a convergent center was around 120ºE, 5ºS, and a divergent center was over 100WºE, 10ºN. At upper troposphere (200hPa), two divergent centers were near 100ºE, 5ºS and 180º, 10ºS, and a convergent center was around 95ºW, 10ºN.

5. ENSO Monitoring and Outlook

At present, neutral condition dominates the equatorial Pacific with weak warming over its western region and weak cooling over its eastern region. The heat content anomalies of the central and eastern Pacific upper Ocean (0-300 m) keep a weakly negative anomaly. Besides, the atmospheric circulation is near normal. It is predicted that the neutral condition is expected to last through January-February-March 2013.

Therefore, we will closely monitor the development of ENSO conditions and update our ENSO wrap-up in time.