Annual Highlights

1. Climate in China

During 2012, annual mean surface air temperature of China was 9.4℃ which was near normal (9.6℃). The temperatures were warmer in Southwest China and obviously colder in North China and Northeast China, with the temperatures near the normal or a bit colder in the rest of China. The temperatures were observed 0.5-1.0℃ below normal in middle and southern Northeast China, middle and eastern Inner Mongolia, middle and western Xinjiang and northern Guizhou, with 1.0-2.0℃ below normal in locations. Meanwhile, the temperatures were observed 0.5-1.0℃ above normal in Yunnan, southern Sichuan, southern Qinghai and northeastern Heilongjiang, with 1.0-2.0℃ above normal in locations.

During 2012, annual mean precipitation over China was 669.3 mm, which was 6.3% more than normal (629.9 mm). The precipitations were observed 20-50% more than normal in middle and western Northeast China, middle Northwestern China, middle and eastern Jiangnan and most of Inner Mongolia, Beijing and Tianjin and western Xinjiang, with more than 50% above normal in locations. While precipitations were observed 20-50% less than normal in middle and western Huanghuai, northern Jianghan and middle Yunnan.  

2. General Circulation and Monsoon

1) In the boreal winter of 2012/2013，the East Asia winter monsoon was strong than normal

During the boreal winter (Dec. 2012-.Feb. 2013), in the field of 500hPa geopotential height anomaly, significant wave trains were observed from the Atlantic to Eurasia. In the field of lower tropospheric, the monitoring of daily Arctic Oscillation Index kept weaker than normal features, the Siberian High exhibited strong intra-seasonal variations. In 2012, the intensity of East Asian winter monsoon was stronger than normal.  

2) In the boreal summer, the northwestern Pacific subtropical high was weaker than normal.

In the boreal summer of 2012, the area and intensity of Northwest Pacific Subtropical High were smaller and weaker than normal, and its western ridge point and ridge line were more eastward and northward, respectively.

3) SCS summer monsoon onset was earlier than normal, the ending was later than normal, and its intensity was near average.

The South China Sea (SCS) summer monsoon (SCSSM) broke out in the 4th pentad of May in 2012with one pentad earlier than normal, and it withdrew in the 2rd pentad of October with two pentads later than normal. The intensity of the SCS summer monsoon was -0.14, which was near normal (-0.5-0.5). In 2012, the intensity of the East Asia summer monsoon was -1.94, which was much weaker than normal.

During the period from the onset of the SCS summer monsoon in the 4th pentad of May to the 5th pentad of June, the front of the East Asian subtropical summer monsoon maintained over the region from South China to south of the Yangtze River Valley (YRV). In June 26, with the northward advancement of the EASSM and the northward jump of the subtropical high over the western North Pacific (WNP), the front of the summer monsoon advanced to the middle and lower reaches of the YRV, and correspondingly the Meiyu period started. The Meiyu period ended in July 5, and then the monsoonal rain belt in eastern China advanced northward to North China, in the 2nd pentad of July, the rainy season over these regions started. In the 5th pentad of August, with the subtropical high over the WNP retreating southward, the rain belt in eastern China shifted southward from North China. Since the 3rd pentad of September, the autumn rain started in West China. In the 5th pentad of September, the warm and wet air moved southward to region from the Jiangnan area to South China, which resulted in the persistent strong precipitations over South China and its neighboring areas. In the 2rd pentad of October, with the cold air from the North intruding into the coastal areas and the SCS, thermodynamic property of the air mass changed obviously over the SCS. Then, the front of summer monsoon began to withdraw from the SCS and then the SCS summer monsoon ended.

3. Tropical oceanic condition

The last La Nina event, which began in September 2011, decreased gradually after January 2012, and ended in March 2012. During the summer of 2012, the equatorial eastern and central Pacific experienced an apparent fluctuation of abnormally warm water. After that, weak warm conditions dominated over most equatorial eastern and central Pacific.