Annual Highlights
1. Climate in China
During 2014 the annual surface air temperature averaged over China was 10.1¡æ, with 0.5¡æ above normal (9.6¡æ), ranking the 6th highest since 1961.The annual mean precipitation was 636.2 mm over China, which was 3.0% less than normal (629.9mm).
2. General Circulation Feature
1) In the boreal winter of 2014/2015£¬the East Asia winter monsoon was weaker than normal
During the boreal winter (Dec.2014-Feb.2015), in the field of 500hPa geopotential height, zonal circulation prevailed over mid-high latitude of Eurasia, the center of Arcticpolar vortex shifted to the western Hemisphere. During the winter, the Arctic Oscillation was in the remarkable positive phase, and the Siberian High exhibited strong intraseasonal variations, stronger in the early winter and weaker in the late winter. And, the intensity of East Asian winter monsoon was weaker than normal.
2) In the boreal summer, the northwestern Pacific subtropical high shifted further southward than normal.
In the boreal summer of 2014, the area and intensity of Northwest Pacific Subtropical High were near normal, separately. The western ridge point and ridge line extended more westward and southward, respectively.
3) South China Sea summer monsoon onset was later than normal, and its intensity was weaker than normal.
The South China Sea (SCS) summer monsoon broke out in the 2nd pentad of June in 2014 with 3 pentads later than normal, and it withdrew in the 6th pentad of September with the same as normal. The intensity of the SCS summer monsoon was -0.29, which was weaker than normal. In 2014, the intensity of the East Asia summer monsoon (EASM) was -0.2, which was weaker than normal.
During the period from the onset of the SCS summer monsoon in the 2nd to the 3rd 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 4th pentad of June, with the northward advancement of the EASM and the northward jump of the northern western Pacific subtropical high, the front of the summer monsoon advanced to the middle and lower reaches of the YRV, indicating the emergence of the Meiyu period. During the period from late June to mid-July, the monsoonal rain belt was located along YRV and northern Jiangnan. In the late July, accompanied with southward withdraw of the northern western Pacific subtropical high, the monsoon rain belt shifted southward to the Jiangnan and South China, resulting in non-occurrence of North China rainy season. During the period from late August to mid-September, the northern western Pacific subtropical high advanced westward and shifted northward again, which enhanced the northward transport of monsoonal moisture, resulting in occurrence of strong precipitation process over Huanghuai and eastern West China. In 5th pentad of September, with intrusion of the cold air from the high latitude into the coastal areas of South China and the SCS, thermodynamic property changed obviously over the SCS. The summer monsoon began to retreat from the SCS, causing the end of SCS monsoon in the 6th pentad of September.
3. Tropical oceanic condition
In April 2014, SSTA increased swiftly over the central-eastern equatorial Pacific and ENSO-neutral conditions turned into warm conditions. During May-October 2014, the sea surface temperature anomaly indexes of Nino Z region have been reached or exceeded 0.5¡æ for 6 months. It is indicated that a new El Niño event has formed, which began in May and reached standard in October. The El Niño event continued to develop during October-December.