Annual Highlights

1. Climate in China

During 2015, the annual surface air temperature averaged over China was 10.5℃, with 0.9℃ above normal (9.6℃), ranking the 1^st highest since 1961. The annual mean precipitation was 649.1 mm over China, which was 3.0% more than normal (629.9mm).

2. General Circulation Feature

1) In the boreal winter of 2014/2015，the polar votex was split and shifted southward, and the East Asian Winter Monsoon transferred from weak to strong

During the boreal winter (Dec.2014-Feb.2015), in the field of 500hPa geopotential height, the polar vortex was split and shifted southward. The circulation over mid-high latitude of Eurasia was prevailed by “a west ridge and an east trough”. During the winter, the Arctic Oscillation transferred from the positive phase to negative phase. The Siberian High was slightly stronger than normal on the whole, but transferred from weak to strong on the low-frequency time scale. The northwestern Pacific subtropical high was stronger than normal, with the area larger than normal. The northwestern Pacific subtropical high shifted westward than normal.

2) In the boreal summer, the northwestern Pacific subtropical high was stronger than normal with the area larger than normal and shifted further southward than normal.

In the boreal summer of 2015, the area and intensity of Northwest Pacific Subtropical High were larger than normal, separately. The western ridge point and ridge line extended more eastward and southward, respectively.

3) The East Asian summer monsoon was overall weaker than normal. The main rain band in Eastern China was more southward than normal. The precipitation during the Mei-yu season was much more than normal.

During the summer 2015, the date of South China Sea (SCS) summer monsoon broke out was close to normal. The intensity of the East Asian summer monsoon was stronger from late June to early July, and was weaker during other period in the summer. The Indian summer monsoon was weaker than normal on the whole. The northwestern Pacific subtropical high was stronger than normal, with the ridge line more southward. Thus, the weaker summer monsoon could not further shift northward, resulting in a more southward located main rain band. During the summer, the precipitation in the Mei-yu period was much more than normal, while the precipitation in other regions such as North China, Southwest China and West China were less than normal.

3. Tropical oceanic condition

During January-March 2015, the SSTA was decreased resulting from the cooler water in the central-eastern equatorial Pacific, which led to the stagnation of El Nino development. From April 2015, the sea surface temperature anomaly indexes of Nino Z region rose rapidly, and reached the peak in November, forming a super El Niño event. The index was decreased in December.