1. Climate in China

In December 2015, the surface air temperature averaged over China was -2.1ºC, with 1.1ºC above normal (-3.2ºC). The mean precipitation was 24.1 mm over China, which was 128.9% more than normal (10.5 mm). For the month, extremes of Daily Temperature Drop (DTD) were observed in China.

2. General Circulation Features

Northern Hemisphere: During December 2015, in the field of mean 500hPa geopotential height anomaly, positive anomalies above 4 dam covered the region over much of Europe, northern East Asian, the central North Pacific and the eastern North America, with central values above 16 dam over East Europe. Meanwhile, negative anomalies below -4 dam covered the western West Siberia, the northern North Pacific and southern Greenland, with the central values below -12 dam over southern Greenland. During the month, the northwestern Pacific subtropical high was stronger than normal, with the area larger than normal. The position of its west ridge shifted further westward than normal.

Southern Hemisphere: For the month, in the field of mean 500hPa geopotential height anomaly, positive anomalies above 4 dam were observed over Marie Byrd Land, South of southeastern Australia, southeastern South America, with central values above 12 dam over Marie Byrd Land. Meanwhile, negative anomalies below -4 dam covered other regions of Antarctica, Central of South Pacific, with central values below -12 dam over part of the South Pacific.

3. Tropical Features

Sea Surface Temperatures (SSTs): In December 2015, SSTs were over 0.5℃ above normal in most of the central and eastern equatorial Pacific, with SSTs 3.5℃above normal around the eastern equatorial Pacific. Indices of Niño1+2，Niño3，Niño4，Niño3.4 and Niño Z were 2.0℃，2.8℃，1.7℃，2.8℃ and 2.3℃, respectively. The Indian Ocean Basin-Wide SSTA variation index (IOBW) was 0.8. The North Atlantic Triple (NAT) index was 1.2.

Subsurface Temperatures: In the month, the anomalously warm subsurface water located at the central-eastern equatorial Pacific, with the central values above 7.0℃. Meanwhile, the anomalously cool subsurface water shifted eastward and crossed the dateline, with the central value below -3℃.

Warm Pools: For the month, the areas of both the Indian Ocean and the western Pacific warm pools were larger than normal. Meanwhile, their intensities were above normal.

Wind Field: For the month, at lower troposphere (850hPa), the westerly anomalies dominated over most of the central and eastern equatorial Pacific, while the weak easterly anomalies dominated over the Maritime continent. At upper troposphere (200hPa), the easterly anomalies prevailed over the central and eastern equatorial Pacific Ocean, while the debilitated westerly anomalies were observed over most of the Maritime continent.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was -0.6.

Convections over the Tropics: During the month, the anomalous outgoing longwave radiation (OLR) showed that convections were active over the central equatorial Pacific region, with central value below -60W/m². However, convections were suppressed over the Indo - China Peninsula and Indonesia region.

4. ENSO Monitoring and Outlook

At present, positive equatorial sea surface temperature anomalies persisted across most of the central and eastern Pacific Ocean, the anomalies of both tropical atmospheric and oceanic circulation are well coupled and show a clear El Nino - South Oscillation pattern. The positive heat content anomaly of equatorial upper-ocean began to decrease since early November, accompanied with the eastward propagation of the down-welling Kelvin wave going to the end. The present El Nino event may begin to decay from January 2016 and last through May 2016.

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