1. Climate in China

In October 2015, the surface air temperature averaged over China was 11.0ºC, with 0.7ºC above normal (10.3ºC). The mean precipitation was 39.5 mm over China, which was 10.2% more than normal (35.8mm). For the month, extremes of Daily Temperature Drop (DTD) and Daily Precipitation (DP) were observed in China.

2. General Circulation Features

Northern Hemisphere: During October 2015, in the field of mean 500hPa geopotential height anomaly, positive anomalies above 4 dam covered the region from North Europe to the Laptev Sea via the Arctic, northwestern North America, the mid-northern North Atlantic, with central values above 12 dam over North Europe. Meanwhile, negative anomalies below -4 dam covered western Russia, northern Japan, the northeastern North Pacific, and the region from south of Greenland to northeastern North America, with the central values below -8 dam. 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 the region from the Antarctica to southern South America, south of Australia, South Africa and their adjacent waters, with the central values above 12 dam over south of Australia. Meanwhile, negative anomalies below -4 dam covered south of the South Atlantic, south of the South India Ocean, south of New Zealand in the Southwest Pacific and the adjacent sea of central Chile in the Southeast Pacific, with central values below -16 dam over part of the Southwest Pacific.

3. Tropical Features

Sea Surface Temperatures (SSTs): In October 2015, SSTs were over 0.5℃ above normal in most of the central and eastern equatorial Pacific, with SSTs 3.0℃above normal around 120°W. Indices of Niño1+2，Niño3，Niño4，Niño3.4 and Niño Z were 2.5℃、2.6℃、1.1℃、2.4℃ and 2.0℃, respectively. The Indian Ocean Basin-Wide SSTA variation index (IOBW) was 0.7 and the Indian Ocean Dipole (IOD) index was 0.8. The North Atlantic Triple (NAT) index was 0.3.

Subsurface Temperatures: In October, the anomalously warm subsurface water centered on the region around 90-140°W, with the central values above 6℃. Meanwhile, the anomalously cool subsurface water controlled over the equatorial western Pacific, with the central value below -2℃.

Warm Pools: For the month, the areas of both the Indian Ocean and the western Pacific warm pools were much larger than normal. Meanwhile, the intensity was above normal in Indian Ocean and was below normal in the western Pacific Ocean.

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

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was -1.7.

Convections over the Tropics: During October 2015, the anomalous outgoing longwave radiation (OLR) showed that convections were active over the equatorial Pacific region to the east of 160°E, with central values below -60 W/m². However, convections were suppressed over regions from the eastern equatorial Indian Ocean to the western equatorial Pacific.

4. ENSO Monitoring and Outlook

With the continuous and strong warming over the eastern and central Pacific, 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 increase since the late September, accompanied with the eastward propagation of the recent down-welling Kelvin wave. The present El Nino event is expected to reach its peak in November or December 2015 and continue through the boreal spring of 2016.

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