1. Climate in China

In January 2015, the averaged surface air temperature was -3.1ºC in China, which was 1.9ºC above normal (-5.0ºC), ranking the 1st highest since 1961. The mean precipitation was 144.4 mm in China, which was 9.0% more than normal (13.2mm). For the month, extremes of Daily Temperature Drop (DTD) and Daily Precipitation (DP) were observed in China.

2. General Circulation Features

Northern Hemisphere: During January 2014, in the field of mean 500hPa geopotential height anomaly, positive anomalies above 4 dam covered polar region, central North Atlantic Ocean, the regions from northeastern Asia to western North America via northern North Pacific, with central values above 12 dam in central North Atlantic, locations of the Arctic Ocean and western North America. Meanwhile, negative anomalies below -4 dam covered regions from northeastern North America to northwestern Europe via northern North Atlantic Ocean, Central Siberia and central North Pacific, with central values below -12 dam in locations of northern North Atlantic Ocean. During the month, the northwestern Pacific subtropical high was weaker than normal with the area smaller than normal, its position shifted further southward than normal, while the location of western ridge point reached to its normal position.

Southern Hemisphere: For the month, in the field of mean 500hPa geopotential height anomaly, positive anomalies over 4 dam were observed over southwestern and southeastern South Pacific. Meanwhile, negative anomalies below -4 dam were observed over central South Pacific Ocean, southern South Atlantic Ocean and parts of polar region.

3. Tropical Features

Sea Surface Temperatures (SSTs): In January 2015, SSTs were over 0.5℃ above normal in most of the central and eastern equatorial Pacific, especially above 1℃ in some parts. Indices of Niño1+2，Niño3，Niño4，Niño3.4 and Niño Z were -0.3℃，0.4℃，0.9℃，0.6℃ and 0.5℃, respectively. The Indian Ocean Basin-Wide SSTA variation index  (IOBW) was 0.1℃ and kept in the persistent positive phase. The North Atlantic tripole index was 1.2, indicating the development of positive phase of North Atlantic tripole mode.

Subsurface Temperatures: In January, the anomalously warm subsurface water shifted eastward to the central equatorial Pacific around the dateline. Meanwhile, the anomalously cool subsurface water upwelled in the eastern equatorial Pacific.

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

Wind Field: For the month, at lower troposphere (850hPa), the westerly anomalies dominated over most equatorial central and eastern Pacific, and the easterly anomalies prevailed to the coastal areas of South America over eastern Pacific. At upper troposphere (200hPa), the westerly anomalies prevailed over the equatorial Indian Ocean and the coastal areas of South America over eastern Pacific, while the easterly anomalies ruled the equatorial central-eastern Pacific.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was -0.7.

Convections over the Tropics: During January 2015, the anomalous outgoing longwave radiation (OLR) showed that convections were active around the extratropical South Indian Ocean, Maritime Continent, and Western Pacific, with central values below -15W/m². However, convections were suppressed in the region of tropical Indian Ocean, with central values above 15W/m².

4. ENSO Monitoring and Outlook

Recently, another downwelling Kelvin wave with warm phase developed and pushed eastward. Meanwhile, active convection and strong low-level westerly anomalies prevailed over the equatorial central Pacific. Based on models’ prediction and diagnoses of the oceanic variations, the El Nino event will again intensify slightly in February 2015, with ENSO-neutral condition favored during mid-later spring 2015.

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