Highlights

General Circulation Features

Northern Hemisphere

During February, the mean 500hPa geopotential height fields exhibited a 3-wave pattern in the mid-high latitudes. The polar vortex was stronger than normal. The trough over East Asia was weaker and the trough over North America was obviously stronger than normal. In the height anomaly field, positive anomalies were over the region between Europe and North Atlantic, the northeastern Pacific and East Asia, with maximum center value above 16 dam over the northwestern Europe. Negative anomalies between –4~–8 dam controlled the other regions. The Northwest Pacific subtropical high was obviously stronger than normal and its position slightly shifted southward.

Southern Hemisphere

During February, in the mean 500hPa geopotential height fields，zonal circulation prevailed over the mid-high latitudes. In the height anomaly field, negative anomalies were over the region south to the Southern America and the southern South Atlantic. Meanwhile, positive anomalies between 4~8 dam covered the other region.

Climate for China

In February, monthly mean surface air temperatures were generally obviously above normal 2~4℃ in China. In the central Northeast China and parts of Xinjiang, temperatures were 4℃ above normal. During February, rainfall totals of 50~200% more than normal received in such regions as most of Xinjiang, the northwestern and central Tibet, parts of Qinghai and Inner Mongolia, the regions between the Huaihe River and the Yellow River and the middle and lower reaches of the Yangtze River. The monthly precipitation totals was 50~90% less than normal in most of South China, the eastern Southwest China, most of Northeast China, the eastern North China, Ningxia, the central Gansu and the eastern Qinghai. .

Tropical Features

Sea Surface Temperatures (SSTs)

During February, positive SST anomalies across the central equatorial Pacific decreased obviously. The maximum center value was 1.5℃, which was 2.0℃ in January. The area controlled by positive anomalies shrank during this month. Meanwhile, negative SST anomalies expanded in the offshore of South America. Correspondingly, the SST indices of NINO4, NINO 3 and NINO 1+2 were1.0, 0.3 and –0.3. NINO3 index dropped sharply, with the value being 0.3 from 0.8 last month. In addition, positive SST anomalies above 0.5℃ were observed in most of the equatorial Indian Ocean.

Circulation

Wind Field

In this month, at the lower troposphere (850hPa), weak easterly anomalies were observed over the western Pacific while westerly anomalies of 2~4 m/s remained over the east-central equatorial Pacific. Westerly anomalies about 2 m/s were over the equatorial Indian Ocean. At the upper troposphere (200hPa), zonal wind was near normal over the central equatorial Pacific and weak easterly anomalies dominated the eastern equatorial Pacific. Meanwhile, weak westerly anomalies were observed over the region from the western equatorial Pacific to the equatorial Indian Ocean.

Southern Oscillation

The Southern Oscillation Index (SOI) was –0.6.

Convection over the Tropics

During February, the anomalous outgoing longwave radiation (OLR) distribution displayed that enhanced convections center was nearby the dateline over the equatorial Pacific and was weaker than last month. Suppressed convection was over the Pacific northeast to Australia. Convection over Indonesia was near normal. In the lower troposphere (850hPa) divergent wind field over the tropical Pacific, the convergent center was around 135°E，10°S; while the divergent center was around 95°W，10°S. Correspondingly, at 200hPa, the divergent center was over 130°E，10°N；while the convergent center was around 90°W，10°S.