Monthly Highlights

Climate in China

During February, monthly mean surface air temperatures were observed 2-4℃ below normal in most of eastern China, most of Northeast China, Inner Mongolia and northern Xinjiang，with more than 4℃ below normal in northern Xinjiang and central Inner Mongolia. Meanwhile, temperatures were found 2℃ above normal in Qing-Zang Plateau and much of Yunnan. For the month, precipitations were found 30-100% more than average in most of China, while precipitations were found 30-100% below average in southeastern Southwest China, most of South China, most of Northeast China and western Inner Mongolia.

Climate in the World

During February, monthly mean surface air temperatures were observed more than 2℃ below normal in Eurasia between 40～60°N, with 4-8℃ below normal in Mongolia and nearby regions. Meanwhile, temperatures were observed near or above normal in the remainders of the world, with more than 2℃ above normal in most of North America, the nearby coast of northwestern Russia, central Northwest Africa, the Qing-Zang Plateau and the Indochina Peninsula.

For the month, precipitations were observed 30-100% above average in southwestern America, Central Europe and the nearby east regions, eastern China and the eastern Qing-Zang Plateau. Meanwhile, precipitations were observed near or more than 30% below average in other regions of the world, with no precipitation in the western Indian Peninsula and central Australia.

General Circulation Features

Northern Hemisphere: During February, the mean 500hPa geopotential height field exhibited a 3-wave pattern at the mid-high latitudes. An abnormal ridge developed over the North Atlantic Ocean. In the height anomaly field, the Altay Mountains and most of Europe were covered by negative anomalies below -4 dam. Meanwhile, most of other mid-high latitudes were covered by positive anomalies, with central values above 28 dam over the North Atlantic Ocean. The Northwest Pacific subtropical high was larger than normal and extended remarkably westward.

Southern Hemisphere: For the month, the mean 500hPa geopotential height field showed a 3-wave pattern at the mid-high latitudes. Positive anomalies above 4 dam covered the central South Pacific. Meanwhile, heights in other regions were observed near or below normal, with central values below -8 dam over the southwestern South Atlantic Ocean.

Tropical Features

Sea Surface Temperatures (SSTs): During February, the equatorial Pacific SST anomalies dropped obviously compared with last month. The SSTs returned to near normal generally. Above 0.5℃ SST anomalies dominated the equatorial Pacific around the dateline（160ºE-160ºW）. Meanwhile, below -0.5℃ SST anomalies controlled the eastern equatorial Pacific east to 120°W. The indices of NINO Z, NINO 3, NINO 4 and NINO 1+2 were 0.2℃, -0.2℃, 0.8℃and -0.6℃, respectively, with decreases from 0.3℃ to 0.5℃. The eastern equatorial Indian Ocean SST anomalies were observed above 0.5℃.

Subsurface Temperatures: During February, the abnormally warm water enhanced in the central equatorial Pacific and the abnormally cold water enhanced in the eastern equatorial Pacific either.

Warm Pools: During February, the areas of the western equatorial Pacific warm pool and the equatorial Indian Ocean warm pool were found larger than normal, and the intensities were stronger than normal.

Wind Field: During February, at the lower troposphere (850hPa), westerly anomalies controlled the equatorial Pacific between 140ºE-130ºW with central values above 8m/s. At the upper troposphere (200hPa), easterly anomalies above 4m/s controlled the equatorial Pacific east to the dateline, with central values above 12m/s. Westerly anomalies above 4m/s controlled the equatorial Pacific west to the dateline and most of the equatorial Indian Ocean.

Southern Oscillation: During February, the Southern Oscillation Index (SOI) was -2.4, with a decrease of 2.7 since last month.

Convection over the Tropics: For the month, the anomalous outgoing longwave radiation (OLR) distribution along the equator exhibited that convections were enhanced significantly around the dateline and suppressed over the western equatorial Pacific. In the lower troposphere (850hPa) divergent wind field, a convergent center was found near 175°W, 10°S and a divergent center was observed over the equator at 105ºW. Correspondingly, at the upper troposphere (200hPa), a divergent center was found near 180°, 7.5°S and a convergent center was observed over the equator at 105ºW.

ENSO Monitoring and Forecasting

a)   The SSTs returned to normal conditions generally.

b)   During February, the abnormally warm water enhanced in the central equatorial Pacific and the abnormally cold water enhanced in the eastern equatorial Pacific either.

c)   During February, the Southern Oscillation Index (SOI) was -2.4, with a decrease of 2.7 since last month.

d)   At the lower troposphere (850hPa), strong westerly anomalies covered most of the equatorial Pacific.

SSTs in the equatorial Pacific were found in ENSO-neutral conditions. The evolution of this activity will continue to be monitored.