Highlights

General Circulation Features

Northern Hemisphere

During October, the mean 500hPa geopotential height field exhibited a 4-wave pattern at mid-high latitudes. The polar vortex was stronger than normal. Correspondingly, negative anomalies below –4 dam covered the regions of Europe, offshore of Taymyr Peninsula, northeastern North Pacific and eastern North America. Meanwhile, positive anomalies above 4 dam controlled the regions between the northern North Atlantic to Greenland and northern Canada, western North America and western Siberia, with center values above 12 dam over the northern North Atlantic. In this month, Northern Hemisphere subtropical high was obviously stronger than normal. The Northwest Pacific subtropical high was also stronger than normal and extended westward remarkably.

Southern Hemisphere

In the mean 500hPa geopotential height field during October, a 3-wave pattern dominated the mid-high latitudes. Positive anomalies dominated the Antarctica and the south-central Pacific, the southwestern Atlantic, and the south-central India Ocean. Meanwhile, negative anomalies covered the southeastern Australia and southwest to South America.

Climate for China

During October, the mean surface air temperatures were 1℃~2℃higher than normal in the north-central Northeast China, west-central Southwest China, most of Tibet and Qinghai, northern Xinjiang. The monthly mean surface air temperatures were near or above normal in the rest regions. During October, rainfall totals of 50% more than normal received in the regions such as south-central Northeast China, North China, most of the regions between the Yellow River and the Huaihe River, central Shanxi, northeastern Gansu, southern Ningxia and southwestern Xinjiang. Meanwhile, rainfall totals were 50% below normal in the regions south to the Yangtze River and most of South China, with 80% below normal in central Northwest China, Hainan, southern Zhejiang, southern Jiangxi, southern Hunan, southeastern Guangxi and southwestern Guangdong. 

Tropical Features

Sea Surface Temperatures(SSTs)

During October, most of the equatorial Pacific were controlled by the positive SST anomalies above 0.5℃. Positive SST anomalies above 1.0℃ were observed in part of the eastern equatorial Pacific. Negative SST anomalies in the offshore of South America were weaker than that in September. Correspondingly, the SST indices of NINO 4, NINO 3 and NINO 1+2 regions were 0.8℃, 0.4℃ and 0.1℃, respectively. In addition, positive anomalies around 0.5°C remained in the equatorial India Ocean.

Circulation

Wind Field

In this month, at the lower troposphere (850hPa), weak westerly anomalies about 2m/s covered the central and eastern equatorial Pacific and the equatorial India Ocean. At the upper troposphere (200hPa), zonal wind anomalies were near normal.

Southern Oscillation

During October, the Southern Oscillation Index was -0.6.

Convection over the Tropics

During October, the anomalous outgoing longwave radiation (OLR) distribution exhibited that slightly enhanced convections were nearby the dateline over the equatorial Pacific and suppressed convections were over the equatorial western Pacific. In the lower troposphere (850hPa) divergent wind field, the convergent center was over 150°E, 7°N, and the divergent center was around 110°W, 15°S. Correspondingly, the divergent and the convergent centers at the upper troposphere (200hPa) were over 150°E, 10°N and around 95°W, 25°S, respectively.