Monthly Highlights

1．Climate in China

During October 2009, the whole country monthly mean surface air temperature was 11.1℃, with 1.5℃ above normal and being the third highest since 1951. The monthly mean surface air temperatures were at least 1℃ above normal in most China, with temperatures at least 2-4℃ above normal in southern North China, the Huanghuai, the Jianghan, the Jianghuai, the western and northern Jiangnan areas, western Inner Mongolia and northern Xinjiang, except that temperatures were at least 1℃ below normal in locations of Xizang.

For the month, precipitations were observed 30-80% less than normal in southern North China, the Huanghuai, the Jianghan, the Jianghuai and the Jiangnan areas, most South China, southern Southwest China, and most Heilongjiang and most Inner Mongolia, most Shaanxi, western Gansu and most Xinjiang, with at least 80% less than normal in locations. Meanwhile, precipitations were observed 30-200% more than normal in eastern Jilin, northeastern Liaoning, Hainan, most Qinghai and western Xizang, with precipitations at least 200% more than normal in some places of the Qinghai-Xizang Plateau.

In October, Daily precipitation extremes occurred in Lingao and Chengmai station of Hainan. New record of maximum daily precipitation was reported in Lingao station(346.4mm).

2．Climate in the World

During October 2009, in the temperature anomaly field, temperatures were observed above normal in most of the world, with 1-2℃ above normal in most Siberia, most China, the Korea Peninsula, the northern Indo-China Peninsula, Central Asia, most West Asia, western Europe, most North Africa, southern North America and Alaska, central South America and western Australia, with temperatures at least 4℃ above normal in locations of northern Central Siberia and western Alaska. While, temperatures were 1-2℃ below normal in central and northern Europe, part of southern South America and Mongolia, with temperatures at least 2-5℃ below normal in most America.

For the month, precipitations were observed 50-100% less than normal in parts of southwestern and northern Europe, the central part of Central Siberia, eastern and northwestern China，Central Asia, most West Asia, western North Africa, southwestern North America, parts of western South America and most Australia, with no precipitation in parts of above regions. Meanwhile, precipitations were 50-100% more than normal in central Europe, western East Siberia, the area from the western Qinghai-Xizang Plateau to northern South Asia, northwestern West Asia, most West Africa, central-northern South Africa, central North America and locations of the west, parts of eastern and southern South America, with precipitations at least 200% more than normal in locations.

3．General Circulation Features

Northern Hemisphere: During October 2009, the mean 500hPa geopotential height field exhibited a 5-wave pattern at the mid-high latitudes. In the 500hPa geopotential height anomaly field, positive anomalies above 4 dam covered most of the high latitude area from Asia to North America, the area from eastern Europe to Central Asia, the area from the eastern North Atlantic Ocean to the western coasts of Europe, the Northeast Pacific Basin, with central values above 16 dam over the eastern Arctic. Meanwhile, negative anomalies below -4 dam covered central Europe. Also, negative anomalies dominated parts of the northwestern North Atlantic, central North America and the northern Pacific, with central values below -8 dam, respectively. Furthermore, the subtropical high over the Northwest Pacific was obviously larger and stronger, its ridge position was southward than normal and its location was more westward than normal.

Southern Hemisphere: In October, in the 500hPa geopotential height anomaly field, positive anomalies above 4 dam covered the most Antarctic and the mid-high latitude sea area, with central values above 24 dam except that the negative anomalies below -4 dam was observed over the vicinity of New Zealand and locations in the mid-high latitude west of Chile.

4. Tropical Features

Sea Surface Temperatures (SSTs): During October, the SSTs were more than 0.5℃ above normal in the central-eastern equatorial Pacific, with central value above 1.5℃. The indices of NINO 1+2, NINO 3, NINO 4, NINO 3.4 and NINO Z were 0.0℃, 0.8℃, 1.3℃, 1.0℃ and 0.9℃, with a rise of 0.5℃, 0.2℃ and 0.1℃ for NINO 4, NINO 3.4 and NINO Z, a drop of 0.3℃ for NINO 1+2, and the same for NINO 3 from last month.

Subsurface Temperatures: During October, the anomalously warm subsurface water in the central equatorial Pacific further strengthened in comparison to last month indicating consolidation of El Nino. Meanwhile, the anomalously warm subsurface water weakened in the upwelling region of the eastern equatorial Pacific compared with past months.

Warm Pools: During October, both the area and intensity of the western Pacific and Indian Ocean warm pool were above normal.

Wind Field：For the month, at lower troposphere (850hPa), westerly anomalies prevailed over most of the equatorial Pacific. At upper troposphere (200hPa), easterly anomalies covered most of the equatorial Pacific.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was -1.3, with a drop of 1.6 from last month.

Convections over the Tropics: During October, the anomalous outgoing longwave radiation (OLR) in the tropical Pacific showed that the convection enhanced over the regions from 150ºE to the dateline, and suppressed over the vicinity of the Philippines. In the lower troposphere (850hPa) divergent wind field, a convergent center in the tropical Pacific was near 165ºE, 5ºN, and a divergent center was near 105ºW, 5ºS. At the upper troposphere (200hPa), the corresponding divergent and convergent centers were near 155ºE, 5ºN; 120ºW, 10ºS, respectively.

5．ENSO Monitoring and Outlook

Monitoring showed that the El Nino persisted in the tropical Pacific Ocean during October 2009. Meanwhile, the El Nino condition have reached its threshold of being an El Nino event since onset in June 2009, with exceeding 0.5℃ for 5 consecutive months of the positive SSTA in the central and eastern equatorial Pacific and 4.0℃ of the accumulated threshold value of NINO Z index. Further, predictions of most statistical and dynamic models indicated the SST anomalies in the central and eastern equatorial Pacific will continue to be above 0.5℃ in the coming 3 months.

Based on aforementioned analysis, El Nino event will persist within the subsequent 3 months. Therefore, we need to closely monitor the developments of ENSO conditions and update our ENSO wrap-up in time.