Monthly Highlights

Climate in China

During October 2006，the monthly mean surface air temperature was the highest over China since 1951. Monthly mean surface air temperatures were generally 2℃above normal in most of China, with maximum 4~6ºC in middle Inner Mongolia，but temperatures were slightly below normal in northern Helongjiang and most of Tibet.

For the month, precipitations were observed less than normal in most of China. Precipitations were observed 30~80% below average in northern Northeast China, most of Inner Mongolia, most of eastern China, southern Xinjiang, western Tibet, with no precipitation in southern North China, most of regions between the Yellow River and Huaihe River, southeastern Fujian and western Inner Mongolia. Precipitations were 30~50% above normal in southern Northeast China, most of Southwest China and Qinhai, northern and eastern Xinjiang, with 50~200% above normal in most of Yunnan, western Guizhou and northwestern Qinghai.

Climate in the world

During October 2006，monthly mean surface air temperatures were above normal in most the mid-low latitudes of Eurasia, northeastern Russia, most of Africa, northwestern North America, most of South America and most of Australia. Temperatures were observed 2~4ºC above normal in most of Europe, western and Central Asia, most China，northeastern Russia and Australia, with maximum above 6ºC in locations. Meanwhile, temperatures were 1~2ºC below normal in central and western Russia and most of United States and more than 2ºC below normal in locations.

For the month, precipitations were observed 50~100% above average in northern and southwestern Europe, parts of West Asia, northeastern and southern Russia, Kazakhstan, western Mongolia, northern Pakistan, Southern India, most of Indochina Peninsula, southern West Africa, eastern and middle United States and western Alaska, eastern and middle South America and western Australia，with 200% above normal in locations. Meanwhile, precipitations were more than 50% below average in regions from central Europe to northeastern Africa, northern Indian, northwestern and eastern China, eastern Mongolia, northern and middle Russia, western coastal regions and part of middle regions in United States, part of southwestern South America.

General Circulation Features

Northern Hemisphere: During October 2006, the mean 500hPa geopotential height field exhibited mainly a 4-wave pattern at the mid-high latitudes. In the 500hPa height anomaly field, positive anomalies above 4 dam covered the northeastern North Pacific, regions from northern North America to the polar region, Asia in the middle latitudes and western Mediterranean Sea, with maximum above 16 dam nearby Greenland. Negative anomalies below –4 dam were over middle Russia, the eastern North Atlantic Ocean and east-central North America with minimums below –8 dam over middle Russia. For the month, the Northwest Pacific subtropical high was larger and stronger than normal, and it was located in slightly farther north and extended farther west than normal.

Southern Hemisphere: For the month, the mean 500hPa geopotential height field exhibited mainly a 3-wave pattern at the mid-high latitudes. In the 500hPa height anomaly field, negative anomalies below –4 dam were over the southern South Pacific and most of Polar Regions, with central value below –12 dam over the southeastern South Pacific. Positive anomalies above 4 dam covered the western South Indian Ocean, western South Atlantic Ocean, southern Australia and region south to Australia, east-central South Pacific, with maximums above 8 dam. Heights were near normal in other regions.

Tropical Features

Sea Surface Temperatures (SSTs): During October 2006, positive SST anomalies above 0.5ºC were observed in the equatorial Pacific east to 160ºE with two maximum centers above 1.5ºC and 2.0ºC, which located at around 180º and 100ºW, respectively. SSTA indices increased compared with last month and NINO Z, NINO 3.4, NINO 3, NINO 4 and NINO 1+2 indices were 1.1ºC, 0.9ºC, 1.1ºC, 1.0ºC and 1.2ºC，respectively. Meanwhile, negative SST anomalies below -0.5ºC were observed in the eastern Indian Ocean south to the equator.

Warm Pools: During October 2006, areas of the western Pacific and Indian Ocean warm pools were near normal. Intensity of warm pool was near normal in the western Pacific and intensity was above normal in the Indian Ocean.

Subsurface Temperatures: During October 2006, abnormal subsurface warm water persisted in the most equatorial Pacific Ocean, with its intensities decreased obviously. Meanwhile, cold water in offshore of South America maintained.

Wind Field：During October 2006, at the lower troposphere (850hPa), westerly anomalies covered most of the equatorial Pacific, while easterly anomalies were over the equatorial Indian Ocean. At the upper troposphere (200hPa), easterly anomalies above 4m/s were over most of the equatorial Pacific and westerly anomies were over the equatorial Indian Ocean.

Southern Oscillation: For the month, Southern Oscillation Index (SOI) was –1.3, with a decrease of 0.9 from last month.

Convection over the Tropics: During October 2006, the anomalous outgoing longwave radiation (OLR) showed that convections were suppressed over regions from the eastern equatorial Indian Ocean to Indonesia and enhanced over the equatorial Pacific from 160°E to the date line. In the lower troposphere (850hPa) divergent wind field, a convergent center was over 145ºE, 15ºN, and a divergent center located around 100ºW, 20ºS. Correspondingly, at the upper troposphere (200hPa), the divergent center was found over 147.5ºE, 12.5ºN, and the convergent center was observed over 95ºW, 25ºS.

ENSO Monitoring and Prediction

(1) During October 2006, positive SST anomalies above 0.5ºC covered the equatorial Pacific Ocean east to160ºE. The index of NINO Z was 1.1ºC.

(2) Compared with last month, abnormal warm subsurface water persisted in the most equatorial Pacific but its intensity weakened obviously.

(3) Southern Oscillation Index (SOI) was –1.3.

(4) Westerly anomalies covered most of the equatorial Pacific Ocean.

(5) The anomalous outgoing longwave radiation (OLR) showed that convections were suppressed over Indonesia and enhanced over the equatorial western Pacific.

(6) Most of models predicted that SSTs would be abnormally above normal during following 3-6 months.

In conclusion, tropical oceanic and atmospheric conditions showed obvious features of ENSO warm phase which has been maintained for 3 months and these features are expected to persist in the following 2~3 months.