Monthly Highlights

Climate in China

During December 2006, monthly mean surface air temperatures were generally close to and above normal in most of China, with 1- 4℃ above normal in most of the Northeast, northern Xinjiang, most of Tibet and Hainan, while temperatures were below normal in southwestern Xinjiang, western Inner Mongolia. For the month, precipitations were 30-200% more than normal in southwestern and eastern Xinjiang, most of Qinghai, southern Gansu, western and central Inner Mongolia, southwestern Sichuan and southeastern coast. Meanwhile, precipitations were observed 30-80% below average in most of the Northeast, central and southern Xinjiang, northern Jiangnan, western South China, southern Yunan and southern Tibet, with no precipitation in parts of above regions.

Climate in the world

During December 2006，monthly mean surface air temperatures were more than 2℃ above normal in most Eurasia north to 45°N , most of Tibet, mid-east of America and most of Alaska, with 4-9℃ above normal in northern Europe, southwestern Russia and northeastern America. Meanwhile, temperatures were 1-3ºC below normal in parts of northeastern Asia, most of West Asia, parts of Central Asia, southwestern Alaska, parts of eastern West Africa and eastern coast of Australia, with 3-7℃ below normal in western Kazakhstan.

For the month, precipitations were observed 50~100% more than average in parts of northern Europe, western and part of northeastern Russia, regions from Arabia to Pakistan, western East Asia, northwestern and southeastern Africa, middle America, middle and southern South America and western Australia, with 200% above normal in locations. Meanwhile, precipitations were more than 50% below average in southern and eastern Europe, most of India, northwestern and northeastern China, southern West Africa, parts of northern America and northern Alaska, northern and eastern South America and eastern Australia, with no precipitation in parts of above regions.

General Circulation Features

Northern Hemisphere: During December 2006, 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 covered the North Pacific, the central North Atlantic Ocean, western Russia, with center value below –16 dam over the northeastern North Pacific. Meanwhile, positive anomalies above 4 dam covered most Europe, east-central North America with maximum above 12 dam over Europe. For the month, the Northwest Pacific subtropical high was larger, stronger than normal and extended farther west than normal.

Southern Hemisphere: For the month, zonal circulation mainly dominated the western Hemisphere and meridional circulation prevailed in the eastern Hemisphere in the mean 500hPa geopotential height field at the mid-high latitudes. In the 500hPa height anomaly field, obviously negative anomalies were found over regions south to southern South America with central values below –8 dam. Meanwhile, obviously positive anomalies were observed over the western South Atlantic Ocean and the central South Pacific with maximums above 8 dam. Heights were near normal in the other regions.

Tropical Features

Sea Surface Temperatures (SSTs): During December 2006, positive SST anomalies above 0.5℃ maintained in the equatorial Pacific east of 160ºE with maximums above 2.0℃　in the eastern and the central Pacific, respectively. All of the NINO indices changed little with the exception of NINO1+2. NINO Z，NINO 3.4, NINO 3, NINO 4 and NINO 1+2 indices were 1.2℃，1.3℃，1.3℃，1.2℃ and 0.4℃, respectively. Meanwhile, SSTs were more than 0.5℃ above normal in the equatorial Indian Ocean.

Warm Pools: During December 2006, areas of the western Pacific and Indian Ocean warm pools were above normal and their intensities were both stronger than normal.

Subsurface Temperatures: During December 2006, the anomalously subsurface warm waters in the east-central equatorial Pacific Ocean weakened and shifted eastward and upward. Meanwhile, the anomalously cold water in offshore of South America enhanced compared with last month.

Wind Field：During December 2006, at the lower troposphere (850hPa), easterly anomalies covered the west-central equatorial Pacific and the west-central equatorial Indian Ocean and weak westerly anomalies were observed over the eastern equatorial Pacific. At the upper troposphere (200hPa), strong easterly anomalies covered the eastern equatorial Pacific. Zonal winds were near normal over the west-central equatorial Pacific and the equatorial Indian Ocean.

Southern Oscillation: For the month, Southern Oscillation Index (SOI) was -0.2, with a decrease of 0.4 from last month.

Convection over the Tropics: During December 2006, the anomalous outgoing longwave radiation (OLR) showed that convections were suppressed over Indonesia and the western equatorial pacific and enhanced slightly over the equatorial India and the equatorial central Pacific around the Date Line. In the lower troposphere (850hPa) divergent wind field, a convergent center was observed over 130ºE, 5ºS, and a divergent center was located in 110ºW, 5ºS. Correspondingly, at the upper troposphere (200hPa), the divergent center was found over 162.5ºE, 2.5ºS, and the convergent center was over 105ºW, 5ºS.

ENSO Monitoring and Prediction

(1) Positive SST anomalies above 0.5ºC maintained in the equatorial Pacific Ocean east of 160ºE. The index of NINO Z was 1.2ºC.

(2) The anomalously subsurface warm waters in the east-central equatorial Pacific Ocean weakened and shifted eastward and upward.

(3) Southern Oscillation Index (SOI) was -0.2,

(4) At the lower troposphere (850hPa), easterly anomalies covered the west-central equatorial Pacific and weak westerly anomalies were observed over the eastern equatorial Pacific.

(5) Convections were suppressed over Indonesia and the western equatorial Pacific and enhanced slightly over the equatorial central Pacific around the Date Line.

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

In conclusion, tropical oceanic and atmospheric conditions showed obvious features of ENSO warm phase, which had been maintaining for 5 months. A warm ENSO event came into being and these features are expected to persist in the following 2~3 months.