Monthly Highlights

1.Climate in China

During January 2006, monthly mean surface air temperatures were 1~4℃ below normal in most of Xinjiang, northwestern Gansu, western Inner Mongolia and parts of Heilongjiang. In the rest areas, temperatures were generally observed near normal, with 1～4℃ above normal in most of the Tibet Plateau, western Yunnan, South China，most of North China and East China.

During the month, precipitations were 30~200% above normal in most of West China, western North China, the western Huanghuai Region, the Jianghuai Region, the Low valley of the Yangtze River, Northeast China. Meanwhile, precipitations were near or below normal in the rest areas, with 30~80% below normal in most of Southwest China, most of South China, eastern North China and the northeastern Huanghuai Region, and no rainfall in locations of above regions.

2. Climate in the World

During January 2006, monthly mean surface temperatures exhibited globally a feature of values large-scale abnormally lower, as well as higher than normal. Temperatures were 2~6℃ below normal in mid-high latitudes of Eurasia, Alaska, with more than 6℃ below normal in West Siberia, Far East region and Alaska, and 10~14℃ below normal in parts of West Siberia. Meanwhile, temperatures were 2~8℃ above normal in most of North America and most of the Tibet Plateau, with 8~10℃ above normal in the regions around the common boundary between Canada and USA. Temperatures were 2~4℃ above normal in the Scandinavia Peninsula, Russia’s polar regions, parts of East Asia, southern South America and southeastern Australia. In the rest areas, temperatures were generally near or slightly higher than normal (Fig.1).

During January 2006, precipitations were observed less than normal in most of the global. Precipitations were more than 50% above normal in southwestern and southeastern Europe, western North Africa, from Middle Asia to central and eastern China, from Lake Baykal to Northeast China, western Australia, South Africa, northern South America, northwestern USA. Meanwhile, in the rest areas, precipitations were observed less than normal, with more than 50% below normal in most of Europe, most of Russia, Egypt, West Asia, South Asia, most of East Asia and Southeast Asia, eastern Australia, Alaska and central and southern USA, eastern Brazil, and no precipitation in regions from West Asia to Southwest China and northern Mongolia (Fig.2).

3. General Circulation Features

Northern Hemisphere: During January, the mean 500hPa geopotential height field exhibited a 4-wave pattern at the mid-high latitudes. In the 500hPa height anomaly field, anomalies above 4 dam were over the regions around the Novaya Zemlya Island, the mid-high latitudes of the northern Pacific, southeastern Canada, with maximum above 20 dam around the Novaya Zemlya Island. Meanwhile, anomalies below -4 dam were observed over the southeastern West Siberia, the Gulf of Alaska, central Greenland and North Africa, with central value below -12 dam over West Siberia. For the month, the Northwest Pacific subtropical high was larger and slightly stronger than normal (Fig.4).

Southern Hemisphere: During January, in the mean 500hPa geopotential height field, zonal circulation was dominant in the east hemisphere, while meridional circulation was the main feature in the west hemisphere. In the height anomaly field, anomalies more than 4 dam were observed over the central South Pacific, southeastern Australia, the southern Indian Ocean and the southwestern South Atlantic Ocean. Meanwhile, anomalies below -12 dam covered the southern South Pacific.

4. Tropical Features

Sea Surface Temperatures (SSTs): During January, SST anomalies decreased obviously in the central equatorial Pacific and increased in the eastern equatorial Pacific, with negative SST anomalies below -0.5℃ in the above regions east to the date line, and central value below -1.0℃ between 120-170ºW. In the meantime, positive SST anomalies near 0.5℃ were observed in the western equatorial Pacific. Near normal SST appeared in the eastern equatorial Indian Ocean, and negative SST anomalies were observed in the western Indian Ocean. The indices of NINO1＋2 and NINO 3 were -0.2℃, -0.6℃, with rises of 0.3℃ and 0.2℃ from last month, respectively. The indices of NINO3.4, NINO 4 and NINO Z were -0.9℃,-0.5℃, -0.5℃, and with drops of 0.3℃, 0.6℃ and 0.1℃, respectively (Fig.5).

Subsurface Temperatures: During January, the intensity of the abnormal subsurface cold water in the eastern equatorial Pacific was almost the same as that in last month, while the areas of anomalies below -1℃ extended westward. Meanwhile, the warm water strengthened slightly in the western equatorial Pacific compared with last month (Fig.6).

Warm Pools: During January, the area and the intensity of the western Pacific and Indian Ocean warm pool were larger and stronger than normal, respectively.

Wind Field：During January, at the lower troposphere (850hPa), 2-4m/s easterly anomalies were over most of the central and western equatorial Pacific, while weak westerly anomalies were over the equatorial Indian Ocean and the eastern equatorial Pacific. At the upper troposphere (200hPa), westerly anomalies were mainly over the equatorial Pacific and the equatorial Indian Ocean (Fig.7).

Southern Oscillation: During January, Southern Oscillation Index (SOI) was1.3, with a rise of 1.1 from last month.

Convection over the Tropics: During January, the anomalous outgoing longwave radiation (OLR) showed that convections were enhanced over the regions from the western tropical Pacific to the eastern Indian Ocean, and suppressed around the date line (Fig.8). In the lower troposphere (850hPa) divergent wind field, a convergent center was over 150ºE, 10ºS, and a divergent center was over 110ºW, 7ºS. Correspondingly, at the upper troposphere (200hPa), the divergent center was found over 145ºE, 7.5ºS, and the convergent center was observed over nearby 90ºW, 23ºS.

5. ENSO Monitoring and Forecasting

① During January 2006, SST anomalies rose in the eastern equatorial Pacific, and dropped obviously in the central equatorial Pacific， with indices of NINO 3, NINO 4, NINO 3.4, NINO Z all being ≤ -0.5℃.

② The SOI was 1.3 in January 2006, with a rise of 1.1 from last month.

③ The intensity of the abnormal subsurface cold water in the eastern equatorial Pacific was almost the same as that in last month, while the areas of anomalies below -1℃ extended westward. Meanwhile, the warm water strengthened slightly in the western equatorial Pacific compared with last month.

④ At the lower troposphere, easterly anomalies were over most of the central and western equatorial Pacific, while westerly anomalies covered the eastern equatorial Pacific.

⑤ Most of ENSO models showed that negative SST anomalies will persist in the eastern equatorial Pacific in the following 1~3 months.

In conclusion, tropical oceanic and atmospheric conditions reflected obvious characteristics of cold phase, and these conditions were predicted to persist during the following 1~3 months. The air – sea development in the tropical Pacific will continue to be carefully monitored.