Monthly Highlights

Climate in China

During January 2008, the monthly mean surface air temperatures were obviously below normal in most China. Temperatures were observed 2-4℃ below normal in most Xinjiang, eastern Northwest China, Guangxi, Guizhou, Hunan, Hubei and southern Henan with over 4℃ below normal in parts of above regions. Meanwhile, temperatures were 2-4℃ above normal in most of the Tibetan Plateau, parts of Yunnan and Heilongjiang with over 4℃ above normal in parts of above regions. For the month, precipitations were observed 20-80% below normal in Northeast China, eastern North China, eastern Inner Mongolia, northern Xinjiang, central Tibet, Chongqing and Guizhou with over 80% below normal in parts of above regions. Meanwhile, above normal precipitations mainly dominated other regions with 50-200% above normal in most of the regions north to the Yangtze River, southern South China and western Yunnan.

Climate in the World

During the month, temperatures were 1-2℃ above normal in most Europe, most Russia, the Tibetan Plateau, northern West Africa, central and western Australia, parts of eastern North America and South America with temperatures 4-9℃ above normal in most of Eurasia north to 60°N. Meanwhile, temperatures were over 1℃ below normal in most Asia, southern Russia and the Far East Russia, southern West Africa, eastern Australia and western America with 6-10℃ below normal in central Asia.

For the month, precipitations were observed 50-100% more than average in northern Europe, eastern Russia, most China, eastern South Asia, eastern Australia, central and western South America, the western coasts of America and the regions around the Great Lakes and western Alaska with precipitations at least 200% above normal in locations. Meanwhile, precipitations were at least 50% less than average in most North America, parts of northern South America, most West Africa, central and western Australia, most South Asia, most of Asia between 40°N to 60°N and the Far East Russia with no precipitations in parts of above regions.

General Circulation Features

Northern Hemisphere: During January 2008, the mean 500hPa geopotential height field exhibited a 3-wave pattern at the mid-high latitudes. In the 500hPa geopotential height anomaly field, positive anomalies above 4 dam covered most Europe, the Ural Mountains, the mid latitudes of the North Atlantic Ocean, northeastern North America, the northeastern North Pacific and eastern East Asia, with central values above 12 and 16 dam over the Ural Mountains and the northeastern North Pacific, respectively. Meanwhile, negative anomalies below -4 dam covered the regions from Northeastern Asia to the North Pole, northwestern North America, the northern North Atlantic Ocean and Central Asia, with central values below -12 dam over the Arctic Ocean. For the month, the Northwest Pacific subtropical high extended westward and its ridge line position was more northward than normal.

Southern Hemisphere: For the month, zonal circulation prevailed at most of the mid-high latitudes. In the 500hPa geopotential height anomaly field, positive anomalies above 4 dam mainly covered the mid latitudes of the oceans. Meanwhile, negative anomalies below -4 dam covered most of the regions south to 60°S.

Tropical features

Sea Surface Temperatures (SSTs): During January 2008, the sea surface temperature anomalies (SSTAs) below -0.5℃ covered the central and eastern equatorial Pacific. Compared with last month, SSTAs ascended remarkably in the offshore of South America, while dropped obviously in the central equatorial Pacific. Indices of NINO Z, NINO 4, NINO 3.4 were -1.4℃, -1.6℃ and -1.8℃, with drops of 0.1℃, 0.6℃ and 0.3℃ from last month, respectively. NINO 1+2 index was -0.6℃, with a increase of 1.2℃ from last month. And NINO 3 index was –1.5℃ as same as that in last month. Meanwhile, SSTs in most of the equatorial Indian Ocean were near normal.

Subsurface Temperatures: Compared with last month, the intensity of anomalously cold subsurface water in the central and eastern equatorial Pacific strengthened slightly. Meanwhile, the intensity of anomalously warm subsurface water in the western equatorial Pacific also enhanced slightly.

Warm Pools: During January 2008, the western Pacific warm pool was near normal in area but strengthened in intensity, and shifted westward and northward slightly compared with normal. Meanwhile, the Indian Ocean warm pool was above normal both in area and intensity.

Wind Field：For the month, at lower troposphere (850hPa), weak westerly anomalies were over the eastern equatorial Pacific and the region from the eastern equatorial Indian Ocean to the western equatorial Pacific, and the easterly anomalies covered the central equatorial Pacific, with central value above 6m/s. At upper troposphere (200hPa), westerly anomalies dominated most of the central and eastern tropical Pacific and the eastern equatorial Indian Ocean.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 1.3, with a drop of 0.2 from last month.

Convections over the Tropics: During January 2008, the anomalous outgoing long wave radiation (OLR) showed that convections were enhanced over the western equatorial Pacific and suppressed over the central equatorial Pacific. For the tropical Pacific, in the divergent wind field at lower troposphere (850hPa), a convergent center was observed over 170ºE，10ºS, and a divergent center was located in 110ºW, 5ºS. Correspondingly, at the upper troposphere (200hPa), the divergent center was found over 175ºE，15ºS, and the convergent center was over the equator near 95ºW.

ENSO Monitoring and Prediction

(1) For the month, anomalously cold surface water lasted in the central and eastern equatorial Pacific, the NINO Z index was -1.4℃.

(2) Anomalously cold subsurface water maintained in the central and eastern equatorial Pacific with the intensity enhanced slightly, while the anomalously intensity of anomalously warm subsurface water in the western equatorial Pacific also enhanced slightly.

(3) Southern Oscillation Index (SOI) was 1.3 during this month, with a drop of 0.2 from last month.

(4) At lower troposphere (850hPa), easterly anomalies covered the central equatorial Pacific.

(5) Convections were suppressed over the central equatorial Pacific.

(6) Most ENSO models predicted SSTA below -0.5℃ are likely to persist in the central and eastern equatorial Pacific during the following 3 months but its intensity slightly weaken.

In a word, it keeps La Nina status in the central and eastern equatorial Pacific, and will persist through the following 3 months.