Monthly Highlights

Climate in China

During November 2007, monthly mean surface air temperatures were 1-2ºC below normal in southwestern Guangxi and northern Tibet. Meanwhile, temperatures were near or above normal in the remainder of China, with 1-2 ºC above normal in most of Northwest China, western North China, mid-western and northeastern Inner Mongolia and mid-western Heilongjiang and with 2-4ºC above normal in northern Xinjiang. For the month, precipitations were 30-200% above normal in northeastern North China, mid-eastern Tibet and central Southwest China, with more than 200% above normal in parts of above regions. Meanwhile, precipitations were 50-80% below normal in the eastern Jiangnan area, the Huanghuai area, eastern Southwest China, northern North China, parts of northern Xinjiang, southern Northeast China and parts of northern Northeast China, with less than 80% below normal in most of the Jiangnan area, most of North China, most of Inner Mongolia, most of Northwest China and western Tibet.

Climate in the World

During November 2007, monthly mean surface air temperatures were observed 1-2 ºC above normal in most of Asia, coasts of northern Europe, southern Australia, mid-western North America, eastern South America, North Africa and southern South Africa, with 2-8ºC above normal in most Siberia and Alaska. Meanwhile, temperatures were 1-2 ºC below normal in eastern America, most of Europe, southern South America, western South Africa and parts of central Australia.

For the month, precipitations were observed 50-100% above normal in most of Europe, northern Siberia, parts of Southwest China, southern West Africa, southwestern America and western Alaska, parts of central South America, southeastern Australia, with 200% above normal in parts of above regions. Meanwhile, precipitations were more than 50% less than normal in southern Europe and parts of northern Europe, most of Asia, northern Africa, southern East Africa, mid-western Australia, most of America, eastern Alaska, coasts of northeastern South America and southern South America, with no precipitation in parts of above regions.

General Circulation Features

Northern Hemisphere: During November 2007, the mean 500hPa geopotential height field exhibited 3-wave pattern at the mid-high latitudes, with the troughs over the mid-eastern Europe, northern North Pacific and eastern North America. In the 500hPa height anomaly field, negative anomalies below -4 dam covered mid-eastern Europe, northern North Pacific, northeastern North America, with central values below -8 dam over eastern Europe and northern North Pacific. Meanwhile, positive anomalies above 4 dam covered northern North Atlantic, northwestern South Asia, western Siberia, regions from northeastern North Pacific to western North America and parts of the Arctic Ocean, with central values above 16 dam over northern North Atlantic. For the month, the Northwest subtropical high was smaller than normal and its strength is near normal. Its ridge line position was further northward than normal and extended further eastward than normal.

Southern Hemisphere: For the month, circulation appeared to be zonal obviously at the mid-high latitudes. In the 500hPa height anomaly field, positive anomalies above 4 dam covered seas around the Antarctica, most of subtropical areas of South Indian Ocean and South Pacific, with central values above 8 dam over oceans in south of Australia. Meanwhile, negative anomalies below -4 dam covered most of mid-high latitudes, with central values below -8 dam over the oceans in south of South Africa.

Tropical features

Sea Surface Temperatures (SSTs): During November 2007, the cold water in the central-eastern equatorial Pacific strengthened compared with last month, while the warm water in the western equatorial Pacific weakened. Indices of NINO Z, NINO 3.4, NINO 4, NINO 3 were -1.5℃, -1.5℃, -1.0℃ and -1.8℃, with drops of 0.3℃, 0.1℃, 0.4℃ and 0.3℃ from last month, respectively. And NINO 1+2 index was 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, anomalously cold subsurface water shifted westward and upward, while its intensity changed little. Meanwhile, the intensity of warm subsurface water in the western equatorial Pacific enhanced slightly.

Warm Pools: During November 2007, the western Pacific warm pool was near normal in area but strengthened in intensity, and shifted westward slightly compared with normal. Meanwhile, the Indian Ocean warm pool enlarged slightly in area and strengthened in intensity compared with normal.

Wind Field：For the month, at lower troposphere (850hPa), the zonal winds were near normal over the eastern equatorial Pacific, and the easterly anomalies still covered the central equatorial Pacific but strengthened slightly compared with last month. Westerly anomalies covered the western equatorial Pacific west to 150ºE. Meanwhile, weak easterly anomalies covered the central equatorial India Ocean. At upper troposphere (200hPa), westerly anomalies dominated the eastern and central tropical Pacific.

Southern Oscillation: For the month, Southern Oscillation Index (SOI) was 0.8, with no change from last month.

Convections over the Tropics: During November 2007, the anomalous outgoing long wave radiation (OLR) showed that convections were enhanced over the tropical western Pacific, while convections were suppressed over the central equatorial Pacific. For the tropical Pacific, in the divergent wind field at lower troposphere (850hPa), a convergent center and a divergent center located at 160ºE, 5ºS, and 110ºW, 5ºS, respectively, while the corresponding divergent and convergent centers at upper troposphere (200hPa) were over 175ºE, 15ºS, and 110ºW, 10ºS, respectively.

ENSO Monitoring and Prediction

(1) Compared with last month, SSTa in most the equatorial Pacific decreased obviously during November, and the NINO Z index dropped to -1.5℃, and the cumulate value achieved -4.3℃ for recent 4 month from August to November, showing a developing trend of La Nina conditions.

(2) Anomalously cold subsurface water in the central and eastern equatorial Pacific expended westward, while the intensity of warm subsurface water in the western equatorial Pacific enhanced slightly.

(3) Southern Oscillation Index (SOI) was 0.8 during this month, with no change 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 La Nina conditions are likely to persist in the following 3 month but its intensity slightly weaken.

In a word, La Nina conditions are now well established across the central and eastern equatorial Pacific, and will persist through early 2008 and come forth a La Nina event.