Monthly Highlights

Climate in China

During July 2006，the monthly mean surface air temperature was the third highest over China in the same period of history since 1951. Monthly mean surface air temperatures were near or above normal in most of China, with temperatures 1-2ºC above normal in mid-eastern Northwest China, most of Southwest China, the eastern Jiangnan area, central Inner Mongolia and mid-northern Shanxi in which temperatures were 2-4 ºC above normal in most of Northwest China and Southwest China. Near or below normal temperatures were observed in the remainder of China. For the month, precipitations were observed 30-50% more than average in northern Northeast China, the Jianghuai area，South China, eastern and southwestern Northwest China, with precipitations 100-200% more than normal in locations. Meanwhile, precipitations were less than or close to normal in the rest area of China, with precipitations 30-50% less than normal in mid-southern Northeast China, Southeastern North China, most of Southwest China, and parts of Inner Mongolia and Xinjiang.

Climate in the world

During July 2006，monthly mean surface air temperatures were observed 2-4 ºC above normal in most of Europe, mid-western America, southern South America, central Siberia, eastern Southwest China and parts of Northwest China, with temperatures 5-6 ºC above normal in locations of Europe. Temperatures were near or below normal in the rest area of the world, with temperatures 1-3 ºC below normal near the Ural Mountains. For the month, precipitations were observed above 30% less than average in most of Europe, Siberia, most of China, northwestern and southern South Asia, western Australia, West Africa, South Africa, mid-western and southeastern America, and central South America, with no precipitation in parts of them. Precipitations were found above 50% more than average in the Ural Mountains, Central Asia, coasts of southeastern China, most of the Korea Peninsula, central Japan, central India, mid-eastern Australia, southern and northeastern America, coasts of northern South America and southern South America.

General Circulation Features

Northern Hemisphere: During July 2006, the mean 500hPa geopotential height field exhibited mainly a 3-wave pattern at the mid-high latitudes. Abnormal ridges developed over Europe, western North America and north of the Lake Baikal. In the 500hPa height anomaly field, positive anomalies above 4 dam controlled areas from Europe to Greenland, from western North America to the North Pacific, and north of the Lake Baikal, with maximum above 12 dam. The rest areas were covered by near-normal or negative anomalies with anomalies below -20 dam over the Ural Mountains. For the month, the Northwest Pacific subtropical high was larger and stronger than normal. It was located in farther north than normal and it extended farther west than normal.

Southern Hemisphere: For the month, the mean 500hPa geopotential height field exhibited a 3-wave pattern at the mid-high latitudes and troughs were located in south of the South Pacific Ocean, the South Atlantic Ocean and the South Indian Ocean. While parts of the South Pacific Ocean and the Southwest Indian Ocean were covered by positive height anomalies, the rest mid-high latitudes were controlled by negative height anomalies, with central values below -28 dam over south of the South Pacific Ocean.

Tropical Features

Sea Surface Temperatures (SSTs): During July 2006, SSTa increased in the equatorial eastern Pacific especially near the offshore of South America, while positive SST anomalies weakened in the equatorial western Pacific Ocean. Positive anomalies above 0.5ºC appeared in the equatorial central Pacific Ocean and near the offshore of South America. Meanwhile, SSTs were near normal in the rest of the equatorial Pacific and the equatorial Indian Ocean. The indices of NINO Z, NINO 3 and NINO1+2 were 0.4c, 0.3º C and 0.4ºC respectively, with rises of 0.2ºC, 0.2ºC and 0.7ºC respectively since last month, while index of NINO 3.4 was 0.3ºC with a drop of 0.1ºC and index of NINO 4 was 0.5ºC，the same as last month.

Subsurface Temperatures: During July 2006, abnormal subsurface warm water enhanced in the equatorial Pacific Ocean, and its eastern parts slightly ascended, while abnormal subsurface cold water weakened and shrank eastwardly in the offshore of South America.

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

Wind Field：During July 2006, at the lower troposphere (850hPa), weak westerly anomalies covered most of the equatorial Pacific Ocean, while weak easterly anomalies controlled the equatorial Indian Ocean. At the upper troposphere (200hPa), easterly anomalies dominated the equatorial eastern Pacific, while zonal winds were near normal over the rest equatorial Pacific and the equatorial Indian Ocean.

Southern Oscillation: For the month, Southern Oscillation Index (SOI) was -0.8, with a drop of 0.3 from last month.

Convection over the Tropics: During July 2006, the anomalous outgoing longwave radiation (OLR) showed that convections were suppressed over most of the equatorial western Pacific but enhanced in north of Philippine. In the lower troposphere (850hPa) divergent wind field, a convergent center was over 135ºE, 15ºN, and a divergent center located around 105ºW, 15ºS. Correspondingly, at the upper troposphere (200hPa), the divergent center was found over 120ºE, 15ºN, and the convergent center was observed over 120ºW, 20ºS.

ENSO Monitoring and Prediction

① During July 2006, positive SST anomalies above 0.5ºC controlled the equatorial central Pacific Ocean and near the offshore of South America, while SSTs were near normal in the rest of the equatorial Pacific. All the NINO indices were positive but in the range of normal values.

② During July 2006, abnormal subsurface warm water enhanced in the equatorial Pacific Ocean, and its eastern parts slightly ascended, while abnormal subsurface cold water weakened and shrank eastwardly in the offshore of South America.

③ Southern Oscillation Index (SOI) was -0.8, with a drop of 0.3 from last month.

④ During July, at the lower troposphere (850hPa), weak westerly anomalies covered most of the equatorial Pacific Ocean. At the upper troposphere (200hPa), easterly anomalies dominated the equatorial eastern Pacific.

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

⑥ Most of statistical and coupled models predicted that SSTs could be near normal during following six months.

In conclusion, tropical oceanic and atmospheric conditions showed features of weak warm phase, and these features were expected to persist in the following 1~2 months.