Monthly Highlights

Climate in China

During July 2008, the monthly mean surface air temperatures were observed at least 1℃ above normal in northern and eastern Xinjiang, most Gansu, central and eastern Inner Mongolia, most Heilongjiang and eastern East China, with temperatures 2-4℃ above normal in parts of Xinjiang and Inner Mongolia. Meanwhile, temperatures were near normal in other regions of China. For the month, precipitations were observed 30-100% more than normal in the Huanghuai area, the Jianghan area, eastern South China, southern Xinjiang, the central Tibetan Plateau, central Northwest China and western Inner Mongolia, with over 200% more than normal in locations. Meanwhile, precipitations were observed 30-80% less than normal in northern and eastern Xinjiang, the western Tibetan Plateau, eastern Inner Mongolia, most North China, southeastern Northwest China and northern Sichuan, with at least 80% less than normal in eastern Xinjiang and parts of the western Tibetan Plateau.

Climate in the World

During July 2008, temperatures were 1-2℃ above normal in most Eurasia at mid-latitudes, west-central and northeastern North America, central South America, North Africa and central Australia, with temperatures at least 4℃ above normal in part of South America. Meanwhile, temperatures were 1-2℃ below normal in parts of northern Europe, central Russia and Far East Russia, northwestern and southern North America.

For the month, precipitations were observed 50-100% more than normal in central and eastern Europe, central and eastern Russia, northwestern, southwestern and northeastern North America, parts of northern South America, parts of North Africa, northeastern and southwestern Australia, with precipitations at least 200% more than normal in locations. Meanwhile, precipitations were at least 50% less than normal in parts of north-central Russia, southern Europe, northern West Asia, parts of Central Asia, western South Asia, western and southeastern America, central South America, parts of North Africa, most Tanzania and most Australia, with no precipitations in parts of above regions.

General Circulation Features

Northern Hemisphere: During July 2008, in the 500hPa geopotential height anomaly field, positive anomalies above 4 dam covered the regions from the northwestern North Atlantic to polar regions through Greenland and the northwestern North Pacific. Meanwhile, negative anomalies below -4 dam covered parts of the northeastern North Atlantic, parts of central Russia and the regions from Far East Russia to northwestern North America. For the month, the subtropical high over the West Pacific was larger and stronger than normal and its position was more southward.

Southern Hemisphere: For the month, 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 the regions from the southern South Indian Ocean to parts of Antarctica, the southern South Pacific, southern South America and the southwestern South Atlantic, with central values over 8 dam over the southern South Indian Ocean. Meanwhile, negative anomalies below -4 dam covered the southeastern South Pacific and parts of Antarctica.

Tropical Features

Sea Surface Temperatures (SSTs): In July, the area of negative SST anomalies shrank remarkably and only appeared in regions round the dateline, with central value about -0.5℃, while positive SST anomalies dominated the eastern equatorial Pacific. In July, indices of NINO 1+2, NINO 3, NINO 4, NINO 3.4 and NINO Z were 0.8℃, 0.5℃, -0.3℃, 0.1℃ and 0.2℃, with rises of 0.3℃, 0.4℃, 0.3℃, 0.4℃and 0.3℃ from last month, respectively. Meanwhile, SSTs in most of the equatorial Indian Ocean were near normal.

Subsurface Temperatures: During July, anomalously cold subsurface water in the central equatorial Pacific became further weak, while anomalously warm water dominated the whole thermocline and particularly enhanced in the eastern equatorial Pacific.

Warm Pools: During July, areas of the western Pacific warm pool and the Indian Ocean warm pool were near normal and their intensities were slightly above normal.

Wind Field：For the month, at lower troposphere (850hPa), easterly anomalies covered the central equatorial Pacific, with the maximum above 4m/s, while weak westerly anomalies prevailed over the eastern equatorial Pacific. At upper troposphere (200hPa), weak westerly anomalies dominated the western and central equatorial Pacific, while easterly anomalies covered the eastern equatorial Pacific.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 0.2, with a drop of 0.1 from last month.

Convections over the Tropics: During July, the anomalous outgoing long wave radiation (OLR) showed that convection was near or slightly weaker than normal over the western and central equatorial Pacific. For the tropical Pacific, in the divergent wind field at lower troposphere (850hPa), convergent wind appeared in the western tropical Pacific with no obvious center, while divergent wind covered the eastern Pacific with a center over 110ºW, 20ºS. Correspondingly, at upper troposphere (200hPa), the divergent center was over 120ºE, 15º N, and the convergent center was over 110ºW, 25ºS.

ENSO Monitoring and Prediction

(1) During July, SST anomalies in the central and eastern equatorial Pacific showed a pattern of “cold in the west and warm in the east”, with obvious warmer than normal surface water in the eastern equatorial Pacific.

(2) For the month, anomalously warm subsurface water in the eastern equatorial Pacific enhanced distinctly.

(3) Southern Oscillation Index (SOI) was 0.2.

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

(5) Convection was near or slightly weaker than normal over the western and central equatorial Pacific.

(6) For the prediction of ENSO cycle within 6 months, there existed different results from statistical and dynamical models, but for the next 2-3 months, most models predicted ENSO-neutral conditions.

During July, generally the oceanic and atmospheric status showed ENSO-neutral conditions in the equatorial Pacific, but anomalously warm conditions were obvious in the eastern equatorial Pacific. For the next 2-3 months, the intensity of the warm water in the eastern equatorial Pacific may decrease and ENSO-neutral conditions are expected to continue.