Highlights

    General Circulation Features

    Northern Hemisphere

During July, the mean 500hPa geopotential height fields exhibited a 4-wave pattern in the mid-high latitudes. In the height anomaly field, positive anomalies covered most of Europe, with the maximum anomalies above 8 dam. Meanwhile, negative anomalies covered the northeastern Atlantic and western Siberia. In addition, positive anomalies above 8 dam dominated the regions from eastern Siberia to the Aleutian. Meridional circulation enhanced remarkably over East Asia. The trough over eastern North America was deeper than normal. In this month, the Northwest Pacific subtropical high was obviously stronger than normal and extended westward remarkably.

    Southern Hemisphere

During this month, the mean 500hPa geopotential height fields exhibited a 3-wave pattern in the mid-high latitudes. Troughs were over the southern parts of the Pacific, the Atlantic and the Indian Ocean, respectively. The Antarctic Continent was covered by positive anomalies, with the center values above 20 dam over Ellsworth Land and above 16 dam over George V Coast.

Climate for China

In July, monthly mean surface air temperatures were above normal in most of southern China, with 2~3C above normal in most of the area south to the Yangtze River and part of southern Xinjiang. The heat wave persisted in most of the area south to the Yangtze River. Meanwhile, temperatures were near or below normal in most of northern China, with 2~3C below normal in northwestern Xinjiang.

As to precipitation, rainfall totals were near or more than normal in most of northern China, with 50~200% more than normal in the most region between the Yangtz River and the Huaihe River, western Heilongjiang, central Inner Mongolia and part of northern Xinjiang. Serious flood occurred in the Reaches of the Huaihe River. Meanwhile, in the area south to the Yangtze River, rainfall totals were more than 50% below normal and serious drought occurred.

Tropical Features

    Sea Surface Temperatures (SSTs)

During July, sea surface temperature anomalies increased continuously across most of the equatorial Pacific. Positive SST anomalies of around 0.5C covered the regions west to 100W, but negative anomalies remained near the South American coast. Correspondingly, the indices of NINO 4, NINO 3 and NINO 1+2 were 0.5℃, 0.2℃ and -1.1℃, which increased sharply from 0.4℃, -0.5℃ and -1.5℃ in last month, respectively. In addition, positive SST anomalies of 0.5~1.0C were observed in most of the equatorial Indian Ocean.

    Circulation

    Wind Field

In this month, at the lower troposphere (850hPa), westerly anomalies above 2m/s expanded over the western equatorial Pacific and the area of weak westerly anomalies shrank over the central and eastern equatorial Pacific. Weak easterly anomalies dominated the area around the dateline. Westerly anomalies expanded eastward over the western equatorial Indian Ocean. At the upper troposphere (200hPa), easterly anomalies of 4~8m/s covered the eastern equatorial Pacific. The central and western equatorial Pacific and the equatorial Indian Ocean were dominated by weak westerly anomalies.

    Southern Oscillation

The Southern Oscillation Index (SOI) increased sharply from -1.0 in last month to -0.1 in this month.

    Convection over the Tropics

During July, the anomalous outgoing longwave radiation (OLR) distribution displayed that convections were stronger than normal over the western equatorial Pacific and the equatorial Indian Ocean while convective activity was near normal over the central and eastern equatorial Pacific. In the lower troposphere (850hPa) divergent wind field, a weak convergent center was nearby 130E, 20N, while a weak divergent center was around 105W, 12S. Correspondingly, at the upper troposphere (200hPa), the divergent centers were around 90E, 15N and 95W, 15N, respectively, while the convergent center was around 95W, 25S.