Monthly Highlights

1.Climate in China

During　July, China’s mean surface air temperature was the third highest for the past 40 years. Monthly mean surface air temperatures were 1-2℃above normal in north-central North China, west-central Inner Mongolia, west-central Gansu, eastern and northern Xinjiang, the eastern Tibet Plateau, most of the regions south to the Yangtze River , with more than 2℃above normal in western Inner Mongolia and northwestern Xinjiang. For the month, precipitations were mainly featured below normal. While precipitations were 30-100% above normal in the Huaihe River and the Hanshui River, the coast of Zhejiang and Fujian, southwestern Heilongjiang, southwestern and western Xinjiang and the northern Tibet Plateau, with 100-200% more than above normal in parts of above regions, precipitations were near or below normal in most of the remainder of China, with 50-80% below normal in northern Xinjiang, west-centrral Inner Mongolia, northeastern Heilongjiang and parts of South China.

2. Climate in the World

During July, monthly mean surface air temperatures were mainly featured above normal in the world. While temperatures were about 1℃ below normal in the region from western Canada to eastern Alaska, temperatures were near or above normal, with 2-3℃above normal in Mongolia and the region west to Lake Baikal, most of Turkey, northern Algeria, western South Africa and much of western USA.

During July, precipitations were mainly featured below normal. Precipitations were more than 50% above normal in much of Russia’s Far East region, the region from the Huaihe River westward to southern Xinjiang in China, north-central Europe, central Australia and eastern USA, with more than 200% above normal in parts of above regions. Meanwhile, precipitations were near or below normal in the remainder of the world, with 50-100% below normal in North China and South China, Central Asia, the East European Plan, the coast north to the Mediterranean Sea and northern Northwest Africa, South Africa, northern and southwestern Australia, west-central USA and most of South America.

3. General Circulation Features

Northern Hemisphere: During July, the mean 500hPa geopotential height field exhibited that zonal circulation prevailed over Eurasia, and the polar vortex was weaker than normal. In the height anomaly field, above 4 dam height anomalies were over the regions around Lake Baikal, the northern North Atlantic Ocean and the regions around the Aleutian Islands, with central value above 8 dam. Meanwhile, heights were more than 4 dam below normal over northwestern Canada. For the month, the Northwest Pacific subtropical high was larger, stronger and expanded more westward than normal.

Southern Hemisphere: During July, the mean 500hPa geopotential height field exhibited a 3-wave pattern at the mid-high latitudes. In the height anomaly field, negative anomalies below -4 dam covered the South Indian Ocean south to 40ºS and the regions eastward to New Zealand, and the southwestern South Atlantic Ocean, with central value below -8 dam. Meanwhile, heights were near or more than 4 dam above normal over the remainder of the mid-high latitudes, with maximum above 12 dam over the Weddell Sea.

4. Tropical Features

Sea Surface Temperatures (SSTs): During July, while SST anomalies below -0.5℃ were observed in the offshore of South America, near or above normal SST dominated most of the equatorial Pacific, with a generally slight weakening in intensity of the positive anomalies. The indices of NINO Z, NINO3.4 and NINO1＋2 were 0.3℃, 0.4℃ and -0.7℃, with drops of 0.1℃, 0.2℃ and 0.1℃ since last month, respectively, while those of NINO 3 and NINO 4 were the same as those for last month.

Subsurface Temperatures: During July, subsurface ocean temperatures were near normal in the central and eastern equatorial Pacific, while the abnormally subsurface cold water in the offshore of South America weakened slightly since last month and shifted upward.

Warm Pools: During July, the area and the intensity of the western Pacific warm pool were larger and stronger than normal, respectively, and those of the Indian Ocean warm pool were close to and stronger than normal, respectively.

Wind Field：During July, at the lower troposphere (850hPa), westerly anomalies about 2-4m/s covered most of the equatorial Pacific. Meanwhile, at the upper troposphere (200hPa), zonal winds were near normal over the equatorial Pacific and the equatorial Indian Ocean.

Southern Oscillation: During July, Southern Oscillation Index (SOI) was 0.0.

Convection over the Tropics: For the month, the anomalous outgoing longwave radiation (OLR) showed that convections were slightly enhanced over the western Pacific. In the lower troposphere (850hPa) divergent wind field, a convergent center was over 125ºE, 15ºN, and a divergent center was close to 100ºW, 15ºS. Correspondingly, at the upper troposphere (200hPa), a divergent center and a convergent center were around 117.5ºE, 12.5ºN and 112.5ºW, 17.5ºS, respectively.

5. ENSO Monitoring and Forecasting

①  During July, sea surface temperatures were generally close to normal in the equatorial Pacific.

②   During July, subsurface ocean temperatures were near normal in the central and eastern equatorial Pacific.

③   The Southern Oscillation Index (SOI) was 0.0 in July.

④ During July, convections were slightly enhanced over the western Pacific.

⑤ Forecasts of most ENSO statistical models showed that SSTA index for NINO 3 will continue to be near normal in the following 3 months.

Above results showed that generally tropical atmospheric and oceanic conditions were near normal in July and ENSO cycle will likely be neutral in the following 3 months. The evolution will be monitored closely and continuously.