Monthly Highlights

1. Climate in China

In July 2011, the monthly mean surface air temperature was 22.1℃, with 0.7℃ above normal (21.4℃) being the 7th highest since 1951. The temperatures were near and above normal in most China, with temperatures 1~2℃ above normal in eastern Xinjiang, part of west and northeast of Inner Mongolia, middle and northern Gansu, northwestern Tibet, northwestern Qinghai, middle Jilin, most of Heilongjiang, eastern Jiangnan, eastern Yunnan, mid-northern Guangxi, northwestern Guizhou, southeastern Hunan, and 2～4℃ above normal in parts of above locations. For the month, average precipitation over China was 105.8 mm, with 8.7% less than normal (115.9 mm) being the 1^st least since 2001. The Precipitations were near and less than normal in most China, with precipitations were observed at least 30% ~ 80% less than normal in mid-western Northwest China, middle and western Inner Mongolia, southern North China, most Huanghuai and Jianghan, middle and western Jiangnan, western South China, eastern Southwest China, southeastern Northeast China, and at least 80% less than normal in parts of above locations. Meanwhile, precipitations were 30-100% more than normal in Northern Xinjiang, eastern Inner Mongolia,  western Northeast China, middle Tibet, part of eastern Northwest China, most Jianghuai, and 100% ~ 200% more than normal in parts of above locations.

During July, daily maximum temperature extremes, daily rainfall amounts extremes, persistent rainfall amounts extremes and persistent rainy days extremes were observed mainly in China. Daily maximum temperature extremes occurred in 129 stations, with daily maximum temperatures reached or broke historical records in 15 stations of them.  Consecutive hot day extremes occurred in 46 stations in China. They reached or broke history records in Yiliang station (11days), Yunnan and Hongliuhe station ( 8days ), Xinjiang. Mainly during second and third 10 days of July, consecutive hot day extremes occurred at 38 stations in the Jiangnan area, South China, northeastern Southwest China, Gansu, Hebei. Persistent rainfall amount extremes occurred at 52 stations of China, with amounts breaking records at 10 stations, such as Gaoping, Shanxi (146.7mm), Rushan, Shandong (323.5mm), and Ganluo, Sicuan (114.1mm). Persistent rainy day extremes were observed at 42 stations in China, with days breaking records at Fuyu station, Heilongjiang. The events occurred mainly at 30 stations in mid-western Heilongjiang, mid-northern North China, Beijing and Tianjin, northeastern Northwest China and Jiangsu during first-second ten days, and 7 stations during second-third ten days of July. The events kept for 9-11 days in general.

2. World Climate

During July 2011, monthly mean temperatures were observed 2℃ above normal in most eastern Europe, northeastern Asia, partly northwestern China, parts of eastern Africa, central and eastern America and central South America, with temperatures at least 4℃ above normal in locations of northeastern Europe and northeastern Asia. Meanwhile, monthly mean surface air temperatures were observed 1-4℃ below normal in regions from southeastern Europe, regions from east of West Siberia to west of central Siberia, northern Central Asia, locations of northern Africa and southern Africa, central and western North America, northern Australia.

For the month, precipitations were at least 50% more than normal in Central and southern Europe, central Siberia and partly eastern Siberia, northern Northeast China, the central Indochina Peninsular, northwestern and northeastern America, northern West Africa, southeastern South Africa, southwestern Australia, eastern Argentina, locations of Peru, with precipitations at least 200% above normal in locations.  Meanwhile, precipitations were at least 50% less than normal in southwestern Europe and coasts of Mediterranean Sea, regions from the Caspian Sea to western Central Asia, northern West Siberia, southern East Siberia, central Mongolia, northwestern China, eastern Northeast China, central and southern America, central South America, central and eastern Australia western coasts, partly central and eastern Africa, with no precipitation in central Asia, eastern Africa, north-central South America and northwestern Australia.

3. General Circulation Features

Northern Hemisphere: During July 2011, the field of mean 500hPa geopotential height exhibited a 5-wave pattern over the mid-high latitudes. In the field of height anomaly, positive anomalies above 4 dam were located in most of Arctic region, regions from the Sea of Okhotsk to eastern Russia, the northeastern North Pacific Ocean, central North America, the central North Atlantic Ocean and regions around the Ural mountain, respectively, with central values above 12 dam over the polar region. Meanwhile, negative anomalies below -4 dam covered West Europe, central Russia and northwestern North America. For the month, the area and intensity of West Pacific Subtropical High were smaller and weaker than normal, while the western ridge point and ridge line position were a bit more eastern and northern, respectively.

Southern Hemisphere: During July 2011, the field of mean 500hPa geopotential height exhibited a 3-wave pattern over the mid-high latitudes. In the field of height anomaly, positive anomalies above 4 dam covered the southern South Pacific Ocean south to Australia, the southeastern South Atlantic Ocean, the southeastern South Pacific Ocean, with central values above 20 dam over the South Pacific Ocean south to Australia and the southeastern South Pacific Ocean. Meanwhile, negative anomalies below -4 dam mainly covered the sea basin of South Indian Ocean and southwestern South Pacific Ocean, with central values below -20 dam over the southeastern South Pacific Ocean.

4. Tropical Features

Sea Surface Temperatures (SSTs): During July 2011, SSTs in most of the central and eastern equatorial Pacific were near normal. The positive SSTA in the eastern equatorial Pacific Ocean near the South America coastline decreased, with values within 1.0℃. The SSTA in NINO 1+2, NINO 3, NINO 4, NINO 3.4, and NINO Z regions were 0.3℃, 0℃, -0.1℃, -0.1℃, and 0℃, respectively. Except for the NINO4 index increased 0.1℃, the indices in the other four areas respectively decreased 0.4℃, 0.2℃, 0.1℃, and 0.1℃ compared with those in June.

Subsurface Temperatures: During July 2011, positive sea temperature anomalies dominated subsurface equatorial Pacific Ocean except for the negative sea temperature anomalies in the central and eastern equatorial Pacific Ocean to the east of 160°W at the depth of -100~-150 m and in the western equatorial Pacific at the depth of -200~-300 m. The central value of positive anomalies in the western and central equatorial Pacific at the depth of -100~-200 m reached 3℃, but was slightly lower than that in June.

Warm Pools: During July 2011, the area of the Indian Ocean warm pool was slightly larger than normal and its intensity was above normal. The intensity of the western Pacific warm pool was obviously greater than normal. Meanwhile, its area was larger than normal in the northeastern and southern parts of warm pool.

Wind Field: In July 2011, at lower troposphere (850hPa), easterly anomalies dominated over the central and western equatorial Pacific to the west of 150°W, and westerly anomalies were observed over the central and eastern equatorial Pacific to the east of 150°W. At upper troposphere (200hPa), westerly anomalies above 4 m/s covered most of the equatorial Pacific except for weak easterly anomalies over the eastern equatorial Pacific around 110°W.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 0.9, with an increase of 0.6 compared with that in June (0.3).

Convections over the Tropics: During July, the anomalous outgoing long-wave radiation (OLR) showed that the region of active convection was still over the western equatorial Pacific, but the intensity was slightly larger than that in June. Meanwhile, the region of inactive convection over the central Pacific Ocean to the south of the equator around the dateline was slightly developed.

In the divergent wind field at lower troposphere (850hPa), the convergent and divergent centers were around 140°E, 10°N and 100°W, 20°S, respectively. At upper troposphere (200hPa), the corresponding divergent and convergent centers were near 130°E, 10°N and 100°W, 25°S, respectively.

5. ENSO Monitoring and Outlook

Monitoring on atmospheric and oceanic conditions showed that during July 2011 SSTs in most of the central and eastern equatorial Pacific were near normal. The indices for NINO 3 and NINO Z regions dropped to zero. The subsurface temperatures were above normal in the central and western equatorial Pacific, but below normal in the eastern equatorial Pacific. SOI increased from 0.3 in June to 0.9 in July. The zonal wind anomalies at lower level maintained the pattern of June in the equatorial Pacific, but the westerly anomalies at higher level enlarged in the central and eastern equatorial Pacific with intensity weakening notably. The convection over the equatorial western Pacific was a little more active than that in June. All above features indicate that ENSO-neutral conditions continued across the equatorial Pacific, while the anomalous convection, zonal wind, and sea level pressure in the tropical Pacific still reflected the aspects of La Niña.

At present, the predictions of most statistical and dynamic models shows that SST in the equatorial central and eastern Pacific will mainly maintain normal status in fall 2011. Based on the above-stated results of model forecasts and monitoring information, it is expected that ENSO-neutral condition will last through the boreal fall 2011, with slightly below normal SSTs over most Niño regions. We will closely monitor the development of ENSO conditions and update our ENSO wrap-up in time.