Monthly Highlights

1. Climate in China

During September 2012, the surface air temperature averaged over China was 16.6℃, which was equal to the normal. Monthly mean surface air temperatures were 1-2℃ above normal in northern and southwestern Xinjiang, northwestern Tibet, northeastern Inner Mongolia, northeastern Northeast China. Meanwhile, temperatures were below normal in eastern Northwest China, southern Northeast China, North China, Huanghuai, Jianghuai, Jiangnan, Jianghan, eastern Southwest China and South China, with 1-2℃ below normal in western North China, southern Jianghuai, western Jiangnan, eastern Jianghan and eastern Southwest China.

In September, average precipitation over China was 73.8 mm, which was 13.2% more than normal (65.2mm). Precipitations were observed 20-100% above normal in parts of northern Xinjiang, southeastern Northwest China, North China, Northeast China, Jianghuai, Jiangnan, Jianghan, eastern Southwest China, with over 100% above normal in locations. Meanwhile, precipitations were observed 20-50% below normal in most Xinjiang, western Gansu, most Qinghai, northern Tibet, western Yunnan and South China, with over 80% below normal in southern Xinjiang and western Qinghai.

In September, extremes of Daily Precipitation (DP), Consecutive Precipitation (CP) and Consecutive Precipitation Days (CPD) were sporadically observed in China, while no extreme events of air temperature occurred.

DP extreme events occurred in Baoqing and Jixi station of Heilongjiang Province, Wangqing station of Jilin Province, Yunxi and Enshi station of Hubei Province. CP extreme events occurred in Hechuan station (233.6 mm) of Chongqing city; CPD extreme events occurred in Nyalam station (46 days) of Tibet Autonomous Region, which setting a new record.

2. World Climate

During September 2012, monthly mean temperatures were 1-4℃ above normal in mid-eastern Europe, mid-northern Asia，most North America and mid-southern South America, with temperatures 2-4℃ above normal in locations of southern Middle Europe, mid-northern Russia, northwestern Canada, central South America. Meanwhile, monthly mean temperatures were 1-2℃ below normal in the Russian Far East, parts of northern South America, central North Africa and southern South Africa, with temperatures at least 2℃ below normal in locations.

For the month, precipitations were at least 50% above normal in mid-northern Russia, northeastern East Asia, most South Asia, southeastern North America, parts of northern South America, with precipitations at least 200% above normal in locations. Meanwhile, precipitations were at least 50% below normal in most West Asia and Central Asia, northwestern China, mid-northern North America, central South America, northern Africa and most Australia, with no precipitation in locations.

3. General Circulation Features

Northern Hemisphere: During September 2012, the field of mean 500hPa geopotential height exhibited a three-wave pattern over the mid-high latitudes. In the field of height anomaly, positive anomalies above 4 dam covered northwestern America, the northwestern North Atlantic Ocean, and regions from central Siberia to the western Bering Sea, with central values above 12 dam over locations of central Siberia and the Okhotsk Sea. Meanwhile, negative anomalies below -4 dam covered regions from the eastern Bering Sea to the northwestern Alaska, central northern America, regions from the northeastern North Atlantic Ocean to Scandinavia. During the month, the northwestern Pacific subtropical high was stronger than normal, with a bigger area and a little more southward high ridge, and the west end of its ridge shifted more eastward than normal.

Southern Hemisphere: For the month, in the field of mean 500hPa geopotential height zonal circulation dominated the mid-high latitudes. In the field of height anomaly, positive anomalies above 4 dam covered locations of Antarctic, the South Atlantic Ocean and the South Pacific. Meanwhile, negative anomalies below -4 dam covered the southern South Pacific, the southern South Atlantic Ocean, and regions from the southern South Indian Ocean to northern rim of East Antarctic.

4. Tropical Features

Sea Surface Temperatures (SSTs): During September 2012, SSTs were above normal over most of the central and eastern equatorial Pacific with central anomaly values above 0.5℃. NINO 1+2 index was 0.5℃, with an increase of 0.3℃, NINO 3, NINO 3.4 and NINO Z indices were 0.4℃, 0.5℃ and 0.4℃, with a drop of 0.3℃, 0.2℃ and 0.2℃, respectively, and NINO 4 index was 0.4℃, the same as in August.

Subsurface Temperatures: During September 2012, anomalously warm subsurface water maintained in the eastern and western equatorial Pacific. Anomalously warm subsurface water in the central equatorial Pacific weakened and shrank, while anomalously cold subsurface water below -0.5℃ controlled a part of the central equatorial Pacific.

Warm Pools: During September 2012, the areas of the Indian Ocean warm pool and the western Pacific warm pool were near normal. The warm pool intensity was above normal in the Indian Ocean and near normal in the western Pacific.

Wind Field: During September 2012, at lower troposphere (850hPa), zonal winds were near normal over the eastern equatorial Pacific, while westerly anomalies dominated the central and western equatorial Pacific. At upper troposphere (200hPa), zonal winds were near normal over the central and western equatorial western Pacific, while westerly anomalies controlled the eastern equatorial Pacific with central value above 12m/s.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 0.4, with an increase of 0.8 from last month.

Convections over the Tropics: During September 2012, the anomalous outgoing long wave radiation (OLRa) showed that enhanced convection was observed over the western Pacific west of the international dateline, while convection was near normal over the central and eastern Pacific. At lower troposphere (850hPa) divergent wind field, a convergent center was around 125ºE, 17.5ºN, and a divergent center was near 105ºW, 15ºS. At upper troposphere (200hPa), the corresponding divergent center was near 135ºE, 10ºN, and the convergent center was around 100ºW, 25ºS.

5. ENSO Monitoring and Outlook

During the recent period, positive anomalies weakened in the east-central and eastern equatorial Pacific. Based on models’ prediction and trend diagnoses of the oceanic variations, the ENSO-neutral conditions are expected to persist through the coming autumn and winter.

Therefore, we will closely monitor the development of ENSO conditions and update our ENSO wrap-up in time.