Monthly Highlights

1. Climate in China

In October 2011, China monthly mean surface air temperature was 10.6℃. It was 1.0℃ higher than normal (9.6℃), which rank the 6^th highest since 1951. Temperatures were observed at least 1℃ above normal in most Northeast China, mid-western Northwest China, Inner Mongolia, northern Shanxi, and northwestern Tibet, with temperatures 2-4℃ above normal in northern Northeast China, eastern Inner Mongolia, northern Xinjiang. Meanwhile, temperatures were observed 1-2℃ near normal in rest of China.  

For the month, the mean precipitation over China was 37.8 mm, with precipitation 4.6% more than normal (37.0 mm). Precipitations were observed at least 30% more than normal in most South China, the western Jiangnan area, Guizhou, Chongqing, northern Xinjiang, parts of mid-western Inner Mongolia, northern Shaanxi and northern Ningxia, with precipitations at least 100% more than normal in locations of above regions. Meanwhile, precipitations were 30%-80% less than normal in most Northeast China, eastern Inner Mongolia, most Shandong and Jiangsu, northwestern Gansu, southern Xinjiang, western and southern Tibet, northwestern Qinghai and most Yunnan, with precipitations 80% less than normal in locations of above regions.

In October, daily rainfall amount extremes，consecutive rainfall amount extremes，consecutive rainy day extremes and daily temperature drop extremes were observed in China. Daily rainfall amount extremes occurred in 7 stations, with 5 stations breaking record, such as Binyang (347.0mm), Shanglin (271.2mm) and Haikou (334.0mm). During the month, consecutive rainfall amount extremes were observed in 22 stations，distributed in western South China and Hainan, with 9 stations breaking record, such as Yongning (584.5mm), Binyang (508.9mm)，Danzhou（870.2mm）and Haikou (828.3mm). Consecutive rainy day extremes occurred in 9 stations，which were located in Hainan and Ningxia. Rainy days generally kept for 5-20 days and more than 20 days at some sites of Hainan. Additionally, daily temperature drop extremes occurred in 23 stations, which were mainly located in Hebei and Liaoning, and decreasing amplitude of temperatures reached up to 10-17 ℃.

2. World Climate

During October 2011, monthly mean temperatures were 1-4℃ above normal in North Europe, southwestern Europe, Siberia, Central Asia, northern China, parts of West Africa and South Africa, most North America, parts of northern South America and coastal areas of Southern Australia, with temperatures at least 4℃ above normal in most areas of west Siberia. Monthly mean surface air temperatures were observed 1-2℃ below normal in parts of southeastern Europe, southeastern United States, southern South America, with temperatures 2-3℃ below normal in locations.

For the month, precipitations were at least 50% more than normal in parts of northern mid-western Siberia, northwestern North Europe, Central Asia, parts of southern and northwestern China, the northern Indochina Peninsular, southern Africa, parts of northwestern and eastern United States, western Australia, central North America and most of eastern South America, with precipitations at least 100% above normal in locations. Meanwhile, precipitations were at least 50% less than normal in central and southern Europe, southern west Siberia, northeastern China, South Asia, parts of West Africa, central America and eastern Alaska, parts of coasts of west South America, with no precipitation in locations.

3. General Circulation Features

Northern Hemisphere: During October 2011, in the field of 500hPa geopotential height anomaly, positive anomalies above 4 dam covered regions from Europe to central Russia, northeastern North America, with central values above 8 dam over northeastern North America. Meanwhile, negative anomalies below -4 dam covered northeastern Siberia, the northeastern North Pacific Ocean and the northern North Atlantic Ocean. For the month, the area and intensity of Northwest Pacific Subtropical High were near normal, while its ridge line and western ridge point were found further  northern and western than normal, respectively.

Southern Hemisphere: During October 2011, in the field of 500hPa geopotential height anomaly, positive anomalies above 4 dam covered most of the polar region, the southwestern South Indian Ocean, the southern South Atlantic Ocean and location of the southeastern southern Pacific Ocean, with central values above 8 dam over the southwestern South Indian Ocean and location of the southeastern southern Pacific Ocean. Meanwhile, negative anomalies below -4 dam covered the southeastern South Pacific Ocean, the southwestern and southeastern South Indian Ocean, with central values below -8 dam over the southeastern South Pacific Ocean.

4. Tropical Features

Sea Surface Temperatures (SSTs): During October 2011, SSTs were -0.5℃below normal  in almost all the equatorial central and eastern Pacific, and the minimum SSTs is below -2.0℃. NINO 1+2, NINO 3, NINO 4, NINO 3.4 and NINO Z indices were -0.9℃, -0.9℃, -0.5℃, -0.8℃ and -0.7℃, with drops of 0.2℃, 0.3℃ 0.1℃, 0.1℃ and 0.1℃ from last month, respectively. Meanwhile, SSTs were about 0.5-1.0℃ above normal in the equatorial Indian Ocean.

Subsurface Temperatures: During October 2011, anomalously cold subsurface water controlled most of the central and eastern equatorial Pacific. Negative anomalies were strengthened, expanded and upraised evidently in the east-central Pacific, with central values below -5.0℃.

Warm Pools: During October 2011, the area of the Indian Ocean warm pool was expanded westward and became slightly larger than normal, and that of the western Pacific warm pool withdrew westward and became slightly smaller. The intensities of the Indian Ocean warm pool was significantly stronger than normal, and that of the western Pacific warm pool was above normal.

Wind Field: In October 2011, at lower troposphere (850hPa), easterly wind anomalies dominated the equatorial central and western Pacific west of 170°W with central values -4m/s, and westerly wind anomalies dominated the equatorial central and eastern Pacific east of 160°W, with central values 4m/s. At upper troposphere (200hPa), westerly wind anomalies covered most of the equatorial central and western Pacific with westerly anomalous above 4 m/s and the central values exceedding 8 m/s.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 1.0, down 0.2 from last month.

Convections over the Tropics: During October, the anomalous outgoing long-wave radiation (OLR) showed that convection was suppressed over the most equatorial western Pacific and the South China Sea.

In the divergent wind field at lower troposphere (850hPa) of the tropical Pacific, the convergent and divergent centers were around 130°E, 10°N and 110°W, 15°S, respectively. At upper troposphere (200hPa), the corresponding divergent and convergent centers were near 120°E, 10°N and 110°W, 25°S, respectively.

5. ENSO Outlook

The ending of a moderate La Niña episode in early May 2011 was followed by neutral ENSO conditions until early August, when weak La Niña conditions returned and have been gradually strengthening. Current monitoring results showed that the negative SSTA enhanced steadily in the central and eastern Pacific. The index NINO Z was at -0.7℃ in October,with drop of 0.1℃ from last month. Corresponding to the cold La Niña conditions, Southern Oscillation Index (SOI) was at 1.0,with drop of 1.2 from last month.

Based on model predictions and current monitoring of the ocean and atmosphere features, the La Niña conditions will continue enhancing in the central and eastern equatorial Pacific and reach its peak during December 2011 - January 2012. It is predicted that the La Niña conditions may decrease in spring 2012.

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