Monthly Highlights
1. Climate in China
During October 2012, the surface air temperature averaged over China was 10.3℃, which was equal to normal. Monthly mean surface air temperatures were generally below normal in western and northeastern China and above normal in most of eastern and central China. Positive anomalies about 1~2℃ were in east-central Henan, locations in Shandong, southwestern Jiangxi, southeastern Hunan, west-central Guangxi and southeastern Yunnan. Negative anomalies about -1~-2℃were west-central Xinjiang and locations of the Tibetan Plateau, with minimum about -2~-4℃in Xinjiang locations. Temperatures were near normal in the rest regions in China.
In October, average precipitation over China was 29.1 mm, which was 18.9% less than normal (35.9mm). Precipitations percentage anomalies were observed 20-100% above normal in parts of western Heilongjiang, most Liaoning and Jilin, northeast Hebei, most of eastern Inner Mongolia and locations of central Inner Mongolia, locations of Ningxia, northern Xinjiang, southern Qinghai, northwestern Sichuang, eastern and southern Hubei, northern Hunan, southern Guangxi and western Guangdong, with central values over 100% in eastern Inner Mongolia, western Heilongjiang, eastern Jilin, south-central Liaoning and southern Guangxi. Meanwhile, precipitations were over 20% less than average in the rest regions, and over 80% less than average in southern Xinjiang, western Tibet, northern Qinghai, west-central Gansu, locations of Ningxia and Shaanxi and northern Jiangsu.
In October, extremes of Daily Temperature Drop (DTD) were observed in China. DTD extremes occurred in 62 stations, which were located in Xinjiang, Jilin, Liaoning, Inner Mongolia, Beijing, Tianjin, Hebei, Shanxi, Shandong, Henan, Shanxi, Jiangsu, Fujian and other provinces (districts), with widespread DTDs of 10~14℃ and new records in Xingcheng(14.1℃), Qinhuangdao(13.0℃) and Ruoqiang(13.3℃).
2. World Climate
During October 2012, monthly mean temperatures were 1~4℃ above normal in eastern Europe, most West Asia and Central Asia，the Russian Far East, southwestern and part of eastern North America, eastern Alaska, mid-eastern South America, northeastern Africa, southwestern Australia, with temperatures 4~6℃ above normal in locations of the Russia Far East. Meanwhile, monthly mean temperatures were 1~2℃ below normal in central Russian, western North Europe, central North America, parts of northern South America, parts of central and southern South Africa, and northeastern Australia, with temperatures 2~4℃below normal in mid-northern North America.
For the month, precipitations were at least 50% above normal in eastern Europe, mid-western and eastern Russia, northeastern China, southern Central Asia, parts of West Asia, mid-northern North America, northwestern and part of southern South America, parts of northwestern and eastern Africa, and locations of northwestern Australia, with precipitations at least 200% above normal in locations. Meanwhile, precipitations were at least 50% below normal in eastern Central Siberia Plateau, western China, central South Asia, central Saudi Arabia, southern North America, mid-eastern South America, mid-northern Africa and central Australia, with no precipitation in locations.
3. General Circulation Features
Northern Hemisphere: During October 2012, the field of mean 500hPa geopotential height exhibited a three-wave pattern over the mid-high latitudes, and the vortex centers located near the north polar. In the field of height anomaly, 3 positive anomalies centers above 4 dam covered most of Bering Sea, eastern Kara Sea and northeastern Greenland respectively, with central values above 16 dam over the Bering Sea surrounding north polar. Meanwhile, the subtropics ring-like area mainly the negative anomalous control, the negative centers below -4 dam covered the central North Pacific Ocean, central North America, from the northeastern Atlantic Ocean to the northwestern Europe. During the month, the northwestern Pacific subtropical high intensity and area index were weaker than normal.
Southern Hemisphere: For the month, in the field of mean 500hPa geopotential height exhibited a four-wave pattern over the mid-high latitudes, South polar vortex split 2 centers in the eastern hemisphere. In the field of height anomaly, positive anomalies above 4 dam covered the South Pacific near 120ºW, the central Antarctica in eastern hemisphere, the middle latitude sea area of the Atlantic, with central values above 12 dam over the South Pacific. Meanwhile, negative anomalies below -4 dam covered the southern South Pacific Ocean along southward of New Zealand, southern South Indian Ocean and southern South Atlantic Ocean near the Antarctica.
4. Tropical Features
Sea Surface Temperatures (SSTs): During October 2012, SSTs were slightly above normal over most of the equatorial central and eastern Pacific, with central anomaly value above 0.5℃ near the dateline. However, negative SST anomalies covered the eastern part of the equatorial eastern Pacific, with central value below -0.5℃. NINO 1+2, NINO 3, NINO 3.4 and NINO Z indices were -0.2℃, 0.0℃, 0.3℃ and 0.2℃, with a drop of 0.7℃、0.4℃、0.2℃ and 0.2℃ from last month, respectively. However, NINO4 index was 0.5℃, with an increase of 0.1℃ from last month.
Subsurface Temperatures: During October 2012, anomalously warm subsurface water maintained in the equatorial central Pacific and moved eastward to the east of the dateline. However, anomalously cold subsurface water in the equatorial eastern Pacific weakened significantly.
Warm Pools: During October 2012, the areas of the Indian Ocean warm pool and the western Pacific warm pool were near normal. The warm pool intensity was largely above normal in the Indian Ocean and slightly above normal in the western Pacific.
Wind Field: During October 2012, at lower troposphere (850hPa), westerly anomalies dominated over most of the equatorial eastern-central Pacific, while easterly anomalies prevailed from the equatorial western Pacific to the eastern Indian Ocean. At upper troposphere (200hPa), zonal winds were near normal over the equatorial central and western Pacific, while westerly anomalies controlled most equatorial eastern Pacific.
Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 0.4, the same as last month.
Convections over the Tropics: During October 2012, the anomalous outgoing long wave radiation (OLR) showed that enhanced convection was observed over the equatorial western Pacific east of the Philippines, while decreased convection covered the regions near the dateline. At lower troposphere (850hPa) divergent wind field, a convergent center was around 100ºE, 10ºN, and a divergent center was near 115ºW, 10ºS. At upper troposphere (200hPa), the corresponding divergent center was near 145ºE, 5ºN, and a convergent center was around 100ºW, 25ºS.
5. ENSO Monitoring and Outlook
The tropical central Pacific is warming up again because of the eastward warm Kelvin wave. The persistence of warm condition over central Pacific is favored by the quick decline of previous strong negative sea surface temperature anomaly from North America to central Pacific. Based on models’ prediction and recent oceanic and atmospheric variations, the ENSO-neutral conditions are expected to persist during the 2012/2013 winter.
Therefore, we will closely monitor the development of ENSO conditions and update our ENSO wrap-up in time.