Monthly Highlights

1. Climate in China

During February 2013, the surface air temperature averaged over China was -1.2℃, which was warmer than normal (-1.7℃) by 0.5℃. Monthly mean surface air temperatures were generally below normal in most of Northeast China, eastern Inner Mongolia, eastern North China, northern Huanghuai, parts of Central China, northern Xinjiang and western Tibet, with 2-4℃ below normal in most of Northeast China, eastern Inner Mongolia, eastern North China, northern Xinjiang and parts of western Tibet. Meanwhile, positive anomalies were around 2-4℃ in most of Yunnan, southern Sichuan, most of Qinghai, most of Guangdong, southern Jiangxi and western Zhejiang, with 4℃above normal in locations .

For the month, the mean precipitation amount over China was 14.1 mm, which was 19.0% less than normal (17.4mm). The mean precipitation over Northeast China was 10.2mm, which was 92.5% more than normal (4.9mm). Percentages of precipitation anomalies were observed 50-200% above normal in most of Northeast China, northeastern Inner-Mongolia, southern North China, northern East China, southwestern Tibet, southeastern Qinghai and parts of Xinjiang, with values above 200% than normal in locations. Meanwhile, the precipitation amounts were 50-80% less than normal in most of Southwest China, most of South China, middle and western Inner Mongolia and southwestern Xinjiang, with values 80% less than normal in locations.

In February, extremes of Daily Temperature Drop (DTD), Consecutive Temperature Drop (CTD) and Consecutive No Measurable Precipitation Days (CNMPD) were observed in China. Impacted by cold air activities, DTD extremes occurred in 68 stations, which were located in central of Northeast China, central-eastern of Inner-Mongolia, South China, Yunnan Province and Xizang Autonomous Region, et al., with new records in 6 stations, such as Shiquanhe station (20.0℃) of Xizang Autonomous Region, Sunitezuoqi station (18.7℃) of Inner-Mongolia. CTD extremes occurred in 21 stations, which were located in northern Northeast China, southern of the Jiangnan Region，Qinghai Province and Xizang Autonomous Region, et al., with widespread CTDs of 12 ~26℃ and new records in Qingshuihe station (26.0℃) and Shiquanhe station (24.7℃) of Xizang Autonomous Region, Wudalianchi station (25.9℃) of Heilongjiang Province. Meanwhile, CNMPDs occurred in 69 stations in Southwest China, et al.

2. Climate in the World

In February 2013, temperatures were 1-4℃ above normal in most Europe, western and southeastern Asia, central Africa, southern Australia, northwestern and northeastern North America, with temperatures more than 6℃ above normal in northwestern Canada and parts of northwestern Russia. Meanwhile, temperatures were 1-4℃ below normal in northeastern Asia, western North Africa, central-southern North America, and northwestern South America, with temperatures more than 4℃ below normal in northeastern Russia and parts of Northwest China.

For the month, precipitations were at least 50% less than normal in central-northern Europe, most West Asia, northeastern Russia, most southern parts of China and North China, most Africa, central Australia, western and northeastern North America, with no precipitations in parts of above regions. Meanwhile, precipitations were observed at least 50% more than normal in southern Europe, most South Asia, most Northeast China, central-northern North America and northern South America, with precipitations at least 200% above normal in parts of above regions.

3. General Circulation Features

Northern Hemisphere: During February 2013, the field of mean 500hPa geopotential height exhibited a three-wave pattern over mid-high latitudes. In the field of height anomaly, positive anomalies above 4 dam covered regions over the northern North Atlantic Ocean, the Ural of western Russia and the eastern North Pacific, with central values above 12 dam over part of northern North Atlantic Ocean and eastern North Pacific. Meanwhile, negative anomalies below -4 dam covered the western Europe, the eastern Russia, the northern North Pacific and the southeastern North America, with central values below -12 dam. During the month, the northwestern Pacific subtropical high was larger than normal, and extended to the north of its normal position.

Southern Hemisphere: For the month, zonal circulation mainly dominated over mid-high latitudes in the mean 500hPa geopotential height field. In the field of height anomaly, negative anomalies below -4 dam covered the polar region, with central values below -8 dam. Meanwhile, positive anomalies above 4 dam covered the regions over the southern Southwest Pacific Basin and the Southeast Pacific Basin.

4. Tropical Features

Sea Surface Temperatures (SSTs): During February 2013, weak negative SST anomalies (SSTA) dominated over most equatorial eastern and central Pacific, with the central value below -1.0℃ and the negative SSTA center located in the eastern part of the equatorial eastern Pacific. Niño 1+2, Niño 3, Niño 4, Niño 3.4 and Niño Z indices were -0.5℃, -0.6℃, 0.0℃, -0.5℃ and -0.4℃,with a drop of 0.1℃ for Niño 3.4 and Niño Z indices from last month, and no change in other Niño zones.

Subsurface Temperatures: During February 2013, anomalously warm subsurface water in the equatorial western Pacific moved to the dateline and  intensified slightly, with the central value above 3℃. Meanwhile, anomalously cold subsurface water in the equatorial eastern and central Pacific also enhanced slightly from last month, and continually accumulated and upwelled in the eastern Pacific.

Warm Pools: During February 2013, the areas of the Indian Ocean warm pool and the western Pacific warm pool were larger than normal, and their intensities were both above normal.

Wind Field: During February 2013, at lower troposphere (850hPa), the westerly anomalies covered most equatorial eastern and central Pacific, indicating decreased equatorial easterly winds. At upper troposphere (200hPa), weak westerly anomalies controlled the eastern part of the equatorial eastern Pacific, while in other regions of the equatorial Pacific the winds were near normal.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was -0.2, with a drop of 0.2 from last month.

Convections over the Tropics: During February 2013, the anomalous outgoing long wave radiation (OLR) showed that convection was active in the equatorial western Pacific and the tropical eastern Indian Ocean; while inactive over other regions of the equatorial Pacific.

At lower troposphere (850hPa) divergent wind field, a convergent center was around 135ºE, 10ºS, and a divergent center was over 110Wº, 15ºN. At upper troposphere (200hPa), a divergent center was near 140ºE, 5ºS, and a convergent center was around 60ºW, 20ºN in the tropical Atlantic Ocean.

5. ENSO Monitoring and Outlook

Since December 2012 sea surface temperatures (SSTs) in the central-eastern tropical Pacific Ocean have been ENSO-neutral conditions with below average, but SSTs in the Nino regions are distinctly increasing in the recent beginning of March 2013. Considering the predictions of dynamical and statistical models, it is most likely for ENSO to turn gradually into above-average neutral conditions in following 3 months (from April to June).

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