Monthly Highlights

1. Climate in China

During January 2013, the surface air temperature averaged over China was -5.2℃, which was slightly lower than normal (-5.0℃) by 0.2℃. Monthly mean surface air temperatures were generally 1.0℃ below normal in most of Northeast China, eastern Inner Mongolia, mid-southern Hebei, northwestern Shandong, mid-northern Henan, central Xinjiang and western Tibet，with 2-4℃ below normal in most of Northeast China, eastern Inner Mongolia, central Xinjiang and parts of western Tibet. Meanwhile, positive anomalies were around 1~2℃ in parts of northern Xinjiang, middle and western Inner Mongolia, Ningxia and parts of northern Shanxi.

In January 2013, mean precipitation amount over China was 6.5 mm, which was 50.8% less than normal (13.2mm) and was the least since 1987. Percentages of precipitation anomalies were observed 30-200% in most North China, central-eastern Inner-Mongolia, southwestern Heilongjiang, mid-western Jilin, northern Shandong, northwestern and southeastern Qinghai, western Gansu and southwestern Tibet, with central values above 200% in locations. Meanwhile, the precipitation amounts were 30~80% less than normal in the rest regions, with central values below -80% in eastern of South China, southern Sichuan, northwestern Yunnan, central Tibet, most of south Xinjiang, western Inner Mongolia, parts of Gansu and parts of Shanxi.

In January, the extremes of Daily Minimum Temperatures (DMT), Daily Temperature Drop (DTD), Consecutive Temperature Drop (CTD) and Consecutive No Measurable Precipitation Day (CNMPD) were observed in China. DMT extremes occurred in 79 stations, which were located in Shanxi, Hebei, Sichuan, Chongqing,  Heilongjiang and Inner Mongolia, and new records was reported in Meishan（-3.4 ℃）. DTD extremes occurred in 21 stations, which were located in Tibet, Qinghai and Inner Mongolia, with widespread DTDs of 10-19℃, and new records in Dangxiong（19.3℃）and Dingqing（14.0℃）of Tibet, and Yushu（15.8℃）of Qinghai province. CTD extremes were observed in 6 stations, which were located in Tibet and Qinghai. Meanwhile, CNMPD extremes occurred in 143 stations, which were located in Sichuan and Yunnan province, with widespread of CNMPD from 20 to145 days and reporting of new records in 43 stations.

2. Climate in the World

During January 2013, mean temperatures were 1-4℃ below normal in most Eurasian continent to north of 40ºN, central South Asia and central and southwestern North America , with temperature 6℃ below normal in parts of southwestern North America and northwestern Russia. Meanwhile, mean temperatures were 1-4℃ above normal in northern and southern Europe, West Asia, Central Asia , northwestern and southeastern North America, parts of southern South America, northwestern Africa and most Australia, with temperatures 4℃ above normal in parts of western Alaska.

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

3. General Circulation Features

Northern Hemisphere: During January 2013, the field of mean 500hPa geopotential height exhibited a three-wave pattern over the mid- and high-latitudes. In the field of height anomaly, positive anomalies mainly covered the polar region, with above 12 dam covering part of the regions. The positive anomalies above 4 dam were observed over eastern North America and northern North Pacific, with central values above 8 dam over parts of northern North Pacific. Meanwhile, the negative anomalies below -4 dam covered northern North Atlantic Ocean, western Europe, northwestern Asia and the area to the east of Japan, with central values below -8 dam in locations. For the month, the intensity of the Northwestern Pacific subtropical high (WPSH) was weaker than normal. And the WPSH extended to the west and north of its normal position.

Southern Hemisphere:  For the month, the field of mean 500hPa geopotential height exhibited obviously meridional circulation over the mid- and high-latitudes of South Pacific. In the field of height anomaly, the negative anomalies mainly covered most of the mid- and high-latitudes (north of 60^oS), except for the positive anomalies which were located over southern South America and western South Pacific Ocean.

4. Tropical Features

  Sea Surface Temperatures (SSTs): During January 2013, negative SST anomalies were below -0.5℃ in most central and eastern equatorial Pacific, with central anomaly value below -1.5℃ around the coastal South America. Meanwhile, the positive SST anomalies  above 0.5℃ were observed near 160ºE in western equatorial Pacific. Niño 1+2, Niño 3, Niño 4, Niño 3.4 and Niño Z indices were -0.5℃, -0.6℃, 0.0℃, -0.4℃ and -0.3℃, with a rise of 0.2℃of Niño 1+2, and drop of 0.5℃, 0.4℃, 0.3℃, 0.4℃ and 0.3℃for the other Niño zones from last month, respectively.

Subsurface Temperatures: During January 2013, anomalously cold subsurface water in the equatorial eastern Pacific expanded eastward, upwelled obviously around the coast area of eastern equatorial Pacific, and its intensity enhanced rapidly, with central anomaly value below -6℃.

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

Wind Field: During January 2013, at lower troposphere (850hPa), the westerly anomalies covered the most equatorial Pacific. At upper troposphere (200hPa), weak easterly anomalies were observed over the central and western equatorial Pacific, while westerly anomalies covered the most eastern equatorial Pacific.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 0, with a rise of 0.4 from last month.

Convections over the Tropics: During January 2013, the anomalous outgoing long wave radiation (OLR) showed that convections suppressed in the central and eastern equatorial Pacific, while it enhanced over the western equatorial Pacific and the vicinity of the Philippines.

At lower troposphere (850hPa) divergent wind field, a convergent center was around 140ºE, 10ºS, and a divergent center was over 20Wº, 15ºN. At upper troposphere (200hPa), a divergent center was near 175ºE, 10ºS, and a convergent center was around 2.5ºW of the equator.

5. ENSO Monitoring and Outlook

At present, the equatorial sea surface temperature was below normal over the Central and Eastern Pacific but accompanied with a negative Southern Oscillation Index. Recently, the heat content anomalies of the Central and Eastern Pacific Upper Ocean (0-300 m) tended to decrease after reaching a weak peak. It was predicted that the neutral condition was expected to last through March-April-May 2003.

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