Monthly Highlights

Climate in China

During December, monthly mean surface air temperatures were 1-2℃ below normal in most of Northeast China. Meanwhile, temperatures were near or above normal in the rest of China, with more than 2℃ above normal in western Xinjiang, western Tibet, Qinghai, central Inner Mongolia, eastern Zhejiang and most of Jiangsu.

In this month, rainfall totals were 50-100% below average in western Xinjiang, western Inner Mongolia, most of Tibet, part of Yunnan and most of South China. Meanwhile, rainfall totals were more than 200% above average in most of Jilin, central Inner Mongolia, northern Shanxi, central Shanxi and part of northwestern China.

Climate in the world

During December, monthly mean surface air temperatures were 1-2℃ below normal in northern Asia and part of West Asia, with about 4-6℃ below normal in Siberia. Meanwhile, temperatures were 2℃ above normal in northwestern USA, Alaska, eastern and northern Europe, southern Japan and part of China.

For the month, rainfall totals were about 50-100% less than average in most of America, part of Europe and Siberia, India, southern China, Indo-china Peninsula, western and central Australia, southern Argentina. Meanwhile, rainfall were more than 50% above average in western America, most Norway, Kazakhstan, eastern and northwestern China, southern Iran, northeast Australia, northern Argentina, with more than 200% above average in part of regions.

General Circulation Features

Northern Hemisphere: In December, the mean 500hPa geopotential height field exhibited a 3-wave pattern at the mid-high latitudes. The pressure ridge over the northern North Atlantic Ocean was stronger than normal. In the height anomaly field, negative anomalies below –4 dam dominated the regions from northeastern Canada to Greenland, with center values below –12 dam. Meanwhile, the eastern North Pacific Ocean, West Siberia and the regions from the northern North Atlantic Ocean to western Europe were covered by positive anomalies above 4 dam, with center values over 16 dam in the northern North Atlantic Ocean. The area of the Northwest Pacific subtropical high was slightly larger than normal.

Southern Hemisphere: For the month, the mean 500hPa geopotential height field exhibited a 4-wave pattern at the mid-high latitudes. In the height anomaly field, negative departures below –4 dam covered the southeastern Atlantic, the southeastern and southwestern Pacific, and the southeastern Indian Ocean, with center values under –12 dam. Meanwhile, heights in the other regions were near or above normal. Positive anomalies above 4 dam dominated the Antarctic, and positive departures above 8 dam covered the areas south to Australia.

Tropical Features

Sea Surface Temperatures (SSTs): During December, above 0.5℃ SST anomalies still dominated most of the equatorial Pacific. SSTs in the Nino 3 region increased remarkably but decreased slightly in offshore of Peru. Positive anomalies above 0.5℃ controlled most of the equatorial Indian Ocean. In this month, the SSTa indices of NINO 4, NINO 3, NINO 1+2 and NINO Z were 1.1℃, 0.7℃, 0℃, 0.8℃, respectively.

Subsurface Temperatures: During December, the abnormally warm water in the equatorial Pacific moved eastward and upward, with the intensity weakened slightly. For the month, positive anomalies greater than 2℃ reached near 110 °W. Correspondingly, the abnormally cold water in the eastern equatorial Pacific shrinked eastward and weakened obviously compared with last month.

Warm Pools: During December, the areas of the western equatorial Pacific and equatorial Indian Ocean warm pool were both appreciably larger than normal, and the intensities were both stronger than normal.

Wind Field: In this month, at the lower troposphere (850hPa), westerly anomalies around 2m/s still controlled the central and eastern equatorial Pacific. Meanwhile, the westerly anomalies weakened over the western equatorial Pacific. Weak easterly anomalies covered most of the equatorial Indian Ocean. At the upper troposphere (200hPa), easterly anomalies controlled most of the equatorial Pacific, with center values strengthened obviously over the eastern equatorial Pacific compared with last month.

Southern Oscillation: During December, the Southern Oscillation Index was –0.5, which ascended 0.2 compared with last month.

Convection over the Tropics: During this month, the anomalous outgoing longwave radiation (OLR) distribution exhibited that suppressed convections covered the equatorial Pacific between 120°E and 150°E. In the lower troposphere (850hPa) divergent wind field, the convergent center was near 165°E, 5ºS and the divergent center was around 110°W, 5°S. Correspondingly, at the upper troposphere (200hPa), the convergent center was over 110°W, 5°S and the divergent centers were near 165°E and 110°E over the equator, respectively.

ENSO Monitoring and Forecasting

a) During December, above 0.5℃ SST anomalies still dominated most of the equatorial Pacific. The SSTa indices of NINO 4 and NINO 1+2 decreased to 1.1℃ and 0℃, respectively. While the SSTa index of NINO 3 increased to 0.7℃.

b) For the month, the abnormally warm water in the equatorial Pacific moved remarkably eastward and upward, with the center values dropped slightly compared with last month. Correspondingly, the abnormally cold water in the eastern equatorial Pacific shrinked eastwardly and weakened obviously.

c) In December, the SOI increased to –0.5.

d) During December, at the lower troposphere (850hPa), westerly anomalies over the western equatorial Pacific weakened compared with last month.

e) Most statistical forecasting models showed that the SSTa index of NINO 3 is expected to decrease for the next three months, but the positive SSTa will remain.

Recent oceanic and atmospheric status in the tropical Pacific showed that El Nino conditions remained.