Climate Monitoring Bulletin

Highlights General Circulation Features

Northern Hemisphere

   During January，the mean 500hPa geopotential height fields exhibited a 4-wave pattern in the mid-high latitudes．The polar vortex was weaker than normal． The ridge over the coast areas of Europe enhanced remarkably，with the maximum anomalies more than 20 dam．In addition， positive anomalies above 8 dam maintained over the central subtropical Pacific． Meanwhile，negative anomalies below -12 dam were over the Ural，the Bering Sea and the Hudson Bay，with the minimum anomalies less than -16 dam．The Northwest Pacific subtropical high Was Persistently stronger than normal and westward shifted．

Southern Hemisphere

   During this month，in the mean 500hPa geopotential height field，most regions in the mid-high latitudes Were covered by positive anomalies，with the maximum above 8 dam over the southwestern Indian Ocean and above 16 dam over the southwestern Pacific． Meanwhile，negative anomalies covered the southeastern Pacific in the middle latitudes，With the minimum below -4 dam.

Climate for China

   In January，monthly mean surface air temperatures were above l－2℃ than normal in most of China。With 2－4℃ above normal in most of eastern China and most of Northwest China、and 4-6℃ above normal in most of Northeastern China。central and northern North China and northeastern Part of Northwest China，With the center values above 6-8℃ in part of Inner Mongolia。Temperatures of l-2℃ below normal were observed in Western Tibet and northwestern Sichuan．Monthly Precipitation totals Were near or less than normal in most of eastern China、With 50-90% less than normal in central and northern North China、 southwestern Henan and northem Hubei．Meanwhile，rainfalls Were 50% more than normal in most of Northeastern China and Northwest China、western Southwest China，Zhejiang and most of Fujian，in Which precipitation totals Were 400% more than normal in parts of Heilongjiang，southern Xinjiang and northeastern Inner Mongolia。

Tropical Features

        Sea Surface Temperatures(SSTS)

   During January，positive SST anomalies enhanced obviously in the central and western equatorial Pacific．The area with SST anomalies more than 0.5℃ expanded eastward to 155°W，With the center value above1.0℃ around the date line。Meanwhile，negative SST anomalies with -0.5℃--1.0℃ over the eastern equatorial Pacific shrank eastward obviously．Correspondingly，the SST indices of NINO 3。NINO 1+2 and NINO 4 regions were -0.3，-0.8 and 0.7，respectively．Positive SST anomalies above1.0℃ were persistent over most Of the equatorial Indian Ocean．

Circulation

        Wind Field

   In this month，at the lower troposphere(850hPa)，westerly anomalies of 4-6m／s Covered the eastern and western．equatorial Pacific．Easterly anomalies of 2-4m／s controlled the central equatorial Pacific．Westerly anomalies With 4-6m／s remained over the equatorial Indian Ocean．At the upper troposphere (200hPa)，westerly anomalies covered most of the equatoria1 Pacific，with values above 16m／s obviously over the central equatorial Pacific．Meanwhile，easterly anomalies above l2m／s covered the equatorial Indian Ocean．

        Southern Oscillation

   During January，the Southern Oscillation Index (SOI) was 0.1，displaying strong intra-seasonal oscillation characteristics during the past months．

        Convection over the Tropics

   During January，the anomalous outgoing longwave radiation(OLR) distribution displayed that enhanced convection remained in the area west to 170°E but suppressed convection was around the dateline over the equatorial Pacific．In the lower troposphere(850hPa) divergent wind field，a convergent center Was nearby l60°E，10°S，and a divergent center was around 100°W，5°S．Correspondingly，at the upper。troposphere(200hPa)，the divergent and the convergent centers were around 165°E，10°S and 100°W，10°S，respectively．