The sensitivity of the East Asian summer monsoon to soil moisture anomalies over China was investigated based on ensembles of seasonal simulations(March–September) using the NCEP GCM coupled with the Simplified Simple Biosphere Model(NCEP GCM/SSi B). After a control experiment with free-running soil moisture, two ensembles were performed in which the soil moisture over the vast region from the lower and middle reaches of the Yangtze River valley to North China(YRNC) was double and half that in the control, with the maximum less than the field capacity. The simulation results showed significant sensitivity of the East Asian summer monsoon to wet soil in YRNC. The wetter soil was associated with increased surface latent heat flux and reduced surface sensible heat flux. In turn, these changes resulted in a wetter and colder local land surface and reduced land–sea temperature gradients, corresponding to a weakened East Asian monsoon circulation in an anomalous anticyclone over southeastern China, and a strengthened East Asian trough southward over Northeast China. Consequently, less precipitation appeared over southeastern China and North China and more rainfall over Northeast China. The weakened monsoon circulation and strengthened East Asian trough was accompanied by the convergence of abnormal northerly and southerly flow over the Yangtze River valley, resulting in more rainfall in this region.In the drier soil experiments, less precipitation appeared over YRNC. The East Asian monsoon circulation seems to show little sensitivity to dry soil anomalies in NCEP GCM/SSi B.
Trend uncertainty in the ozone valley over the Tibetan Plateau(OVTP)and the South Asian high(SAH)during1979–2009 in ERA-Interim(interim reanalysis data from the ECMWF),JRA-55(55-yr reanalysis data from the Japan Meteorological Agency),and NCEP-CFSR(Climate Forecast System Reanalysis)datasets was evaluated.The results showed that the NCEP-CFSR OVTP became strong in the summers of 1979–2009,whereas it became weak according to ERA-Interim and JRA-55.Satellite data merged with TOMS(Total Ozone Mapping Spectrometer)and OMI(Ozone Monitoring Instrument)agreed with the OVTP trend of NCEP-CFSR.The OVTP strengthening in NCEP-CFSR may have been caused by SAH intensification,a rising tropopause,and increasing ozone over non-TP(non-Tibetan Plateau)areas(27°–37°N,<75°E and>105°E).Analogously,the OVTP weakening in ERA-Interim and JRA-55 may have been affected by weakening SAH,descending tropopause,and decreasing non-TP ozone.
Dong GUOYucheng SUXiuji ZHOUJianjun XUChunhua SHIYu LIUWeiliang LIZhenkun LI
Global warming and its climatic and environmental effects have mainly been investigated in terms of the absolute warming rate.Little attention has been paid to the contribution of absolute warming rate to variability on various time scales of surface air temperature(SAT),which may be a more direct index for measuring the ecoclimatic effect of warming trend.The present study analyzed the role of secular warming trend in the variations of global land SAT for 1901–2016.Less than one-third of annual SAT variations were contributed by the warming trend over large parts of the globe generally.The ratios were up to two-thirds over eastern South America,parts of South Africa and the regions around the southwestern Mediterranean and Sunda islands where the absolute warming rate was moderate but the endemic species were undergoing exceptional loss of habitat.The ratios also exhibited smallest seasonal difference over these regions.Therefore,the ratio of the warming trend to the SAT variations may be a better measure compared to the absolute warming rate for the local ecoclimate.We should also pay more attention to the regions with high ratio,not only the regions with the high absolute warming rate.
利用观测资料及模式结果探讨了EP/CP El Nino事件对华南前汛期(4-6月)降水异常的影响。结果发现,EP和CP型相关的华南前汛期降水异常分布之间存在明显月际差异,表现为4、5月EP(CP)型相关的降水异常以偏多(少)为主;6月则相反,EP(CP)型的降水呈负(正)异常分布。分析表明,EP型相关的4、5月偏强的副热带高压与850hPa上西北太平洋反气旋异常相配合,有利于水汽从海洋向陆地输送,且两广地区水汽辐合,降水异常偏多;而6月相关的500hPa异常场上对应偏强的东亚大槽,不利于水汽输送,且广东地区处于水汽辐散区,对应降水偏少。CP型相关的4、5月对应500hPa上东亚大槽偏强,不利于水汽往陆地输送,且华南为水汽辐散,降水偏少;6月的500hPa上呈现“+-+”的东亚-太平洋遥相关波列(EAP)型,华南地区为明显的水汽辐合,降水偏多。GFDL模式较好地再现了EP/CP型的4、5月降水异常分布及大气环流形势,但是对6月的模拟存在一定偏差。
