Agriculture Development-induced Surface Albedo Changes and Climatic Implications Across Northeastern China

To improve the understandings on regional climatic effects of past human-induced land cover changes,the surface albedo changes caused by conversions from natural vegetation to cropland were estimated across northeastern China over the last 300 years,and its climatic effects were simulated by using the Weather Research and Forecasting (WRF) model.Essential natural vegetation records compiled from historical documents and regional optimal surface albedo dataset were used.The results show that the surface albedo decreased by 0.01-0.03 due to conversions from grassland to cropland in the Northeast China Plain and it increased by 0.005-0.015 due to conversions from forests to cropland in the surrounding mountains.As a consequence,in the Northeast China Plain,the surface net radiation increased by 4-8 W/m 2,2-5 W/m 2,and 1-3 W/m 2,and the climate was therefore warmed by 0.1℃-0.2℃、0.1℃-0.2℃、 0.1℃-0.3 ℃ in the spring,autumn and winter,respectively.In the surrounding mountain area,the net radiation decreased by less than 1.5 W/m 2,and the climate was therefore cooled too slight to be detected.In summer,effects of surface albedo changes on climate were closely associated with moisture dynamics,such as evapotranspiration and cloud,instead of being merely determined by surface radiation budget.The simulated summer climatic effects have large uncertainties.These findings demonstrate that surface albedo changes resulted in warming climate effects in the non-rainy seasons in Northeast China Plain through surface radiation processes while the climatic effects in summer could hardly be concluded so far.

A modeling study of aerosol effects on cloud radiative property and precipitation

A two-moment (mass and number) warm cloud scheme together with ground and aircraft measurements over Beijing is used in a regional model to study the effects of aerosols on cloud radiative property and precipitation.Using a prescribed tri-modal lognormal aerosol size distribution,the aerosol numbers are calculated from prognostic aerosol masses,for which advection,diffusion,and cloud drop activation/deactivation are considered.Specifically,the accumulation mode of a tri-lognormal aerosol size distribution is fitted to the aircraft measured values for a cold front case passed through northern China during June 25-26,2005.In the simulations,the warm cloud scheme simulates explicitly the cloud drops and subsequently affects the radiative heating and cooling,and circulations.Simulations with different initial conditions for being fitted with aircraft measurements,continental and maritime aerosol numbers were conducted.It is found that more aerosols result in more but smaller cloud drops and more cloud water,leading to an increase in albedo.The effects on rains are complex:smaller cloud drops have less efficient coagulation for raindrop to form (autoconversion),leading to fewer raindrop numbers and less rainwater;while more cloud water enhances the accretion for raindrop growth.Nevertheless,for the whole cloud system,the impact of increasing aerosols inhibits precipitation.

A DIAGNOSTIC STUDY OF FEEDBACK MECHANISM IN GREENHOUSE EFFECTS SIMULATED BY NCAR CCM1

This paper describes a diagnostic study of the feedback mechanism in greenhouse effects of increased CO_2 and oth- er trace gases(CH_4,N_2O and CFCs),simulated by general circulation model.The study is based on two sensitivity exper- iments for doubled CO_2 and the inclusion of other trace gases,respectively,using version one of the community climate model(CCM1)developed at the National Centre for Atmospheric Research.A one-dimensional(1-D)and a two-dimensional(2-D)radiative-convective models are used to diagnose the feedback effect.It shows that the feedback factors in global and annual mean conditions are in the sequence of surface albedo,water vapor amount,water vapor distribution,cloud height,critical lapse rate and cloud cover,while in zonal and annual mean conditions in the tropical region the above sequence does not change except the two water vapor terms being the largest feedback compo- nents.Among the feedback components,the total water vapor feedback is the largest(about 50%).The diagnosis also gives a very small feedback of either the cloud cover or the lapse rate,which is substantially different from the 1-D feedback analysis by Hansen et al.(1984).The small lapse rate feedback is considered to be partly caused by the convective adjustment scheme adopted by CCM1 model. The feedback effect for doubled CO_2 is very different from that of the addition of other trace gases because of their different vertical distributions of radiative forcing although the non-feedback responses of surface air temperature for both cases are almost the same.For instance,the larger forcing at surface by the addition of other trace gases can cause stronger surface albedo feedback than by doubled CO_2.Besides,because of the negative forcing of doubled CO_2 in the stratosphere,cloud height feedback is more intense.The larger surface forcing in the case of other trace gases can also in- fluence atmospheric water vapor amount as well as the water vapor distribution,which will in turn have stronger feedback effects.All these indicate that it is incorrect to use“effective CO_2”to replace other trace gases in the general circulation model.

THE FORMATION AND THE DEVELOPMENT OF CAMS TWO-DIMENSIONAL DYNAMICAL-PHYSICAL CLIMATE MODEL

In the paper,we have developed a 2-D physical-dynamical coupled climate model.Some sensitive experiments have been done by use of this model.First of all,we have studied the effects of different results by two radiational calcu- lation schemes on circulation variation.The calculated results have shown that the different radiation parameterization schemes give different results,therefore the variational effects of wind,temperature,and humidity field are presented on the medium-range circulation variation. Besides,we have also studied the role of the meridional eddy momentum fluxes in formation of the monsoon over East Asia.The results of study have shown that on the average,the roles of meridional eddy flux of momentum formative processes of monsoon which is added to momentum equations by using the scheme of moist process parameterization with plateau are manifest.