Cloud Overlapping And Tropical Aerosol Indirect Effect

The radiation impact of clouds and the interaction between clouds and aeorosols play akey role in the radiation processing in climate system. But they are still one of the biggestuncertainties in the climate prediction due to many reasons. Therefore, by the combination ofactive and passive remote sensing and the stochastic cloud generator, we first analyzed thespatial and temporal distribution of an important parameter in cloud overlappingparameterizations-decorrelation depth which can be used as reference for the development ofnew parameterization in the future. On the other hand, we performed a statistical analysis ofglobal deep cloud systems, and studied the aerosol invigoration effect on tropical clouds withspecial focus on the impact of invigoration effect on cloud radiative forcing (CRF). Themainly findings are:1) The decorrelation depth which represents the cloud vertical structure has significanttemperol and spatial variations. Simply fix it to2km will result about15%differencesbetween simulated and observed column cloud amount. The differences would havesignificant impact on the cloud radiation calculation and radiation budget in climate model.Therefore precisely parameterization of decorrelation depth is one of the major directionfor climate model development infuture.2) The macro-physical properties of global deep cloud systems (DCS) have very differentcharacteristics in different latitudes. The vertical (horizontal) development of DCS increase(decrease) towards higher latitudes, which indicate the different mechanism of DCSs’generation. Most of the DCS in low latitudes are deep convective cloud which highlydeveloped in vertical direction but cover relative small horizontal extent, therefore havethe strongest vertical development but weekest horizontal development. DCS in middlelatitudes are mainly caused in front system thus have weaker vertical development thanthose in low latitudes. Influenced by the mooson, the vertical developments of DCSincrease sharply in summer of north hemisphere. The DCS in high latitudes are formed inthe large scale front system formed by the convergence of warm air mass from sub-tropicalregion and cold air mass from polar region. Therefore they have the weekest verticaldevelopment but strongest horizontal development.3) The analyzing of the aerosol impact on the macro and micro physical properties of tropicalclouds indicate that: with the increase of aeorosol loading, no obviously change shows forliquid cloud, but the cloud top height and cloud thickness of mixed-phase clouds increase significantly and their ice processing are stronger as well while the effective radius of alltypes of clouds are decrease. The agreements of all above clouds’ properties change withaerosol are consist with aerosol invigoration effect hypothesis, which give the provementof the exsiting of aerosol invigoration effect on tropical clouds. The analyzing of therelationship between aerosol and CRF demonstrate that: with the increase of aerosols, noobviously change of longwave CRF for liquid clouds which is consist with no change of itsgeomoety. But due to the combination of first indirect effect and sem-direct effect, theshortwave CRF of liquid clouds increase first and decrease after. Both shortwave CRF andlongwave CRF of mixed-phase clouds increase significant with the increase of aeorosols.That is because invigorated cloud will have higher cloud top and thicker cloud thickness,therefore would reflect more solar radiation back to space and capture more longwaveradiation from surface. Using a simple sample number weighted calculation method, theaerosol net effect of all the clouds in tropical regions are estimated to be-4.18W/m2.Further tests on the dependence of multiple meteorological parameters shows that, thetargeted relationship between cloud physical and radiative properties can not be explainedby dynamical impact.