The Effects Of Aerosols On Cloud Drop Concentrations And Radiation Forcing In Southeast Atlantic Ship Track

Clouds cover nearly 60%of the Earth’s surfaces,interact with atmospheric radiation,and play an important role in the energy balance of the earth system.Aerosols have a significant impact on climate by scattering,absorbing radiation and changing cloud properties.The radiative forcing from aerosol-cloud interactions remains the largest uncertainty in estimating the anthropogenic radiative forcing.When studying aerosol-cloud interaction,it is difficult to identify the causal relationship between aerosol and cloud properties due to meteorological influences.A better understanding of the aerosol-cloud interaction will help understand the climate and the energy balance of the earth-atmosphere system,improve model simulations,and make better climate predictions.Therefore,"natural experiment"such as ship tracks,which is aerosol disturbance independent of meteorology,is considered a better method to analyze the relationship between aerosol effects and cloud changes.Cloud properties changes are mainly affected by aerosols,which can greatly exclude the interference of large scales meteorological factors.Then,the interaction between aerosols and clouds can be better understood.Focusing on the interaction between aerosols and ocean shallow clouds,based on MODIS observation data products,the cloud drop concentration（N_d）at the convective core is inverted,which reduced the N_d inversion errors caused by the"plane parallel"assumption.This study comprehensively analyzed the ocean shallow clouds in the shipping lane in the southeast Atlantic in the spring of 2003-2015 and explored the impact of shipping aerosols on clouds and their radiation effects.To summarize,our works and findings are as follows:（1）The aerosol effect has a strong dependence on the aerosol background and cloud properties,so it is necessary to evaluate the overall effect of the ship emissions and its relationship with the background Nd.It is found that the effect within the shipping lane was larger by only-1 Wm^-2 compared to the adjacent clouds.However,this near-zero averaged effect was composed of large negative cloud radiative forcing（CRF）for the cleanest of the cases with N_d-bg<50 cm^-3.（2）This paper analyzed the contribution of the albedo and cloud fraction（Cf）effects to cloud radiation in a clean background.The negative forcing was 45%for the cloud fraction（Cf）effect and 55%for the albedo effects,including a small contribution of the liquid water path（LWP）effect.（3）This article analyzes the dependence relationship between cloud properties susceptibility to N_d-bg.The results showed that cloud is very sensitive to aerosols when N_d-core<50 cm^-3,and it should be taken into account in calculating the Earth energy balance.