Simulation On The Influence Of Collision-coalescence And Turbulence On The Spectral Characteristics Of Cloud Droplets In Oceanic Boundary Layer

The development of marine boundary layer clouds is simulated by the one-dimensional cloud model MISTRA.Through two groups of control experiments: 1)with and without collision-coalescence,2)with strong and weak disturbance;the influence of collision-coalescence and disturbance on cloud microphysical properties and ?-N correlation at different stages of cloud development and different heights are obtained.Then,we determine the main factors affecting dispersion and ?-N correlation by the cloud droplet spectrum.The main contents of this thesis are summarized:(1)The microphysical quantities of marine boundary layer cloud have obvious diurnal character.During the condensation process,the cloud microphysical quantities obviously increased in the daytime and dissipated at night due toradiation and so on,and due to the accumulation of inversion layer and strong disturbance on the cloud top,there is a maximum of the liquid water content and cloud droplet number concentration around the top of the cloud and not far below it.The average liquid water content of individual droplets,dispersion,average radius and standard deviation appear extreme value in the middle and lower part of the clouds due to the joint restriction of liquid water content and cloud droplet number concentration.Through the collision-coalescence process,the cloud layer develops rapidly,which obviously shortens the life of the cloud layer;the liquid water content in the cloud layer decreases obviously;the concentration of cloud droplets changes little in the early stage and decreases slightly in the late stage;The average liquid water content of individual droplets,dispersion,average radius and standard deviation have extreme values at the cloud bottom due to the sedimentation of large-scale cloud droplets.(2)The ?-N has a nonlinear correlation in the lower part of the cloud and a positive correlation on the cloud top during the condensation;and the positive correlation increases on the cloud top in the stage of dissipation.The collision-coalescence reinforcethe trend that dispersion degree decrease with the increase of the number concentration in the lower part of the cloud,weaken the positive correlation of ?-N on the cloud top,and reduce the dispersion degree in the dissipation stage.With the increase of liquid water content,the concentration of cloud droplets in the lower part of the cloud layer increases,the dispersion decreases,and the ?-N positive correlation at the cloud top increases.The effect of liquid water content on dispersion and its correlation with cloud droplet number concentration under collision-coalescence process is similar to condensation process,but it is more sensitive to the change of liquid water content.During condensation process,the spectral width of clouddroplets has no obvious with time and height,and the average radius is the main factor affecting the dispersion.The factors affecting the dispersion during the collision-coalescence process are more complicated: the dispersion in the lower part of the cloud is mainly affected by the standard deviation,while the dispersion near the cloud top is mainly affected by the average radius.Comparing the two simulation of the evolution of cloud droplet spectra,we found that the impact of collision-coalescence process on dispersion is mainly to change the standard deviation of cloud droplets.(3)Under the same initial field,the dissipative term plays a dominant role in affecting the intensity of disturbance,and the large dissipative term means that the cloud layer is in a weak disturbance state.The disturbance kinetic energy has obviousdiurnal cycle,the maximum value of the disturbance kinetic energy appears at about 15 o'clock.The liquid water content and cloud droplet number concentration change little during the first 15 hours of a day under different disturbance intensities,but the liquid water content and cloud droplet number concentration increase due to less consumption at night under weak disturbance.The average liquid water content of individual droplets,dispersion,average radius and standard deviation are small in the first 15 hours under weak disturbance,and then show the opposite state.Strong disturbances reduce the concentration of cloud droplets in the middle and lower part of the cloud layer and increase the dispersion range in the dissipation stage.The positive correlation of ?-N increases with the increase of disturbance in the cloud top,and increases more overtime.The enhancement of the disturbance in the cloud top will increase the mean and standard deviation of the dispersion at the same concentration of cloud droplets,and the high frequency center of dispersion will also increase.The average radius is themain factors affecting the variation of dispersion under strong and weak disturbances.The change of dispersion caused by disturbance is mainly due to the change of the average radius of cloud droplets.The spectral width of cloud droplets changes little over time and height.The concentration of cloud droplets increases first and then decreases over time,and increases continuously over height.The increase of cloud droplet concentration over height under strong disturbance is slightly larger than that under weak disturbance.