Cumulus anvil cloud properties, large-scale conditions, and climate change

In light of the importance of clouds and upper troposphere water vapor in the climate system, this thesis investigates the large scale conditions in the pre-convective environment of mesoscale convective systems, CAPE variabilities in the current climate and in the climate change as well as the variability of upper troposphere water vapor. By combining satellite remote sensing data and radiosonde data observed during TOGA COARE period in the tropical western Pacific, we find that tropical storms with large size and thick anvil clouds tend to develop in the pre-convective environment characterized by moderate to strong uprising motion in the middle troposphere, strong moisture convergence in the boundary layer, wet middle troposphere air, high CAPE and moderate shear of horizontal wind. GCM simulations suggest that CAPE variation in time and space in the current climate is mainly controlled by regional changes in boundary layer temperature and moisture while CAPE variation in the climate change is mainly constrained by moist adiabatic lapse rate change. Therefore, climate change in CAPE in response to a 2 K increase in surface temperature is only about 200 J/kg which is probably too small to enhance lightning activities so that the signal can be detected. Analysis of Raman Lidar moisture budget indicates that the moisture changes in the lower and upper troposphere are mainly in response to local cloud formation and convection and the middle troposphere moisture change is largely controlled by horizontal advection. The EOF analysis shows that the first three leading EOF modes can explain more 72% of the total variability. The absence of an obvious diurnal cycle in moisture sink suggests that a continuously operating lidar will be capable of documenting the true moisture budget.