Numerical Study On Effects Of Initial Perturbation On Convective Cloud Development

The effects of the initial perturbation on the development of convective cloud arestudied through observations and simulations. Observation data during theConvection and Precipitation/Electrification (CAPE) illustrates that horizontalconvection roils are able to initiate deep convection. However it is difficult toestimate the potential for deep convection from the parameters of primal sounding.The original sounding was modified with the maximum moisture obtained within theroll updraft branches using aircraft. Analyzing the parameters of the modifiedsounding shows that deep convection will be initialized in these conditions: (1) Theboundary layer depth is nearly equal to the level of free convection; (2) Highconvective available potential energy and low absolute value of convectiveinhibition; (3) Low absolute value of convective inhibition and high midlevelrelative humidity. So these fit together parameters can be effective predictor toinitiate deep convection when the soundings of the storm area were modified.A three-dimensional hailstorm numerical model with fully elastic primitiveequations is used in this thesis. Firstly three disturbance schemes: humidity,temperature, and humidity-temperature perturbation were designed to simulate theeffects of initial disturbance on the development of convective clouds. And theeffects of disturbance thickness, perturbation center height, initial potentialtemperature deviation, and disturbance horizontal radius on the development ofconvective clouds were studied with the temperature perturbation. The simulationresults show: (1) The cumulus develops faster and stronger with warm-wet bubbleperturbation, the developing rate of the cumulus is mostly affected by warm bubbleperturbation, and the wet bubble perturbation mostly affects the cumulus developingstrength with the same disturbance area; (2) However the cumulus develops fasterwith the warm or warm-wet bubble perturbation and slower with wet bubbleperturbation when the height of simulation cumulus was the same. In addition thetotal precipitation and hail shooting on the ground was larger with wet bubbleperturbation but smaller with warm-wet bubble perturbation. (3) Under the conditionof warm bubble perturbation increasing the disturbance thickness or reducing theperturbation center height separately will strengthen and quicken the cumulus; theconvective will develop faster with a smaller disturbance horizontal radius, but itwill be weakened under this condition; nevertheless the cumulus develops faster andmore intensely with a larger disturbance potential temperature deviation.Considering stability the developing intensity of the cumulus is directly proportionalto the initial perturbation and the instability of the stratification; however the moreunstable of the stratification the lower initial disturbance demanding for triggeringconvection, the smaller effect of initial disturbance on the cumulus.