Sensitivity Analysis and Application of an Entraining Plume Model

Abstract

Data derived from radiosonde soundings and stereoscopic photographs collected during a field experiment were input to a steady-state entraining plume cloud model to predict cumulus cloud development. The basic data input requirements of the model include cloud-base height, vertical profiles of temperature and dew point, and initial radius and vertical velocity at cloud base. The model was used to simulate convection on three different days, using the average of each day's measured cloud-base heights, its radiosonde data, and each of four combinations of initial cloud radius and vertical velocity. The dimensions of the four clouds predicted for each day were compared with dimensions of the photogrammetrically observed clouds that formed over mountainous terrain. Variability of measured cloud-top heights corresponded closely with model predictions from three of the combinations of initial radius and vertical velocity for each day's medium and large sized clouds. A sensitivity analysis of the model was conducted to examine the dependence of various model-calculated values (e.g., cloud radius, vertical velocity, mass flux, buoyancy) on a number of factors: cloud-base level, initial radius and vertical velocity at cloud base, location of radiosonde sounding input levels and upper level humidity profile.