Properties of Precipitation and In-Cloud Vertical Motion in a Global Nonhydrostatic Aquaplanet Experiment

Abstract

To gain insight into properties of in-cloud vertical motion and precipitation production in the tropics, three-dimensional outputs from an aquaplanet experiment using a 3.5-km mesh global cloud-system resolving model (GCRM) were analyzed.
Probability distributions of precipitation and latent heating in the 10°N–10°S domain are evaluated in comparison with Tropical Rainfall Measurement Mission (TRMM) observations. Despite biases of generally higher precipitation top height (PTH) and deficiencies near the melting level, the model reproduced the general morphology of the precipitation and total latent heating profiles. Relationship between PTH and cloud top height (CTH) in the simulated clouds reproduced clear contrast between deep and shallow convection in active and suppressed environments, respectively.
The simulated in-cloud vertical velocities were on the order of O(0.1 m s^-1) in anvil clouds and O(1 m s^-1) in updraft cores, as in the range of those in previous observations. Focusing on relatively strong upward motion, the maximum in-cloud vertical motion (w_max) was defined in each column. Probabilities of w_max had double peaks (z = 1–4 and 7–12 km) with minima in the middle troposphere. Vigorous upward motions most frequently occurred in the upper troposphere as the active portion of well-organized convective systems. They were often surrounded by updrafts with w_max height in the lower to middle troposphere, forming a group of updraft regions (w_max > 1 m s^-1) with horizontal scale of O(10 km). In the regions of compensating subsidence, updrafts tended to be capped below the middle troposphere and small in horizontal size. In both regions the updrafts were accompanied by cold pools of their characteristic horizontal scale.
Finally, time evolutions of in-cloud updrafts were analyzed to explore the roles of in-cloud updrafts at different altitude. It was found that the updrafts with w_max height in the middle troposphere produced the heaviest surface precipitation, preceded by moisture transport in the lower to middle troposphere. This suggests that middle tropospheric updrafts most efficiently produced surface precipitation through tight linkage between dynamics and cloud processes, although their occurrence was rare.