From AMIE/DYNAMO Field Observations to Global Cloud-Permitting Models
Author
Chidong Zhang — NOAA/PMEL
Category
MJO: Madden-Julian Oscillation
Description
Summary of the contribution of different physical processes and cloud types to the evolution of
moisture in the simulated MJO event. Radiative cooling (red arrow) contributes to drying in the
convectively suppressed phase. Moistening (drying) occurs in regions of w'qv' flux convergence
(divergence). Condensation (re-evaporation) contributes to moistening. Ice growth alone contributes to drying. Non-precipitating cirrus reduces drying due to radiative cooling induced subsidence in the convectively enhanced phase. Large-scale horizontal dry air advection contributes to drying in the convectively dissipating phase.
A framework of using AMIE/DYNAMO field observations (soundings, radars) to support the development and assessment of global cloud-permitting models is presented. The framework takes the following steps to connect the field observations to global cloud-permitting models:
(1) Local cloud-permitting model (CPM) simulations over an AMIE/DYNAMO sounding array, heavily constrained by forcing data from the field observations. The purpose of this step is to assess roles of different types of clouds in the observed moisture budget at different stages of the Madden-Julian Oscillation (MJO) and to explore the sensitivity of these roles in CPM simulations to microphysics schemes.
(2) Regional CPM simulations over a large-scale area over the tropical Indian Ocean, weakly constrained by lateral boundary conditions from global reanalysis products. The purpose of this step is to evaluate the capability of the regional CPM to reproduce the cloud life cycle observed by the field campaign at different stages of the MJO and its sensitivity to microphysics.
(3) Applications of the diagnostic procedures developed from Steps 1 and 2 to global model simulations with adaptive refinement to cloud permitting grid over the field campaign domain. The purpose of this step is to assess the degree to which the observed and simulated cloud life cycle and their roles in the moisture budget can be reproduced by a global CPM with minimal observational constraints (initial and lower boundary conditions).
The main results are: At the suppressed stage of the MJO, shallow precipitating clouds may moisten the lower troposphere by turbulent transport and the vertical circulation induced by their diabatic heating, which overwhelms the direct removal of moisture by condensation. Turbulent transport within congestus and deep convective clouds and reduced subsidence from radiative cooling lead to moistening of the mid and upper troposphere. The drying following the MJO peak is primarily associated with low-level horizontal advection and the efficient removal of moisture by stratiform clouds aloft. These roles of different types of clouds in the moisture budget are sensitive to microphysics primarily through long-wave radiation but also through other processes. Without a strong observational constraint, the regional and global CPMs cannot completely reproduce the results from local CPMs. Simulations by the global CPM also sensitively depend on initial conditions.
