Journal of Geophysical Research: Atmospheres
© 2014 American Geophysical Union
Impact Factor: 3.174
ISI Journal Citation Reports © Ranking: 2012: 23/170 (Geosciences Multidisciplinary)
Online ISSN: 2169-8996
Associated Title(s): Journal of Geophysical Research
Causality of deep convection from a cloud-resolving model
Understanding deep convection and clouds is among the most important goals of tropical weather and climate dynamics. Deep convection, the vertical transport of buoyant air through the depths of the atmosphere, controls cloud formation and precipitation rates. To help forecast the weather, operational forecasters are beginning to use cloud-resolving models: atmospheric models with resolutions high enough to adequately represent individual clouds and often a scale broad enough to capture large-scale patterns in deep convection.
When cloud-resolving models are used for research, and particularly when they are tested against field observations, researchers typically prescribe the values of the atmosphere's large-scale vertical motion based on observed values. Because of basic constraints on the heat and moisture budgets, the imposed large-scale vertical velocity strongly controls the simulated deep convection. In reality, however, the convection is as much a cause of the large-scale vertical velocity as the other way around. Imposing the large-scale vertical velocity prevents the model from being used to understand the real causes of the convection.
To work around this limitation, Wang et al. ran a cloud-resolving model in which the atmospheric vertical velocity was parameterized rather than imposed. The authors tested two different approaches to parameterize the vertical velocity. They tested the model's skill in reproducing the observations made during the Tropical Ocean Global Atmosphere–Coupled Ocean-Atmosphere Response experiment (TOGA-COARE). The authors found that the model was able to reproduce the observed precipitation variability reasonably well, including two active phases of the Madden-Julian Oscillation.
Further, by imposing the time average values of some environmental parameters—such as sea surface temperature—rather than including the observed variations in those parameters, the authors assessed the role of each in driving deep convection. They found that the net sources of moist static energy to the column play an important role in controlling atmospheric deep convection.