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Evaluating Convection Parameterization Assumptions Using TWP-ICE Data

Guang Zhang University of California, San Diego

Category: Modeling

Convection parameterization schemes involve many assumptions, from closure to convection trigger, to 1D cloud models that determine in-cloud updraft and downdraft properties. GCM simulations of global climate are sensitive to these assumptions. This study evaluates several assumptions in the Zhang-McFarlane convection scheme, including the original convective available potential energy (CAPE)-based closure, the free tropospheric quasi-equilibrium closure, and the recently proposed dilute CAPE modification being considered by the National Center for Atmospheric Research (NCAR) Atmospheric Model Working Group (AMWG). We will rely on the Tropical Warm Pool International Cloud Experiment (TWP-ICE) single-column model forcing data, together with other relevant datasets. Our observational analyses suggest that undiluted CAPE is least correlated with convection, followed by the dilute CAPE, which shows a modest correlation with convection, yielding a relaxation time of about five hours. The free tropospheric quasi-equilibrium has the highest correlation with convection. To incorporate the effect of planetary boundary layer (PBL) properties on convection, entrainment dilution to CAPE also is introduced to the free tropospheric quasi-equilibrium. Tests of these closure assumptions are performed using the single-column climate model (SCAM). In addition, cloud liquid and ice water contents within convective updrafts from the convection parameterization are evaluated against satellite and radar retrievals and compared with cloud-resolving model simulations from other ARM principal investigators (PIs). The realism of the parameterized updraft liquid and ice water contents directly affects the anvil cloud properties through detrainment of ice and water from convection.

This poster will be displayed at ARM Science Team Meeting.

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