Evaluating deep updraft formulation in NCAR CAM3 with high-resolution WRF simulations during ARM TWP-ICE



[1] The updraft formulation used in NCAR CAM3 deep convection parameterization assumes that the mass flux for a single updraft increases exponentially with height to its top and detrainment is confined only to a thin layer at the updraft top. These assumptions are evaluated against three-dimensional high-resolution simulations from the Weather Research and Forecast (WRF) model during the monsoon period of the DOE Atmospheric Radiation Measurement (ARM) Program Tropical Warm Pool–International Cloud Experiment (TWP-ICE). Analyses of the WRF-generated updrafts suggest that the mass flux for a single updraft increases with height below the top of the conditionally unstable layer and decreases above. Detrainment may dominate above the conditionally unstable layer rather than only over a thin layer at the updraft top. It is argued that the assumed updraft mass flux profile in CAM3 might be unrealistic in many cases because the updraft acceleration is affected by other drag processes in addition to entrainment. Our analyses suggest that the CAM3-parameterized convection could be too active and, as a result, excess moisture and heat could be transported to the upper troposphere by the parameterized convection. Future improvement is envisioned.