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Mechanisms of convective cloud organization by cold pools over tropical warm ocean during the AMIE/DYNAMO field campaign

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  • This paper investigates the mechanisms of convective cloud organization by precipitation-driven cold pools over the warm tropical Indian Ocean during the 2011 Atmospheric Radiation Measurement (ARM) Madden-Julian Oscillation (MJO) Investigation Experiment/Dynamics of the MJO (AMIE/DYNAMO) field campaign. A high-resolution regional model simulation is performed using the Weather Research and Forecasting model during the transition from suppressed to active phases of the November 2011 MJO. The simulated cold pool lifetimes, spatial extent, and thermodynamic properties agree well with the radar and ship-borne observations from the field campaign. The thermodynamic and dynamic structures of the outflow boundaries of isolated and intersecting cold pools in the simulation and the associated secondary cloud populations are examined. Intersecting cold pools last more than twice as long, are twice as large, 41% more intense (measured with buoyancy), and 62% deeper than isolated cold pools. Consequently, intersecting cold pools trigger 73% more convection than do isolated ones. This is due to stronger outflows that enhance secondary updraft velocities by up to 45%. However, cold pool-triggered convective clouds grow into deep convection not because of the stronger secondary updrafts at cloud base, but rather due to closer spacing (aggregation) between clouds and larger cloud clusters that form along the cold pool boundaries when they intersect. The close spacing of large clouds moistens the local environment and reduces entrainment drying, increasing the probability that the clouds further develop into deep convection. Implications for the design of future convective parameterization with cold pool-modulated entrainment rates are discussed.
  • The DYNAMO field campaign data used in this paper is available at NCAR's Earth Observing Laboratory's DYNAMO Data Catalogue https://www.eol.ucar.edu/field_projects/dynamo. The data set names are: R/V Roger Revelle Flux, Near-Surface Meteorology, and Navigation Data and S-PolKa Radar, fully corrected, merged, final moments data in cfRadial format.
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  • Feng, Z., Hagos, S., Rowe, A. K., Burleyson, C. D., Martini, M. N., & de Szoeke, S. P. (2015). Mechanisms of convective cloud organization by cold pools over tropical warm ocean during the AMIE/DYNAMO field campaign. Journal of Advances in Modeling Earth Systems, 7(2), 357-381. doi:10.1002/2014MS000384
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  • 7
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  • 2
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  • This research is based on work supported by the Biological and Environmental Research of the U.S. Department of Energy (DOE) Office of Science as part of the Atmospheric System Research Program and the Regional and Global Climate Modeling Program. The author at the University of Washington is supported by NSF grant AGS-1355567 and DOE ASR grant DE-SC0008452. Computing resources for the simulations are provided by the Oak Ridge Leadership Computing Facility (OLCF) and the National Energy Research Scientific Computing Center (NERSC). The Pacific Northwest National Laboratory is operated for DOE by Battelle Memorial Institute under contract DE-AC05-76RL01830.
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