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Parameterized Coastal C onvective O rganization and Maritime Continent Rainfall in a GCM

Parameterized Coastal C onvective O rganization and Maritime Continent Rainfall in a GCM. Brian Mapes 1 , Rich Neale 2 Baohua Chen 1 1. RSMAS, University of Miami 2. National Center for Atmospheric Research(NCAR). Convective Organization.

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Parameterized Coastal C onvective O rganization and Maritime Continent Rainfall in a GCM

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  1. Parameterized Coastal Convective Organization and Maritime Continent Rainfall in a GCM Brian Mapes1 , Rich Neale2 Baohua Chen1 1. RSMAS, University of Miami 2. National Center for Atmospheric Research(NCAR)

  2. Convective Organization • What is organization exactly? In this model, a force-damped prognostic scalar which shifts the partitioning between low and high entrainment plumes.

  3. Model Versions and Simulations • Models versions: CESM1_0_3-CAM5.1 Resolution: 1.9x2.5 • Unified shallow-deep convection scheme: University of Washington shallow convection scheme plus org to govern the transitions and relationships between two convections • Disable the CAM5’s deep convection scheme (Zhang and McFarlane, 1995)

  4. Model Versions and Simulations • Control experiment: only one org source of evap2org, NO coastal effect on organization • Test experiment: evap2org+coast2org • 3-year (1979-1981) CAM5 runs , with a fixed boundary condition consisting of climatological monthly SST and sea ice conditions

  5. Figure 1: Annual mean of convective organization with & without coastal source. Scalar org (space, time) is dimensionless. Coastal source makes stronger organization over the equatorial regions of North America, South America, Africa and the Indonesian Maritime Continent .

  6. Figure 2: Annual mean total precipitation with & without coastal source Three year-averaged annual precipitation over Indonesian Maritime Continent significantly becomes LESS with coastal org source.

  7. Figure 3: Net, time integrated direct coastal effects on organization. Coastal source generates the stronger organization along the coastline of Africa, Australian, South America, United States, Southeast Asia and Indonesia MC. While in tropical oceans, organization becomes relatively smaller. Figure 4: Net, time integrated effect of coastally generated organization on total rainfall. Associated with the stronger org, precipitation increases along the above coastline. But in land, coastally generated org make less rainfall. Maritime Continent annual rainfall is reduced significantly with more org.

  8. Figure 5: Longitude-time distribution of difference between total precipitation with and without coastal source, averaged over the tropical belt 10 o S-5 o N. Rectangle indicates the region Indonesia Maritime continent (MC). In the whole year, total annual rainfall in MC becomes 3-4 mm day-1 less than no coastal source.

  9. Figure 6: Moist static energy for Indonesia (10S-5N, 100E-150E) in December. Low MSE at surface in MC with coastal org, this is explanation for having less convection even with more org. But why does it work out this way??

  10. Puzzle-Question • Coastlines are known to help generate convective organization. • In any given setting, high-organization convection is more successful than low-organization convection. • And YET (at least in our model): the net, time integrated effect of coastally generated organization is LESS rainfall in Indonesia Maritime Continents. WHY??

  11. Reference • Mapes, B.E., and R.B. Neale, 2011: Parameterizing Convective Organization to Evade the Entrainment Dilema, J.Adv.Model.Earth Syst., 3,M06004 • Park,S., and C.S. Bertherton, 2009: The University og Washington Shallow Convection and Moist Turbulence Schemes and Their Impact on Climate Simulations with the Community Atmosphere Model. J.Clim., 22,3449-3469

  12. The net, time integrated effect of coastally generated organization is LESS rainfall in Indonesia Maritime Continents. Other regions with stronger organization have more rainfall, as expected. This discrepancy seems not to be related to the organization but could due to the stabilization or insufficient model resolution that is too coarse to resolve the complex land-sea contrast.

  13. Further work • Do you have a hypothesis or guess at an answer? Yes, perhaps it involves the stabilization of the mean state. • Hypothesis: If org source had a diurnal cycle, its rectified effect on the mean might depend on the PHASE of that cycle relative to the sun, which governs the diurnal cycle of PBL heating and moistening over land. • How will you test these ideas more or get closer to answering the question? • With a closer look(seasonal, diurnal), with a more refined coastal source function. For example, to multiply coast2org by a sine or cosine of the hour, maybe make a semidiurnal cycle, representing sea breeze in daytime and land breeze at night. Do runs with different phase offsets and see if the annual-mean PRECT over MC is different and its MSE.

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