Extended Abstract (1.1M)15B.6
MJO-like coherent structures in idealized aquaplanet simulations
Wojciech W. Grabowski, NCAR, Boulder, CO
Interaction between equatorially-trapped disturbances and tropical convection is investigated using a nonhydrostatic global model which applies the cloud-resolving convection parameterization (CRCP). The CRCP represents subgrid scales of the global model by embedding a 2D cloud-resolving model in each column of the global model. The cloud-resolving models are aligned along the east-west direction and allow for coupling of not only thermodynamic variables, but the zonal momentum as well. The modeling setup is a constant SST aquaplanet (with the size and rotation as Earth) in radiative-convective equilibrium. No large-scale organization of convection is present outside the equatorial waveguide. Inside the waveguide, on the other hand, spontaneous formation of coherent structures with deep convection on the leading edge and strong surface westerly winds to the west (the westerly wind bursts) is simulated. These coherent structures resemble the Madden-Julian Oscillations (MJO) observed in the terrestrial tropics and are present in simulations applying prescribed and interactive radiation, various orientation of CRCP domains (east-west versus north-south), and various horizontal resolutions of the global model. Sensitivity simulations suggest that interactive surface fluxes appear to be essential for the development, but not the maintenance, of strong MJO-like coherent structures. The presentation will discuss these results in the context the current theories explaining the coupling between convection and the large-scale dynamics in the tropics on intraseasonal time scales.
Session 15B, Intraseasonal variability (Parallel with Sessions 15A and 15D)
Thursday, 2 May 2002, 4:00 PM-5:15 PM
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