Thursday, 2 May 2002: 4:58 PM
MJO-like coherent structures in idealized aquaplanet simulations
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.
Supplementary URL: