TROPICAL WAVE INSTABILITIES - CONVECTIVE INTERACTION WITH DYNAMICS USING THE EMANUEL CONVECTIVE PARAMETERIZATION

Wave-CISK and evaporation-wind feedback modes, also known as WISHE (wi nd-induced surface heat exchange) modes, are investigated using a two- dimensional (x-p), hydrostatic, nonrotational model linearized about a basic state in radiative-convective equilibrium with no vertical shea r. Cumulus convection is parameterized using version 1.22 of the Emanu el convective parameterization scheme, a mass flux scheme that include s the effects of evaporatively driven unsaturated downdrafts. It is fo und that the only unstable modes are long-wavelength WISHE modes. All wave-CISK modes are damped, though the longest-wavelength modes have n early neutral growth rates. It is demonstrated that the presence of ev aporatively driven unsaturated downdrafts plays a major role in dampin g both short-wave WISHE and wave-CISK modes in the model. The model fa vors approximately the same horizontal scale as observed for the Madde n-Julian oscillation (40-60 day wave), but the phase speed is too larg e by a factor of approximately4-5. A general analytical two-dimensiona l model designed to work with any convective parameterization is used to show that the unusually high phase speeds are most likely a result of a time lag in the vertical transport of water vapor by the Emanuel convective parameterization.