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- Author or Editor: W. Ridgway x
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Abstract
An idealized energy-balance model for a closed circulation is first presented to illustrate the coupling between the net tropospheric radiative cooling, the surface fluxes and the mean subsidence away from the precipitation zones. Then a one-dimensional diagnostic model and a radiation model with boundary layer clouds are combined to explore this coupling for a specific region using mean sounding data over the tropical Pacific. The radiatively driven subsidence rate at the top of the convective boundary layer is approximately 35 mb day−1 (0.04 Pa s−1 and is largely independent of boundary layer cloud fraction. The sensitivity of the corresponding convective heat flux profiles to the mass divergence profile and cloud fraction within the boundary layer is explored. Reasonable assumptions give realistic surface sensible and latent heat fluxes for this region of approximately 10 and 130 W m−1. The paper illustrates the important background climatic control of the radiation field on the tropical surface fluxes.
Abstract
An idealized energy-balance model for a closed circulation is first presented to illustrate the coupling between the net tropospheric radiative cooling, the surface fluxes and the mean subsidence away from the precipitation zones. Then a one-dimensional diagnostic model and a radiation model with boundary layer clouds are combined to explore this coupling for a specific region using mean sounding data over the tropical Pacific. The radiatively driven subsidence rate at the top of the convective boundary layer is approximately 35 mb day−1 (0.04 Pa s−1 and is largely independent of boundary layer cloud fraction. The sensitivity of the corresponding convective heat flux profiles to the mass divergence profile and cloud fraction within the boundary layer is explored. Reasonable assumptions give realistic surface sensible and latent heat fluxes for this region of approximately 10 and 130 W m−1. The paper illustrates the important background climatic control of the radiation field on the tropical surface fluxes.
Abstract
A one-dimensional thermodynamic model for a partially mixed, partly cloudy, convective boundary layer (CBL) is coupled to a radiation model to compute equilibrium solutions for a tropical CBL and troposphere in energy balance over the ocean. For a sea surface temperature (SST) of 300 K, the model gives an equilibrium cloud base ≈ 950 mb, a CBL top ≈ 800 mb and a low level θ e ≈ 347 K, close to climatic values. The CBL deepens and low level θ e rises with increasing wind speed and SST. We explore the change in CBL structure and surface fluxes with external parameters on three timescales; namely, the CBL (∼1 day); the tropospheric radiative equilibrium (∼10 days); and the oceanic thermal equilibrium (>100 days). The variation in cloud top decreases with greater coupling to atmosphere and ocean. The slope of the latent heat flux with increasing SST decreases with more tropospheric coupling, and reverse sign with a coupled ocean. This simplified model gives an increase of tropical SST with a doubling of CO2 on climatic timscales of 2–3°K, increasing with upper tropospheric moisture.
Abstract
A one-dimensional thermodynamic model for a partially mixed, partly cloudy, convective boundary layer (CBL) is coupled to a radiation model to compute equilibrium solutions for a tropical CBL and troposphere in energy balance over the ocean. For a sea surface temperature (SST) of 300 K, the model gives an equilibrium cloud base ≈ 950 mb, a CBL top ≈ 800 mb and a low level θ e ≈ 347 K, close to climatic values. The CBL deepens and low level θ e rises with increasing wind speed and SST. We explore the change in CBL structure and surface fluxes with external parameters on three timescales; namely, the CBL (∼1 day); the tropospheric radiative equilibrium (∼10 days); and the oceanic thermal equilibrium (>100 days). The variation in cloud top decreases with greater coupling to atmosphere and ocean. The slope of the latent heat flux with increasing SST decreases with more tropospheric coupling, and reverse sign with a coupled ocean. This simplified model gives an increase of tropical SST with a doubling of CO2 on climatic timscales of 2–3°K, increasing with upper tropospheric moisture.
