Radiative-Convective Equilibrium with Explicit Two-Dimensional Moist Convection

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  • 1 Geophysical Fluid Dynamics Laboratory/NOAA, Princeton, University, Princeton, New Jersey
  • | 2 Program in Atmospheric and Oceanic Sciences, Princeton University, Princeton, New Jersey
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Abstract

Radiative-convective statistical equilibria are obtained using a two-dimensional model in which radiative transfer is interactive with the predicted moisture and cloud fields. The domain is periodic in x, with a width of 640 km, and extends from the ground to 26 km. The lower boundary is a fixed-temperature water-saturated surface. The model produces a temperature profile resembling the mean profile observed in the tropics. A number of integrations of several months' duration are described in this preliminary examination of the model's qualitative behavior.

The model generates a QBO-like oscillation in the x-averaged winds with an apparent period of ∼60 days. This oscillation extends into the troposphere and influences the convective organization. In order to avoid the associated large vertical wind shears, calculations are also performed in which the x-averaged winds are constrained to vanish. The convection then evolves into a pattern in which rain falls only within a small part of the domain. The moisture field appears to provide the memory that localizes the convection.

If the vertical shears are fixed at a modest nonzero value, this localization is avoided. Comparing calculations with surface temperatures of 25° and 30°C, the planetary albedo is found to decrease with increasing temperature, primarily due to a reduction in low-level cloudiness.

Abstract

Radiative-convective statistical equilibria are obtained using a two-dimensional model in which radiative transfer is interactive with the predicted moisture and cloud fields. The domain is periodic in x, with a width of 640 km, and extends from the ground to 26 km. The lower boundary is a fixed-temperature water-saturated surface. The model produces a temperature profile resembling the mean profile observed in the tropics. A number of integrations of several months' duration are described in this preliminary examination of the model's qualitative behavior.

The model generates a QBO-like oscillation in the x-averaged winds with an apparent period of ∼60 days. This oscillation extends into the troposphere and influences the convective organization. In order to avoid the associated large vertical wind shears, calculations are also performed in which the x-averaged winds are constrained to vanish. The convection then evolves into a pattern in which rain falls only within a small part of the domain. The moisture field appears to provide the memory that localizes the convection.

If the vertical shears are fixed at a modest nonzero value, this localization is avoided. Comparing calculations with surface temperatures of 25° and 30°C, the planetary albedo is found to decrease with increasing temperature, primarily due to a reduction in low-level cloudiness.

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