Diurnal Oscillation of the Convective Boundary Layer Part 2: Cloudy Atmosphere

  • Author(s): Ching-Chi Wu and Wen-Yih Sun
  • DOI: 10.3319/TAO.1990.1.2.157(A)
  • Keywords:
  • Citation: Wu, C.-C. and W.-Y. Sun, 1990: Diurnal oscillation of the convective boundary layer. Part 2: Cloudy atmosphere. Terr. Atmos. Ocean. Sci., 1, 157-174, doi: 10.3319/TAO.1990.1.2.157(A)

A simple one-dimensional ensemble average PBL model, including condensation, evaporation, and atmospheric radiation is used to study the evolution of PBL in a cloudy atmosphere. The turbulent kinetic energy E is predicted by the TKE equation. The eddy coefficient is proportional to l; the length scale l is determined by Sun and Ogura's method. Meanwhile, the similarity equations are used in the surface layer; the force restoring method is adopted to calculate the surface soil temperature and moisture.

The observed fields at 0900 EST on Day 33 in the Wangara Experiment are used for the first 3 hours (to 1200 EST). After that time, the temperature and moisture are modified in order to initiate a cloud layer and then, the model is integrated for 45 hours. The simulated mean fields and eddy fluxes are comparable with other higher-order model and observations.

During the daytime, the linear decreases of with height in the lower convective layer are consistent with a uniform change of mean temperature within the subcloud layer. A slightly negative heat flux exists near the cloud base and just above the cloud top. A substantial positive heat flux exists in the cloud layer, primarily attributed to the latent heat release and enhanced by the strong radiative cooling. During the night, the heat flux near the surface becomes negative. Like the daytime results, a positive heat flux exists inside the cloud and a negative heat flux exists just above the cloud top.

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