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Development and Evaluation of a New Spectral Planetary Boundary-Layer Architecture for the MM5

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The Otte-Wyngaard spectral PBL architecture, which represents the vertical structure of mean variables in the PBL with a truncated series of Legendre polynomials, is inserted within the framework of the non-hydrostatic, three-dimensional Penn StateNational Center for Atmospheric Research Mesoscale Model version 5.2 MM5. It is important to note that the focus of this work is the new spectral architecture, and that the specific closure used within this general framework can easily be changed. Preliminary experiments found that the prognostic equation for PBL height employed by the spectral model is inappropriate during deep convection. Therefore, two algorithms for PBL height diagnosis were tested, at gridpoints experiencing deep convection as well as for initialization of the PBL height field for the prognostic equation. A comparison between the spectral model and two high-resolution models, the Blackadar and Gayno-Seaman models, is performed using two cases an idealized coastal-zone domain with a single-sounding initialization, and a real-data case focused on the U.S. Department of Energy Atmospheric Radiation Measurement Southern Great Plains Cloud and Radiation Testbed ARM-CART during an intense observation period from 0000 UTC 12 April 1997 to 0000 UTC 14 April 1997. Special data from the ARM-CART site were used for independent verification. Experimental results show that the spectral model within MM5 produces realistic vertical structure within the boundary layer, comparable to that of the other two PBL models, and computationally, the spectral mode is several times faster than the other high-resolution models.

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  • Meteorology
  • Fluid Mechanics

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