Technical Report -- Essentials of which will be published as a journal paper

Fernando, Harindra J. S. ; Anderson, James ; Boyer, Don

Arizona State University

关键词: Heat Flux;    Diffusion;    Lakes;    Implementation;    Stratification;   

DOI  :  10.2172/859144
RP-ID  :  DOE/ER/63704-1
RP-ID  :  FG02-04ER63704
RP-ID  :  859144

美国|英语

来源: UNT Digital Library

【 摘 要 】

Vertical Transport and Mixing in Complex Terrain Airsheds: Implementation of a Stable PBL Turbulence Parameterization for the Mesoscale Model MM5 The difficulties associated with parameterization of turbulence in the stable nocturnal atmospheric boundary layer have been a great challenge for the night-time predictions of mesoscale meteorological models such as MM5. As such, there is a general consensus on the need for better stable boundary-layer parameterizations. To this end, two new turbulence parameterizations based on the measurements of the Vertical Transport and Mixing (VTMX) field campaign were implemented and evaluated in MM5. A unique aspect of this parameterization is the use of a stability dependent turbulent Prandtl number that allows momentum to be transported by the internal waves, while heat diffusion is impeded by the stratification. This improvement alleviates the problem of over-prediction of heat diffusion under stable conditions, which is a characteristic of conventional PBL schemes, such as MRF and Blackadar schemes employed in MM5. The predictions made with the new PBL scheme for the complex terrain airshed of Salt Lake City were compared with those made with a default scheme of MM5 and with observations made during the VTMX campaign. The new schemes showed an improvement in predictions, particularly for the nocturnal near surface temperature. Surface wind predictions also improved slightly, but not to the extent of temperature predictions. The default MRF scheme showed a significantly warmer surface temperature than observed, which could be attributed to the enhanced vertical heat exchange brought about by its turbulence parameterization. The modified parameterizations reduced the surface sensible heat flux, thus enhancing the strength of the near surface inversion and lowering the temperature toward the observed values.