Other
Scientific paper
Jan 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990phdt........91h&link_type=abstract
Thesis (PH.D.)--NORTH CAROLINA STATE UNIVERSITY, 1990.Source: Dissertation Abstracts International, Volume: 51-04, Section: B, p
Other
4
Scientific paper
A mesoscale planetary boundary layer (PBL) numerical model is developed to investigate airflow over complex topography. The model physics includes PBL turbulent transfer, atmospheric longwave and shortwave radiation, diurnal energy budgets over ground, cloud microphysics and subgrid cumulus parameterization. The model utilizes a new fourth order Crowley advection scheme which preserves phase and amplitude much better than other Crowley schemes. Turbulence closures using the turbulent kinetic energy (TKE) and dissipation (varepsilon ) equations are investigated with the level 2.5 scheme of Mellor and Yamada (1982) to better determine eddy diffusivities. One-dimensional (1-D) model results show that the PBL flows under various stability conditions are not significantly sensitive to the modified Blackadar's and Kolmogorov's eddy mixing length formations, although the latter yields excessively large mixing lengths in the entrainment region of the upper PBL. With the same prognostic TKE equation, the model results show insensitivity of the 1-D flow to the details of diagnostic formulations in the closures and to eddy Prandtl numbers. A 2-D model is used to stimulate January 28 cold -air outbreak over the Gulf Stream region during the IOP -2 (Intensive Observation Period) of the 1986 Genesis of Atlantic Lows Experiment (GALE). The modeled 2-D circulation system is found to be sensitive to Prandtl number, in contrast to the 1-D model results. Prandtl number becomes increasingly important as the clouds begin to interact with the marine boundary layer (MBL). Using the E-varepsilon closure, the model predicts the observed MBL structure that includes a low level jet west of the Gulf Stream warm core and a constrained boundary layer height due to the middle-level stable layer. Two cases with 3-D idealized flow are also simulated for the same GALE IOP. For the easterly onshore ambient flow, a confluence zone appears near the coastline in response to the strong oceanic baroclinicity due to the Gulf Stream. With the increased coastal confluence, a shallow coastal front (below 2 km) begins to form. Stationary rainbands are produced along the coastal front. For the northerly offshore ambient flow, the rainband first appears along the eastern edge of the Gulf Stream and moves slowly downstream. The model is also applied to simulate the 3-D airflow past Taiwan mountains. For both north-westerly and the south-westerly prevailing winds (with a Froude number of about 0.3), a mesoscale low pressure center occurs at the south-eastern (downstream) slopes of the steep mountains. The role of the PBL effects in changing the flow separation and stagnation points is found to be more important for the upstream flow than the downstream flow.
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