Planetary Boundary Layer Schemes for Sub-kilometer Urban Canopy Simulations

Authors: Melissa Allen-Dumas*, Oak Ridge National Laboratory, William Pendergrass, National Oceanic and Atmospheric Administration Atmospheric Turbulence and Dispersion Division
Topics: Climatology and Meteorology
Keywords: planetary boundary layer schemes, urban meteorology, microclimate modeling
Session Type: Virtual Paper
Day: 4/11/2021
Start / End Time: 9:35 AM / 10:50 AM
Room: Virtual 19
Presentation File: No File Uploaded

Spatial distribution of urban heat islands within a city rely on the ways in which the urban surface exchanges fluxes with adjacent atmospheric layers, including solar and longwave radiation to and from buildings, roads, and green spaces, along with their ventilation, exhaust, moisture, energy budgets, and small-scale advection. Thus, appropriate parameterization of vertical turbulent fluxes in meteorological modelling is important for correct spatial representation of diurnal temperature, water vapour and winds within the planetary boundary layer (PBL) of the complex terrain of a city’s morphology. Capturing small-scale turbulence at various horizontal resolutions, especially at resolutions relevant to processes at urban scale, is critical to understanding how meteorological processes interact among urban structures and land use. Such processes generally occur at horizontal resolutions between 1 kilometer and approximately 100 meters. These resolutions are often referred to as the ``gray zone'' because none of the traditional turbulence modeling methods was designed for this resolution, and errors related to assumptions in the parameterizations are expected in near-kilometer resolution simulations. Here, we compare results of Weather Research and Forecasting (WRF) model simulations using three different PBL schemes (BouLac, MYNN2 and Shin-Hong) at 1km resolution to determine which best captures the diurnal trend of measured data at specific measurement locations for each of these parameters for a three-day period over Washington, DC. Results are analyzed statistically for point accuracy and overall trends.

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