Plume or bubble? The non-linear impact of an urban heat island on city-scale atmospheric circulation
Abstract
Air flow in the atmospheric boundary layer (ABL) over metropolitan and surrounding rural areas is primarily modulated by the wind speed, the urban surface roughness, and the urban heat island (UHI) intensity. When the winds are strong and the UHI is weak, a warm polluted plume of air is expected to develop in the wake of the city as urban emissions are advected downwind. This pattern maintains a minimal ventilation of the city and limits the UHI and elevated air pollutant concentrations. However, if the wind weakens, the ABL structure could shift to a thermally-driven bubble in which a rising warm plume of air forms a circulation above the city and traps pollutants and heat over the urban core. Urban temperature and air quality are expected to be significantly different depending on which regime dominates. In this study, we use large eddy simulations (LES) to probe these different possible flow regimes. First, we reduce the parameter space by conducting a dimensional analysis of the problem and testing it using the LES. Subsequently, we examine how the dimensionless parameter relating the wind speed and UHI intensity, similar conceptually to a Richardson number, modulates ABL circulation and turbulence, and what are the implications for urban environmental quality.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMGC33C..07B
- Keywords:
-
- 0345 Pollution: urban and regional;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 3322 Land/atmosphere interactions;
- ATMOSPHERIC PROCESSESDE: 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 0493 Urban systems;
- BIOGEOSCIENCES