Role of advection on the evolution of near-surface temperature and wind in urban-aware simulations
The role of advection of heat and momentum on the evolution of near-surface temperature and wind is evaluated in urban-aware simulations over Houston, Texas, under dry conditions on a light-wind day. Two sets of exper-iments, each consisting of four simulations using different planetary boundary layer (PBL) schemes, were conducted over 48 h using the default urban scheme (BULK) and the single-layer urban canopy model (SLUCM) available within the Weather Research and Forecasting Model. We focus on understanding and quantifying the role played by temperature and momentum advection, particularly on the windward and leeward sides of the city. Previous studies have largely ignored any quantitative analysis of impacts from the advection of momentum over an urban area. The horizontal advection of temperature was found to be more important in the BULK because of the larger surface temperature gradient caused by warmer surface temperatures over urban areas than in the SLUCM. An analysis of the momentum budget shows that horizontal advection of zonal and meridional momentum plays a prominent role during the period of peak near-surface winds and that this effect is more pronounced in the windward side of the city. The local tendency in peak winds in the leeward side lags that in the windward side by about 1–2 h, similar to the lag found in horizontal momentum advection. The sensitivity of the results to different urban and PBL schemes was explored. The results imply that representation and influence of land-use patterns via sophisticated urban parameterizations generate locally driven winds that best resemble observations.