The Houston Heat Pump: Modulation of a land-sea breeze by an urban heat island

Houston, Texas, is subject to frequent warm-season air pollution events during which ozone levels exceed federal standards. These events are most likely to occur when the large-scale pressure gradient is weak and winds are dominated by locally-driven circulations.

We investigate the dynamics and transport properties of these locally-driven circulations using high-resolution simulations with the PSU/NCAR MM5 numerical model. The modeling results are consistent with the limited observational evidence. The urban area is found to locally enhance convergence and strengthen the daytime bay breeze from Galveston Bay, while suppressing the formation of a sea breeze front. The enhancement causes increased flow over the Houston Ship Channel, a major industrial and petrochemical center, and advects pollutants and precursors toward Houston, where they ascend and are brought back over Galveston Bay in the return branch of the circulation. This air mass may return onshore later in the day, during the following day, or cause high point pollution concentrations at remote locations.