Abstract

Although previous studies have shown that large cities can modify the regional distribution of convective precipitation, many questions remain regarding the physical processes most responsible for this modification. To date there has been relatively little emphasis on changes to cloud-scale processes within deep convective storms as they encounter large cities. This study uses an idealized atmospheric model to investigate changes in cloud-scale structure as convective storms interact with a simplified representation of a city. Two sets of simulations are shown for comparison. The first set uses the traditional approach of a horizontally homogeneous surface field while the second configuration approximates a large city via a circular area in the center of the model domain characterized by enhanced surface temperature, emissivity, and surface roughness compared to the surrounding region. Over several hours, an urban heat island feature evolves in the simulation containing the idealized city. In both model configurations, a continuous squall line is initiated in the western half of the model domain. As this line of storms propagates east and approaches the center of the domain, noticeable structural differences, particularly updraft strength and simulated radar reflectivity, are evident between simulations using the two different model configurations. Sensitivity tests are also conducted to show how the environmental wind profile impacts the magnitude and structure of convective storm modification by the idealized city.