Urban Aerosol Impacts on Downwind Convective Storms

Abstract

The impacts of urban-enhanced aerosol concentrations on convective storm development and precipitation over and downwind of St. Louis, Missouri, are investigated. This is achieved through the use of a cloud-resolving mesoscale model, in which sophisticated land use processes and aerosol microphysics are both incorporated. The results indicate that urban-forced convergence downwind of the city, rather than the presence of greater aerosol concentrations, determines whether storms actually develop in the downwind region. Once convection is initiated, urban-enhanced aerosols can exert a significant effect on the dynamics, microphysics, and precipitation produced by these storms. The model results indicate, however, that the response to urban-enhanced aerosol depends on the background concentrations of aerosols; a weaker response occurs with increasing background aerosol concentrations. The effects of aerosols influence the rate and amount of liquid water and ice produced within these storms, the accumulated surface precipitation, the strength and timing of the updrafts and downdrafts, the longevity of the updrafts, and the strength and influence of the cold pool. Complex, nonlinear relationships and feedbacks between the microphysics and storm dynamics exist, making it difficult to make definitive statements about the effects of urbanenhanced aerosols on downwind precipitation and convection. Because the impacts of urban aerosol on downwind storms decrease with increasing background aerosol concentrations, generalization of these results depends on the unique character of background aerosol for each urban area. For urban centers in coastal areas where background aerosol concentrations may be very low, it is speculated that urban aerosol can have very large influences on convective storm dynamics, microphysics, and precipitation.

Relative influence of meteorological conditions and aerosols on the lifetime of mesoscale convective systems

“…These effects could reduce sedimentation of ice particles and dissipation of convective anvils. We cannot rule out an influence of the reduced background aerosol loading on lifetime (5,38). Fig.…”

Connections of ENSO/IOD and aerosols with Thai rainfall anomalies and associated implications for local rainfall forecasts

“…This high rainfall was hypothesized as being a result of an interaction between an urban heat island convergence and sea-breeze circulation patterns but the role of aerosol forcing is unclear (Shepherd and Burian, 2003). Van Den Heever and Cotton (2007) conducted a cloud-resolving mesoscale model simulation to investigate the impact of urban aerosol concentrations on convective storm development. They speculated that for urban centres in coastal areas, urban aerosol can have large influences on convective storms and precipitation formation (Van Den Heever and Cotton, 2007).…”

“…Van Den Heever and Cotton (2007) conducted a cloud-resolving mesoscale model simulation to investigate the impact of urban aerosol concentrations on convective storm development. They speculated that for urban centres in coastal areas, urban aerosol can have large influences on convective storms and precipitation formation (Van Den Heever and Cotton, 2007). Bangkok has both urban heat island characteristics (Memon et al, 2008) and coastal influences.…”

Role and Impact of the Urban Environment in a Numerical Forecast of an Intense Summertime Precipitation Event over Tokyo

“…Depending on their type and concentration, aerosols were also argued to accelerate or delay cloud formation through collision-coalescence with impact on the timing and intensity of precipitation (Van den Heever andCotton 2007, Han et al 2012).…”