The Budget of Turbulence Kinetic Energy and Heat in the Urban Roughness Sublayer

The urban atmospheric roughness sublayer exhibits many micrometeorological complexities that are distinct from rural surface layer processes. An understanding of such complexities is crucially important for model development and appropriate mitigation of adverse climate and air quality effects due to urbanization. One approach to understand the urban roughness sublayer is the budget analysis of meteorological variables using field observations. Such classical and historical budget analyses have been limited to Turbulence Kinetic Energy (TKE), considering near neutral thermal stability conditions, assuming horizontal homogeneity while closing the budget equations, and occasionally only considering dominant wind directions. In this study we extend the budget analysis of TKE to heat and explicitly apportion the budgets of TKE and heat into storage, advection, production, transport, and dissipation terms while considering thermal stability and wind direction effects. The field observation campaign occurred in Guelph, Ontario, Canada during July and August 2018. To calculate the budget terms, five ultrasonic anemometers spread horizontally and vertically measured wind velocity components and ultrasonic temperature with a sampling frequency of 20 Hz. To explain the budget terms more carefully, additional measurements included urban surface temperatures using infrared thermal imaging, relative humidity, and downwelling solar radiation. Results indicate an intricate behaviour and balance among budget terms as a function thermal stability and wind direction. The findings can inform more accurate model development toward better understanding of urban climate and air quality issues. The results can also inform mitigation measured to circumvent adverse climate and air quality issues toward more resilient urban development.