Flow Regimes of Mesoscale Circulations Forced by Inhomogeneous Surface Heating

TL;DR

This study investigates how inhomogeneous surface heating from urbanization influences mesoscale circulations, revealing that heat flux anomalies induce strong oscillations and energy transfers in the convective boundary layer, impacting regional climate models.

Contribution

The paper introduces a wavelet-based CFD model validated against experiments to analyze urban-induced mesoscale flow regimes under varying surface heat fluxes.

Findings

Urban heat flux anomalies cause strong oscillations in the convective boundary layer.

Energy transfer occurs vertically through internal waves due to urban heating.

Results support the hypothesis of a downscale energy cascade in urban-induced circulations.

Abstract

Urbanization is one of the extreme process that increases uncertainty in future climate projections. Flow regimes of mesoscale circulations associated with surface heating due to urbanization have been investigated using a wavelet based computational fluid dynamics~(CFD) model. The results of our numerical model have been validated against that of a laboratory model, as well as reference numerical simulations. Characteristics of urban induced circulations have been studied for surface heat flux perturbation ($H_0$) between $28.93$Wm$^{-2}$ and $925.92$Wm$^{-2}$, and the results have been analyzed against available boundary layer measurements under similar physical conditions. Our primary study shows that urban/rural heat flux anomalies introduce strong oscillations in the convective boundary layer (CBL), and transfers a fraction of the turbulent kinetic energy vertically through internal waves. Such results complement previous investigators' hypothesis that temporal oscillations in urban-induced mesoscale circulations are primarily due to a downscale energy cascade. Although a further detailed study is necessary, the present numerical observations provide useful feedback for the impacts of urbanization on regional climate.