The “urban meteorology island”: a multi-model ensemble analysis

Abstract

Abstract. Cities and urban areas are well-known for their impact on meteorological variables and thereby modification of the local climate. Our study aims to generalize the urban-induced changes in specific meteorological variables by introducing a single phenomenon – the urban meteorology island (UMI). A wide ensemble of 24 model simulations with the Weather Research and Forecasting (WRF) regional climate model and the Regional Climate Model (RegCM) on a European domain with 9 km horizontal resolution were performed to investigate various urban-induced modifications as individual components of the UMI. The results show that such an approach is meaningful, because in nearly all meteorological variables considered, statistically significant changes occur in cities. Besides previously documented urban-induced changes in temperature, wind speed and boundary-layer height, the study is also focused on changes in cloud cover, precipitation and humidity. An increase in cloud cover in cities, together with a higher amount of sub-grid-scale precipitation, is detected on summer afternoons. Specific humidity is significantly lower in cities. Further, the study shows that different models and parameterizations can have a strong impact on discussed components of the UMI. Multi-layer urban schemes with anthropogenic heat considered increase winter temperatures by more than 2 ∘C and reduce wind speed more strongly than other urban models. The selection of the planetary-boundary-layer scheme also influences the urban wind speed reduction, as well as the boundary-layer height, to the greatest extent. Finally, urban changes in cloud cover and precipitation are mostly sensitive to the parameterization of convection.

Attribution of surface ozone to NO<sub>x</sub> and VOC sources during two different high ozone events

“…Therefore, the T2MAX is underestimated, on average, by 1.1° C in 2015 and 1.4° C in 2018, still lower than Wyszogrodzki et al (2013), Chen et al (2014), Karlický et al (2020). The simulated relative humidity is fairly close to the observed one (NMB's of 14.5 and 20.1%, r's > 0.75).…”

Attribution of surface ozone to NOx and volatile organic compound sources during two different high ozone events

“…1). Therefore, the T2MAX is underestimated, on average, by 1.1 • C in 2015 and 1.4 • C in 2018, which is still lower than Wyszogrodzki et al (2013), Chen et al (2014), and Karlický et al (2020). The simulated relative humidity is fairly close to the observed one (NMB of 14.5 % and 20.1 %; r > 0.75).…”

Impact of urbanization on gas-phase pollutant concentrations: a regional-scale, model-based analysis of the contributing factors

“…Chemistry was resolved with the chemical transport model CAMx in version 7.10. The decision behind choosing two regional meteorological drivers is to achieve, at least to some degree, more robust results given the fact that the modeled meteorological conditions over cities greatly impacts the chemical concentrations ( Ďoubalová et al, 2020;Huszar et al, 2018b).…”

“…Urbanization, however, influences the final air pollution in other ways too. One of the most studied aspects of RUT is the modulation of the pollutant concentration due to the meteorological forcing represented by the urban canopy, which includes effects like increased temperatures (urban heat island, UHI) (Oke, 1982;Oke et al, 2017;Karlický et al, 2018Karlický et al, , 2020Sokhi et al, 2022), lower wind speeds (Jacobson et al, 2015;Zha et al, 2019), or elevated boundary layer height along with enhanced vertical eddy diffusion (Ren et al, 2019;Huszar et al, 2020a;. Huszar et al (2020a) introduced the term urban canopy meteorological forcing (UCMF), which represents the forcing that the land surface modified by RUT represents for the physical state of the air above via perturbed exchange of momentum, heat, radiation, and moisture.…”