Interactions Between the Nocturnal Low-Level Jets and the Urban Boundary Layer: A Case Study over London

Abstract

Understanding the physical processes that affect the turbulent structure of the nocturnal urban boundary layer (UBL) is essential for improving forecasts of air quality and the air temperature in urban areas. Low-level jets (LLJs) have been shown to affect turbulence in the nocturnal UBL. We investigate the interaction of a mesoscale LLJ with the UBL during a 60-h case study. We use observations from two Doppler lidars and results from two high-resolution numerical-weather-prediction models (Weather Research and Forecasting model, and the Met Office Unified Model for limited-area forecasts for the U.K.) to study differences in the occurrence frequency, height, wind speed, and fall-off of LLJs between an urban (London, U.K.) and a rural (Chilbolton, U.K.) site. The LLJs are elevated ($$\approx $$ ≈ 70 m) over London, due to the deeper UBL, while the wind speed and fall-off are slightly reduced with respect to the rural LLJ. Utilizing two idealized experiments in the WRF model, we find that topography strongly affects LLJ characteristics, but there is still a substantial urban influence. Finally, we find that the increase in wind shear under the LLJ enhances the shear production of turbulent kinetic energy and helps to maintain the vertical mixing in the nocturnal UBL.

Investigating the Interaction Between Transboundary Haze and Planetary Boundary Layer in Singapore

“…Nevertheless, the ingress of transboundary aerosols into the PBL was not considered, which is a pivotal step in deteriorating ground‐level air quality via turbulent mixing (Geiß et al., 2017; Tang et al., 2016; Zhu et al., 2018). Furthermore, the mechanism during nighttime is complicated because nocturnal low‐level jet (LLJ) also plays a vital role in urban haze formation (Tsiringakis et al., 2022). More evidence is needed from direct observations of haze in the upper atmosphere to understand the interaction mechanism between transboundary haze and PBL.…”

What added value of CNRM-AROME convection-permitting regional climate model compared to CNRM-ALADIN regional climate model for urban climate studies ? Evaluation over Paris area (France)

“…As a result, cities can interact with local or even regional weather and climate, and change environmental conditions. In particular, studies have shown effects on atmospheric circulation, cloud cover, and precipitation (Lorentz et al 2019;Theeuwes et al 2019;Tsiringakis et al 2022).…”

Understanding the Role of Sea Surface Temperature and Urbanization on Severe Thunderstorms Dynamics: A Case Study in Surabaya, Indonesia

“…The majority of thunderstorms induced‐hail events between 2014 and 2017 are reported within the Surabaya urban area (Figure 1) (Baskoro, 2017), suggesting that the urban area might induce or enhance a thunderstorm. Three mechanisms are associated to the modification of a storm over cities; (a) the urban heat island' effect (UHI)'s due to the modified urban surface radiation and energy balance (Lin et al., 2011; Ma et al., 2017), (b) the roughness effect of urban surface (D. Li et al., 2013; Bender et al., 2019; Tsiringakis et al., 2022) and (c) the urban aerosol effects (Yang et al., 2017). These three might trigger or enhance the convective cloud formation (Han et al., 2012), increase or modify the precipitation over and downwind of the city, (D. Li et al., 2013; Kim et al., 2021).…”