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Atmosphere
Special Issues
Multiscale Aspects of Mesoscale and Microscale Flows
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Multiscale Aspects of Mesoscale and Microscale Flows

A special issue of Atmosphere (ISSN 2073-4433). This special issue belongs to the section "Meteorology".

Deadline for manuscript submissions: closed (20 December 2021) | Viewed by 8966

Special Issue Editors

Dr. Keith Ngan

E-Mail Website
Guest Editor
School of Energy and Environment, City University of Hong Kong, Kowloon, Hong Kong
Interests: urban boundary layers; computational fluid dynamics; turbulence; numerical weather prediction; geophysical fluid dynamics
Dr. Chun-Ho Liu

E-Mail Website
Guest Editor
Department of Mechanical Engineering, Faculty of Engineering, The University of Hong Kong, Hong Kong
Interests: air pollution physics and chemistry; geophysical turbulence; scientific computing
Dr. Tetsuya Takemi

E-Mail Website
Guest Editor
Disaster Prevention Research Institute, Kyoto University, Kyoto 606-8501, Japan
Interests: meteorology; mesoscale meteorology; environmental fluid dynamics; engineering meteorology; severe storm; heavy rain; gusty wind; tropical cyclone; atmospheric convection; turbulence; transport; numerical modeling; applied meteorology; urban meteorology; impact assessment of climate change

Special Issue Information

Dear Colleagues,

There is currently great interest in “bridging the gap” between mesoscale and microscale models. Traditionally, these models have been used for different applications, e.g., weather prediction in the former case and pollutant dispersion in the latter case.  With increasing computational power, however, the horizontal scales to which they apply are beginning to overlap: whereas state-of-the-art CFD models have horizontal dimensions of a few kilometres, high-resolution mesoscale models are now frequently run with a horizontal resolution of a kilometre or less. Hence, there is a need for improved understanding of the multiscale aspects of mesoscale and microscale flows. To this end, this Special Issue of Atmosphere will examine how atmospheric models on one hand, and CFD models on the other, benefit from the inclusion of processes across the nominal mesoscale-microscale divide. Potential topics include (but are not limited to) the following:

  • Downscaling, coupling, and data assimilation;
  • Flow and dispersion over complex topography;
  • Roughness interfaces;
  • Scale interactions;
  • Urban and vegetation canopies;
  • Subgrid-scale parameterisations.

Review papers that summarise recent developments and discuss implications for future research are particularly welcome.

Dr. Keith Ngan
Dr. Chun-Ho Liu
Dr. Tetsuya Takemi
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Atmosphere is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Mesoscale meteorological modelling
  • Computational fluid dynamics
  • Air quality
  • Urban ventilation

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Published Papers (3 papers)

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Research

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30 pages, 3246 KiB  
Article
Fast Models for Predicting Pollutant Dispersion inside Urban Canopies
by Huanhuan Wang, Eden Furtak-Cole and Keith Ngan
Atmosphere 2023, 14(9), 1337; https://doi.org/10.3390/atmos14091337 - 24 Aug 2023
Cited by 1 | Viewed by 1295
Abstract
A fast pollutant dispersion model for urban canopies is developed by coupling mean wind profiles to a parameterisation of turbulent diffusion and solving the time-dependent advection–diffusion equation. The performance of a simplified, coarse-grained representation of the velocity field is investigated. Spatially averaged mean [...] Read more.
A fast pollutant dispersion model for urban canopies is developed by coupling mean wind profiles to a parameterisation of turbulent diffusion and solving the time-dependent advection–diffusion equation. The performance of a simplified, coarse-grained representation of the velocity field is investigated. Spatially averaged mean wind profiles within local averaging regions or repeating units are predicted by solving the three-dimensional Poisson equation for a set of discrete vortex sheets. For each averaging region, the turbulent diffusion is parameterised in terms of the mean wind profile using empirical constants derived from large-eddy simulation (LES). Nearly identical results are obtained whether the turbulent fluctuations are specified explicitly or an effective diffusivity is used in their place: either version of the fast dispersion model shows much better agreement with LES than does the Gaussian plume model (e.g., the normalized mean square error inside the canopy is several times smaller). Passive scalar statistics for a regular cubic building array show improved agreement with LES when wind profiles vary in the horizontal. The current implementation is around 50 times faster than LES. With its combination of computational efficiency and moderate accuracy, the fast model may be suitable for time-critical applications such as emergency dispersion modelling. Full article
(This article belongs to the Special Issue Multiscale Aspects of Mesoscale and Microscale Flows)
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35 pages, 4688 KiB  
Article
Estimating Mean Wind Profiles Inside Realistic Urban Canopies
by Huanhuan Wang, Eden Furtak-Cole and Keith Ngan
Atmosphere 2023, 14(1), 50; https://doi.org/10.3390/atmos14010050 - 27 Dec 2022
Cited by 8 | Viewed by 2140
Abstract
Mean wind profiles within a unit-aspect-ratio street canyon have been estimated by solving the three-dimensional Poisson equation for a set of discrete vortex sheets. The validity of this approach, which assumes inviscid vortex dynamics away from boundaries and a small nonlinear contribution to [...] Read more.
Mean wind profiles within a unit-aspect-ratio street canyon have been estimated by solving the three-dimensional Poisson equation for a set of discrete vortex sheets. The validity of this approach, which assumes inviscid vortex dynamics away from boundaries and a small nonlinear contribution to the growth of turbulent fluctuations, is tested for a series of idealised and realistic flows. In this paper, the effects of urban geometry on accuracy are examined with neutral flow over shallow, deep, asymmetric and realistic canyons, while thermal effects are investigated for a single street canyon and both bottom cooling and heating. The estimated mean profiles of the streamwise and spanwise velocity components show good agreement with reference profiles obtained from the large-eddy simulation: the canyon-averaged errors (e.g., normalised absolute errors around 1%) are of the same order of magnitude as those for the unit-aspect-ratio street canyon. It is argued that the approach generalises to more realistic flows because strong spatial localisation of the vorticity field is preserved. This work may be applied to high-resolution modelling of winds and pollutants, for which mean wind profiles are required, and fast statistical modelling, for which physically-based estimates can serve as initial guesses or substitutes for analytical models. Full article
(This article belongs to the Special Issue Multiscale Aspects of Mesoscale and Microscale Flows)
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Review

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17 pages, 1805 KiB  
Review
An Overview of Triggering Mechanisms and Characteristics of Local Strong Sandstorms in China and Haboobs
by Zhaolin Gu, Yuanping He, Yunwei Zhang, Junwei Su, Renjian Zhang, Chuck Wah Yu and Daizhou Zhang
Atmosphere 2021, 12(6), 752; https://doi.org/10.3390/atmos12060752 - 10 Jun 2021
Cited by 12 | Viewed by 4118
Abstract
The local strong sandstorms (LSS), similar to haboobs in Sahara and the North America, often occur suddenly, in tens of minutes during the late afternoon, and before dusk in deserts in China, causing a significant impact on the local atmospheric environment. The Sudan [...] Read more.
The local strong sandstorms (LSS), similar to haboobs in Sahara and the North America, often occur suddenly, in tens of minutes during the late afternoon, and before dusk in deserts in China, causing a significant impact on the local atmospheric environment. The Sudan haboob or American haboob often appears in the wet season, followed by thunderstorm events. In contrast, the LSS in China appears most frequently in relatively dry season. The lack of observational data in weather conditions before their formation, during their development and after their disappearance have hindered our understanding of the evolution mechanism of LSS/haboobs. This paper provides a review of the current status and model studies on LSS/haboobs in different time and space to characterize the weather conditions and triggering mechanisms for LSS/haboobs occurrence, as well as highlight the subject for further understanding of LSS/haboobs. LSS are always followed by the occurrence of a dry squall. The interaction of dust radiation heating in the near-surface mixing layer with a mesoscale anticyclone air mass (cold-air pool) in the upper layer is the key process that leads to an LSS. Haboobs are followed by the occurrence of a wet squall. The release of latent heat due to the condensation of water vapor, involving moist convection and cold downdraughts, is the main driving force that cause the occurrence of a haboob. For a better understanding of the characteristics of the wind-sand two-phase flow and the mechanism of energy dissipation in LSS/haboobs, further accumulation of meteorological observation data and small-scale multiple-phase numerical simulations are required. Full article
(This article belongs to the Special Issue Multiscale Aspects of Mesoscale and Microscale Flows)
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