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Atmosphere
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Atmospheric Processes over Complex Terrain
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Atmospheric Processes over Complex Terrain

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

Deadline for manuscript submissions: closed (31 January 2018) | Viewed by 129104

Special Issue Editors

Prof. Dr. Mathias Rotach

E-Mail Website
Guest Editor
Institute of Atmospheric and Cryospheric Sciences, University of Innsbruck, Innsbruck, Austria
Interests: boundary layer dynamics; turbulence and exchange processes; atmospheric dynamics; high-resolution numerical modeling; mountain meteorology; air pollution modeling; complex topography; complex surfaces
Prof. Dr. Dino Zardi

E-Mail Website
Guest Editor
University of Trento, Department of Civil, Environmental and Mechanical Engineering, Trento, Italy
Interests: atmospheric boundary layer processes; turbulence measurements and analysis; earth-atmosphere exchange processes; mountain meteorology; air pollution measurement and modelling

Special Issue Information

Dear Colleagues,

The Earth’s surface has a profound impact on atmospheric flows, i.e., it constitutes their lower boundary condition and determines the occurrence and efficiency of exchange processes of energy, mass and momentum from and to the free atmosphere. While over flat terrain, this exchange is largely determined by the state of the Atmospheric Boundary Layer (ABL), over complex terrain this exchange is additionally modified by meso-scale flows and, in particular, the interaction between the latter and the (complex) ABL. ABLs over complex topography are intrinsically inhomogeneous and thus violate the basic assumptions, on which our current understanding of ABL turbulence and exchange efficiency is based. Out of necessity, numerical models of all spatial resolutions, except for the very highest (i.e., below the so-called grey zone of turbulence) use ABL parameterizations that are based on previous knowledge from flat and horizontally homogeneous terrain. On the other hand, many aspects of the involved meso-scale flows, such as thermally forced valley winds, are quite well known—but their role in the earth-atmosphere exchange and in particular the interaction with turbulent exchange (efficiency) has received much less attention.

The increase in computing power over the last decades has led to the use of ‘high-resolution (km-scale) numerical modeling’ even in operational settings (numerical weather forecast and climate scenarios). Validation and verification efforts, however, even lack the basic knowledge about the processes those models should be able to reproduce. A number of recent field campaigns have started to address these questions; therefore, it seems timely to establish the current state of affairs in this Special Issue on Atmospheric Processes over Complex Terrain.

Papers are welcome on all aspects of exchange processes over complex terrain, including, but not restricted to:

  • Atmospheric boundary layer characteristics and processes over complex terrain

  • Wet and dry processes—and their interaction

  • Convective initiation in complex terrain

  • Gravity waves and their role in atmospheric transport

  • Numerical methods over steep and complex terrain

  • Physics parameterizations

  • Verification strategies in intrinsically inhomogeneous environments

  • Experimental methods and data processing

  • Exchange efficiency over complex topography

  • Theoretical advancements

Prof. Dr. Mathias Rotach
Prof. Dr. Dino Zardi
Guest Editors

Manuscript Submission Information

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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.

Published Papers (21 papers)

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Editorial

Jump to: Research, Review

3 pages, 152 KiB  
Editorial
Transport and Exchange Processes in the Atmosphere over Mountainous Terrain: Perspectives and Challenges for Observational and Modelling Systems, from Local to Climate Scales
by Dino Zardi and Mathias W. Rotach
Atmosphere 2021, 12(2), 199; https://doi.org/10.3390/atmos12020199 - 02 Feb 2021
Cited by 2 | Viewed by 1785
Abstract
This Editorial offers an overview of the results presented in the series of coordinated articles included in the Atmosphere special issue on Atmospheric Processes over Complex Terrain. In particular, the variety of approaches and methods, as well as the main outcomes of recent [...] Read more.
This Editorial offers an overview of the results presented in the series of coordinated articles included in the Atmosphere special issue on Atmospheric Processes over Complex Terrain. In particular, the variety of approaches and methods, as well as the main outcomes of recent progress in the field, are outlined, along with open questions and challenges for future developments. The possible outreach of future research in the field is also pointed out, especially in connection with the ongoing international cooperation initiative Multi-scale transport and exchange processes in the atmosphere over mountains programme and experiment (TEAMx). Full article
(This article belongs to the Special Issue Atmospheric Processes over Complex Terrain)

Research

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18 pages, 2647 KiB  
Article
Impact of Along-Valley Orographic Variations on the Dispersion of Passive Tracers in a Stable Atmosphere
by Julian Quimbayo-Duarte, Chantal Staquet, Charles Chemel and Gabriele Arduini
Atmosphere 2019, 10(4), 225; https://doi.org/10.3390/atmos10040225 - 25 Apr 2019
Cited by 8 | Viewed by 3334
Abstract
A numerical model is used to investigate the transport of passive tracers in an idealized Alpine valley during stable wintertime conditions after the evening transition. The valley is composed of an upstream-valley section, which opens on a narrower downstream valley section, which opens [...] Read more.
A numerical model is used to investigate the transport of passive tracers in an idealized Alpine valley during stable wintertime conditions after the evening transition. The valley is composed of an upstream-valley section, which opens on a narrower downstream valley section, which opens onto a plain. The ratio between the valley-floor widths of the upstream and downstream sections is either 4 (simulation P1) or 11.5 (P2). The change in the thermal structure of the atmosphere in the along-valley direction and over the plain leads to the development of an along-valley flow. This flow is up-valley in the upstream section during the first three hours of the P1 simulation, reversing to the down-valley direction afterwards, but remains up-valley during the six hours of the P2 simulation. The effect of wind dynamics on the dispersion of passive scalars is identified by tracking areas prone to stagnation, recirculation, and ventilation using the methodology developed by Allwine and Whiteman (1994). Zones identified as prone to stagnation are consistent with those of high tracer concentration in both simulations. The narrowing of the valley is found to significantly reduce ventilation in the upstream section, an observation quantified by a ventilation efficiency. Full article
(This article belongs to the Special Issue Atmospheric Processes over Complex Terrain)
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28 pages, 5329 KiB  
Article
High-Resolution Observations of Transport and Exchange Processes in Mountainous Terrain
by Stefan Emeis, Norbert Kalthoff, Bianca Adler, Eric Pardyjak, Alexandre Paci and Wolfgang Junkermann
Atmosphere 2018, 9(12), 457; https://doi.org/10.3390/atmos9120457 - 22 Nov 2018
Cited by 15 | Viewed by 4533
Abstract
Mountainous areas require appropriate measurement strategies to cover the full spectrum of details concerning the energy exchange at the Earth’s surface and to capture the spatiotemporal distribution of atmospheric dynamic and thermodynamic fields over them. This includes the range from turbulence to mesoscale [...] Read more.
Mountainous areas require appropriate measurement strategies to cover the full spectrum of details concerning the energy exchange at the Earth’s surface and to capture the spatiotemporal distribution of atmospheric dynamic and thermodynamic fields over them. This includes the range from turbulence to mesoscale processes and its interaction. The surface energy balance needs appropriate measurement strategies as well. In this paper, we present an overview of important experiments performed over mountainous terrain and summarize the available techniques for flow and energy measurements in complex terrain. The description includes ground-based and airborne in situ observations as well as ground-based and airborne remote sensing (passive and active) observations. Emphasis is placed on systems which retrieve spatiotemporal information on mesoscale and smaller scales, fitting mountainous terrain research needs. Finally, we conclude with a short list summarizing challenges and gaps one faces when dealing with measurements over complex terrain. Full article
(This article belongs to the Special Issue Atmospheric Processes over Complex Terrain)
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16 pages, 4890 KiB  
Article
The Impact of Mount Washington on the Height of the Boundary Layer and the Vertical Structure of Temperature and Moisture
by Eric Kelsey, Adriana Bailey and Georgia Murray
Atmosphere 2018, 9(8), 293; https://doi.org/10.3390/atmos9080293 - 27 Jul 2018
Cited by 3 | Viewed by 4320
Abstract
Discrimination of the type of air mass along mountain slopes can be a challenge and is not commonly performed, but is critical for identifying factors responsible for influencing montane weather, climate, and air quality. A field campaign to measure air mass type and [...] Read more.
Discrimination of the type of air mass along mountain slopes can be a challenge and is not commonly performed, but is critical for identifying factors responsible for influencing montane weather, climate, and air quality. A field campaign to measure air mass type and transitions on the summit of Mount Washington, New Hampshire, USA was performed on 19 August 2016. Meteorological observations were taken at the summit and at several sites along the east and west slopes. Ozone concentrations were measured at the summit and on the valley floor. Additionally, water vapor stable isotopes were measured from a truck that drove up and down the Mount Washington Auto Road concurrent with radiosonde launches that profiled the free atmosphere. This multivariate perspective revealed thermal, moisture, and air mass height differences among the free atmosphere, leeward, and windward mountain slopes. Both thermally and mechanically forced upslope flows helped shape these differences by altering the height of the boundary layer with respect to the mountain surface. Recommendations for measurement strategies hoping to develop accurate observational climatologies of air mass exposure in complex terrain are discussed and will be important for evaluating elevation-dependent warming and improving forecasting for weather and air quality. Full article
(This article belongs to the Special Issue Atmospheric Processes over Complex Terrain)
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18 pages, 3584 KiB  
Article
Accuracy of Simulated Diurnal Valley Winds in the Swiss Alps: Influence of Grid Resolution, Topography Filtering, and Land Surface Datasets
by Juerg Schmidli, Steven Böing and Oliver Fuhrer
Atmosphere 2018, 9(5), 196; https://doi.org/10.3390/atmos9050196 - 18 May 2018
Cited by 30 | Viewed by 5364
Abstract
We evaluate the near-surface representation of thermally driven winds in the Swiss Alps in a numerical weather prediction model at km-scale resolution. In addition, the influence of grid resolution (2.2 km and 1.1 km), topography filtering, and land surface datasets on the accuracy [...] Read more.
We evaluate the near-surface representation of thermally driven winds in the Swiss Alps in a numerical weather prediction model at km-scale resolution. In addition, the influence of grid resolution (2.2 km and 1.1 km), topography filtering, and land surface datasets on the accuracy of the simulated valley winds is investigated. The simulations are evaluated against a comprehensive set of surface observations for an 18-day fair-weather summer period in July 2006. The episode is characterized by strong diurnal wind systems and the formation of shallow convection over the mountains, which transitions to precipitating convection in some areas. The near-surface winds (10 m above ground level) follow a typical diurnal pattern with strong daytime up-valley flow and weaker nighttime down-valley flow. At a 2.2 km resolution the valley winds are poorly simulated for most stations, while at a 1.1 km resolution the diurnal cycle of the valley winds is well represented in most large (e.g., Rhein valley at Chur and Rhone valley at Visp) and medium-sized valleys (e.g., Linth valley at Glarus). In the smaller valleys (e.g., Maggia valley at Cevio), the amplitude of the valley wind is still significantly underestimated, even at a 1.1 km resolution. Detailed sensitivity experiments show that the use of high-resolution land surface datasets, for both the soil characteristics as well as for the land cover, and reduced filtering of the topography are essential to achieve good performance at a 1.1 km resolution. Full article
(This article belongs to the Special Issue Atmospheric Processes over Complex Terrain)
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18 pages, 3103 KiB  
Article
Atmospheric Processes in the South Baikal Basin and Their Role in Relief Formation
by Elizaveta М. Tyumentseva and Galina F. Orel
Atmosphere 2018, 9(5), 176; https://doi.org/10.3390/atmos9050176 - 07 May 2018
Cited by 2 | Viewed by 3030
Abstract
Climatic conditions and the solar and circulation features in the Lake Baikal basin are analyzed. The relationship between the heat balance and surface temperature of slopes is shown, taking into account each features’ physical state. The dependence of the heat balance values and [...] Read more.
Climatic conditions and the solar and circulation features in the Lake Baikal basin are analyzed. The relationship between the heat balance and surface temperature of slopes is shown, taking into account each features’ physical state. The dependence of the heat balance values and the underlying surface temperature were revealed. The quantitative material allowed us to reveal regional patterns of geomorphological regimes, seasonal rhythm, and the dynamics of processes. In Cisbaikalia, within the denudation cycle, semi-humid states under water erosion and aeolian processes of moderate intensity predominate. The semi-arid state manifests itself under decreasing humidification. In these years, the probability of extreme manifestations of aeolian processes is high. The humid states occur in 1% of cases, primarily in extremely wet years, when fluvial processes are dramatically activated. In Cisbaikalia, climate warming and an increase in mean annual temperature have been observed in recent years. Depending on the moisture amplitude and heat availability, the intensity and direction of water erosion and aeolian processes is changing now. The dynamics of relief-forming processes cause an increase in loose substance in the lake and the exacerbation of the ecological situation. Full article
(This article belongs to the Special Issue Atmospheric Processes over Complex Terrain)
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Graphical abstract

11 pages, 3781 KiB  
Article
Separation of Upslope Flow over a Plateau
by Roni Hilel Goldshmid, Stef L. Bardoel, Christopher M. Hocut, Qiang Zhong, Dan Liberzon and Harindra J. S. Fernando
Atmosphere 2018, 9(5), 165; https://doi.org/10.3390/atmos9050165 - 30 Apr 2018
Cited by 6 | Viewed by 3606
Abstract
A laboratory study was conducted in order to gain an understanding of thermal convection in a complex terrain that is characterized by a plateaued mountain. In particular, the separation of upslope (anabatic) flow over a two-dimensional uniform smooth slope, topped by a plateau, [...] Read more.
A laboratory study was conducted in order to gain an understanding of thermal convection in a complex terrain that is characterized by a plateaued mountain. In particular, the separation of upslope (anabatic) flow over a two-dimensional uniform smooth slope, topped by a plateau, was considered. The working fluid was homogeneous water (neutral stratification). The topographic model was immersed in a large water tank with no mean flow. The entire topographic model was uniformly heated, and the width of the plateau, the slope angle, and the heating rate were varied. The upslope velocity field was measured by the Particle Tracking Velocimetry, aided by Feature Tracking Visualizations in order to detect the flow separation location. An analysis of the resulting flow showed a quantitative similarity to separating the upslope flow over steeper slopes, in the absence of a plateau when an effective angle that incorporates the normalized plateau width, the slope length, and the geometric slope angle, was used. Predictions for the dependence of the separation location and velocity on the geometry and heat flux were presented and compared with the existing data. Full article
(This article belongs to the Special Issue Atmospheric Processes over Complex Terrain)
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13 pages, 45478 KiB  
Article
Challenges and Opportunities for Data Assimilation in Mountainous Environments
by Joshua Hacker, Clara Draper and Luke Madaus
Atmosphere 2018, 9(4), 127; https://doi.org/10.3390/atmos9040127 - 27 Mar 2018
Cited by 15 | Viewed by 4404
Abstract
This contribution aims to summarize the current state of data assimilation research as applied to land and atmosphere simulation and prediction in mountainous environments. It identifies and explains critical challenges, and offers opportunities for productive research based on both models and observations. Though [...] Read more.
This contribution aims to summarize the current state of data assimilation research as applied to land and atmosphere simulation and prediction in mountainous environments. It identifies and explains critical challenges, and offers opportunities for productive research based on both models and observations. Though many of the challenges to optimal data assimilation in the mountains are also challenges in flatter terrain, the complex land–atmosphere interactions and increased surface heterogeneity in the mountains violate key assumptions and methods in the data assimilation algorithms and the underlying models. The effects of model inadequacy are particularly acute in complex terrain. Recent research related to some of the key challenges suggest opportunities to make gains in both land and atmospheric data assimilation in the mountains. Research directions are suggested, focusing on model improvement in a data assimilation context, and design of field programs aimed at data assimilation. Full article
(This article belongs to the Special Issue Atmospheric Processes over Complex Terrain)
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28 pages, 7086 KiB  
Article
Wintertime Local Wind Dynamics from Scanning Doppler Lidar and Air Quality in the Arve River Valley
by Tiphaine Sabatier, Alexandre Paci, Guylaine Canut, Yann Largeron, Alain Dabas, Jean-Marie Donier and Thierry Douffet
Atmosphere 2018, 9(4), 118; https://doi.org/10.3390/atmos9040118 - 21 Mar 2018
Cited by 21 | Viewed by 5061
Abstract
Air quality issues are frequent in urbanized valleys, particularly in wintertime when a temperature inversion forms and the air within the valley is stably stratified over several days. In addition to pollutant sources, local winds can have a significant impact on the spatial [...] Read more.
Air quality issues are frequent in urbanized valleys, particularly in wintertime when a temperature inversion forms and the air within the valley is stably stratified over several days. In addition to pollutant sources, local winds can have a significant impact on the spatial distribution and temporal evolution of pollutant concentrations. They can be very complex and difficult to represent in numerical weather prediction models, particularly under stable conditions. Better knowledge of these local winds from observations is also a prerequisite to improving air quality prediction capability. This paper analyses local winds during the Passy-2015 field experiment that took place in a section of the Arve river valley, near Chamonix–Mont-Blanc. This location is one of the worst places in France regarding air quality. The wind analysis, which is mainly based on scanning Doppler lidar data sampling a persistent temperature inversion episode, reveals features consistent with the higher pollutant concentrations observed in this section of the valley as well as their spatial heterogeneities. In particular, an elevated down-valley jet is observed at night in the northern half of the valley, which, combined with a weak daytime up-valley wind, leads to very poor ventilation of the lowest layers. A northeast–southwest gradient in ventilation is observed on a daily-average, and is consistent with the PM10 heterogeneities observed within the valley. Full article
(This article belongs to the Special Issue Atmospheric Processes over Complex Terrain)
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20 pages, 15134 KiB  
Article
Estimating Hourly Beam and Diffuse Solar Radiation in an Alpine Valley: A Critical Assessment of Decomposition Models
by Lavinia Laiti, Lorenzo Giovannini, Dino Zardi, Giorgio Belluardo and David Moser
Atmosphere 2018, 9(4), 117; https://doi.org/10.3390/atmos9040117 - 21 Mar 2018
Cited by 15 | Viewed by 4399
Abstract
Accurate solar radiation estimates in Alpine areas represent a challenging task, because of the strong variability arising from orographic effects and mountain weather phenomena. These factors, together with the scarcity of observations in elevated areas, often cause large modelling uncertainties. In the present [...] Read more.
Accurate solar radiation estimates in Alpine areas represent a challenging task, because of the strong variability arising from orographic effects and mountain weather phenomena. These factors, together with the scarcity of observations in elevated areas, often cause large modelling uncertainties. In the present paper, estimates of hourly mean diffuse fraction values from global radiation data, provided by a number (13) of decomposition models (chosen among the most widely tested in the literature), are evaluated and compared with observations collected near the city of Bolzano, in the Adige Valley (Italian Alps). In addition, the physical factors influencing diffuse fraction values in such a complex orographic context are explored. The average accuracy of the models were found to be around 27% and 14% for diffuse and beam radiation respectively, the largest errors being observed under clear sky and partly cloudy conditions, respectively. The best performances were provided by the more complex models, i.e., those including a predictor specifically explaining the radiation components’ variability associated with scattered clouds. Yet, these models return non-negligible biases. In contrast, the local calibration of a single-equation logistical model with five predictors allows perfectly unbiased estimates, as accurate as those of the best-performing models (20% and 12% for diffuse and beam radiation, respectively), but at much smaller computational costs. Full article
(This article belongs to the Special Issue Atmospheric Processes over Complex Terrain)
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25 pages, 10867 KiB  
Article
Micro-Scale Properties of Different Bora Types
by Vinko Šoljan, Andreina Belušić, Kristina Šarović, Irena Nimac, Stjepana Brzaj, Jurica Suhin, Martin Belavić, Željko Večenaj and Branko Grisogono
Atmosphere 2018, 9(4), 116; https://doi.org/10.3390/atmos9040116 - 21 Mar 2018
Cited by 5 | Viewed by 5192
Abstract
In this paper we use 20 Hz wind measurements on three levels (2, 5, and 10 m) to investigate the differences in micro-scale properties of different bora types, i.e., deep and shallow bora with further subdivision to cyclonic and anticyclonic bora cases. Using [...] Read more.
In this paper we use 20 Hz wind measurements on three levels (2, 5, and 10 m) to investigate the differences in micro-scale properties of different bora types, i.e., deep and shallow bora with further subdivision to cyclonic and anticyclonic bora cases. Using Fourier spectral analysis, we investigate a suitable turbulence averaging scale and bora gust pulsations. The obtained data set is further used to test the Monin–Obukhov similarity theory, the surface layer stratification, the behavior of the terms in the prognostic turbulence kinetic energy equation, and the wind profiles. One of our main goals is to identify possible micro-scale differences between shallow and deep bora types because of the possible different mountain wave dynamics in those flows. We found that a turbulence averaging scale of 30 min is suitable for this location and is in agreement with previous bora studies. The wind speed power spectral densities of all selected bora episodes showed pulsations with periods of 2–8 min. This suggests that mountain wave breaking was present in all cases, regardless of flow depth and synoptic type. The stability parameter analysis confirmed the near-neutral thermal stratification of bora; a consequence of intensive mechanical mixing. No significant differences related to bora type were observed in other micro-scale parameters. Full article
(This article belongs to the Special Issue Atmospheric Processes over Complex Terrain)
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22 pages, 10170 KiB  
Article
Observations and Predictability of Gap Winds in the Salmon River Canyon of Central Idaho, USA
by Natalie S. Wagenbrenner, Jason M. Forthofer, Chris Gibson, Abby Indreland, Brian K. Lamb and Bret W. Butler
Atmosphere 2018, 9(2), 45; https://doi.org/10.3390/atmos9020045 - 31 Jan 2018
Cited by 2 | Viewed by 4372
Abstract
This work investigates gap winds in a steep, deep river canyon prone to wildland fire. The driving mechanisms and the potential for forecasting the gap winds are investigated. The onset and strength of the gap winds are found to be correlated to the [...] Read more.
This work investigates gap winds in a steep, deep river canyon prone to wildland fire. The driving mechanisms and the potential for forecasting the gap winds are investigated. The onset and strength of the gap winds are found to be correlated to the formation of an along-gap pressure gradient linked to periodic development of a thermal trough in the Pacific Northwest, USA. Numerical simulations are performed using a reanalysis dataset to investigate the ability of numerical weather prediction (NWP) to simulate the observed gap wind events, including the timing and flow characteristics within the canyon. The effects of model horizontal grid spacing and terrain representation are considered. The reanalysis simulations suggest that horizontal grid spacings used in operational NWP could be sufficient for simulating the gap flow events given the regional-scale depression in which the Salmon River Canyon is situated. The strength of the events, however, is under-predicted due, at least in part, to terrain smoothing in the model. Routine NWP, however, is found to have mixed results in terms of forecasting the gap wind events, primarily due to problems in simulating the regional sea level pressure system correctly. Full article
(This article belongs to the Special Issue Atmospheric Processes over Complex Terrain)
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12066 KiB  
Article
The Peñalara Mountain Meteorological Network (1999–2014): Description, Preliminary Results and Lessons Learned
by Luis Durán, Irene Rodríguez-Muñoz and Enrique Sánchez
Atmosphere 2017, 8(10), 203; https://doi.org/10.3390/atmos8100203 - 17 Oct 2017
Cited by 10 | Viewed by 4816
Abstract
This work describes a mountain meteorological network that was in operation from 1999 to 2014 in a mountain range with elevations ranging from 1104 to 2428 m in Central Spain. Additionally, some technical details of the network are described, as well as variables [...] Read more.
This work describes a mountain meteorological network that was in operation from 1999 to 2014 in a mountain range with elevations ranging from 1104 to 2428 m in Central Spain. Additionally, some technical details of the network are described, as well as variables measured and some meta information presented, which is expected to be useful for future users of the observational database. A strong emphasis is made on showing the observational methods and protocols evolution, as it will help researchers to understand the sources of errors, data gaps and the final stage of the network. This paper summarizes mostly the common sources of errors when designing and operating a small network of this kind, so it can be useful for individual researchers and small size groups that undertake a similar task on their own. Strengths and weaknesses of some of the variables measured are discussed and some basic calculations are made in order to show the otential of the database and to anticipate future deeper climatological analyses over the area. Finally, the configuration of an automatic mountain meteorology station is suggested as a result of the lessons learned and the the common state of the art automatic measuring techniques Full article
(This article belongs to the Special Issue Atmospheric Processes over Complex Terrain)
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5617 KiB  
Article
Evaluation of Surface Fluxes in the WRF Model: Case Study for Farmland in Rolling Terrain
by Xia Sun, Heather A. Holmes, Olabosipo O. Osibanjo, Yun Sun and Cesunica E. Ivey
Atmosphere 2017, 8(10), 197; https://doi.org/10.3390/atmos8100197 - 08 Oct 2017
Cited by 33 | Viewed by 6116
Abstract
The partitioning of available energy into surface sensible and latent heat fluxes impacts the accuracy of simulated near surface temperature and humidity in numerical weather prediction models. This case study evaluates the performance of the Weather Research and Forecasting (WRF) model on the [...] Read more.
The partitioning of available energy into surface sensible and latent heat fluxes impacts the accuracy of simulated near surface temperature and humidity in numerical weather prediction models. This case study evaluates the performance of the Weather Research and Forecasting (WRF) model on the simulation of surface heat fluxes using field observations collected from a surface flux tower in Oregon, USA. Further, WRF-modeled heat flux sensitivities to North American Mesoscale (NAM) and North American Regional Reanalysis (NARR) large-scale input forcing datasets; U.S. Geological Survey (USGS) and the Moderate Resolution Imaging Spectroradiometer (MODIS) land use datasets; Pleim-Xiu (PX) and Noah land surface models (LSM); Yonsei University (YSU) and Mellor-Yamada-Janjic (MYJ) planetary boundary layer (PBL) schemes using the Noah LSM; and Asymmetric Convective Model version 2 (ACM2) PBL scheme using PX LSM are investigated. The errors for simulating 2-m temperature, 2-m humidity, and 10-m wind speed were reduced on average when using NAM compared with NARR. Simulated friction velocity had a positive bias on average, with the YSU PBL scheme producing the largest overestimation in the innermost domain (0.5 km horizontal grid resolution). The simulated surface sensible heat flux had a similar temporal behavior as the observations but with a larger magnitude. The PX LSM produced lower and more reliable sensible heat fluxes compared with the Noah LSM. However, Noah latent heat fluxes were improved with a lower RMSE compared to PX, when NARR forcing data was used. Overall, these results suggest that there is not one WRF configuration that performs best for all the simulated variables (surface heat fluxes and meteorological variables) and situations (day and night). Full article
(This article belongs to the Special Issue Atmospheric Processes over Complex Terrain)
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Review

Jump to: Editorial, Research

32 pages, 3567 KiB  
Review
Atmospheric Pollutant Dispersion over Complex Terrain: Challenges and Needs for Improving Air Quality Measurements and Modeling
by Lorenzo Giovannini, Enrico Ferrero, Thomas Karl, Mathias W. Rotach, Chantal Staquet, Silvia Trini Castelli and Dino Zardi
Atmosphere 2020, 11(6), 646; https://doi.org/10.3390/atmos11060646 - 18 Jun 2020
Cited by 44 | Viewed by 8886
Abstract
Pollutant dispersion processes over complex terrain are much more complicated than over flat areas, as they are affected by atmospheric interactions with the orography at different spatial scales. This paper reviews recent findings and progress in this field, focusing on both experimental and [...] Read more.
Pollutant dispersion processes over complex terrain are much more complicated than over flat areas, as they are affected by atmospheric interactions with the orography at different spatial scales. This paper reviews recent findings and progress in this field, focusing on both experimental and modeling perspectives. It highlights open questions and challenges to our capability for better understanding and representing atmospheric processes controlling the fate of pollutants over mountainous areas. In particular, attention is focused on new measurement techniques for the retrieval of spatially distributed turbulence information and air quality parameters, and on challenges for meteorological and dispersion models to reproduce fine-scale processes influenced by the orography. Finally, specific needs in this field are discussed, along with possible directions for future research efforts. Full article
(This article belongs to the Special Issue Atmospheric Processes over Complex Terrain)
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38 pages, 7812 KiB  
Review
Crossing Multiple Gray Zones in the Transition from Mesoscale to Microscale Simulation over Complex Terrain
by Fotini Katopodes Chow, Christoph Schär, Nikolina Ban, Katherine A. Lundquist, Linda Schlemmer and Xiaoming Shi
Atmosphere 2019, 10(5), 274; https://doi.org/10.3390/atmos10050274 - 14 May 2019
Cited by 72 | Viewed by 8277
Abstract
This review paper explores the field of mesoscale to microscale modeling over complex terrain as it traverses multiple so-called gray zones. In an attempt to bridge the gap between previous large-scale and small-scale modeling efforts, atmospheric simulations are being run at an unprecedented [...] Read more.
This review paper explores the field of mesoscale to microscale modeling over complex terrain as it traverses multiple so-called gray zones. In an attempt to bridge the gap between previous large-scale and small-scale modeling efforts, atmospheric simulations are being run at an unprecedented range of resolutions. The gray zone is the range of grid resolutions where particular features are neither subgrid nor fully resolved, but rather are partially resolved. The definition of a gray zone depends strongly on the feature being represented and its relationship to the model resolution. This paper explores three gray zones relevant to simulations over complex terrain: turbulence, convection, and topography. Taken together, these may be referred to as the gray continuum. The focus is on horizontal grid resolutions from ∼10 km to ∼10 m. In each case, the challenges are presented together with recent progress in the literature. A common theme is to address cross-scale interaction and scale-awareness in parameterization schemes. How numerical models are designed to cross these gray zones is critical to complex terrain applications in numerical weather prediction, wind resource forecasting, and regional climate modeling, among others. Full article
(This article belongs to the Special Issue Atmospheric Processes over Complex Terrain)
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23 pages, 5618 KiB  
Review
Meteorological Applications Benefiting from an Improved Understanding of Atmospheric Exchange Processes over Mountains
by Stephan F. J. De Wekker, Meinolf Kossmann, Jason C. Knievel, Lorenzo Giovannini, Ethan D. Gutmann and Dino Zardi
Atmosphere 2018, 9(10), 371; https://doi.org/10.3390/atmos9100371 - 25 Sep 2018
Cited by 27 | Viewed by 8752
Abstract
This paper reviews the benefits of a better understanding of atmospheric exchange processes over mountains. These processes affect weather and climate variables that are important in meteorological applications related to many scientific disciplines and sectors of the economy. We focus this review on [...] Read more.
This paper reviews the benefits of a better understanding of atmospheric exchange processes over mountains. These processes affect weather and climate variables that are important in meteorological applications related to many scientific disciplines and sectors of the economy. We focus this review on examples of meteorological applications in hydrology, ecology, agriculture, urban planning, wind energy, transportation, air pollution, and climate change. These examples demonstrate the benefits of a more accurate knowledge of atmospheric exchange processes over mountains, including a better understanding of snow redistribution, microclimate, land-cover change, frost hazards, urban ventilation, wind gusts, road temperatures, air pollution, and the impacts of climate change. The examples show that continued research on atmospheric exchange processes over mountains is warranted, and that a recognition of the potential benefits can inspire new research directions. An awareness of the links between basic research topics and applications is important to the success and impact of new efforts that aim at better understanding atmospheric exchange processes over mountains. To maximize the benefits of future research for meteorological applications, coordinated international efforts involving scientists studying atmospheric exchange processes, as well as scientists and stakeholders representing many other scientific disciplines and economic sectors are required. Full article
(This article belongs to the Special Issue Atmospheric Processes over Complex Terrain)
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18 pages, 4196 KiB  
Review
Current Challenges in Orographic Flow Dynamics: Turbulent Exchange Due to Low-Level Gravity-Wave Processes
by Simon B. Vosper, Andrew N. Ross, Ian A. Renfrew, Peter Sheridan, Andrew D. Elvidge and Vanda Grubišić
Atmosphere 2018, 9(9), 361; https://doi.org/10.3390/atmos9090361 - 18 Sep 2018
Cited by 22 | Viewed by 5562
Abstract
This paper examines current understanding of the influence of orographic flow dynamics on the turbulent transport of momentum and scalar quantities above complex terrain. It highlights three key low-level orographic flow phenomena governed by gravity-wave dynamics: Foehn flow, atmospheric rotors and gravity-wave modulation [...] Read more.
This paper examines current understanding of the influence of orographic flow dynamics on the turbulent transport of momentum and scalar quantities above complex terrain. It highlights three key low-level orographic flow phenomena governed by gravity-wave dynamics: Foehn flow, atmospheric rotors and gravity-wave modulation of the stable boundary layer. Recent observations and numerical simulations are used to illustrate how these flows can cause significant departures from the turbulent fluxes, which occur over flat terrain. Orographically forced fluxes of heat, moisture and chemical constituents are currently unaccounted for in numerical models. Moreover, whilst turbulent orographic drag parameterisation schemes are available (in some models), these do not represent the large gravity-wave scales associated with foehn dynamics; nor do they account for the spatio-temporal heterogeneity and non-local turbulence advection observed in wave-rotor dynamics or the gravity waves, which modulate turbulence in the boundary layer. The implications for numerical models, which do not resolve these flows, and for the parametrisation schemes, which should account for the unresolved fluxes, are discussed. An overarching need is identified for improved understanding of the heterogeneity in sub-grid-scale processes, such as turbulent fluxes, associated with orographic flows, and to develop new physically-based approaches for parameterizing these processes. Full article
(This article belongs to the Special Issue Atmospheric Processes over Complex Terrain)
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28 pages, 4270 KiB  
Review
Current Challenges in Understanding and Predicting Transport and Exchange in the Atmosphere over Mountainous Terrain
by Manuela Lehner and Mathias W. Rotach
Atmosphere 2018, 9(7), 276; https://doi.org/10.3390/atmos9070276 - 18 Jul 2018
Cited by 70 | Viewed by 8195
Abstract
Coupling of the earth’s surface with the atmosphere is achieved through an exchange of momentum, energy, and mass in the atmospheric boundary layer. In mountainous terrain, this exchange results from a combination of multiple transport processes, which act and interact on different spatial [...] Read more.
Coupling of the earth’s surface with the atmosphere is achieved through an exchange of momentum, energy, and mass in the atmospheric boundary layer. In mountainous terrain, this exchange results from a combination of multiple transport processes, which act and interact on different spatial and temporal scales, including, for example, orographic gravity waves, thermally driven circulations, moist convection, and turbulent motions. Incorporating these exchange processes and previous studies, a new definition of the atmospheric boundary layer in mountainous terrain, a mountain boundary layer (MBL), is defined. This paper summarizes some of the major current challenges in measuring, understanding, and eventually parameterizing the relevant transport processes and the overall exchange between the MBL and the free atmosphere. Further details on many aspects of the exchange in the MBL are discussed in several other papers in this issue. Full article
(This article belongs to the Special Issue Atmospheric Processes over Complex Terrain)
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32 pages, 1081 KiB  
Review
Exchange Processes in the Atmospheric Boundary Layer Over Mountainous Terrain
by Stefano Serafin, Bianca Adler, Joan Cuxart, Stephan F. J. De Wekker, Alexander Gohm, Branko Grisogono, Norbert Kalthoff, Daniel J. Kirshbaum, Mathias W. Rotach, Jürg Schmidli, Ivana Stiperski, Željko Večenaj and Dino Zardi
Atmosphere 2018, 9(3), 102; https://doi.org/10.3390/atmos9030102 - 12 Mar 2018
Cited by 131 | Viewed by 15552
Abstract
The exchange of heat, momentum, and mass in the atmosphere over mountainous terrain is controlled by synoptic-scale dynamics, thermally driven mesoscale circulations, and turbulence. This article reviews the key challenges relevant to the understanding of exchange processes in the mountain boundary layer and [...] Read more.
The exchange of heat, momentum, and mass in the atmosphere over mountainous terrain is controlled by synoptic-scale dynamics, thermally driven mesoscale circulations, and turbulence. This article reviews the key challenges relevant to the understanding of exchange processes in the mountain boundary layer and outlines possible research priorities for the future. The review describes the limitations of the experimental study of turbulent exchange over complex terrain, the impact of slope and valley breezes on the structure of the convective boundary layer, and the role of intermittent mixing and wave–turbulence interaction in the stable boundary layer. The interplay between exchange processes at different spatial scales is discussed in depth, emphasizing the role of elevated and ground-based stable layers in controlling multi-scale interactions in the atmosphere over and near mountains. Implications of the current understanding of exchange processes over mountains towards the improvement of numerical weather prediction and climate models are discussed, considering in particular the representation of surface boundary conditions, the parameterization of sub-grid-scale exchange, and the development of stochastic perturbation schemes. Full article
(This article belongs to the Special Issue Atmospheric Processes over Complex Terrain)
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26 pages, 4422 KiB  
Review
Moist Orographic Convection: Physical Mechanisms and Links to Surface-Exchange Processes
by Daniel J. Kirshbaum, Bianca Adler, Norbert Kalthoff, Christian Barthlott and Stefano Serafin
Atmosphere 2018, 9(3), 80; https://doi.org/10.3390/atmos9030080 - 25 Feb 2018
Cited by 121 | Viewed by 10846
Abstract
This paper reviews the current understanding of moist orographic convection and its regulation by surface-exchange processes. Such convection tends to develop when and where moist instability coincides with sufficient terrain-induced ascent to locally overcome convective inhibition. The terrain-induced ascent can be owing to [...] Read more.
This paper reviews the current understanding of moist orographic convection and its regulation by surface-exchange processes. Such convection tends to develop when and where moist instability coincides with sufficient terrain-induced ascent to locally overcome convective inhibition. The terrain-induced ascent can be owing to mechanical (airflow over or around an obstacle) and/or thermal (differential heating over sloping terrain) forcing. For the former, the location of convective initiation depends on the dynamical flow regime. In “unblocked” flows that ascend the barrier, the convection tends to initiate over the windward slopes, while in “blocked” flows that detour around the barrier, the convection tends to initiate upstream and/or downstream of the high terrain where impinging flows split and rejoin, respectively. Processes that destabilize the upstream flow for mechanically forced moist convection include large-scale moistening and ascent, positive surface sensible and latent heat fluxes, and differential advection in baroclinic zones. For thermally forced flows, convective initiation is driven by thermally direct circulations with sharp updrafts over or downwind of the mountain crest (daytime) or foot (nighttime). Along with the larger-scale background flow, local evapotranspiration and transport of moisture, as well as thermodynamic heterogeneities over the complex terrain, regulate moist instability in such events. Longstanding limitations in the quantitative understanding of related processes, including both convective preconditioning and initiation, must be overcome to improve the prediction of this convection, and its collective effects, in weather and climate models. Full article
(This article belongs to the Special Issue Atmospheric Processes over Complex Terrain)
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