Simulations of the Bergen orographic wind shelter

Jonassen, Marius O.; Ólafsson, Haraldur; Valved, A.; Reuder, Joachim; Olseth, Jan Asle

doi:10.3402/tellusa.v65i0.19206

Cited by 8 publications

(10 citation statements)

References 28 publications

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“…This coastal city is located at 60.4 • N and 5.3 • E. The mountains around the city have peak elevations between 284 and 643 m a.s.l. They protect the valley from storms, significantly reducing the surface layer wind speed (Jonassen et al, 2013). The northern location with its weak solar irradiation during wintertime and cold air pooling in lower parts of the relief causes frequently observed but highly local temperature inversions during periods with persistently calm and clear weather.…”

Section: Site Descriptionmentioning

confidence: 99%

A very high-resolution assessment and modelling of urban air quality

Wolf¹,

Pettersson²,

Esau³

2020

Atmos. Chem. Phys.

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Abstract. Urban air quality is one of the most prominent environmental concerns for modern city residents and authorities. Accurate monitoring of air quality is difficult due to intrinsic urban landscape heterogeneity and superposition of multiple polluting sources. Existing approaches often do not provide the necessary spatial details and peak concentrations of pollutants, especially at larger distances from monitoring stations. A more advanced integrated approach is needed. This study presents a very high-resolution air quality assessment with the Parallelized Large-Eddy Simulation Model (PALM), capitalising on local measurements. This fully three-dimensional primitive-equation hydrodynamical model resolves both structural details of the complex urban surface and turbulent eddies larger than 10 m in size. We ran a set of 27 meteorological weather scenarios in order to assess the dispersion of pollutants in Bergen, a middle-sized Norwegian city embedded in a coastal valley. This set of scenarios represents typically observed weather conditions with high air pollution from nitrogen dioxide (NO2) and particulate matter (PM2.5). The modelling methodology helped to identify pathways and patterns of air pollution caused by the three main local air pollution sources in the city. These are road vehicle traffic, domestic house heating with wood-burning fireplaces and ships docked in the harbour area next to the city centre. The study produced vulnerability maps, highlighting the most impacted districts for each weather and emission scenario. Overall, the largest contribution to air pollution over inhabited areas in Bergen was caused by road traffic emissions for NO2 and wood-burning fireplaces for PM2.5 pollution. The effect of emission from ships in the port was mostly restricted to the areas close to the harbour and moderate in comparison. However, the results have contributed to implementation of measures to reduce emissions from ships in Bergen harbour, including provision of shore power.

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Section: Site Descriptionmentioning

confidence: 99%

A very high-resolution assessment and modelling of urban air quality

Wolf¹,

Pettersson²,

Esau³

2020

Atmos. Chem. Phys.

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“…The mean duration of such persistent inversions is 13.1 h. The height of their mean tops was around 220 m asl. The abrupt decrease of the number of inversion episodes with mean tops above 270 m asl might be connected to the local mountain shelter effect [Jonassen et al, 2013]. A few G-inversion episodes coincided with large-scale warm air advection, leading to unusually deep and strong G-inversions where the inversion tops reached levels of above 470 m asl.…”

Section: G-inversionsmentioning

confidence: 99%

“…This view motivated the present analysis of the data set obtained with the microwave temperature profiler MTP‐5HE from March 2011 through February 2013 in the central Bergen valley (60.4°N, 5.3°E), with a population of about 75,000. This rather complex area has been and still is subject to meteorological research [e.g., Jonassen et al ., , ; Valved , ]. The importance of the SBL temperature structure in the Bergen valley was realized decades ago.…”

Section: Introductionmentioning

confidence: 99%

Analysis of the vertical temperature structure in the Bergen valley, Norway, and its connection to pollution episodes

Wolf¹,

Esau

Reuder

2014

J. Geophys. Res. Atmos.

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The vertical temperature profile in the lowest 1000 m of the atmosphere determines a number of important physical processes and meteorological phenomena such as high concentrations of anthropogenic air pollutants in urban areas. Long-term monitoring of temperature profiles at high vertical and temporal resolution has only become feasible only recently with the introduction of affordable angular scanning microwave temperature profile radiometers. In this study, we analyzed 2 years of continuous temperature profile measurements with the MTP-5HE instrument in the urbanized coastal Bergen valley, Norway. The data have a 10 min temporal and 50 m vertical spatial resolution, thus, constituting a unique data set for a microclimatic characterization of the atmosphere in this high-latitude valley. We studied a 2 year record of ground-based (G-) and elevated (E-) inversions, their dynamics and connection to large-scale circulations, and the links between the urban air quality and the temperature inversions. G-inversions are commonly observed during wintertime nocturnal hours. The local topographic features allow for the frequent occurrence of G-inversions, even during strong winds of up to 16 m/s. E-inversions exist mostly during spring and summer and only during unusual synoptic circulation with large-scale warm air advection directly above the valley. Events with high air pollution, identified based on measurements of NO 2 and particulate matter concentrations, are highly dependent on the existence of G-inversions. Meteorological models poorly capture both G-inversions and E-inversions reducing their utility for the assessment of urban air quality and local weather forecasts.

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“…While the valley shelters the city from extreme wind events from most directions (Jonassen et al, 2013), it also favours the existence of persistent ground-based temperature inversions during wintertime . In such conditions, the prolonged accumulation of NO 2 from road traffic as the largest source causes exceedances of legally regulated air quality thresholds.…”

Section: Area Of Interest and Local Air Quality Measurementsmentioning

confidence: 99%

The large-scale circulation during air quality hazards in Bergen, Norway

Wolf

Esau

Reuder

2017

Tellus A: Dynamic Meteorology and Oceanography

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In this study, we assessed the large-scale circulation anomalies leading to wintertime air pollution episodes in Bergen, Norway. Bergen is an example of a city, where a strong interplay between large-scale and local circulation features is relevant. Certain large-scale circulation regimes that are different from the usually assumed large-scale stagnation, lead to local air pollution episodes. We assessed these circulation regimes and their predictability. For this, we modified and applied a previously developed atmospheric circulation proxy for the identification of air pollution episodes. Use of this proxy on data from a high-resolution atmospheric general circulation model showed a good reproduction of the total number of potentially polluted days per month and their inter-monthly variability. We also found a link between the persistence of the flow above the Bergen valley and the occurrence and severity of the local air pollution episodes. Analysis of the large-scale circulation over the North Atlantic-European region, with respect to air pollution in Bergen, revealed that the persistence in the meteorological conditions connected to the air pollution episodes is not necessarily caused by large-scale anomalies of the atmospheric circulation over the Norwegian west coast. It is rather connected to anomalies further upstream as far away as Greenland.

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Simulations of the Bergen orographic wind shelter

Cited by 8 publications

References 28 publications

A very high-resolution assessment and modelling of urban air quality

A very high-resolution assessment and modelling of urban air quality

Analysis of the vertical temperature structure in the Bergen valley, Norway, and its connection to pollution episodes

The large-scale circulation during air quality hazards in Bergen, Norway

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