Temporal evolution and spatial variation of the boundary layer over complex terrain

Kalthoff, Norbert; Binder, H.-J.; Koßmann, M.; Vögtlin, R.; Corsmeier, U.; Fiedler, F.; Schläger, Hans

doi:10.1016/s1352-2310(97)00193-3

Cited by 66 publications

(32 citation statements)

References 15 publications

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“…Factors such as atmospheric stability, synoptic wind speed, vertical and horizontal scales of the orography and the presence of embedded valleys have been found to be important. Deep CBLs are less terrain-following than shallow ones, and the CBL top is subject to larger vertical displacements over orographic features that have a large horizontal extent [174]. Conclusions on whether advection effects make the CBL height more uniform over mountains differ between observations [175] and theoretical models [176].…”

Section: The Vertical Extent Of the Cbl Over Complex Orographymentioning

confidence: 98%

Exchange Processes in the Atmospheric Boundary Layer Over Mountainous Terrain

et al. 2018

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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 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.

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Section: The Vertical Extent Of the Cbl Over Complex Orographymentioning

confidence: 98%

Exchange Processes in the Atmospheric Boundary Layer Over Mountainous Terrain

et al. 2018

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“…The changes in the mixing layer depth (MLD, i.e., the height of the convective atmospheric boundary layer marked by the base of a thermal inversion) is governed by several factors: surface heating (Holtslag and Van Ulden, 1983), horizontal advection determined by the intensity of the sea breeze in coastal areas (McElroy and Smith, 1991;Lensky and Dayan, 2012), local terrain over the continent (Kalthoff et al, 1998), and the strength of the subsiding atmospheric air mass capping the mixed layer, defined by the temperature profile within this stable layer and synoptic-scale vertical motion (Dayan et al, 1988). Beside these factors, the MLD is controlled also by thermal advection associated with synoptic weather systems and therefore develops under strong forcing by synoptic-scale circulations (Businger and Charnock, 1983;Holt and Raman, 1990;Sinclair et al, 2010).…”

Section: Atmospheric Dispersion Conditions Over the Eastern Mediterramentioning

confidence: 99%

Atmospheric pollution over the eastern Mediterranean during summer – a review

et al. 2017

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Abstract. The eastern Mediterranean (EM) is one of the regions in the world where elevated concentrations of primary and secondary gaseous air pollutants have been reported frequently, mainly in summer. This review discusses published studies of the atmospheric dispersion and transport conditions characterizing this region during the summer, followed by a description of some essential studies dealing with the corresponding concentrations of air pollutants such as ozone, carbon monoxide, total reactive nitrogen, methane, and sulfate aerosols observed there.The interlaced relationship between the downward motion of the subsiding air aloft induced by global circulation systems affecting the EM and the depth of the Persian Trough, a low-pressure trough that extends from the Asian monsoon at the surface controlling the spatiotemporal distribution of the mixed boundary layer during summer, is discussed. The strength of the wind flow within the mixed layer and its depth affect much the amount of pollutants transported and determine the potential of the atmosphere to disperse contaminants off their origins in the EM. The reduced mixed layer and the accompanying weak westerlies, characterizing the summer in this region, led to reduced ventilation rates, preventing an effective dilution of the contaminants. Several studies pointing at specific local (e.g., ventilation rates) and regional peculiarities (long-range transport) enhancing the build-up of air pollutant concentrations are presented.Tropospheric ozone (O 3 ) concentrations observed in the summer over the EM are among the highest over the Northern Hemisphere. The three essential processes controlling its formation (i.e., long-range transport of polluted air masses, dynamic subsidence at mid-tropospheric levels, and stratosphere-to-troposphere exchange) are reviewed. Airborne campaigns and satellite-borne initiatives have indicated that the concentration values of reactive nitrogen identified as precursors in the formation of O 3 over the EM were found to be 2 to 10 times higher than in the hemispheric background troposphere. Several factors favor sulfate particulate abundance over the EM. Models, aircraft measurements, and satellite-derived data have clearly shown that sulfate has a maximum during spring and summer over the EM. The carbon monoxide (CO) seasonal cycle, as obtained from global background monitoring sites in the EM, is mostly controlled by the tropospheric concentration of the hydroxyl radical (OH) and therefore demonstrates high concentrations over winter months and the lowest concentrations during summer when photochemistry is active. Modeling studies have shown that the diurnal variations in CO concentration during the summer result from long-range CO transport from European anthropogenic sources, contributing 60 to 80 % of the boundary-layer CO over the EM. The values retrieved from satellite data enable us to derive the spatial distribution of methane (CH 4 ), identifying August as the month with the highest levels over the EM. The outcomes of a...

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“…determine the height of the boundary layer (e.g. Tennekes, 1970;Kalthoff et al, 1998). Hence, well-defined local airmass discontinuities, namely 'topographically induced boundaries' (Weckwerth and Parsons, 2006) or geographically aligned local fronts, are generated near the surface.…”

Section: Local Frontsmentioning

confidence: 99%

“…The latter mostly refer to 850 or 700 hPa. Special challenges arise over mountainous terrain where the boundary layer height strongly varies (Kalthoff et al, 1998) and pressure levels usually cut into the topography.…”

Section: The Detection Heightmentioning

confidence: 99%

Detection and climatology of fronts in a high‐resolution model reanalysis over the Alps

Jenkner

Sprenger

Schwenk

et al. 2009

Meteorological Applications

103

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The identification of low-level thermal fronts is particularly challenging in high-resolution model fields over complex terrain. Firstly, direct model output often contains numerical noise which spuriously influences the highfrequency variability of thermal parameters. Secondly, the boundary layer interferes via convection and consequently leaves its thermal marks on low levels. Here, an automated objective method for the detection of frontal lines is introduced which is designed to be insusceptible to consequences of small grid spacings. To this end, existing algorithms are readopted and combined in a novel way. The overall technique subdivides into a basic detection of fronts and a supplemental division into local fronts and synoptic fronts. The fundamental parts of the detection are: (1) a smoothing of the initial fields, (2) a definition of the frontal strength, and, (3) a localisation with the thermal front parameter. The local fronts are identified by means of a classification of open and closed thermal contours. The resulting data comprise the spatial outline of the frontal structures in a binary field as well as their type and movement. The novel methodology is applied to a 3 year high-resolution reanalysis over central Europe computed with the COSMO model using a grid spacing of 7 km. Grid-point based climatologies are derived for the Alpine region. Frequencies of occurrence and characteristics of motion are analysed for different frontal types. The novel climatology also provides quantitative evidence of dynamical properties such as the retardation of cold fronts ahead of mountains and the dissolution of warm fronts over mountains.

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Temporal evolution and spatial variation of the boundary layer over complex terrain

Cited by 66 publications

References 15 publications

Exchange Processes in the Atmospheric Boundary Layer Over Mountainous Terrain

Exchange Processes in the Atmospheric Boundary Layer Over Mountainous Terrain

Atmospheric pollution over the eastern Mediterranean during summer – a review

Detection and climatology of fronts in a high‐resolution model reanalysis over the Alps

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