ZusammenfassungDie untere Atmosphäre spielt in der Meteorologie und Klimatologie eine besondere Rolle, ihre Modellierung ist jedoch wegen des hohen Turbulenzanteils bis heute eine Herausforderung. Ein wichtiger erster Schritt war der Mischungswegansatz, den Ludwig Prandtl vor fast 100 Jahren in der Hydrodynamik entwickelte. Vor 90 Jahren skizzierte er dessen Anwendung in der Meteorologie. Dieser Artikel gibt einen kurzen Abriss der Prandtlschen Mischungswegtheorie und älterer Arbeiten zur Konvektion von Henri Claude Bénard und Lord Rayleigh. Dann beschreibt er deren Anwendung in der Meteorologie, speziell bezogen auf die Atmosphärische Grenzschicht. Er geht auf die Maßstabsbezogenheit atmosphärischer Prozesse, zugrundeliegende theoretische Ansätze und messtechnische Lösungen anhand ausgewählter Beispiele ein und schildert die Bedeutung konvektiver Prozesse sowie offene Fragestellungen.
ZusammenfassungDie untere Atmosphäre spielt in der Meteorologie und Klimatologie eine besondere Rolle, ihre Modellierung ist jedoch wegen des hohen Turbulenzanteils bis heute eine Herausforderung. Ein wichtiger erster Schritt war der Mischungswegansatz, den Ludwig Prandtl vor fast 100 Jahren in der Hydrodynamik entwickelte. Vor 90 Jahren skizzierte er dessen Anwendung in der Meteorologie. Dieser Artikel gibt einen kurzen Abriss der Prandtlschen Mischungswegtheorie und älterer Arbeiten zur Konvektion von Henri Claude Bénard und Lord Rayleigh. Dann beschreibt er deren Anwendung in der Meteorologie, speziell bezogen auf die Atmosphärische Grenzschicht. Er geht auf die Maßstabsbezogenheit atmosphärischer Prozesse, zugrundeliegende theoretische Ansätze und messtechnische Lösungen anhand ausgewählter Beispiele ein und schildert die Bedeutung konvektiver Prozesse sowie offene Fragestellungen.
“…where u zi and v zi are the horizontal wind speed components at the inversion, Γ is the static stability above the inversion, ∆ θ is the potential temperature jump at the inversion, w ′ θ ′ 0 and w ′ θ ′ zi are the kinematic sensible heat fluxes at the surface and inversion, respectively, and w L is the large-scale subsidence above the inversion, with subsidence w L < 0 by definition. Using conventional observational systems such as radiosoundings or remote sensing systems (Banta et al, 2013;Emeis et al, 2018;Kottmeier et al, 2021), only a handful of terms in Eq. 1 are usually obtainable along single columns, resulting in a simplified, one-dimensional CBL growth framework, known also as the encroachment model (Stull, 1988;Batchvarova and Gryning, 1991):…”
Abstract. Over heterogeneous, mountainous terrain, the determination of spatial heterogeneity of any type of a turbulent layer has been known to pose substantial challenges in mountain meteorology. In addition to the combined effect in which buoyancy and shear contribute to the turbulence intensity of such layers, it is well known that mountains add an additional degree of complexity via non-local transport mechanisms, compared to flatter topography. It is therefore the aim of this study to determine the vertical depths of both daytime convectively and shear-driven boundary layers within a fairly wide and deep Alpine Valley during summertime. Specifically, three Doppler lidars deployed during the CROSSINN (Cross-valley flow in the Inn Valley investigated by dual-Doppler lidar measurements) campaign within a single week in August 2019 are used to this end, as they were deployed along a transect nearly perpendicular to the along-valley axis. To achieve this, a bottom-up exceedance threshold method based on turbulent Doppler spectrum width sampled by the three lidars has been developed and calibrated against a more traditional bulk-Richardson number approach applied to radiosonde profiles obtained above the valley floor. The method was found to adequately capture the depths of convective turbulent boundary layers at a 1-min temporal and 50-m spatial resolution across the valley, with the degree of ambiguity increasing once surface convection decayed and upvalley flows gained in intensity over the course of the afternoon and evening hours. Analysis of four Intensive Observation Period (IOP) events elucidated three regimes of the daytime mountain boundary layer in this section of the Inn Valley. Each of the three regimes has been analyzed as a function of surface sensible heat flux $H$, upper-level valley stability $\\Gamma$, and upper-level subsidence $w_L$ estimated with the coplanar retrieval method. Finally, the positioning of the three Doppler lidars in a cross-valley configuration enabled one of the most highly spatially and temporally resolved observational convective boundary layer depth data sets during daytime and over complex terrain to date.
Abstract. Over heterogeneous, mountainous terrain, the determination of spatial heterogeneity of any type of a turbulent layer has been known to pose substantial challenges in mountain meteorology. In addition to the combined effect in which buoyancy and shear contribute to the turbulence intensity of such layers, it is well known that mountains add an additional degree of complexity via non-local transport mechanisms, compared to flatter topography. It is therefore the aim of this study to determine the vertical depths of both daytime convectively and shear-driven boundary layers within a fairly wide and deep Alpine valley during summertime. Specifically, three Doppler lidars deployed during the CROSSINN (Cross-valley flow in the Inn Valley investigated by dual-Doppler lidar measurements) campaign within a single week in August 2019 are used to this end, as they were deployed along a transect nearly perpendicular to the along-valley axis. To achieve this, a bottom-up exceedance threshold method based on turbulent Doppler spectrum width sampled by the three lidars has been developed and validated against a more traditional bulk Richardson number approach applied to radiosonde profiles obtained above the valley floor. The method was found to adequately capture the depths of convective turbulent boundary layers at a 1 min temporal and 50 m spatial resolution across the valley, with the degree of ambiguity increasing once surface convection decayed and upvalley flows gained in intensity over the course of the afternoon and evening hours. Analysis of four intensive observation period (IOP) events elucidated three regimes of the daytime mountain boundary layer in this section of the Inn Valley. Each of the three regimes has been analysed as a function of surface sensible heat flux H, upper-level valley stability Γ, and upper-level subsidence wL estimated with the coplanar retrieval method. Finally, the positioning of the three Doppler lidars in a cross-valley configuration enabled one of the most highly spatially and temporally resolved observational convective boundary layer depth data sets during daytime and over complex terrain to date.
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