Vergleiche von Profilen der turbulenten kinetischen Energie in der Atmosphärischen Grenzschicht auf der Basis von Doppler-Lidar-Messungen mit Simulationsergebnissen des NWV-Modells ICON 

2021 ◽  
Author(s):  
Claudia Becker ◽  
Eileen Päschke ◽  
Frank Beyrich
Keyword(s):  
Cold Pool ◽  
Doppler Lidar ◽  
Low Level ◽  
Statistische Analyse ◽  
Low Level Jet

<p>Bestandteil des Gleichungssystems im Wettervorhersage-Modell ICON des DWD ist neben den klassischen Gleichungen für die zeitliche Änderung der Temperatur, des Windes und des Wassergehaltes der Atmosphäre in allen drei Phasen auch eine prognostische Gleichung für die turbulente kinetische Energie (TKE). Hieraus ergibt sich zunehmend der Bedarf nach Messdaten zur Verifikation der Modellergebnisse auch für diese Variable. Operationelle Messungen der TKE werden in der Praxis nur an wenigen Standorten mittels 3D-Ultraschall-Anemometern durchgeführt und sind damit oft auf Höhen in Bodennähe, in Einzelfällen auf Mastmessungen bis etwa 200 m Höhe beschränkt.</p> <p>Am Meteorologischen Observatorium Lindenberg – Richard-Aßmann-Observatorium des DWD wurde in den letzten Jahren ein in der Literatur beschriebenes Verfahren zur Ableitung von Profilen der turbulenten kinetischen Energie (TKE) aus Doppler-Lidar-Messungen implementiert, getestet und anhand mehrmonatiger Datensätze bewertet (vgl. Beitrag von Päschke et al., diese Session). Im vorliegenden Beitrag werden die Ergebnisse dieser Messungen mit den Ergebnissen der operationellen Modellvorhersagen mit ICON verglichen.</p> <p>In einem ersten Schritt werden charakteristische Einzelfälle betrachtet (Cold-Pool-Event, nächtlicher Low-Level Jet, Strahlungstag). Im zweiten Schritt erfolgt eine statistische Analyse gemittelter Tagesgänge der TKE aus Messungen im Vergleich zu den Ergebnissen der NWV-Modelle ICON global, ICON-EU und ICON-D2 unter Berücksichtigung von Jahreszeit, Strahlungsbilanz, Stabilitätsverhältnissen und Windgeschwindigkeit. Besonderes Augenmerk wird dabei auf das seit Februar 2021 im operationellen Betrieb laufende Regionalmodell ICON-D2 gerichtet, das bei einer horizontalen Auflösung von 2.2 km die Auflösung von Konvektion erlaubt. </p>

scholarly journals Mixed layer depths via Doppler lidar during low-level jet events

2018 ◽  
Vol 176 ◽  
pp. 06017
Author(s):  
Brian Carroll ◽  
Belay Demoz ◽  
Timothy Bonin ◽  
Ruben Delgado
Keyword(s):  
Fuzzy Logic ◽  
Wind Speed ◽  
Mixed Layer ◽  
Wind Shear ◽  
Lower Troposphere ◽  
Doppler Lidar ◽  
High Wind ◽  
Fuzzy Logic Algorithm ◽  
Low Level ◽  
Low Level Jet

A low-level jet (LLJ) is a prominent wind speed peak in the lower troposphere. Nocturnal LLJs have been shown to transport and mix atmospheric constituents from the residual layer down to the surface, breaching quiescent nocturnal conditions due to high wind shear. A new fuzzy logic algorithm combining turbulence and aerosol information from Doppler lidar scans can resolve the strength and depth of this mixing below the jet. Conclusions will be drawn about LLJ relations to turbulence and mixing.

scholarly journals The Structure, Evolution, and Dynamics of a Nocturnal Convective System Simulated Using the WRF-ARW Model

2017 ◽  
Vol 145 (8) ◽  
pp. 3179-3201 ◽  
Author(s):  
Benjamin T. Blake ◽  
David B. Parsons ◽  
Kevin R. Haghi ◽  
Stephen G. Castleberry
Keyword(s):  
Boundary Layer ◽  
Deep Convection ◽  
Vertical Shear ◽  
Structure Evolution ◽  
Cold Pool ◽  
Density Current ◽  
Convective System ◽  
Low Level ◽  
Arw Model ◽  
Low Level Jet

Previous studies have documented a nocturnal maximum in thunderstorm frequency during the summer across the central United States. Forecast skill for these systems remains relatively low and the explanation for this nocturnal maximum is still an area of active debate. This study utilized the WRF-ARW Model to simulate a nocturnal mesoscale convective system that occurred over the southern Great Plains on 3–4 June 2013. A low-level jet transported a narrow corridor of air above the nocturnal boundary layer with convective instability that exceeded what was observed in the daytime boundary layer. The storm was elevated and associated with bores that assisted in the maintenance of the system. Three-dimensional variations in the system’s structure were found along the cold pool, which were examined using convective system dynamics and wave theory. Shallow lifting occurred on the southern flank of the storm. Conversely, the southeastern flank had deep lifting, with favorable integrated vertical shear over the layer of maximum CAPE. The bore assisted in transporting high-CAPE air toward its LFC, and the additional lifting by the density current allowed for deep convection to occur. The bore was not coupled to the convective system and it slowly pulled away, while the convection remained in phase with the density current. These results provide a possible explanation for how convection is maintained at night in the presence of a low-level jet and a stable boundary layer, and emphasize the importance of the three-dimensionality of these systems.

Properties of the offshore low level jet and rotor layer wind shear as measured by scanning Doppler Lidar

Wind Energy ◽  
2016 ◽  
Vol 20 (6) ◽  
pp. 987-1002 ◽  
Author(s):  
Y. L. Pichugina ◽  
W. A. Brewer ◽  
R. M. Banta ◽  
A. Choukulkar ◽  
C. T. M. Clack ◽  
...  
Keyword(s):  
Wind Shear ◽  
Doppler Lidar ◽  
Low Level ◽  
Low Level Jet

scholarly journals Long-lived high-frequency gravity waves in the atmospheric boundary layer: observations and simulations

2019 ◽  
Vol 19 (24) ◽  
pp. 15431-15446 ◽  
Author(s):  
Mingjiao Jia ◽  
Jinlong Yuan ◽  
Chong Wang ◽  
Haiyun Xia ◽  
Yunbin Wu ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Gravity Waves ◽  
Horizontal Wind ◽  
Doppler Lidar ◽  
Low Level ◽  
Coherent Doppler Lidar ◽  
Computational Fluid Dynamics Cfd ◽  
Phase Progression ◽  
Low Level Jet

Abstract. A long-lived gravity wave (GW) in the atmospheric boundary layer (ABL) is analysed during a field experiment in Anqing, China (30∘37′ N, 116∘58′ E). Persistent GWs with periods ranging from 10 to 30 min over 10 h in the ABL within a 2 km height are detected by a coherent Doppler lidar from 4 to 5 September 2018. The amplitudes of the vertical wind due to these GWs are approximately 0.15–0.2 m s−1. The lifetimes of these GWs are longer than 20 wave cycles. There is no apparent phase progression with altitude. The vertical and zonal perturbations in the GWs are 90∘ out of phase, with vertical perturbations generally leading to zonal ones. Based on experiments and simplified two-dimensional computational fluid dynamics (CFD) numerical simulations, a reasonable generation mechanism of this persistent wave is proposed. A westerly low-level jet of ∼5 m s−1 exists at an altitude of 1–2 km in the ABL. The wind shear around the low-level jet leads to wave generation under the condition of light horizontal wind. Furthermore, a combination of thermal and Doppler ducts occurs in the ABL. Thus, the ducted wave motions are trapped in the ABL and have long lifetimes.

Response of Simulated Squall Lines to Low-Level Cooling

2008 ◽  
Vol 65 (4) ◽  
pp. 1323-1341 ◽  
Author(s):  
Matthew D. Parker
Keyword(s):  
Boundary Layer ◽  
Initial Conditions ◽  
Cold Pool ◽  
Jet Streams ◽  
Near Surface ◽  
Low Level ◽  
Convective Systems ◽  
Central United States ◽  
Low Level Jet ◽  
Nocturnal Inversion

Abstract Organized convection has long been recognized to have a nocturnal maximum over the central United States. The present study uses idealized numerical simulations to investigate the mechanisms for the maintenance, propagation, and evolution of nocturnal-like convective systems. As a litmus test for the basic governing dynamics, the experiments use horizontally homogeneous initial conditions (i.e., they include neither fronts nor low-level jet streams). The simulated storms are allowed to mature as surface-based convective systems before the boundary layer is cooled. In this case it is then surprisingly difficult to cut the mature convective systems off from their source of near-surface inflow parcels. Even when 10 K of the low-level cooling has been applied, the preexisting system cold pool is sufficient to lift boundary layer parcels to their levels of free convection. The present results suggest that many of the nocturnal convective systems that were previously thought to be elevated may actually be surface based. With additional cooling, the simulated systems do, indeed, become elevated. First, the CAPE of the near-surface air goes to zero: second, as the cold pool’s temperature deficit vanishes, the lifting mechanism evolves toward a bore atop the nocturnal inversion. Provided that air above the inversion has CAPE, the system then survives and begins to move at the characteristic speed of the bore. Interestingly, as the preconvective environment is cooled and approaches the temperature of the convective outflow, but before the system becomes elevated, yet another distinct behavior emerges. The comparatively weaker cold pool entails slower system motion but also more intense lifting, apparently because it is more nearly balanced by the lower-tropospheric shear. This could explain the frequent observation of intensifying convective systems in the evening hours without the need for a nocturnal low-level jet. The governing dynamics of the simulated systems, as well as the behavior of low-level tracers and parcel trajectories, are addressed for a variety of environments and degrees of stabilization.

Nocturnal Low-Level Jet in a Mountain Basin Complex. Part I: Evolution and Effects on Local Flows

2004 ◽  
Vol 43 (10) ◽  
pp. 1348-1365 ◽  
Author(s):  
Robert M. Banta ◽  
Lisa S. Darby ◽  
Jerome D. Fast ◽  
James O. Pinto ◽  
C. David Whiteman ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Salt Lake ◽  
Great Salt Lake ◽  
Vertical Motion ◽  
Cold Pool ◽  
Lake Basin ◽  
The South ◽  
Low Level ◽  
Low Level Jet ◽  
Convergence Zones

Abstract A Doppler lidar deployed to the center of the Great Salt Lake (GSL) basin during the Vertical Transport and Mixing (VTMX) field campaign in October 2000 found a diurnal cycle of the along-basin winds with northerly up-basin flow during the day and a southerly down-basin low-level jet at night. The emphasis of VTMX was on stable atmospheric processes in the cold-air pool that formed in the basin at night. During the night the jet was fully formed as it entered the GSL basin from the south. Thus, it was a feature of the complex string of basins draining toward the Great Salt Lake, which included at least the Utah Lake basin to the south. The timing of the evening reversal to down-basin flow was sensitive to the larger-scale north–south pressure gradient imposed on the basin complex. On nights when the pressure gradient was not too strong, local drainage flow (slope flows and canyon outflow) was well developed along the Wasatch Range to the east and coexisted with the basin jet. The coexistence of these two types of flow generated localized regions of convergence and divergence, in which regions of vertical motion and transport were focused. Mesoscale numerical simulations captured these features and indicated that updrafts on the order of 5 cm s−1 could persist in these localized convergence zones, contributing to vertical displacement of air masses within the basin cold pool.

scholarly journals Long-live High Frequency Gravity Wavesin Atmospheric Boundary Layer: Observations and Simulations

2019 ◽  
Author(s):  
Mingjiao Jia ◽  
Jinlong Yuan ◽  
Chong Wang ◽  
Haiyun Xia ◽  
Yunbin Wu ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Horizontal Wind ◽  
Doppler Lidar ◽  
Low Level ◽  
Coherent Doppler Lidar ◽  
Long Lifetime ◽  
Computational Fluid Dynamics Cfd ◽  
Phase Progression ◽  
Low Level Jet

Abstract. A long-live gravity wave (GW) in atmospheric boundary layer (ABL) during a field experiment in Anqing, China (116°58′ E, 30°37′ N) is analysed. Persistent GWs over 10 hours with periods ranging from 10 to 30 min in the ABL within 2 km height are detected by a coherent Doppler lidar from 4 to 5 in September 2018. The amplitudes of the vertical wind due to these GWs are about 0.15~0.2 m s−1. The lifetime of the GWs is more than 20 wave cycles. There is no apparent phase progression with altitude. The vertical and zonal perturbations of the GWs are apparent quadrature with vertical perturbations generally leading ahead of zonal ones. Based on experiments and simplified 2-Dimensional Computational Fluid Dynamics (CFD) numerical simulations, a reasonable generation mechanism of this persistent wave is proposed. A westerly low-level jet of ~ 5 m s−1 exists at the altitude of 1~2 km in the ABL. The wind shear around the low-level jet lead to the wave generation in the condition of light horizontal wind. Furthermore, a combination of thermal and Doppler ducts occurs in the ABL. Thus, the ducted wave motions are trapped in the ABL with long lifetime.

scholarly journals Nocturnal Low-level Jet Evolution in a Broad Valley Observed by Dual Doppler Lidar

2014 ◽  
Vol 23 (3) ◽  
pp. 305-313 ◽  
Author(s):  
Thomas Damian ◽  
Andreas Wieser ◽  
Katja Träumner ◽  
Ulrich Corsmeier ◽  
Christoph Kottmeier
Keyword(s):  
Doppler Lidar ◽  
Low Level ◽  
Low Level Jet

The 8 May 2009 Superderecho: Analysis of a Real-Time Explicit Convective Forecast

2013 ◽  
Vol 28 (3) ◽  
pp. 863-892 ◽  
Author(s):  
Morris L. Weisman ◽  
Clark Evans ◽  
Lance Bosart
Keyword(s):  
Wind Shear ◽  
Convective Available Potential Energy ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Cold Pool ◽  
Low Level ◽  
Warm Core ◽  
Bow Echo ◽  
Low Level Jet ◽  
Baroclinic Zone

Abstract Herein, an analysis of a 3-km explicit convective simulation of an unusually intense bow echo and associated mesoscale vortex that were responsible for producing an extensive swath of high winds across Kansas, southern Missouri, and southern Illinois on 8 May 2009 is presented. The simulation was able to reproduce many of the key attributes of the observed system, including an intense [~100 kt (51.4 m s−1) at 850 hPa], 10-km-deep, 100-km-wide warm-core mesovortex and associated surface mesolow associated with a tropical storm–like reflectivity eye. A detailed analysis suggests that the simulated convection develops north of a weak east–west lower-tropospheric baroclinic zone, at the nose of an intensifying low-level jet. The system organizes into a north–south-oriented bow echo as it moves eastward along the preexisting baroclinic zone in an environment of large convective available potential energy (CAPE) and strong tropospheric vertical wind shear. Once the system moves east of the low-level jet and into an environment of weaker CAPE and weaker vertical wind shear, it begins an occlusion-like phase, producing a pronounced comma-shaped reflectivity echo with an intense warm-core mesovortex at the head of the comma. During this phase, a deep strip of cyclonic vertical vorticity located on the backside of the bow echo consolidates into a single vortex core. A notable weakening of the low-level convectively generated cold pool also occurs during this phase, perhaps drawing parallels to theories of tropical cyclogenesis wherein cold convective downdrafts must be substantially mitigated for subsequent system intensification.

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