scholarly journals Escoamento de drenagem sobre terreno ondulado

2020 ◽  
Vol 42 ◽  
pp. e16
Author(s):  
Maicon Fonseca Andrades ◽  
Luis Eduardo Medeiros ◽  
Felipe Denardin Costa ◽  
Luis Fernando Camponogara ◽  
Débora Regina Roberti
Keyword(s):  
Drainage Flow ◽  
Cold Air ◽  
Ambient Flow ◽  
Surface Drainage ◽  
Weather Stations

The present work investigates drainage events of cold air that occur over an undulating terrain, with elevations differences of some tens meters and grassy surface. For this, data collected in the autumn of 2015 from a micrometeorological tower and four weather stations are used. The results show two different cases of drainage, one when the ambient flow is upslope against the near the surface drainage flow, and another when the ambient flow is downslope in favor of the drainage.

scholarly journals Dynamical Aspects of Wintertime Cold-Air Pools in an Alpine Valley System

2005 ◽  
Vol 133 (9) ◽  
pp. 2721-2740 ◽  
Author(s):  
Günther Zängl
Keyword(s):  
Pressure Gradient ◽  
Cold Pool ◽  
Drainage Flow ◽  
Dynamical Mechanism ◽  
Cold Air ◽  
Ambient Wind ◽  
Alpine Valley ◽  
Ambient Flow ◽  
Alpine Foreland

Abstract This study presents high-resolution numerical simulations in order to examine the dynamical mechanisms controlling the persistence of wintertime cold-air pools in an Alpine valley system. First, a case study of a cold-pool episode is conducted, the formation of which was related to the passage of a warm front north of the Alps. While the preexisting cold air was rapidly advected away in the Alpine foreland, a persistent cold pool was maintained in the inner-Alpine part of the valley system, associated with sustained horizontal temperature differences of up to 10 K over a distance of 30 km. The case study is complemented by a series of semi-idealized simulations, combining realistic topography with idealized large-scale flow conditions. These simulations consider a range of different ambient wind directions in order to investigate their impact on the cold-pool persistence. The results indicate that the most important dynamical mechanism controlling the persistence of cold-air pools in deep Alpine valleys is cold-air drainage toward the Alpine foreland. The preferred direction for such a drainage flow is down the pressure gradient imposed by the (geostrophically balanced) ambient flow. Thus, for a given valley geometry and a given strength of the ambient flow, the probability for persistent cold-air pools mainly depends on the ambient wind direction. If the direction of the imposed pressure gradient matches a sufficiently wide connection to the foreland (a valley or a low pass), then a drainage flow will lead to a rapid removal of the cold air. However, the presence of pronounced lateral constrictions in the connecting valley may strongly reduce the drainage efficiency. Cold-pool erosion by turbulent vertical mixing seems to play a comparatively minor role in deep valley systems as considered in this study.

Warm-Air Intrusions in Arizona’s Meteor Crater

2012 ◽  
Vol 51 (6) ◽  
pp. 1010-1025 ◽  
Author(s):  
Bianca Adler ◽  
C. David Whiteman ◽  
Sebastian W. Hoch ◽  
Manuela Lehner ◽  
Norbert Kalthoff
Keyword(s):  
Surface Layer ◽  
Atmospheric Stability ◽  
Crater Floor ◽  
Drainage Flow ◽  
Cold Air ◽  
Stable Surface ◽  
Isothermal Layer ◽  
Stable Surface Layer ◽  
Strong Winds ◽  
Spatial And Temporal Characteristics

AbstractEpisodic nighttime intrusions of warm air, accompanied by strong winds, enter the enclosed near-circular Meteor Crater basin on clear, synoptically undisturbed nights. Data analysis is used to document these events and to determine their spatial and temporal characteristics, their effects on the atmospheric structure inside the crater, and their relationship to larger-scale flows and atmospheric stability. A conceptual model that is based on hydraulic flow theory is offered to explain warm-air-intrusion events at the crater. The intermittent warm-air-intrusion events were closely related to a stable surface layer and a mesoscale (~50 km) drainage flow on the inclined plain outside the crater and to a continuous shallow cold-air inflow that came over the upstream crater rim. Depending on the upstream conditions, the cold-air inflow at the crater rim deepened temporarily and warmer air from above the stable surface layer on the surrounding plain descended into the crater, as part of the flowing layer. The flow descended up to 140 m into the 170-m-deep crater and did not penetrate the approximately 30-m-deep crater-floor inversion. The intruding air, which was up to 5 K warmer than the crater atmosphere, did not extend into the center of the crater, where the nighttime near-isothermal layer in the ambient crater atmosphere remained largely undisturbed. New investigations are suggested to test the hypothesis that the warm-air intrusions are associated with hydraulic jumps.

Meteorological Events Affecting Cold-Air Pools in a Small Basin

2011 ◽  
Vol 50 (11) ◽  
pp. 2223-2234 ◽  
Author(s):  
Manfred Dorninger ◽  
C. David Whiteman ◽  
Benedikt Bica ◽  
Stefan Eisenbach ◽  
Bernhard Pospichal ◽  
...  
Keyword(s):  
Meteorological Parameters ◽  
Eastern Alps ◽  
Cold Air ◽  
Different Types ◽  
Weather Stations ◽  
Strong Winds ◽  
Using Data ◽  
Temperature Inversions ◽  
And Inversion ◽  
Small Basin

AbstractMeteorological events affecting the evolution of temperature inversions or cold-air pools in the 1-km-diameter, high-altitude (~1300 m MSL) Grünloch basin in the eastern Alps are investigated using data from lines of temperature dataloggers running up the basin sidewalls, nearby weather stations, and weather charts. Nighttime cold-air-pool events observed from October 2001 to June 2002 are categorized into undisturbed inversion evolution, late buildups, early breakups, mixing events, layered erosion at the inversion top, temperature disturbances occurring in the lower or upper elevations of the pool, and inversion buildup caused by the temporary clearing of clouds. In addition, persistent multiday cold-air pools are sometimes seen. Analyses show that strong winds and cloud cover are the governing meteorological parameters that cause the inversion behavior to deviate from its undisturbed state, but wind direction can also play an important role in the life cycle of the cold-air pools, because it governs the interaction with steep or gentle slopes of the underlying topography. Undisturbed cold-air pools are unusual in the Grünloch basin. A schematic diagram illustrates the different types of cold-air-pool events.

scholarly journals Wind tunnel experiments: cold-air pooling and atmospheric decoupling above a melting snow patch

2016 ◽  
Vol 10 (1) ◽  
pp. 445-458 ◽  
Author(s):  
Rebecca Mott ◽  
Enrico Paterna ◽  
Stefan Horender ◽  
Philip Crivelli ◽  
Michael Lehning
Keyword(s):  
Wind Tunnel ◽  
Atmospheric Stability ◽  
Strong Stability ◽  
Snow Surface ◽  
Near Surface ◽  
Cold Air ◽  
Melting Snow ◽  
Ambient Flow ◽  
Wind Speeds ◽  
Two Factors

Abstract. The longevity of perennial snowfields is not fully understood, but it is known that strong atmospheric stability and thus boundary-layer decoupling limit the amount of (sensible and latent) heat that can be transmitted from the atmosphere to the snow surface. The strong stability is typically caused by two factors, (i) the temperature difference between the (melting) snow surface and the near-surface atmosphere and (ii) cold-air pooling in topographic depressions. These factors are almost always a prerequisite for perennial snowfields to exist. For the first time, this contribution investigates the relative importance of the two factors in a controlled wind tunnel environment. Vertical profiles of sensible heat and momentum fluxes are measured using two-component hot-wire and one-component cold-wire anemometry directly over the melting snow patch. The comparison between a flat snow surface and one that has a depression shows that atmospheric decoupling is strongly increased in the case of topographic sheltering but only for low to moderate wind speeds. For those conditions, the near-surface suppression of turbulent mixing was observed to be strongest, and the ambient flow was decoupled from the surface, enhancing near-surface atmospheric stability over the single snow patch.

scholarly journals SPATIOTEMPORAL EVALUATION OF NOCTURNAL COLD AIR DRAINAGE OVER A SIMPLE SLOPE USING THERMAL INFRARED IMAGERY

2016 ◽  
Vol XLI-B8 ◽  
pp. 265-269
Author(s):  
V. Ikani ◽  
K. Chokmani ◽  
L. Fathollahi ◽  
H. Granberg ◽  
R. Fournier
Keyword(s):  
Temperature Gradient ◽  
Infrared Camera ◽  
Thermal Infrared ◽  
Infrared Analysis ◽  
Agricultural Field ◽  
Drainage Flow ◽  
Cold Air ◽  
Drainage Flows ◽  
Infrared Measurement ◽  
Thermal Infrared Imagery

Measurements of climatic processes such as cold air drainage flows are problematic over mountainous areas. Observation of cold air drainage is not available in the existing observation network and it requires a special methodology. The main objective of this study was to characterize the cold air drainage over regions with a slope. A high resolution infrared camera, a meteorological station and Digital Elevation Model (DEM) were used. The specific objective was to derive nocturnal cold air drainage velocity over the slope. To address these objectives, a number of infrared measurement campaigns were conducted during calm and clear sky conditions over an agricultural zone (blackcurrant farm) in Canada. Using thermal infrared images, the nocturnal surface temperature gradient were computed in hourly basis. The largest gradient magnitudes were found between 17h -20h. The cooling rates at basin area were two times higher in comparison to the magnitudes observed within slope area. The image analysis illustrated this considerable temperature gradient of the basin may be partly due to transport of cold air drainage into the basin from the slope. The results show that thermal imagery can be used to characterize and understand the microclimate related to the occurrence of radiation frost in the agricultural field. This study provided the opportunity to track the cold air drainage flow and pooling of cold air in low lying areas. The infrared analysis demonstrated that nocturnal drainage flow displayed continuous variation in terms of space and time in response to microscale slope heterogeneities. In addition, the analysis highlighted the periodic aspect for cold air drainage flow.

scholarly journals SPATIOTEMPORAL EVALUATION OF NOCTURNAL COLD AIR DRAINAGE OVER A SIMPLE SLOPE USING THERMAL INFRARED IMAGERY

2016 ◽  
Vol XLI-B8 ◽  
pp. 265-269
Author(s):  
V. Ikani ◽  
K. Chokmani ◽  
L. Fathollahi ◽  
H. Granberg ◽  
R. Fournier
Keyword(s):  
Temperature Gradient ◽  
Infrared Camera ◽  
Thermal Infrared ◽  
Infrared Analysis ◽  
Agricultural Field ◽  
Drainage Flow ◽  
Cold Air ◽  
Drainage Flows ◽  
Infrared Measurement ◽  
Thermal Infrared Imagery

Measurements of climatic processes such as cold air drainage flows are problematic over mountainous areas. Observation of cold air drainage is not available in the existing observation network and it requires a special methodology. The main objective of this study was to characterize the cold air drainage over regions with a slope. A high resolution infrared camera, a meteorological station and Digital Elevation Model (DEM) were used. The specific objective was to derive nocturnal cold air drainage velocity over the slope. To address these objectives, a number of infrared measurement campaigns were conducted during calm and clear sky conditions over an agricultural zone (blackcurrant farm) in Canada. Using thermal infrared images, the nocturnal surface temperature gradient were computed in hourly basis. The largest gradient magnitudes were found between 17h -20h. The cooling rates at basin area were two times higher in comparison to the magnitudes observed within slope area. The image analysis illustrated this considerable temperature gradient of the basin may be partly due to transport of cold air drainage into the basin from the slope. The results show that thermal imagery can be used to characterize and understand the microclimate related to the occurrence of radiation frost in the agricultural field. This study provided the opportunity to track the cold air drainage flow and pooling of cold air in low lying areas. The infrared analysis demonstrated that nocturnal drainage flow displayed continuous variation in terms of space and time in response to microscale slope heterogeneities. In addition, the analysis highlighted the periodic aspect for cold air drainage flow.

scholarly journals Dual-Doppler Observations of Severe Tropical Storm Maggie 1999

2005 ◽  
Vol 20 (1) ◽  
pp. 112-123
Author(s):  
Sai-Choi Tai ◽  
Edwin Wing-Lui Ginn ◽  
Chiu-Ying Lam
Keyword(s):  
Hong Kong ◽  
Storm Track ◽  
Tropical Storm ◽  
Vertical Shear ◽  
Ambient Flow ◽  
Steering Flow ◽  
Nonhydrostatic Model ◽  
Tropical Areas ◽  
Weather Stations ◽  
Experimental Runs

Abstract Severe Tropical Storm Maggie crossed Hong Kong, China, in June 1999. The dual-Doppler winds of Maggie captured by the Hong Kong Observatory's (HKO) S-band Doppler weather radar array were studied. The tracks of Maggie's vorticity centers at 1–3-km levels were analyzed and compared with that at the surface as determined from the wind observations of automatic weather stations. The results indicated that the storm had a vertical tilt toward the west to northwest during the transit over Hong Kong. The tracks also deviated significantly from the deep-layer environmental steering flow. The southward movement and vertical tilt could be partly attributed to the easterly vertical shear in the ambient flow. But the terrain of Hong Kong could have also played a significant role in the lowest 1 km of the atmosphere. The tendency of the storm track to avoid mountains was well illustrated and may serve as a useful forecasting guidance indicator for tropical areas with significant terrain. Experimental runs of a nonhydrostatic model at 5-km resolution were able to simulate the broad west-southwestward movement of Maggie and the vertical tilt of the circulation near the center of the tropical cyclone as revealed by the dual-Doppler observations.

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