scholarly journals Validation of a simple diagnostic relationship for downslope flows

2020 ◽  
Vol 21 (5) ◽  
Author(s):  
Joan Cuxart ◽  
Daniel Martínez‐Villagrasa ◽  
Ivana Stiperski
Keyword(s):  
Downslope Flows

scholarly journals Abyssal Circulation Driven by Near-Boundary Mixing: Water Mass Transformations and Interior Stratification

2020 ◽  
Vol 50 (8) ◽  
pp. 2203-2226
Author(s):  
Henri F. Drake ◽  
Raffaele Ferrari ◽  
Jörn Callies
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Water Mass ◽  
Circulation Model ◽  
Global Ocean ◽  
Boundary Mixing ◽  
Downslope Flows ◽  
Abyssal Circulation ◽  
Midocean Ridge ◽  
Water Mass Transformations

AbstractThe emerging view of the abyssal circulation is that it is associated with bottom-enhanced mixing, which results in downwelling in the stratified ocean interior and upwelling in a bottom boundary layer along the insulating and sloping seafloor. In the limit of slowly varying vertical stratification and topography, however, boundary layer theory predicts that these upslope and downslope flows largely compensate, such that net water mass transformations along the slope are vanishingly small. Using a planetary geostrophic circulation model that resolves both the boundary layer dynamics and the large-scale overturning in an idealized basin with bottom-enhanced mixing along a midocean ridge, we show that vertical variations in stratification become sufficiently large at equilibrium to reduce the degree of compensation along the midocean ridge flanks. The resulting large net transformations are similar to estimates for the abyssal ocean and span the vertical extent of the ridge. These results suggest that boundary flows generated by mixing play a crucial role in setting the global ocean stratification and overturning circulation, requiring a revision of abyssal ocean theories.

scholarly journals Interactions Between Downslope Flows and a Developing Cold-Air Pool

2014 ◽  
Vol 154 (1) ◽  
pp. 57-80 ◽  
Author(s):  
Paul Burns ◽  
Charles Chemel
Keyword(s):  
Cold Air ◽  
Downslope Flows

Downslope Flows on a Low-Angle Slope and Their Interactions with Valley Inversions. Part I: Observations

2008 ◽  
Vol 47 (7) ◽  
pp. 2023-2038 ◽  
Author(s):  
C. David Whiteman ◽  
Shiyuan Zhong
Keyword(s):  
Salt Lake ◽  
Temperature Inversion ◽  
Maximum Speed ◽  
Salt Lake Valley ◽  
Typical Situation ◽  
Thermally Driven ◽  
Downslope Flows ◽  
Downslope Flow ◽  
Deep Temperature ◽  
Using Data

Abstract Thermally driven downslope flows were investigated on a low-angle (1.6°) slope on the west side of the floor of Utah’s Salt Lake Valley below the Oquirrh Mountains using data from a line of four tethered balloons running down the topographic gradient and separated by about 1 km. The study focused on the evolution of the temperature and wind structure within and above the slope flow layer and its variation with downslope distance. In a typical situation, on clear, undisturbed October nights a 25-m-deep temperature deficit of 7°C and a 100–150-m-deep downslope flow with a jet maximum speed of 5–6 m s−1 at 10–15 m AGL developed over the slope during the first 2 h following sunset. The jet maximum speed and the downslope volume flux increased with downslope distance. The downslope flows weakened in the late evening as the stronger down-valley flows expanded to take up more of the valley atmosphere and as ambient stability increased in the lower valley with the buildup of a nocturnal temperature inversion. Downslope flows over this low-angle slope were deeper and stronger than has been reported previously by other investigators, who generally investigated steeper slopes and, in many cases, slopes on the sidewalls of isolated mountains where the downslope flows are not subject to the influence of nighttime buildup of ambient stability within valleys.

scholarly journals High-Resolution Doppler Lidar Observations of Transient Downslope Flows and Rotors

2013 ◽  
Vol 141 (10) ◽  
pp. 3257-3272 ◽  
Author(s):  
Christian Kühnlein ◽  
Andreas Dörnbrack ◽  
Martin Weissmann
Keyword(s):  
Sierra Nevada ◽  
Hydraulic Jump ◽  
Leading Edge ◽  
Doppler Lidar ◽  
Coherent Doppler Lidar ◽  
First Case ◽  
Rotor Experiment ◽  
Downslope Flows ◽  
Internal Hydraulic Jump ◽  
Lidar Observations

Abstract The authors present observations of the temporal evolution of downslope windstorms with rotors and internal hydraulic jumps of unprecedented detail and spatiotemporal coverage. The observations were carried out by means of a coherent Doppler lidar in the lee of the southern Sierra Nevada range during the sixth intensive observational period of the Terrain-induced Rotor Experiment (T-REX) in 2006. Two representative flow regimes are analyzed and juxtaposed in this paper. The first case shows pulses of high-momentum air that propagate eastward through the valley with an internal hydraulic jump on the leading edge. The region downstream of the transient internal hydraulic jump is characterized by turbulence but no coherent rotor circulation was observed. During the second case, the strongest windstorm of the field campaign T-REX occurred. The observed features of this event resemble the classical notion of a rotor. Altogether, the Doppler lidar observations of both downslope flow events reveal a complex, turbulent flow that is highly transient, intermittent, 3D, and interacts with a significant along-valley flow.

Stability of downslope flows to two-dimensional perturbations

2019 ◽  
Vol 31 (8) ◽  
pp. 086601 ◽  
Author(s):  
Julia Zayko ◽  
Margarita Eglit
Keyword(s):  
Two Dimensional ◽  
Downslope Flows

scholarly journals From weak to intense downslope winds: origin, interaction with boundary-layer turbulence and impact on CO<sub>2</sub> variability

2019 ◽  
Vol 19 (7) ◽  
pp. 4615-4635
Author(s):  
Jon Ander Arrillaga ◽  
Carlos Yagüe ◽  
Carlos Román-Cascón ◽  
Mariano Sastre ◽  
Maria Antonia Jiménez ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Thermal Structure ◽  
Thermal Inversion ◽  
Stable Boundary ◽  
Driving Mechanisms ◽  
Turbulent Characteristics ◽  
Synoptic Wind ◽  
Downslope Wind ◽  
Downslope Flows ◽  
The Impact

Abstract. The interconnection of local downslope flows of different intensities with the turbulent characteristics and thermal structure of the atmospheric boundary layer (ABL) is investigated through observations. Measurements are carried out in a relatively flat area 2 km away from the steep slopes of the Sierra de Guadarrama (central Iberian Peninsula). A total of 40 thermally driven downslope events are selected from an observational database spanning the summer 2017 period by using an objective and systematic algorithm that accounts for a weak synoptic forcing and local downslope wind direction. We subsequently classify the downslope events into weak, moderate and intense categories, according to their maximum 6 m wind speed. This classification enables us to contrast their main differences regarding the driving mechanisms, associated ABL turbulence and thermal structure, and the major dynamical characteristics. We find that the strongest downslope flows (U > 3.5 m s−1) develop when soil moisture is low ( < 0.07 m3 m−3) and the synoptic wind not so weak (3.5 m s−1 < V850 < 6 m s−1) and roughly parallel to the direction of the downslope flow. The latter adds an important dynamical input, which induces an early flow advection from the nearby steep slope, when the local thermal profile is not stable yet. Consequently, turbulence driven by the bulk shear increases up to friction velocity (u*) ≃ 1 m s−1, preventing the development of the surface-based thermal inversion and giving rise to the so-called weakly stable boundary layer. On the contrary, when the dynamical input is absent, buoyancy acceleration drives the formation of a katabatic flow, which is weak (U < 1.5 m s−1) and generally manifested in the form of a shallow jet below 3 m. The relative flatness of the area favours the formation of very stable boundary layers marked by very weak turbulence (u* < 0.1 m s−1). In between, moderate downslope flows show intermediate characteristics, depending on the strength of the dynamical input and the occasional interaction with down-basin winds. On the other hand, by inspecting individual weak and intense events, we further explore the impact of downslope flows on CO2 variability. By relating the dynamics of the distinct turbulent regimes to the CO2 budget, we are able to estimate the contribution of the different terms. For the intense event, indeed, we infer a horizontal transport of 67 ppm in 3 h driven by the strong downslope advection.

scholarly journals On the impact of atmospheric thermal stability on the characteristics of nocturnal downslope flows

1990 ◽  
Vol 51 (1-2) ◽  
pp. 77-97 ◽  
Author(s):  
Z. J. Ye ◽  
J. R. Garratt ◽  
M. Segal ◽  
R. A. Pielke
Keyword(s):  
Thermal Stability ◽  
Downslope Flows ◽  
The Impact
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