scholarly journals Determining Slope- and Free Air Flow Wind Profiles for WKB Prandtl Models.

2021 ◽  
Author(s):  
Gunter Spoeck ◽  
Maximilian Arbeiter
Keyword(s):  
Thermal Diffusivity ◽  
Similarity Theory ◽  
Slope Angle ◽  
Night Time ◽  
Alpine Valley ◽  
Mountainous Regions ◽  
Wind Speeds ◽  
Prandtl Model ◽  
Free Air ◽  
Diffusivity Function

Abstract During night time, when the air close to the surface cools-down and the atmosphere becomes stable, katabatic down-slope ows may occur in mountainous regions. Contrary, during day time, when the sun heats-up the air close to the surface, and the atmosphere becomes unstable, anabatic upslope ows are prevalent. Up to date, slope winds in the WKB Prandtl model are determined solely by means of specifying the height zj of the maximum turbulent jet above ground. Furthermore, depending on zj parameters K0 and h for a height-dependent eddy thermal diffusivity function KH(z) and a parameter C determining the amplitude for the Prandtl wind speeds must be specified. They are most often estimated from height-dependent wind speeds u, including slope angle α and fixed Prandtl number Pr = KM/KH with KH = KH(z) and KM the eddy viscosity. Having estimated those parameters, friction velocity u*, friction temperature θ* and sensible heat ux QH may be calculated. This article takes the reverse approach: From specified slope angle α, Pr, u*, θ*, QH and specified form of the eddy thermal diffusivity function KH(z) the corresponding WKB Prandtl model is identified. Furthermore, the relationship between u* and θ* calculated via Monin-Obukhov similarity theory for at terrain and those for the WKB Prandtl model are investigated. Using this relationship, we give hints how our new parametrization of the WKB Prandtl model may be used to determine slope ows and free air ows in a micro meteorological model of an alpine valley for pollutant dispersion calculations. We illustrate our derivations by applying our algorithms for the calculation of the WKB Prandtl model to four examples with two taken from Grisogono et al. (2015).

Seismic Fragility Analysis of Hill Buildings with Uneven Ground Column Heights

2014 ◽  
Vol 638-640 ◽  
pp. 1848-1853
Author(s):  
Lin Qing Huang ◽  
Li Ping Wang ◽  
Chao Lie Ning
Keyword(s):  
Seismic Vulnerability ◽  
Fragility Curves ◽  
Slope Angle ◽  
Seismic Fragility ◽  
Exceedance Probability ◽  
Considerable Influence ◽  
Analysis Method ◽  
Ground Acceleration ◽  
Mountainous Regions ◽  
The Hill

The hill buildings sited on slopes have been widely constructed in mountainous regions. In order to estimate the seismic vulnerability of the hill buildings with uneven ground column heights under the effect of potential earthquakes, the exceedance probabilities of the hill buildings sited on different angle slopes in peak ground acceleration (PGA) are calculated and compared by using the incremental dynamic analysis method. The fragility curves show the slope angle has considerable influence on the seismic performance. Specifically, the exceedance probability increases with the increasing of the slope angle at the same performance level.

Stability of the Prandtl model for katabatic slope flows

2019 ◽  
Vol 865 ◽  
Author(s):  
Cheng-Nian Xiao ◽  
Inanc Senocak
Keyword(s):  
Linear Stability ◽  
Stability Theory ◽  
Slope Angle ◽  
Transverse Mode ◽  
Base Flow ◽  
Linear Stability Theory ◽  
Vortical Flow ◽  
Longitudinal Modes ◽  
Prandtl Model ◽  
The Stability

We investigate the stability of the Prandtl model for katabatic slope flows using both linear stability theory and direct numerical simulations. Starting from Prandtl’s analytical solution for uniformly cooled laminar slope flows, we use linear stability theory to identify the onset of instability and features of the most unstable modes. Our results show that the Prandtl model for parallel katabatic slope flows is prone to transverse and longitudinal modes of instability. The transverse mode of instability manifests itself as stationary vortical flow structures aligned in the along-slope direction, whereas the longitudinal mode of instability emerges as waves propagating in the base-flow direction. Beyond the stability limits, these two modes of instability coexist and form a complex flow structure crisscrossing the plane of flow. The emergence of a particular form of these instabilities depends strongly on three dimensionless parameters, which are the slope angle, the Prandtl number and a newly introduced stratification perturbation parameter, which is proportional to the relative importance of the disturbance to the background stratification due to the imposed surface buoyancy flux. We demonstrate that when this parameter is sufficiently large, then the stabilising effect of the background stratification can be overcome. For shallow slopes, the transverse mode of instability emerges despite meeting the Miles–Howard stability criterion of $Ri>0.25$. At steep slope angles, slope flow can remain linearly stable despite attaining Richardson numbers as low as $3\times 10^{-3}$.

scholarly journals Estimates of boundary layer parameters in the atmospheres of the terrestrial planets

1971 ◽  
Vol 40 ◽  
pp. 297-303
Author(s):  
G. S. Golitsyn
Keyword(s):  
Boundary Layers ◽  
Wind Velocity ◽  
Lower Layer ◽  
Similarity Theory ◽  
Potential Temperature ◽  
Terrestrial Planets ◽  
Turbulent Heat ◽  
Low Density ◽  
Free Atmosphere ◽  
Night Time

The similarity theory of atmospheric boundary layers is applied to an estimate of the form of vertical profiles of average wind velocity and potential temperature in the atmospheres of the terrestrial planets in day- and night-time conditions.It is then considered, as in the case of the earth, that the magnitude of the turbulent heat flux qT during the day is about 0.1 of q(1 – A), where q is the solar constant for the planet and A is its albedo; at night, qT is several times smaller still. The friction velocity u* is taken equal to 2–5% (depending upon the stratification) of the mean wind velocity in the free atmosphere, which was adopted from previous calculations (Golitsyn, 1968).The boundary layers in the atmospheres of Mars and Venus and in the hypothetical atmosphere of Mercury are examined in detail. Sharp temperature drops are characteristic of Mars within a few tens of meters from the surface, attaining a magnitude of several tens of degrees, especially during the day. Large changes of the wind velocity also take place in this thin lower layer. This effect results from the low density of the Martian atmosphere.For Venus, owing to the very high density of the atmosphere, the stratification is close to neutral, i.e., the temperature profile is close to the adiabatic one and the wind profile is of a logarithmic shape.Owing to high winds, the stratification on Mercury must also be close to neutral with respect to the wind (the profile being close to the logarithmic), but because of the expected low density, the temperature changes near the ground may still be very great.

Impact of Surface Waves on Wind Stress under Low to Moderate Wind Conditions

2020 ◽  
Author(s):  
Sheng Chen ◽  
Fangli Qiao ◽  
Wenzheng Jiang ◽  
Jingsong Guo ◽  
Dejun Dai
Keyword(s):  
Surface Waves ◽  
Wind Stress ◽  
Climate Models ◽  
Similarity Theory ◽  
Ocean Surface Waves ◽  
China Sea ◽  
Wind Speeds ◽  
Mean Sea Surface ◽  
Wind Profiles ◽  
The Impact

<p>The impact of ocean surface waves on wind stress at the air–sea interface under low to moderate wind<br>conditions was systematically investigated based on a simple constant flux model and flux measurements<br>obtained from two coastal towers in the East China Sea and South China Sea. It is first revealed that the<br>swell-induced perturbations can reach a height of nearly 30m above the mean sea surface, and these perturbations<br>disturb the overlying airflow under low wind and strong swell conditions. The wind profiles severely<br>depart from the classical logarithmic profiles, and the deviations increase with the peak wave phase speeds. At<br>wind speeds of less than 4 m/s, an upward momentumtransfer from the wave to the atmosphere is predicted,<br>which is consistent with previous studies. A comparison between the observations and model indicates that<br>the wind stress calculated by the model is largely consistent with the observational wind stress when considering<br>the effects of surface waves, which provides a solution for accurately calculating wind stress in ocean<br>and climate models. Furthermore, the surface waves at the air–sea interface invalidate the traditional<br>Monin–Obukhov similarity theory (MOST), and this invalidity decreases as observational height increases.</p>

scholarly journals Wind Speeds at Heights Crucial for Wind Energy: Measurements and Verification of Forecasts

2012 ◽  
Vol 51 (9) ◽  
pp. 1602-1617 ◽  
Author(s):  
Susanne Drechsel ◽  
Georg J. Mayr ◽  
Jakob W. Messner ◽  
Reto Stauffer
Keyword(s):  
Wind Speed ◽  
Low Cost ◽  
Good Choice ◽  
Mountainous Regions ◽  
Wind Speeds ◽  
Relative Contribution ◽  
Site Characteristics ◽  
One Year ◽  
Nwp Model ◽  
Ecmwf Model

AbstractWind speed measurements from one year from meteorological towers and wind turbines at heights between 20 and 250 m for various European sites are analyzed and are compared with operational short-term forecasts of the global ECMWF model. The measurement sites encompass a variety of terrain: offshore, coastal, flat, hilly, and mountainous regions, with low and high vegetation and also urban influences. The strongly differing site characteristics modulate the relative contribution of synoptic-scale and smaller-scale forcing to local wind conditions and thus the performance of the NWP model. The goal of this study was to determine the best-verifying model wind among various standard wind outputs and interpolation methods as well as to reveal its skill relative to the different site characteristics. Highest skill is reached by wind from a neighboring model level, as well as by linearly interpolated wind from neighboring model levels, whereas the frequently applied 10-m wind logarithmically extrapolated to higher elevations yields the largest errors. The logarithmically extrapolated 100-m model wind reaches the best compromise between availability and low cost for data even when the vertical resolution of the model changes. It is a good choice as input for further statistical postprocessing. The amplitude of measured, height-dependent diurnal variations is underestimated by the model. At low levels, the model wind speed is smaller than observed during the day and is higher during the night. At higher elevations, the opposite is the case.

scholarly journals Strong Snow-Storms, their Effect on Snow Cover and Snow Accumulation

1977 ◽  
Vol 19 (81) ◽  
pp. 441-449
Author(s):  
A.K. Dyunin ◽  
B.A. Anfilofiyev ◽  
M. G. Istrapilovich ◽  
N.T. Mamayeva ◽  
YA. D. Kvon
Keyword(s):  
Decisive Role ◽  
Snow Accumulation ◽  
Glacier Mass Balance ◽  
Mountainous Regions ◽  
Wind Speeds ◽  
Snow Distribution ◽  
Snow Storm ◽  
Field And Laboratory Conditions ◽  
Snow Storms

AbstractSnow-drifts have been studied by many researchers both in field and laboratory conditions, however these investigations have been carried out mostly at wind speeds up to 20 m/s whereas in many areas of our planet snow-storms occur at winds up to 40 m/s and more. During the winter seasons of 1972-76 the authors carried out a great number of experiments with an artificial snow-storm in a special wind tunnel 27 m long. The wind speeds reached 40 m/s (60-65 m/s at the 10 m anemometer height). The existing theories and hypotheses of snow-drifting, and in particular the “diffusion" model, were tested in a series of the experiments. These have not confirmed the assumption of the Australian scientists on the decisive role of diffusion in drift mechanism at large wind speeds. The problem of strong snow-storm effect on snow accumulation on avalanche-danger slopes, in particular, wind redistribution of snow is no less important.The results obtained may be used for the determination of snow accumulation in avalanche starting zones due to deflation. This is especially important for forecasting very dangerous and frequently-occurring avalanches due to snow-storms. The investigations performed enable us to estimate the snow deposition produced by strong and superstrong snow-storms, to account for the peculiarities of such snow-storms and the means of protection, to forecast snow distribution in mountainous regions, and to define the role of snow-storms in glacier mass balance.

scholarly journals A new approach in the development and analysis of the landslide susceptibility map of the hillslopes of Bujumbura, Burundi

2021 ◽  
pp. 26-34
Author(s):  
Desire Kubwimana ◽  
Lahsen Ait Brahim ◽  
Abdellah Abdelouafi
Keyword(s):  
Landslide Susceptibility ◽  
Slope Angle ◽  
Landslide Inventory ◽  
Slope Aspect ◽  
Susceptibility Map ◽  
Landslide Susceptibility Map ◽  
Aerial Photos ◽  
Conditioning Factors ◽  
Mountainous Regions ◽  
Tropical Environments

As in other hilly and mountainous regions of the world, the hillslopes of Bujumbura are prone to landslides. In this area, landslides impact human lives and infrastructures. Despite the high landslide-induced damages, slope instabilities are less investigated. The aim of this research is to assess the landslide susceptibility using a probabilistic/statistical data modeling approach for predicting the initiation of future landslides. A spatial landslide inventory with their physical characteristics through interpretation of high-resolution optic imageries/aerial photos and intensive fieldwork are carried out. Base on in-depth field knowledge and green literature, let’s select potential landslide conditioning factors. A landslide inventory map with 568 landslides is produced. Out of the total of 568 landslide sites, 50 % of the data taken before the 2000s is used for training and the remaining 50 % (post-2000 events) were used for validation purposes. A landslide susceptibility map with an efficiency of 76 % to predict future slope failures is generated. The main landslides controlling factors in ascendant order are the density of drainage networks, the land use/cover, the lithology, the fault density, the slope angle, the curvature, the elevation, and the slope aspect. The causes of landslides support former regional studies which state that in the region, landslides are related to the geology with the high rapid weathering process in tropical environments, topography, and geodynamics. The susceptibility map will be a powerful decision-making tool for drawing up appropriate development plans in the hillslopes of Bujumbura with high demographic exposure. Such an approach will make it possible to mitigate the socio-economic impacts due to these land instabilities

scholarly journals Renegotiating situativity: transformations of local herbal knowledge in a Western Alpine valley during the past 40 years

2020 ◽  
Vol 16 (1) ◽  
Author(s):  
Michele F. Fontefrancesco ◽  
Andrea Pieroni
Keyword(s):  
Medicinal Plants ◽  
Field Research ◽  
Wild Food ◽  
Natural Environments ◽  
Structured Interviews ◽  
Alpine Valley ◽  
Mountainous Regions ◽  
The Past ◽  
Mountain Environments ◽  
Nw Italy

Abstract Background Mountain environments are fragile socio-ecological systems and the conservation of their biological and cultural diversities— seen as co-evolving, strongly intertwined entities—represents a crucial issue for fostering their sustainability. Very few ethnobiological studies have assessed in the mountainous regions of Europe how local botanical knowledge, which represents a vital portion of the local environmental knowledge (LEK), changes over time, although this may be quintessential for a better understanding of the factors influencing how knowledge and practices are shaped, eroded, or even re-created. Methods In the current study, we compared the gathering and use of local medicinal plants in the Upper Sangone Valley, Western Italian Alps, Piedmont (NW Italy) as described in a field study conducted in the mid-seventies and published in 1977 and those arising from field research that we conducted in the spring of 2015 and 2018, during which time ethnobotanical and ethnomycological information concerning both folk medicinal and wild food uses was obtained via 47 in-depth open and semi-structured interviews with community members. Results In total, one hundred thirty folk taxa represent the past and present medicinal and wild food plant/mushroom heritage of the Sangone Valley: 26 herbal taxa were recorded 40 years ago only; 68 herbal and wild food taxa have been recorded in the current study only; and 36 herbal taxa have been continuously used during the last 40 years. There were no remarkable quantitative differences between the two diachronic medico-ethnobotanical datasets, but the qualitative differences were substantial. The gathering and use of some medicinal plants growing in meadows, forests and higher mountain environments (i.e. Arctostaphylos, Filipendula, Hepatica, Larix, Laserptium, Picea, Polygonatum, Primula, Tussilago and Veronica spp.) disappeared, whereas the collection of plant genera growing in more anthropogenic environments or possibly promoted via popular books and media has been newly introduced (i.e. Aloysia, Apium, Brassica, Crataegus, Epilobium, Fumaria, Geranium, Juniperus, Melissa, Rubus, Rumex, Sedum, Silybum, Taraxacum and Vaccinium spp.). Conclusion The findings show a renegotiation of the situativity that for centuries forged the embeddedness of local communities in their natural environments, probably heavily informed in the past by prevalent pastoralist and forest-centred activities and thus by a deeper knowledge of higher mountain and forest environments. The re-arrangement of a more domestic and more “globalized” herbal knowledge system was possibly inspired by new urban residents, who started to populate the valley at the end of the Seventies, when the original inhabitants abandoned their homes for the urban centres of the Piedmontese plain. The current study suggests that future directions of ethnobiological research should more carefully look at the adaptive capacity of LEK systems.

scholarly journals Strong Snow-Storms, their Effect on Snow Cover and Snow Accumulation

1977 ◽  
Vol 19 (81) ◽  
pp. 441-449 ◽  
Author(s):  
A.K. Dyunin ◽  
B.A. Anfilofiyev ◽  
M. G. Istrapilovich ◽  
N.T. Mamayeva ◽  
YA. D. Kvon
Keyword(s):  
Decisive Role ◽  
Snow Accumulation ◽  
Glacier Mass Balance ◽  
Mountainous Regions ◽  
Wind Speeds ◽  
Snow Distribution ◽  
Snow Storm ◽  
Field And Laboratory Conditions ◽  
Snow Storms

Abstract Snow-drifts have been studied by many researchers both in field and laboratory conditions, however these investigations have been carried out mostly at wind speeds up to 20 m/s whereas in many areas of our planet snow-storms occur at winds up to 40 m/s and more. During the winter seasons of 1972-76 the authors carried out a great number of experiments with an artificial snow-storm in a special wind tunnel 27 m long. The wind speeds reached 40 m/s (60-65 m/s at the 10 m anemometer height). The existing theories and hypotheses of snow-drifting, and in particular the “diffusion" model, were tested in a series of the experiments. These have not confirmed the assumption of the Australian scientists on the decisive role of diffusion in drift mechanism at large wind speeds. The problem of strong snow-storm effect on snow accumulation on avalanche-danger slopes, in particular, wind redistribution of snow is no less important. The results obtained may be used for the determination of snow accumulation in avalanche starting zones due to deflation. This is especially important for forecasting very dangerous and frequently-occurring avalanches due to snow-storms. The investigations performed enable us to estimate the snow deposition produced by strong and superstrong snow-storms, to account for the peculiarities of such snow-storms and the means of protection, to forecast snow distribution in mountainous regions, and to define the role of snow-storms in glacier mass balance.

scholarly journals Description and analysis of the debris flows occurred during 2008 in the Eastern Pyrenees

2010 ◽  
Vol 10 (7) ◽  
pp. 1635-1645 ◽  
Author(s):  
M. Portilla ◽  
G. Chevalier ◽  
M. Hürlimann
Keyword(s):  
Debris Flows ◽  
Regional Scale ◽  
Slope Angle ◽  
Large Mass ◽  
Rainfall Data ◽  
Published Data ◽  
Mountainous Regions ◽  
Initiation Zone ◽  
Eastern Pyrenees ◽  
Fluid Rheology

Abstract. Rainfall-triggered landslides taking place in the Spanish Eastern Pyrenees have usually been analysed on a regional scale. Most research focussed either on terrain susceptibility or on the characteristics of the critical rainfall, neglecting a detailed analysis of individual events. In contrast to other mountainous regions, research on debris flow has only been performed marginally and associated hazard has mostly been neglected. In this study, five debris flows, which occurred in 2008, are selected; and site specific descriptions and analysis regarding geology, morphology, rainfall data and runout were performed. The results are compared with worldwide data and some conclusions on hazard assessment are presented. The five events can be divided into two in-channel debris flows and three landslide-triggered debris flows. The in-channel generated debris flows exceeded 10 000 m3, which are unusually large mass movements compared to historic events which occurred in the Eastern Pyrenees. In contrast, the other events mobilised total volumes less than 2000 m3. The geomorphologic analysis showed that the studied events emphasize similar patterns when compared to published data focussing on slope angle in the initiation zone or catchment area. Rainfall data revealed that all debris flows were triggered by high intensity-short duration rainstorms during the summer season. Unfortunately, existing rainfall thresholds in the Eastern Pyrenees consider long-lasting rainfall, usually occurring in autumn/winter. Therefore, new thresholds should be established taking into account the rainfall peak intensity in mm/h, which seems to be a much more relevant factor for summer than the event's total precipitation. The runout analysis of the 2008 debris flows confirms the trend that larger volumes generally induce higher mobility. The numerical simulation of the Riu Runer event shows that its dynamic behaviour is well represented by Voellmy fluid rheology. A maximum front velocity of 7 m/s was back-analysed for the transit section and even on the fan velocities larger than 2 m/s were obtained. This preliminary analysis of the major Eastern Pyrenean debris flows represents the first background for future studies. Additional research on other events is necessary to support the results presented herein, and to properly assess and reduce hazard related to debris flows.

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