Episode with strong downslope wind in the Southern and Curvature Carpathians in the period 5-6 February 2020

The phenomenon that occurred during the blizzard from February 5-6 in the mountains and especially on the southern slopes of the Southern Carpathians, is known in the literature as "strong downslope winds". This phenomenon occurred in a typical blizzard configuration, in which the differentiated advection of temperature led to the formation of a very stable air layer, with thermal inversion approximately between the levels of 850 and 700 hPa; and it also contributed in this layer to the change of wind direction to vertical. Thus, the existence in the same air layer of two factors favorable to the formation of a critical level, created the ideal conditions for generating strong downslope winds.

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Episode with strong downslope wind in the Southern and Curvature Carpathians in the period 5-6 february 2020

Risks and Catastrophes Journal ◽

10.24193/rcj2021_4 ◽

2021 ◽

Vol 28 (1) ◽

pp. 79-89

Author(s):

M.H. HUȘTIU ◽

A. BOARIU

Keyword(s):

Wind Direction ◽

Critical Level ◽

Thermal Inversion ◽

Downslope Winds ◽

Downslope Wind ◽

Two Factors ◽

Southern Carpathians ◽

The Ideal

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Theoretical Studies of Convectively Forced Mesoscale Flows in Three Dimensions. Part II: Shear Flow with a Critical Level

Journal of the Atmospheric Sciences ◽

10.1175/2009jas3110.1 ◽

2010 ◽

Vol 67 (3) ◽

pp. 694-712 ◽

Cited By ~ 5

Author(s):

Ji-Young Han ◽

Jong-Jin Baik

Keyword(s):

Shear Flow ◽

Gravity Waves ◽

Wind Direction ◽

Critical Level ◽

Deep Convection ◽

Vertical Wind Shear ◽

Finite Depth ◽

Vertical Displacement ◽

Two Dimensions ◽

Three Dimensions

Abstract Convectively forced mesoscale flows in a shear flow with a critical level are theoretically investigated by obtaining analytic solutions for a hydrostatic, nonrotating, inviscid, Boussinesq airflow system. The response to surface pulse heating shows that near the center of the moving mode, the magnitude of the vertical velocity becomes constant after some time, whereas the magnitudes of the vertical displacement and perturbation horizontal velocity increase linearly with time. It is confirmed from the solutions obtained in present and previous studies that this result is valid regardless of the basic-state wind profile and dimension. The response to 3D finite-depth steady heating representing latent heating due to cumulus convection shows that, unlike in two dimensions, a low-level updraft that is necessary to sustain deep convection always occurs at the heating center regardless of the intensity of vertical wind shear and the heating depth. For deep heating across a critical level, little change occurs in the perturbation field below the critical level, although the heating top height increases. This is because downward-propagating gravity waves induced by the heating above, but not near, the critical level can hardly affect the flow response field below the critical level. When the basic-state wind backs with height, the vertex of V-shaped perturbations above the heating top points to a direction rotated a little clockwise from the basic-state wind direction. This is because the V-shaped perturbations above the heating top is induced by upward-propagating gravity waves that have passed through the layer below where the basic-state wind direction is clockwise relative to that above.

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Initial-Condition Sensitivities and the Predictability of Downslope Winds

Journal of the Atmospheric Sciences ◽

10.1175/2009jas3023.1 ◽

2009 ◽

Vol 66 (11) ◽

pp. 3401-3418 ◽

Cited By ~ 48

Author(s):

Patrick A. Reinecke ◽

Dale R. Durran

Keyword(s):

Wave Breaking ◽

Initial Conditions ◽

Static Stability ◽

Synoptic Scale ◽

Wind Speeds ◽

Downslope Winds ◽

First Case ◽

Downslope Wind ◽

The Difference ◽

Strong Winds

Abstract The sensitivity of downslope wind forecasts to small changes in initial conditions is explored by using 70-member ensemble simulations of two prototypical windstorms observed during the Terrain-Induced Rotor Experiment (T-REX). The 10 weakest and 10 strongest ensemble members are composited and compared for each event. In the first case, the 6-h ensemble-mean forecast shows a large-amplitude breaking mountain wave and severe downslope winds. Nevertheless, the forecasts are very sensitive to the initial conditions because the difference in the downslope wind speeds predicted by the strong- and weak-member composites grows to larger than 28 m s−1 over the 6-h forecast. The structure of the synoptic-scale flow one hour prior to the windstorm and during the windstorm is very similar in both the weak- and strong-member composites. Wave breaking is not a significant factor in the second case, in which the strong winds are generated by a layer of high static stability flowing beneath a layer of weaker mid- and upper-tropospheric stability. In this case, the sensitivity to initial conditions is weaker but still significant. The difference in downslope wind speeds between the weak- and strong-member composites grows to 22 m s−1 over 12 h. During and one hour before the windstorm, the synoptic-scale flow exhibits appreciable differences between the strong- and weak-member composites. Although this case appears to be more predictable than the wave-breaking event, neither case suggests that much confidence should be placed in the intensity of downslope winds forecast 12 or more hours in advance.

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Evaluating the Experimental High-Resolution Rapid Refresh–Alaska Modeling System Using USArray Pressure Observations

Weather and Forecasting ◽

10.1175/waf-d-17-0155.1 ◽

2018 ◽

Vol 33 (4) ◽

pp. 933-953 ◽

Cited By ~ 4

Author(s):

Taylor A. McCorkle ◽

John D. Horel ◽

Alexander A. Jacques ◽

Trevor Alcott

Keyword(s):

High Resolution ◽

Surface Pressure ◽

Weather Conditions ◽

Horizontal Resolution ◽

Production Cycle ◽

Downslope Winds ◽

Downslope Wind ◽

Wind Events ◽

Environmental Prediction ◽

Mean Square Errors

Abstract The High-Resolution Rapid Refresh–Alaska (HRRR-AK) modeling system provides 3-km horizontal resolution and 0–36-h forecast guidance for weather conditions over Alaska. This study evaluated the experimental version of the HRRR-AK system available from December 2016 to June 2017, prior to its operational deployment by the National Centers for Environmental Prediction in July 2018. Surface pressure observations from 158 National Weather Service (NWS) stations assimilated during the model’s production cycle and pressure observations from 101 USArray Transportable Array (TA) stations that were not assimilated were used to evaluate 265 complete 0–36-h forecasts of the altimeter setting (surface pressure reduced to sea level). The TA network is the largest recent expansion of Alaskan weather observations and provides an independent evaluation of the model’s performance during this period. Throughout the study period, systematic differences in altimeter setting between the HRRR-AK 0-h forecasts were larger relative to the unassimilated TA observations than relative to the assimilated NWS observations. Upon removal of these initial biases from each of the subsequent 1–36-h altimeter setting forecasts, the model’s 36-h forecast root-mean-square errors at the NWS and TA locations were comparable. The model’s treatment of rapid warming and downslope winds that developed in the lee of the Alaska Range during 12–15 February is examined. The HRRR-AK 0-h forecasts were used to diagnose the synoptic and mesoscale conditions during this period. The model forecasts underestimated the abrupt increases in the temperature and intensity of the downslope winds with smaller errors as the downslope wind events evolved.

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Influence of braking on dynamic stability of car-trailer combinations

Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering ◽

10.1177/0954407020959895 ◽

2020 ◽

pp. 095440702095989

Author(s):

Ning Zhang ◽

Jian-hua Wu ◽

Tian Li ◽

Zi-qian Zhao ◽

Guo-dong Yin

Keyword(s):

Dynamic Stability ◽

Load Transfer ◽

Great Influence ◽

Stability Control ◽

System Dynamic ◽

Force Distribution ◽

Single Track ◽

Two Factors ◽

Braking Force ◽

The Ideal

The influence of braking on dynamic stability of a car-trailer combination (CTC) is studied in this paper. The braking is simply modeled and integrated into a single-track model (STM) with a single-axle trailer. On this basis, some fundamentals and analysis results related to system dynamic stability are given through simulation. Furthermore, it is found that the axle load transfer and braking force distribution have a great influence on system dynamic stability. In order to further analyze the influence of these two factors, both of the braking force distribution and the pitch motion are considered in the modeling. Finally, the ideal braking force distribution domain is proposed. Results can be adopted to explain the experimental phenomenon and serve as a guideline for the differential braking strategy in stability control of the CTC.

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Downslope Flows on a Low-Angle Slope and Their Interactions with Valley Inversions. Part II: Numerical Modeling

Journal of Applied Meteorology and Climatology ◽

10.1175/2007jamc1670.1 ◽

2008 ◽

Vol 47 (7) ◽

pp. 2039-2057 ◽

Cited By ~ 32

Author(s):

Shiyuan Zhong ◽

C. David Whiteman

Keyword(s):

Wind Speed ◽

Pressure Gradient ◽

Buoyancy Force ◽

Atmospheric Modeling ◽

Gradient Force ◽

Ambient Atmosphere ◽

Pressure Gradient Force ◽

Small Contribution ◽

Downslope Winds ◽

Downslope Wind

Abstract The characteristics of well-developed downslope winds observed by tethered balloon soundings at multiple locations over a low-angle slope in the Salt Lake Valley are studied using the Regional Atmospheric Modeling System (RAMS). The model successfully simulated the key properties of the observed wind and temperature structure and evolution and provided insight into the forcing mechanisms. The results show that, although the slope angle is only 1.6°, the buoyancy force associated with the local temperature perturbation caused by nocturnal cooling of the slope surface is capable of producing the unusually strong and deep downslope winds observed by the tethersondes. The hypothesis that the flow is produced locally by the temperature deficit is further confirmed by analysis of the momentum budget that indicates a very small contribution from advection to the downslope mass flux. The analysis also reveals the importance of the along-slope pressure gradient force, which has been neglected by some previous investigators. On an isolated slope, the pressure gradient force, which develops as the downslope-flow layer deepens with downslope distance, is important mostly in the upper part of the downslope wind layer where it counterbalances the buoyancy force. On a slope in a valley, the pressure gradient force interacts with the valley inversion to produce intermittency in the downslope jet and may also significantly slow the flow as the inversion strengthens during the night. The simulations for two different observational nights indicate that the maximum downslope wind speed is sensitive to ambient stability, with near-neutral ambient stability yielding a stronger downslope jet than does a more stable ambient atmosphere. Sensitivity studies suggest that an increase in down-valley winds leads to a decrease in the maximum downslope wind speed and an increase in the thickness of the downslope wind layer. An increase in slope roughness, on the other hand, increases the height of the downslope jet but has little effect on other properties. The downslope wind is stronger over a gentle 1.6° slope than over a much steeper slope of 11°, mainly because of the combination of the stronger buoyancy and weaker pressure gradient over the gentle slope.

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Diurnal Variation of Downslope Winds in Owens Valley during the Sierra Rotor Experiment

Monthly Weather Review ◽

10.1175/2008mwr2469.1 ◽

2008 ◽

Vol 136 (10) ◽

pp. 3760-3780 ◽

Cited By ~ 26

Author(s):

Qingfang Jiang ◽

James D. Doyle

Keyword(s):

Diurnal Variation ◽

Numerical Simulations ◽

Western Slope ◽

Owens Valley ◽

Mountain Waves ◽

Downslope Winds ◽

Wind Event ◽

Downslope Wind ◽

Rotor Experiment ◽

The Impact

The impact of diurnal forcing on a downslope wind event that occurred in Owens Valley in California during the Sierra Rotors Project (SRP) in the spring of 2004 has been examined based on observational analysis and diagnosis of numerical simulations. The observations indicate that while the upstream flow was characterized by persistent westerlies at and above the mountaintop level the cross-valley winds in Owens Valley exhibited strong diurnal variation. The numerical simulations using the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) capture many of the observed salient features and indicate that the in-valley flow evolved among three states during a diurnal cycle. Before sunrise, moderate downslope winds were confined to the western slope of Owens Valley (shallow penetration state). Surface heating after sunrise weakened the downslope winds and mountain waves and eventually led to the decoupling of the well-mixed valley air from the westerlies aloft around local noon (decoupled state). The westerlies plunged into the valley in the afternoon and propagated across the valley floor (in-valley westerly state). After sunset, the westerlies within the valley retreated toward the western slope, where the downslope winds persisted throughout the night.

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Tackling Air Pollution in Krakow

E3S Web of Conferences ◽

10.1051/e3sconf/20184400053 ◽

2018 ◽

Vol 44 ◽

pp. 00053

Author(s):

Artur Jachimowski ◽

Marcin Paprocki ◽

Magdalena Wojnarowska

Keyword(s):

Air Pollution ◽

Air Quality ◽

Meteorological Parameters ◽

Quality Parameters ◽

Heating Season ◽

Thermal Inversion ◽

Two Factors ◽

Air Quality Monitoring Stations ◽

Stack Emissions ◽

Weak Wind

Data used in order to determine the level of pollutants present in the air in Krakow came from three air quality monitoring stations located in Bulwarowa street, Bujaka street and Krasińskiego avenue. Based on these data, an analysis was performed concerning air quality in Krakow in 2010-2016. Also, a correlation analysis was performed to investigate the relation between air quality parameters and meteorological parameters, such as: wind, precipitation, temperature. An analysis of the results obtained showed that two factors are critical for the variability of air pollution in Krakow. The first of them is low-stack emissions from coal stoves and boilers. The other factor is the type of atmospheric circulation. It has been determined that the worst air quality occurs in the heating season as the prevailing circulation is anticyclonic (high-pressure) characterised by low temperature, lack or small amount of precipitation, weak wind and thermal inversion. The paper presents preventive measures aimed at reducing the amount of pollutants in Krakow. It has been found that in order to reduce the level of air pollution in Krakow, especially in the heating season, it is necessary to intensify operations aimed at eliminating coal and wood stoves and boilers.

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How Franchisors Describe Their Ideal Entrepreneurial Franchisee

Journal of Applied Business Research (JABR) ◽

10.19030/jabr.v29i1.7559 ◽

2012 ◽

Vol 29 (1) ◽

pp. 97

Author(s):

Jacques Boulay ◽

Valentina Stan

Keyword(s):

Qualitative Research ◽

Strong Support ◽

Selection Strategy ◽

Font Size ◽

Second Stage ◽

Two Factors ◽

System Developer ◽

System Characteristics ◽

The Ideal

This article has two main objectives: first, to identify the various entrepreneurial profiles of the ideal franchisee, as perceived by franchisors, and second, to describe and compare each profile on the basis of system characteristics. Qualitative research of franchisors is coupled with analyses of data collected from 90 franchise systems. This procedure offers strong sequential evidence in that the results of the first method inform the second-stage sampling and instrumentation (Greene et al., 1989). The study reveals three main entrepreneurial profiles of prospective franchisees - system developer, in-store craftsperson, and opportunistic investor. It also establishes that the term of the franchise agreement and the level of system plurality are two factors on which entrepreneurial profiles differ. These results offer strong support for franchisors in their selection strategy of future franchise partners.

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A qualidade do ar em Lisboa. Valores médios e situações extremas

Finisterra ◽

10.18055/finis1809 ◽

2012 ◽

Vol 31 (61) ◽

Author(s):

Henrique Andrade

Keyword(s):

Air Pollution ◽

Spatial Distribution ◽

Wind Speed ◽

Wind Direction ◽

Extreme Values ◽

Strong Relationship ◽

Thermal Inversion ◽

Cyclical Variation ◽

Pollution Levels ◽

Very High

AIR QUALITY IN LISBON: MEAN AND EXTREME VALUES - Different aspects of the air pollution in Lisbon were analised: spatial distribution, cyclical variation (yearly, weekly and daily) and dependence on athmospheric conditions. During January 1993, when air pollution attained very high levels, we found that a very strong relationship was established between air pollution and wind speed and direction as well as between air pollution and the eight of the thermal inversion over Lisbon. During the more polluted periods, wind speed never reached 2 m/s and the thermal inversion was always under 165m. As for wind direction, pollution roses confirmed that the highest pollution levels occurred with a flux favourable to the transport of pollutants from the main emission areas.

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