scholarly journals Characterization of the morning transition from downslope to upslope winds and its connection with the nocturnal inversion breakup at the foot of a gentle slope.

2021 ◽  
Author(s):  
Sofia Farina ◽  
Francesco Barbano ◽  
Silvana Di Sabatino ◽  
Mattia Marchio ◽  
Dino Zardi
Keyword(s):  
Salt Lake ◽  
Convective Boundary ◽  
Morning Transition ◽  
Driving Mechanisms ◽  
American Meteorological Society ◽  
Thermally Driven ◽  
Slope Wind ◽  
Upward Growth ◽  
Slope Flow ◽  
Nocturnal Inversion

<p>Thermally driven winds observed in complex terrain are characterized by a daily cycle dominated by two main phases: a diurnal phase in which winds blow upslope (anabatic), and a nocturnal one in which they revert their direction and blow downslope (katabatic). This alternating pattern also implies two transition phases, following sunrise and sunset respectively. </p><p>Here we study the upslope component of the slope wind with a focus on the morning transition from the katabatic to the anabatic flow based on data from the MATERHORN experiment, performed in Salt Lake Desert (Utah) between Fall 2012 and Spring 2013 (Fernando et al, 2015). </p><p>First of all, a criterion for the selection of purely thermally driven slope wind days is proposed and adopted to select five case studies, taken from both the spring and the autumn periods. Then, the analysis allowed the investigation of the driving mechanisms through the connection with the patterns of erosion of the nocturnal inversion in the valley bed at the foot of the slope under analysis. Three main patterns of erosion of the inversion in the particular topography of a gentle and isolated slope are identified: a) erosion due to upward growth of a convective boundary layer, b) erosion due to descent of the inversion top, and c) erosion due to a mix of the two previous mechanisms. The three patterns are then linked to the initiation of the transition by two different and competing mechanisms: mixing from above (top-down dilution) and surface heating from below. Finally, an analytical model for the description of slope circulation (Zardi and Serafin, 2015) has been used to diagnose the time of the transition.</p><p>Zardi, D. and S. Serafin, 2015: An analytic solution for daily-periodic thermally-driven slope flow. Quart. J. Roy. Meteor. Soc., 141, 1968–1974. </p><p>Fernando, H. J. S., Pardyjak, E. R., Di Sabatino, S., Chow, F. K., De Wekker, S. F. J., Hoch, S. W, Zsedrovits, T., 2015, The MATERHORN: Unraveling the intricacies of mountain weather. <em>Bulletin Of The American Meteorological Society</em>, 96, 1945-1967. </p>

Characterization of the morning transition from downslope to upslope winds and its connection with the nocturnal inversion breakup at the foot of a gentle slope

2021 ◽  
Author(s):  
Sofia Farina ◽  
Dino Zardi ◽  
Silvana Di Sabatino ◽  
Mattia Marchio ◽  
Francesco Barbano
Keyword(s):  
Salt Lake ◽  
Vertical Direction ◽  
Blow Down ◽  
Physical Mechanisms ◽  
Morning Transition ◽  
Thermally Driven ◽  
Slope Wind ◽  
Slope Flow ◽  
Nocturnal Inversion

<p>Thermally driven winds observed in complex terrain are characterized by a daily cycle dominated by two main phases: a diurnal phase in which winds blow upslope (anabatic), and a nocturnal one in which they revert their direction and blow down slope (katabatic). This alternating pattern also implies two transition phases, following sunrise and sunset respectively. </p><p>Here we study the up-slope component of the slope wind with a focus on the morning transition based on from the MATERHORN experiment, performed in Salt Lake Desert (Utah) between Fall 2012 and Spring 2013. </p><p>The analysis develops along three main paths of investigation. The first one is the selection of the suitable conditions for the study of the diurnal component and the characterization of the morning transition. The second one focuses on the deep analysis of the erosion of the nocturnal inversion at the foot of the slope in order to investigate the physical mechanisms driving it. And the third one consists in the comparison between the experimental data and the results of an analytical model (Zardi and Serafin, 2015). The study of the morning transition in the selected case studies allowed its characterization in terms of the relation with the solar radiation cycle, in terms of its seasonality and in terms of its propagation along the slope and along the vertical direction. Most of the results of this investigation are related to the identification of the main mechanisms of erosion of the nocturnal inversion at the foot of the slope and to its role to the beginning of the transition itself. Finally, it is shown how the above model can fairly reproduce the cycle between anabatic and katabatic flow and their intensity.</p><p>Zardi, D. and S. Serafin, 2015: An analytic solution for daily-periodic thermally-driven slope flow. Quart. J. Roy. Meteor. Soc., 141, 1968–1974.</p>

scholarly journals 100 Years of Progress in Mesoscale Planetary Boundary Layer Meteorological Research

2019 ◽  
Vol 59 ◽  
pp. 19.1-19.41 ◽  
Author(s):  
David A. R. Kristovich ◽  
Eugene Takle ◽  
George S. Young ◽  
Ashish Sharma
Keyword(s):  
Boundary Layer ◽  
Future Research ◽  
Sea Breezes ◽  
Atmospheric Circulations ◽  
American Meteorological Society ◽  
Urban Land Cover ◽  
Scientific Organizations ◽  
Lake Effect ◽  
Thermally Driven ◽  
Hydrological Fields

Abstract This chapter outlines the development of our understanding of several examples of mesoscale atmospheric circulations that are tied directly to surface forcings, starting from thermally driven variations over the ocean and progressing inland to man-made variations in temperature and roughness, and ending with forced boundary layer circulations. Examples include atmospheric responses to 1) overocean temperature variations, 2) coastlines (sea breezes), 3) mesoscale regions of inland water (lake-effect storms), and 4) variations in land-based surface usage (urban land cover). This chapter provides brief summaries of the historical evolution of, and tools for, understanding such mesoscale atmospheric circulations and their importance to the field, as well as physical processes responsible for initiating and determining their evolution. Some avenues of future research we see as critical are provided. The American Meteorological Society (AMS) has played a direct and important role in fostering the development of understanding mesoscale surface-forced circulations. The significance of AMS journal publications and conferences on this and interrelated atmospheric, oceanic, and hydrological fields, as well as those by sister scientific organizations, are demonstrated through extensive relevant citations.

scholarly journals Evolution of Late Wintertime Thermally Driven Local Flows and Temperature Fields over Far-Western Nepal

2016 ◽  
Vol 21 (1) ◽  
pp. 35-47
Author(s):  
Ram P. Regmi ◽  
Sangeeta Maharjan
Keyword(s):  
Thermal Environment ◽  
Flow Characteristics ◽  
Temperature Fields ◽  
Valley Wind ◽  
Plain Area ◽  
Slope Winds ◽  
Thermally Driven ◽  
Slope Wind ◽  
Wrf Modeling ◽  
Southern Plain

Atmospheric processes over the Himalayan complex terrain are yet to be studied extensively. Only a few significant researches are reported from this region and the Far-Western Region (FWR) of Nepal still remains untouched. Thus, the present study was conceived to understand the meteorological flow characteristics and thermal environment over the region and associated areas during the late wintertime with the application of the state-of-the-art-of Weather Research and Forecasting (WRF) Modeling System. The study revealed that the northern mountainous region developed strong down slope wind during the night and morning times, which sweeps out the southern plain area of Nepal and may reach just beyond the border. The wind over the plain was very shallow whose depth was just about 100 m. The down slope winds over the southern slope of the Daijee and Nandhaur mountain ranges were significantly enhanced by the subsidence of the southerly wind that prevails above 1 km height above the mean sea level. Close to the noon time a very gentle southerly valley wind from the southern plain replaced the nighttime down slope. Very shallow but strong surface inversion builds up over the plain that breaks up in the late morning. The depth of the mixed layer and the valley wind may reach up to 1km in the afternoon. The thermal environment over the FWR of Nepal was fairly hot that may remain around 35°C in the afternoon around the Mahendranagar area whereas the temperature during the nighttime may go as low as 23°C. The study revealed that, contrary to the general perception, temperature over plain areas of Nepal was significantly higher than further southern areas belonging to India. The meteorological flow fields over the FWR of Nepal executed diurnal periodicity with little day-to-day variation during the late wintertime.Journal of Institute of Science and TechnologyVolume 21, Issue 1, August 2016, page: 35-47

scholarly journals Daytime Heat Transfer Processes Related to Slope Flows and Turbulent Convection in an Idealized Mountain Valley

2010 ◽  
Vol 67 (11) ◽  
pp. 3739-3756 ◽  
Author(s):  
Stefano Serafin ◽  
Dino Zardi
Keyword(s):  
Heat Transfer ◽  
Ground Surface ◽  
Turbulent Convection ◽  
Mountain Valley ◽  
Transfer Processes ◽  
Slope Winds ◽  
Large Eddy ◽  
Thermally Driven ◽  
Slope Wind ◽  
The Impact

Abstract The mechanisms governing the daytime development of thermally driven circulations along the transverse axis of idealized two-dimensional valleys are investigated by means of large-eddy simulations. In particular, the impact of slope winds and turbulent convection on the heat transfer from the vicinity of the ground surface to the core of the valley atmosphere is examined. The interaction between top-down heating produced by compensating subsidence in the valley core and bottom-up heating due to turbulent convection is described. Finally, an evaluation of the depth of the atmospheric layer affected by the slope wind system is provided.

scholarly journals The impact of embedded valleys on daytime pollution transport over a mountain range

2015 ◽  
Vol 15 (20) ◽  
pp. 11981-11998 ◽  
Author(s):  
M. N. Lang ◽  
A. Gohm ◽  
J. S. Wagner
Keyword(s):  
Boundary Layer ◽  
Complex Terrain ◽  
Mountain Range ◽  
Topographic Effects ◽  
Pollution Transport ◽  
Convective Boundary ◽  
Vertical Exchange ◽  
Boundary Layer Height ◽  
Thermally Driven ◽  
The Impact

Abstract. Idealized large-eddy simulations were performed to investigate the impact of different mountain geometries on daytime pollution transport by thermally driven winds. The main objective was to determine interactions between plain-to-mountain and slope wind systems, and their influence on the pollution distribution over complex terrain. For this purpose, tracer analyses were conducted over a quasi-two-dimensional mountain range with embedded valleys bordered by ridges with different crest heights and a flat foreland in cross-mountain direction. The valley depth was varied systematically. It was found that different flow regimes develop dependent on the valley floor height. In the case of elevated valley floors, the plain-to-mountain wind descends into the potentially warmer valley and replaces the opposing upslope wind. This superimposed plain-to-mountain wind increases the pollution transport towards the main ridge by an additional 20 % compared to the regime with a deep valley. Due to mountain and advective venting, the vertical exchange is 3.6 times higher over complex terrain than over a flat plain. However, the calculated vertical exchange is strongly sensitive to the definition of the convective boundary layer height. In summary, the impact of the terrain geometry on the mechanisms of pollution transport confirms the necessity to account for topographic effects in future boundary layer parameterization schemes.

scholarly journals Role of the residual layer and large-scale subsidence on the development and evolution of the convective boundary layer

2013 ◽  
Vol 13 (12) ◽  
pp. 31527-31562 ◽  
Author(s):  
E. Blay-Carreras ◽  
D. Pino ◽  
A. Van de Boer ◽  
O. De Coster ◽  
C. Darbieu ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Mixed Layer ◽  
Convective Boundary Layer ◽  
Large Scale ◽  
Temporal Evolution ◽  
Residual Layer ◽  
Mixing Ratio ◽  
Convective Boundary ◽  
Previous Night ◽  
Morning Transition

Abstract. Observations, mixed-layer theory and the Dutch Large-Eddy Simulation model (DALES) are used to analyze the dynamics of the boundary layer during an intensive operational period (1 July 2011) of the Boundary Layer Late Afternoon and Sunset Turbulence campaign. Continuous measurements made by remote sensing and in situ instruments in combination with radio soundings, and measurements done by remotely piloted airplane systems and two aircrafts probed the vertical structure and the temporal evolution of the boundary layer during the campaign. The initial vertical profiles of potential temperature, specific humidity and wind, and the temporal evolution of the surface heat and moisture fluxes prescribed in the numerical simulations are inspired by some of these observations. The research focuses on the role played by the residual layer during the morning transition and by the large-scale subsidence on the evolution of the boundary layer. By using DALES, we show the importance of the dynamics of the boundary layer during the previous night in the development of the boundary layer at the morning. DALES numerical experiments including the residual layer are capable to model the observed sudden increase of the boundary-layer depth during the morning transition and the subsequent evolution of the boundary layer. The simulation shows a large increase of the entrainment buoyancy heat flux when the residual layer is incorporated into the mixed layer. We also examine how the inclusion of the residual layer above a shallow convective boundary layer modifies the turbulent kinetic energy budget. Large-scale subsidence mainly acts when the boundary layer is fully developed and, for the studied day, it is necessary to be considered to reproduce the afternoon observations. Additionally, we investigate how carbon dioxide (CO2) mixing ratio stored the previous night in the residual layer plays a fundamental role in the evolution of the CO2 mixing ratio during the following day.

Investigating the dynamics of thermally driven up-slope flows: analysis of data from measurements in the Inn Valley (Austria) and comparison with a simple model

2021 ◽  
Author(s):  
Mattia Marchio ◽  
Sofia Farina ◽  
Dino Zardi
Keyword(s):  
Surface Temperature ◽  
Prediction Models ◽  
Weather Prediction ◽  
Slope Angle ◽  
Turbulent Fluxes ◽  
Surface Energy Budget ◽  
Valley Wind ◽  
Slope Winds ◽  
Slope Wind ◽  
Slope Flow

<p><span>Diurnal wind systems typically develop in mountainous areas following the daytime heating and nighttime cooling of sloping surfaces. While down-slope winds have been extensively treated in the literature, up-slope winds have received much less attention. In particular, the physical mechanisms associated with the development of these winds, as well as the search for appropriate parameterization of turbulent fluxes of mass, momentum, and heat over slopes in numerical weather prediction models are still open research topics.</span></p><p><span>Here we present some preliminary results from the analysis of turbulence data (sonic wind speed, temperature, humidity, and turbulent fluxes) collected at two slope stations which are part of the i-Box initiative. The i-Box project (Rotach et al. 2017) aims at studying turbulent exchange processes in complex terrain areas. The experimental setup is composed of six stations disseminated in the surroundings of the alpine city of Innsbruck, in the Inn Valley. The two stations adopted for the present study are located at different points on the valley sidewalls, one with a slope angle of 27° (labelled NF27) and one with a slope angle of 10° (NF10). Both stations are located over slopes covered by alpine meadow and at an altitude of about 1000 m MSL (400 m above the valley floor). The station NF27 has two measurement points, 1.5 and 6.8 m AGL, while the station NF10 has one measurement point, at 6.2 m AGL.</span></p><p><span>The analysis shows that criteria proposed in the literature for the selection of valley-wind days may not apply for the identification of slope-wind days. Furthermore, from the analysis of second order moments, scaling relationships are derived for up-slope flow conditions. In addition, measurements representing the evolution of the up-slope flow structure from the early morning to the mid-afternoon are compared with an existing, simplified, analytical model, which provides the evolution of the vertical profiles of temperature and along-slope wind velocity as generated by a sinusoidal forcing representing the daily cycle of surface temperature. An improvement of the existing model, where the surface energy budget is considered as the boundary condition for the surface temperature, is also tested.</span></p>

scholarly journals High-Resolution Numerical Modeling of Thermally Driven Slope Winds in a Valley with Strong Capping

2010 ◽  
Vol 49 (9) ◽  
pp. 1859-1880 ◽  
Author(s):  
Franco Catalano ◽  
Antonio Cenedese
Keyword(s):  
Similarity Theory ◽  
Gravity Current ◽  
Wall Layer ◽  
Cold Pool ◽  
Return Flow ◽  
Katabatic Flow ◽  
Thermal Forcing ◽  
Convective Boundary ◽  
Thermally Driven ◽  
The Impact

Abstract The complete day–night cycle of the circulation over a slope under simplified idealized boundary conditions is investigated by means of large-eddy simulations (LES). The thermal forcing is given with a time-varying law for the surface temperature. A surface layer parameterization based on the Monin–Obukhov similarity theory is used as a wall layer model. The domain geometry is symmetric, having an infinitely long straight valley in the y direction. Since the depth of the katabatic flow in midlatitude climates is limited to 5–30 m, the authors introduced a vertically stretched grid to obtain a finer mesh near the ground. The length scale for the calculation of eddy viscosities is modified to take into account the grid anisotropy. A preintegration of 24 h is made to obtain a capping inversion over the valley. Results show that the model is able to reproduce microscale circulation dynamics driven by thermal forcing over sloping terrain. The diurnal growth of the convective boundary layer leading to the development of the anabatic wind as well as the evolution of the cold pool in the valley during the night and its interaction with the katabatic flow are shown. Waves develop at the interface between the anabatic current and the return flow. During the day, as a combined effect of the geometry and the forcing, a horizontal breeze develops directed from the middle of the valley toward the ridges. The impact of the gravity current on the quiescent atmosphere in the valley generates a weak hydraulic jump during the night.

scholarly journals Taklimakan Desert nocturnal low-level jet: climatology and dust activity

2016 ◽  
Vol 16 (12) ◽  
pp. 7773-7783 ◽  
Author(s):  
Jin Ming Ge ◽  
Huayue Liu ◽  
Jianping Huang ◽  
Qiang Fu
Keyword(s):  
Inversion Layer ◽  
Warm Season ◽  
Cold Season ◽  
Lower Atmosphere ◽  
Radiosonde Data ◽  
Taklimakan Desert ◽  
Convective Boundary ◽  
Low Level ◽  
Low Level Jets ◽  
Nocturnal Inversion

Abstract. While nocturnal low-level jets (NLLJs) occur frequently in many parts of the world, the occurrence and other detailed characteristics of NLLJs over the Taklimakan Desert (TD) are not well known. This paper presents a climatology of NLLJs and coincident dust over the TD by analyzing multi-year ERA-Interim reanalysis and satellite observations. It is found that the ERA-Interim dataset can capture the NLLJs' features well by comparison with radiosonde data from two surface sites. The NLLJs occur in more than 60 % of nights, which are primarily easterly to east-northeasterly. They typically appear at 100 to 400 m above the surface with a speed of 4 to 10 m s−1. Most NLLJs are located above the nocturnal inversion during the warm season, while they are embedded in the inversion layer during the cold season. NLLJs above the inversion have a strong annual cycle with a maximum frequency in August. We also quantify the convective boundary layer (CBL) height and construct an index to measure the magnitude of the momentum in the CBL. We find that the magnitude of momentum in the lower atmosphere from the top of the surface layer to the top of mixed layer is larger for NLLJ cases than for non-NLLJ cases, and in the warm season the downward momentum transfer process is more intense and rapid. The winds below the NLLJ core to the desert surface gain strength in summer and autumn, and these summer and autumn winds are coincident with an enhancement of aerosol optical depth. This indicates that the NLLJ is an important mechanism for dust activity and transport during the warm season over the Taklimakan.

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.

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