Evaluation of thermally driven local winds in a deep Alpine valley in a high-resolution numerical weather prediction model

<p>In fair weather conditions, thermally driven local winds are dominant feature of the atmospheric boundary layer over complex terrain. They may dominate the wind climatology in deep Alpine valleys resulting in a unique wind climatology for any given valley. The accurate forecasting of these local wind systems is challenging, as they are the result of complex and multi-scale interactions. Even more so, if the aim is the accurate forecasting of the winds from the near-surface to the free atmosphere, which can be considered a prerequisite for the accurate prediction of mountain weather.  This study investigates the skill of the COSMO model at 1.1 km grid spacing in simulating the thermally driven local winds in the Swiss Alps for a month-long period in September 2016. The study combines the evaluation of the surface winds in several Alpine valleys with a more detailed evaluation of the wind evolution throughout the depth of the valley atmosphere for a particular location in the Swiss Rhone valley, the town of Sion. The former is based on a comparison with observations from the operational measurement network of MeteoSwiss, while the latter uses data from a wind profiler stationed at Sion airport. It is found that the near-surface valley wind is generally well represented for the larger Alpine valleys, except for the Rhone valley at Sion. The reasons for the poor skill at Sion are investigated and shown to be attributable to several factors. One of which is a too strong cross-valley flow reaching down to the valley floor and displacing the daytime up-valley wind. A second factor is the particular local valley geometry. It is shown that an increase of the initial soil moisture and the use a finer horizontal grid spacing results in an improved simulation of the diurnal valley wind at Sion.</p>

The importance of local winds for the aerationof urban areas having hot and windless climatic conditions

Introduction. A city with its high-rise buildings, greenery and landscaping that prevent air motion aggravate windless conditions typical for climates in the cities located in the southern latitudes characterized by heat and lack of wind. Urban built-up areas have stagnant and overheated air that causes sultriness and significant air pollutions caused by anthropogenic sources. These factors require systematization of the local aerodynamics by means of local wind generation using solar energy. Materials and methods. Methods of theoretical research, large-scale field measurements involving the use of instruments, visual observations by means of smoke screening of the urban area’s structure were applied and laboratory research into thermal and wind processes using physical models of cities were applied to identify the role of insolation in the generation of local thermal winds that improve the local environment on the micro- and macroscale. Results. The author has found that if built-up urban areas have no general circulation wind fields, urban aeration systems develop local independent air flows due to the temperature difference between heat and cool islands. The temperature difference was applied as the source material for an urban wind model and it also helped to identify the dependence of the local wind velocity on the thermal contrast of urban islands. A classification of aeration models is developed at macro; meso-; micro- and nanoscales. Conclusions. The practical area of application of the theory of hot and windless processes was identified in respect of urban area planning. The aerodynamics of an urban environment was systematized due to the generation of local thermal winds. The process of local thermal wind generation was studied; the classification of natural aeration models was made for urban areas. Methods of using solar energy were applied to generate local winds, to develop the microclimate and to enhance the environment of urban areas and structures as a prerequisite for targeted urban planning actions, three-dimensional space-planning solutions that apply to urban structures, landscaping, architectural and structural concepts of buildings. Acknowledgments. The work was performed in accordance with the research schedule of Department of Design of Buildings and Structures, NRU MGSU, focused on “Function, Structure, Environment in the Architecture of Buildings and Towns”.

Evaluation of thermally driven local winds in the Swiss Alps simulated by a high-resolution NWP model

<p>In fair weather conditions, thermally driven local winds often dominate the wind climatology in deep Alpine valleys resulting in a unique wind climatology for any given valley. The accurate forecasting of these local wind systems is challenging, as they are the result of complex and multi-scale interactions. Even more so, if the aim is an accurate forecast of the winds from the near-surface to the free atmosphere, which can be considered a prerequisite for the accurate prediction of mountain weather.  This study investigates the skill of a high-resolution numerical weather prediction (NWP) model, the most current version of the COSMO-DWD model,  at 1.1 km grid spacing in simulating the thermally driven local winds in the Swiss Alps for a month-long period in September 2016. The study combines the evaluation of the surface winds in several Alpine valleys with a more detailed evaluation of the wind evolution throughout the valley depth for a particular site in the Swiss Rhone valley. The former is based on a comparison with observations from the operational measurement network of MeteoSwiss, while the latter uses data from a wind profiler stationed at Sion airport.</p>

Local katabatic winds of the Russian Federation and their observation from space using SAR imagery.

Data from the spaceborne synthetic aperture radars (SAR) provide new opportunities for observing and studying local katabatic winds (bora, foehn) in various marine regions of the Russian Federation and adjacent countries. The impact of these winds on the characteristics of small-scale wind waves leads to the formation of characteristic manifestations on the sea surface which are displayed on SAR images. Satellite SAR images, in contrast to sub-satellite observations, make it possible to see the phenomenon in the coastal zones of seas and large lakes, judge the spatial scale of the phenomenon and determine a number of it quantitative characteristics. Analysis of collected SAR images shows that local winds, bora-like and foehn-like, have similar characteristics and cover vast areas of the inland and marginal seas of the Russian Federation. The similarity of the surface manifestations of the local winds, clearly speaks about the same physical and aerohydrodynamic mechanisms of their display on SAR images. It is shown that spaceborne SAR data and images, which are two-dimensional spatial patterns of frozen wind, are extremely useful for research and monitoring local winds over the seas of the Russian Federation, especially where the network of weather stations is extremely rare.

LACUNARITY AS INDEX OF EVALUATION OF WIND DIRECTION IN PERNAMBUCO

Wind direction data were recorded from January 2008 to February 2011, at nine weather stations (Recife, Caruaru, Arcoverde, Garanhuns, Surubim, Floresta, Ibimirim, Serra Talhada and, Cabrobó), in the state of Pernambuco, Brazil, operated by the Instituto Nacional de Meteorology (INMET). Lacunarity analysis was performed in order to evaluate wind direction on those weather stations. In Recife the predominance of the wind was in the east (E)-southeast (SE) direction. In the agreste of the state of Pernambuco the predominant direction of the wind is the same one of Recife. In the Sertão of Pernambuco the wind predominates in the east (E)-sul (S) direction. Small values of lacunarity are caused by the presence of local winds, while large values of lacunarity are caused by lack of wind in a certain direction.

Respective Roles of the Guinea Current and Local Winds on the Coastal Upwelling in the Northern Gulf of Guinea

The northern Gulf of Guinea is a part of the eastern tropical Atlantic where oceanic conditions due to the presence of coastal upwelling may influence the regional climate and fisheries. The dynamics of this coastal upwelling is still poorly understood. A sensitivity experiment based on the Regional Oceanic Modeling System (ROMS) is carried out to assess the role of the detachment of the Guinea Current as a potential mechanism for coastal upwelling. This idealized experiment is performed by canceling the inertia terms responsible for the advection of momentum in the equations and comparing with a realistic experiment. The results exhibit two major differences. First, the Guinea Current is found to be highly sensitive to inertia, as it is no longer detached from the coast in the idealized experiment. The Guinea Current adjusts on an inertial boundary layer, the inertial terms defining its lateral extension. Second, the upwelling east of Cape Palmas disappears in absence of the Guinea Current detachment. This is in contrast with the upwelling east of Cape Three Points, which is still present. The results suggest that two different generation processes of the coastal upwelling need to be considered: the upwelling east of Cape Palmas (which is due to inertia, topographic variations, and advective terms effects resulting in important vertical pumping) and the upwelling east of Cape Three Points (which is principally induced by local winds). In addition to recent work ruling out the role of eddies, this study clarifies the processes responsible for this coastal upwelling.