Local Wind Regime Research Articles

Parabolic dune distribution, morphology and activity during the last 20 000 years: A global overview

AbstractParabolic dunes form and migrate in almost every climate and geographic zones of the world, ranging from the tropical coastlines to the arid continental deserts. Despite their extensive distribution and their importance within the aeolian sediment landscape, the understanding of their morphological development, activity and link with climates remains somewhat limited to local or regional scales. A good understanding of the present climate conditions under which parabolic dunes are formed and/or reactivated would be significantly helpful to constrain past climate models. Similarly, an improved knowledge of parabolic dunes behaviour during past climatic episodes would provide some valuable long‐term data to better predict their future activity. This review first aims at providing a non‐exhaustive global database on parabolic dune morphology and the present wind regimes with which they are associated. To do so, the morphology of 750 dunes distributed worldwide was first analysed using a high‐resolution global digital elevation model, suggesting an intrinsic relationship between the different measured morphoparameters. The analysis of the associated local wind regimes shows that parabolic dunes develop under strong unidirectional winds, which are more conspicuous in coastal than continental environments. Dunes of different ages are globally aligned with present prevailing winds, which suggests a prevalent control of long‐term global atmospheric circulation on dune orientations. Finally, this study explores the link between parabolic dune activity and climates over the past 20 000 years by reviewing ages from the literature and combining them with the ones compiled in the INQUA Dunes Atlas Chronologic Database. Overall, it appears that changes towards drier conditions have triggered dunes migration during both warm and cold periods of the Last Glacial Maximum, Holocene Climate Optimum, Roman Climate Optimum, Medieval Climate Optimum and Little Ice Age. The present day aeolian activity is predominantly linked with deteriorating environmental conditions caused by human disturbances.

Coastal plumes contribution to the suspended sediment transport in the Southwest Atlantic inner continental shelf

Global coastal zones are constantly changing due to the actions of various physical forces. Recent studies show that the supply of suspended sediment of continental origin plays an important role in these changes. Once in the coastal region, this sediment significantly influences the sedimentation process on the inner shelf. Thus, understanding the transport and destination of these suspended sediments is crucial to interpret the morphodynamic evolution of the seabed and biogeochemical processes in the ocean. The Southwest Atlantic Shelf is the largest continental shelf in the Southern Hemisphere and one of the most important in biological production, because of the great continental contribution exercised by both Río de la Plata and Patos Lagoon. Studies in the region showed that these effluents are significantly affected by the El Niño–Southern Oscillation (ENSO) effect, which can interfere with the availability of suspended material inserted into the coastal region. Despite the great efforts of several authors to understand these changes and their interactions with the environment, some questions remain unanswered. Thus, this work aims to fill this gap by answering questions related to the contribution of suspended sediment of continental origin and its behaviour on the Southwest Atlantic Inner Shelf. The behaviour of suspended sediment was investigated in two distinct periods using the hydro-morphodynamic model TELEMAC-3D: one representing normal years, that is, without the effect of ENSO (2005–2006) and the other experiencing the effect of ENSO (2008–2009).The model was calibrated and validated using field data for both studied periods. R esults were based on statistical analysis, such as wavelet and empirical orthogonal function (EOF) analysis, in addition to time series analysis. Results showed that the Southwest Atlantic Inner Shelf is mainly influenced by the fluvial discharge of Río de la Plata and Patos Lagoon, and by the local wind. Río de la Plata is the largest exporter of suspended sediment in the region, with an approximate rate of 1.2 × 108 tons.year-1 in neutral (normal) years and 3.0 × 108 tons.year-1 in years under the influence of ENSO. The Patos Lagoon, on the other hand, exports approximately 1.25 × 107 tons.year-1 in the period without the ENSO effect and 1.35 × 107 tons.year-1 in the period influenced by ENSO. Results also showed that the fluvial discharge interacts with the suspended sediment in seasonal to interannual scales, while the wind contributes to the concentration of suspended sediment on synoptic scales. Still on the wind regime, results show that the local wind regime gains importance particularly when the suspended sediment reaches the coastal region.

Local Wind Regime Induced by Giant Linear Dunes: Comparison of ERA5-Land Reanalysis with Surface Measurements

Emergence and growth of sand dunes results from the dynamic interaction between topography, wind flow and sediment transport. While feedbacks between these variables are well studied at the scale of a single and relatively small dune, the average effect of a periodic large-scale dune pattern on atmospheric flows remains poorly constrained, due to a pressing lack of data in major sand seas. Here, we compare local measurements of surface winds to the predictions of the ERA5-Land climate reanalysis at four locations in Namibia, both within and outside the giant linear dune field of the Namib Sand Sea. In the desert plains to the north of the sand sea, observations and predictions agree well. This is also the case in the interdune areas of the sand sea during the day. During the night, however, an additional wind component aligned with the giant dune orientation is measured, in contrast to the easterly wind predicted by the ERA5-Land reanalysis. For the given dune orientation and measured wind regime, we link the observed wind deviation (over $$50^{\circ }$$ ) to the daily cycle of the turbulent atmospheric boundary layer. During the night, a shallow boundary layer induces a flow confinement above the giant dunes, resulting in large flow deviations, especially for the slower easterly winds. During the day, the feedback of the giant dunes on the atmospheric flow is much weaker due to the thicker boundary layer and higher wind speeds. Finally, we propose that the confinement mechanism and the associated wind deflections induced by giant dunes could explain the development of smaller-scale secondary dunes, which elongate obliquely in the interdune areas of the primary dune pattern.

On the diurnal cycle of rainfall and convection over Lake Victoria and its catchment. Part 2: Meteorological factors in the diurnal and seasonal cycles

AbstractThe purpose of this article is to determine the meteorological factors controlling the lake-effect rains over Lake Victoria. Winds, divergence, vertical motion, specific humidity, Convective Available Potential Energy (CAPE), and Convective Inhibition (CIN) were examined. The local wind regime and associated divergence/convergence are the major factors determining the diurnal cycle of rainfall over the lake and catchment. The major contrast between over-lake rainfall in the wet- and dry-season months is the vertical profile of omega. This appears to be a result of seasonal contrasts in CAPE, CIN, and specific humidity, parameters that play a critical role in vertical motion and convective development.

Parametric CFD analysis of the taper ratio effects of a winglet on the performance of a Horizontal Axis Wind Turbine

Winglets have been used to augment the power extraction of Horizontal Axis Wind Turbines (HAWT). However, despite some understanding on the way they affect the aerodynamics of wind turbines, the influence of specific geometric parameters still requires investigations. To assist with the resolution of this problem, this paper describes the influence of taper ratio and root chord ratio of a winglet on power and thrust coefficients and annual energy output (AEO) of a HAWT. Computational Fluid Dynamics (CFD) simulations obtained the effects by numerically solving the Reynolds-Averaged Navier–Stokes (RANS) equations in steady state using the κ-ω SST turbulence model and a moving reference frame methodology. New Mexico wind turbine experimental data validated the computational results, and computational analyses of the winglets were compared with the validated simulations. The set of winglets is composed by twelve configurations, and the results reveal a higher aerodynamic efficiency with a lower taper ratio and a lower root chord ratio, suggesting winglets can be optimized for enhancing the performance of the horizontal axis wind turbines. Besides that, the AEO is sensitive to the local wind regime and the utilization of winglets is recommended for sites with a medium to high mean wind speed.

Atmospheric CO2 Exchange of a Small Mountain Lake: Limitations of Eddy Covariance and Boundary Layer Modeling Methods in Complex Terrain

AbstractLakes receive and transform significant amounts of terrestrial carbon and are often considered a source of atmospheric carbon dioxide (CO2). Yet, continuous direct measurements of lake‐atmosphere CO2 exchange with high temporal resolution are sparse. In this study, we measured the CO2 exchange of a mountain lake in the eastern Austrian Alps continuously for one year using the eddy covariance (EC) and the boundary layer model (BLM) approaches. Results from both the EC and the BLM methods indicated the lake to be a small source of atmospheric CO2 with highest emissions in fall. EC flux measurements were affected by low‐frequency contributions especially during low wind conditions. The CO2 concentration gradient at the air‐water interface decreased during night‐time due to an increase in atmospheric CO2 above the lake, likely caused by cold and CO2‐rich air draining from the surrounding land. Consequently, BLM fluxes were lower during night‐time than during daytime. This diel pattern was lacking in the EC flux measurements because the EC instruments deployed at the shore of the lake did not capture low nocturnal lake CO2 fluxes due to the local wind regime. Overall, this study illustrates the effect of the surrounding landscape on lake‐atmosphere flux measurements. We conclude that estimating CO2 evasion from lakes situated in complex topography needs to explicitly account for biases in EC flux measurements caused by low‐frequency contributions and local wind regimes.

Day-ahead wind-thermal unit commitment considering historical virtual wind power data

The uncertainty in wind power affects the generation scheduling (unit commitment) of coal-dominated power systems. A reasonable spinning reserve is required to handle this uncertainty. In this study, a method that considers the unique local wind regime into the calculation of spinning reserve requirements and makes the unit commitment more local-adaptive is presented. First, a virtual wind power transfer matrix which displays the probabilities of wind power transferring from one value to another by using the historical wind speed data is formulated. Second, the spinning reserve requirements of the wind-thermal power system are calculated according to the virtual wind power transfer matrix. Finally, the day-ahead unit commitment is conducted based on the spinning reserve calculation. The main advantage of using historical virtual wind power data, instead of historical wind speed data, is the acquisition of real wind power transfer probabilities, which avoids the distortion caused by the nonlinear conversion between wind power and wind speed. Application and comparison studies to demonstrate the effectiveness and cost benefits are performed on two systems. Sensitivity analyses of different parameters used in the method are also investigated.

Triple oxygen isotope systematics of evaporation and mixing processes in a dynamic desert lake system

Abstract. This study investigates the combined hydrogen deuterium and triple oxygen isotope hydrology of the Salar del Huasco, an endorheic salt flat with shallow lakes at its centre that is located on the Altiplano Plateau, N Chile. This lacustrine system is hydrologically dynamic and complex because it receives inflow from multiple surface and groundwater sources. It undergoes seasonal flooding, followed by rapid shrinking of the water body at the prevailing arid climate with very high evaporation rates. At any given point in time, ponds, lakes, and recharge sources capture a large range of evaporation degrees. Samples taken between 2017 and 2019 show a range of δ18O between −13.3 ‰ and 14.5 ‰, d-excess between 7 ‰ and −100 ‰, and 17O-excess between 19 and −108 per meg. A pan evaporation experiment conducted on-site was used to derive the turbulence coefficient of the Craig–Gordon isotope evaporation model for the local wind regime. This, along with sampling of atmospheric vapour at the salar (-21.0±3.3 ‰ for δ18O, 34±6 ‰ for d-excess and 23±9 per meg for 17O-excess), enabled the accurate reproduction of measured ponds and lake isotope data by the Craig–Gordon model. In contrast to classic δ2H–δ18O studies, the 17O-excess data not only allow one to distinguish two different types of evaporation – evaporation with and without recharge – but also to identify mixing processes between evaporated lake water and fresh flood water. Multiple generations of infiltration events can also be inferred from the triple oxygen isotope composition of inflow water, indicating mixing of sources with different evaporation histories. These processes cannot be resolved using classic δ2H–δ18O data alone. Adding triple oxygen isotope measurements to isotope hydrology studies may therefore significantly improve the accuracy of a lake's hydrological balance – i.e. the evaporation-to-inflow ratio (E / I) – estimated by water isotope data and application of the Craig–Gordon isotope evaporation model.

Measuring Ripple and Dune Migration in Coprates Chasma, Valles Marineris: A Source to Sink Aeolian System on Mars?

AbstractActive aeolian systems are present across the martian surface, with active dune fields commonly found in depressions such as craters and valleys. There are many dune fields within the equatorial region of Mars, including Valles Marineris, but the effects of topography on wind regimes and consequently dune migration in Valles Marineris is poorly understood. We investigated both the ripple and dune migration in a dune field in Coprates Chasma using High Resolution Science Experiment Images (HiRISE) and Context Camera (CTX) images. Migration rates of dune brinks and ripples were measured over varying time scales, between Earth years 2007–2014. The dunes here are some of the tallest on Mars, with heights of up to 182 m. The dune brinks are migrating eastwards at a rate of 0.1–0.3 m/EY through the valley due to topographical influences on the local winds. Potential sediment sources for the dune field were identified and investigated by studying thermal inertia and mineralogy. The topographic slope‐related katabatic winds travel down the valley walls and converge with the dominant winds traveling through the center of the valley, causing overall eastwards dune migration. Topography is likely the dominant control on the local wind regime; slope winds travel down the sides of the valley walls and are funneled through the center of the valley. These local winds subsequently facilitate the migration of the large dunes in Coprates Chasma, thus expanding our understanding of local winds in the Martian environment.

Aeolian dunes morphodynamics and wind regime reconstruction in mid-latitudes of the Gondwana during Early Permian, Aracaré Formation, Sergipe-Alagoas Basin, Brazil

Aeolian systems play an important role in palaeoclimatic studies, allowing the inference of arid regions in different geological periods, in addition to being the best records for acquiring palaeowind data. Morphodynamic reconstruction of ancient aeolian dunes is extremely important for understanding the local wind regime. This study aims to contribute to the morphodynamic reconstruction of aeolian deposits of the Aracaré Formation in response to Gondwana's palaeoclimatic variations and to indicate the prevailing wind regime. Permian Aracaré Formation is located in the Sergipe-Alagoas Basin, northeast region of Brazil, and exhibits sand accumulation of successive sets of aeolian cross-strata which are interpreted as dry aeolian system. Aracaré Formation is characterized by smaller cross-bedded sets of barchanoid dunes at the base that are overlaid by larger cross-bedded sets of transverse dunes. Aeolian cross-strata show a repetitive alternation of grainflow and wind-ripple packages, separated by reactivation surfaces indicating seasonal variations in wind direction. Cross-strata mean vectors dip consistently towards ESE when corrected for the palaeogeographic position of the Lower Permian. Cyclic stratification pattern suggests an alternation of westerly transverse winds responsible for dune migration, followed by reverse winds that caused dune reworking and led to the formation of reactivation surfaces and the related deposition of wind-ripple. Sometimes, reverse winds are more intense (storms?), strongly eroding the lee face of the aeolian dunes, generating master reactivation surfaces. The comparison between the wind patterns of Aracaré Formation and Sakmarian climate models showed good correlation with disposition of westerlies wind regime in mid-latitude in Gondwana landmass.

Computational aerodynamics in architectural siting of the structures of agro-industrial complex

The article presents study of wind effect on silo parks, which was carried out by computer simulation methods. A special modeling technique was created as a software module for the Ansys Workbench platform. A finite element mesh was developed in accordance with two requirements. Through the use of this mesh, which doesn’t contain needless elements which can be used for simplification of calculations and reduction of execution time, it is possible to describe the turbulent airflow in sufficient detail. The dimensions of all mesh elements are determined by special relations as the functions of the silo diameter and the Reynolds number. The major stage in this investigation was modeling of various options for flowing silos and their groups. As a result of the study, we have obtained aerodynamic characteristics of individual silos as part of silo parks and plotted charts of the distribution of pressure coefficients over the cylinder surface, changing the size of the silos, distances between them and local wind regime. Based on these data, we have drawn a conclusion about the optimal space planning locations of silos for different wind directions. Visualizations of turbulent flow around models at different speeds have also been obtained in this study.

LONG-TERM SALINITY TENDENCIES IN COASTAL WATERS OF ODESSA REGION, BLACK SEA NORTH-WESTERN PART

Long-term variability of coastal water salinity in the Odessa Region of the North-Western part of the Black Sea (NWBS)is studied using the available information on local river inflows, precipitation and wind regime. The study confirms a strongconnection between the coastal water salinity in the Odessa Region, river runoff into the NWBS region and the regimesof atmospheric circulation over the North Atlantic and Europe. Using the concept of the Black Sea hydrological phasesand their variations under the influence of long-term climate variability, it is predicted that the annual-mean salinity inthe Odessa Region of the NWBS will increase in the coming 6-10 years. This prediction is based on the displacementof trajectories of the majority of cyclones during that period that propagate from the North Atlantic and pass over northernEurope. The displacement will favour a decrease in the Black Sea freshwater balance and, hence, an increase of salinity.In addition, the analysis of wind regime in the Odessa Region of the NWBS in 2000-2019 reveals a decreased frequencyof westward winds and a significantly increased frequency of northerly winds. Assuming that these wind trends continuein the future, and taking into consideration the major hydrodynamic features of the NWBS, it is expected that it will lead toa blocking of freshwater inflow from the Dnieper River mouth into the northern and western coasts of the region. As a result,the increase of annual salinity in the coastal waters will intensify.

Determination of Optimal Parametric Distribution and Technical Evaluation of Wind Resource Characteristics for Wind Power Potential at Jhimpir, Pakistan

The objective of this research work is to analyze wind characteristics and to assess wind power potential by selecting the best fit probability distribution function of Jhimpir Sindh Pakistan. This type of detailed investigation helps wind power generation companies in selecting suitable wind turbine and provides information of wind characteristics of potential site. Eight probability distribution functions are tested on the wind speed data from January 2015 to July 2018. Frequency bins of Weibull and Rayleigh distribution with maximum probabilities of 0.1210 and 0.1143 are most closest representation of our data. In order to, quantitatively analysis which distribution function is best fitting the local wind regime, we have applied the coefficient-of-determination, Kolmogorov-Smirnov, Chi square, Cramer-von Mises, Anderson-Darling tests along with Akaike information and Bayesian information criterion. These statistical test are used to rank the empirical distribution functions in order to identify two distribution function better fitting the actual wind speed data. After selecting two best fitted distribution functions, we analyze wind power potential and compare the error of wind power density based on these distribution functions (Weibull and Rayleigh). The power densities reported varied from 73.67 to 648.73W/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Results indicate that power densities of Weibull and Rayleigh for the candidate site are 84.67-698.65W/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 83.67-1021.4W/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively. The highest error for Weibull and Rayleigh are 0.1850 and 0.5745, respectively. Whereas lowest error are 0.0178 and 0.0180, respectively. Complete analysis suggested that Weibull distribution function is the most suitable for Jhimpir Sindh Pakistan and the studied site is suitable for wind power production. In addition, comprehensive analysis of wind direction at the candidate site suggested that Eastern and Southeastern wind directions are predominant with 38.52% and 33.24% of the total time.

First Evidences of Methyl Chloride (CH3Cl) Transport from the Northern Italy Boundary Layer during Summer 2017

Methyl Chloride (CH3Cl) is a chlorine-containing trace gas in the atmosphere contributing significantly to stratospheric ozone depletion. While the atmospheric CH3Cl emissions are predominantly caused by natural sources on the global budget, significant uncertainties still remain for the anthropogenic CH3Cl emission strengths. In summer 2007 an intensive field campaign within the ACTRIS-2 Project was hosted at the Mt. Cimone World Meteorological Organization/Global Atmosphere Watch global station (CMN, 44.17° N, 10.68° E, 2165 m a.s.l.). High-frequency and high precision in situ measurements of atmospheric CH3Cl revealed significant high-frequency variability superimposed on the seasonally varying regional background levels. The high-frequency CH3Cl variability was characterized by an evident cycle over 24 h with maxima during the afternoon which points towards a systematic role of thermal vertical transport of air-masses from the regional boundary layer. The temporal correlation analysis with specific tracers of anthropogenic activity (traffic, industry, petrochemical industry) together with bivariate analysis as a function of local wind regime suggested that, even if the role of natural marine emissions appears as predominant, the northern Italy boundary layer could potentially represent a non-negligible source of CH3Cl during summer. Since industrial production and use of CH3Cl have not been regulated under the Montreal Protocol (MP) or its successor amendments, continuous monitoring of CH3Cl outflow from the Po Basin is important to properly assess its anthropogenic emissions.

Effects of Wind Velocity and Nebkha Geometry on Shadow Dune Formation

AbstractFlow dynamics and sand deposition processes over nebkhas were investigated using computational fluid dynamics simulations, wind tunnel experiments, and field measurements. The computational fluid dynamics simulations showed that nebkha width affects both the elongation and broadening of the wind shadows. The length of the wind shadows decreased as the wind shear velocity increased, following a power function, irrespective of the width and height of the nebkha. There are some uncertainties about the effect of the aspect ratio of the nebkha on the formation of wind shadows as a result of the omission of the transport of sand in the simulations. It is suggested that the length of wind shadows is dependent on the absolute values of nebkha width and height rather than the nebkha aspect ratio. Although the numerical results were consistent with the results of the wind tunnel experiments, the wind tunnel experiments showed that the height of the nebkha had a negative effect on the elongation of the shadow dunes. The sedimentary structures revealed by ground‐penetrating radar surveys of the dunes in the Taitema Dry Lake, in the eastern Taklimakan Desert, China, showed that the formation of shadow dunes can be divided into three phases. Shadow dunes are initially controlled by horizontal separation flow and then elongate following the same growth mechanisms as linear dunes, eventually breaking up into isolated barchans or short, temporary linear dunes. However, the formation of shadow dunes does not necessarily call for the three phases depending on the local wind regime and sediment supply.

Scarp orientation in regions of active aeolian erosion on Mars

The morphologies of wind-formed features on Mars provide diagnostic information about ancient and modern surface winds. Aeolian erosional features include decimeter-scale ventifacts and kilometer-scale yardangs, but intermediate-scale erosional features are less well-understood. Understanding aeolian erosion may be critical to identifying ancient martian biosignatures. Cosmogenic radiation destroys complex organic molecules during prolonged exposure at the martian surface, but outcrops freshly re-exposed by aeolian erosion provide potential sites where biosignatures could have been protected and made recently available for sampling. Wind-driven scarp retreat has been cited as the cause for young exposure ages measured in Gale crater.Upcoming exploration by the Mars 2020 rover will focus on Jezero crater, another location of extensive aeolian erosion and meter-scale scarps. This work is motivated by the hypothesis that retreating scarps on Mars may prefer orientations that reflect the direction of erosive winds. We mapped scarps in Jezero and Gale craters and compared their orientation distributions with local wind regimes interpreted from other aeolian indicators. No strong correlation between wind direction and scarp orientation was identified. The near-random distribution of scarp orientations suggests that in the locations studied the dominant processes controlling scarp orientation are either processes that do not prefer an orientation (e.g., impact or thermal fracturing processes), or that turbulent flow structures form at the scale of scarp topography and obscure the regional-scale signals of erosion with scarp-scale eddies and flow deflection.

A Validation of ERA5 Reanalysis Data in the Southern Antarctic Peninsula—Ellsworth Land Region, and Its Implications for Ice Core Studies

Climate reanalyses provide key information to calibrate proxy records in regions with scarce direct observations. The climate reanalysis used to perform a proxy calibration should accurately reproduce the local climate variability. Here we present a regional scale evaluation of meteorological parameters using ERA-Interim and ERA5 reanalyses compared to in-situ observations from 13 automatic weather stations (AWS), located in the southern Antarctic Peninsula and Ellsworth Land, Antarctica. Both reanalyses seem to perform better in the escarpment area (&gt;1000 m a.s.l) than on the coast. A significant improvement is observed in the performance of ERA5 over ERA-Interim. ERA5 is highly accurate, representing the magnitude and variability of near-surface air temperature and wind regimes. The higher spatial and temporal resolution provided by ERA5 reduces significantly the cold coastal biases identified in ERA-Interim and increases the accuracy representing the wind direction and wind speed in the escarpment. The slight underestimation in the wind speed obtained from the reanalyses could be attributed to an interplay of topographic factors and the effect of local wind regimes. Three sites in this region are highlighted for their potential for ice core studies. These sites are likely to provide accurate proxy calibrations for future palaeoclimatic reconstructions.

Wind in Jezero Crater, Mars

AbstractWind generates erosional and depositional morphologies across Mars, including in Jezero crater, the planned landing site for the Mars 2020 rover. Known for subaqueously formed sedimentary features, Jezero crater also hosts wind‐formed features that provide insights about the local wind regime. We combine interpretations from dunes, wind streaks, transverse aeolian ridges, and yardangs to holistically understand the recent history of wind in Jezero crater. Together, these features describe modern easterly winds trending toward 263° ± 8° and older southwesterly winds that formed small yardangs. Previous research has suggested that aeolian processes eroded the delta deposit in Jezero crater. We propose early southwesterly winds removed the majority of material, exposing the more lithified units seen today. Modern easterly winds continue to cause erosion, but lithologic heterogeneities remain the dominant control on delta deposit evolution. Aeolian erosion has accentuated existing sedimentary structures, leaving the striking delta remnant seen today.

Dynamical Drivers of the Local Wind Regime in a Himalayan Valley

AbstractUnderstanding the local valley wind regimes in the Hindu‐Kush Karakoram Himalaya is vital for future predictions of the glacio‐hydro‐meteorological system. Here the Weather Research and Forecasting model is employed at a resolution of 1 km to investigate the forces driving the local valley wind regime in a river basin in the Nepalese Himalaya, during July 2013 and January 2014. Comparing with observations shows that the model represents the diurnal cycle of the winds well, with strong daytime up‐valley winds and weak nighttime winds in both months. A momentum budget analysis of the model output shows that in the summer run the physical drivers of the near‐surface valley wind also have a clear diurnal cycle, and are dominated by the pressure gradient, advection, and turbulent vertical mixing, as well as a nonphysical numerical diffusion term. By contrast, the drivers in the winter run have a less consistent diurnal cycle. In both months, the pressure gradient, advection, numerical diffusion, and Coriolis terms dominate up to 5,000 m above the ground. The drivers are extremely variable over the valley, and also influenced by the presence of glaciers. When glaciers are removed from the model in the summer run, the wind continues further up the valley, indicating how the local valley winds might respond to future glacier shrinkage. The spatial variability of the drivers over both months is consistent with the complex topography in the basin, which must therefore be well represented in weather and regional climate models to generate accurate outputs.

Influence of the North Atlantic Oscillation at local and regional scales: a case study of the Belgian coast

Together, large‐scale atmospheric circulation and local winds determine the occurrence of storm surges that may result in disastrous erosion. This study investigates the interrelationships between large‐scale atmospheric flow and local wind regimes as driving factors of erosion at the Belgian coast. The large‐scale atmospheric circulation is examined in terms of the winter North Atlantic Oscillation (NAO) index, and it is analysed and compared with regional‐scale circulation patterns (i.e. circulation weather types) and local wind regimes, on both annual and seasonal timescales. The results indicate that a strengthening of the positive winter NAO phase can result in an increase in the frequencies of west (W), southwest (SW) and northwest (NW) directional weather types, leading to local wind speeds in excess of 8ms−1, propagating towards the coast. These conditions are likely to lead to erosive events at the coast. By contrast, a weakening of the winter NAO phase can favour the development of northeast (NE), north (N), east (E) and southeast (SE) weather types. The NE and E types generate particularly strong winds, which potentially worsen erosion at the coast. The E and SE types do not, however, affect wind at a local scale. Thus, the extent to which the wind regime at the Belgian coast is sensitive to the winter NAO is a function of the equilibrium between the NAO effects and the regional atmospheric flow direction. In this study, a downscaling conceptual model is developed which relates climate to large‐scale and local‐scale coastal erosion forcing factors. A better understanding of the variability of, and the interrelationships between, climate, meteorology and erosion can help us to adapt to the changes in coastal evolution driven by climate change, improving the prospects of long‐term coastal resilience.