Synoptic Wind Research Articles

Three-dimensional landscape features impact on urban surface wind velocity during a heatwave: Relative contribution and marginal effect

Accelerating the flow of surface air through urban areas at a faster rate is one of the important nature-based solutions for reducing the threat of urban overheating. Previous studies have focused on analyzing the correlation between two-dimensional landscape patterns and sky conditions. However, the relative contribution of three-dimensional (3D) landscape features to urban wind and the marginal effect during a heatwave remain unclear. In this study, the Weather Research and Forecasting (WRF) model was used to simulate the development of the wind field during heat events with weak synoptic wind. The regions were clustered based on land cover characteristics. The impact of 3D landscape features on the wind velocities in each cluster was further explored. Results revealed that ventilation corridors predominantly occurred in the morning, dissipating by midday. Diurnal wind velocities were primarily influenced by Forest Canopy Density (FCD), Building Congestion (BC), and Landscape Shape. Specifically, in suburban areas, the negative effect on surface wind velocities stabilized when BC exceeded 0.12. This phenomenon also occurred when the FCDs were higher than 0.75. Based on these findings, the study proposes urban planning strategies aimed at enhancing natural ventilation in cities, assisting planners in developing sustainable cities with cool winds.

Study on the response of a super high-rise guyed mast under synoptic winds based on aeroelastic wind tunnel test

The present study examines the aeroelastic properties and wind-induced displacement response of a super high-rise guyed mast, through a series of aeroelastic model wind tunnel tests. The simulated guyed mast with a prototype height of 356 m is a representative guyed mast in Asia and has not been reported in previous literature. The impact of wind speed on both the alongwind and crosswind displacement response and the Gaussianity along the heights of the aeroelastic model is then investigated using wind tunnel measurements. Furthermore, the characteristics of mode participation and the effect of wind velocity on this phenomenon, as well as the contributions of background and resonant dynamic response, are examined in both the alongwind and crosswind directions. The results indicate that the guyed mast displacement distributions along the heights are different from those observed in the conventional self-standing lattice towers. The characteristics of multi-mode participation are notable. As wind speeds increase, the alongwind resonant response peaks shift to lower frequencies and become less distinct. In contrast, the crosswind response peaks show no significant variation. The contributions of background and resonant response along the heights, respectively, exhibit a decreasing and an increasing tendency, and wind speed exerts an influence on these phenomena.

Bottom–up propagation of synoptic wind intensification and relaxation in the planktonic ecosystem of the South Senegalese Upwelling Sector

ABSTRACT Synoptic intensification or relaxation of upwelling favorable winds are major sources of variability in eastern boundary upwelling systems. This study aims to investigate their impact on the planktonic ecosystem of the South Senegalese Upwelling Sector (SSUS), located south of the Cape Verde peninsula over a wide and shallow continental shelf. Numerical experiments using a three-dimensional coupled physical–biogeochemical model with four plankton functional types simulated the response of the coastal planktonic ecosystem to idealized synoptic (∼10 days) wind intensification and relaxation of the same amplitude. We find that these perturbations induce spatio-temporal oscillations of plankton concentrations. Zooplankton response occurred with a time lag that manifests itself in space as an equatorward/downstream shift in distribution relative to phytoplankton. Overall, the transmission of the synoptic perturbation from the physics to zooplankton is characterized by a damping in relative anomalies. All these elements and the weakness of the asymmetries in the biogeochemical/planktonic ecosystem responses between intensification and relaxation events support the hypothesis that synoptic variability has limited impact on the climatological state of low–latitude upwelling systems such as the SSUS. PLAIN LANGUAGE SUMMARY In some coastal regions of the world such as off Senegal, winds preferentially blow alongshore and induce subsurface, cold and nutrient rich waters to rise to the surface layer and favor the development of plankton blooms. These so-called upwelling favorable winds are not steady. Their fluctuations produce dynamical and biogeochemical variability over a broad range of scales. Here, we studied the biogeochemical effect of 10-day (i.e. weather or synoptic) wind fluctuations over the southern Senegal continental shelf. We used a numerical model with a simplified planktonic ecosystem consisting of two phytoplankton and two zooplankton size classes. The wind perturbations modulate ocean physics, the enrichment of the sun-lit surface layer in nutrients and the planktonic ecosystem. The plankton’s response to wind fluctuations exhibited oscillations more complex and relatively less intense than those of the wind. The modest effect of the studied short-term wind fluctuations on plankton found in this study may be specific to low-latitude coastal oceans with wide continental shelves.

Developing an Explainable Variational Autoencoder (VAE) Framework for Accurate Representation of Local Circulation in Taiwan

AbstractThis study develops an explainable variational autoencoder (VAE) framework to efficiently generate high‐fidelity local circulation patterns in Taiwan, ensuring an accurate representation of the physical relationship between generated local circulation and upstream synoptic flow regimes. Large ensemble semi‐realistic simulations were conducted using a high‐resolution (2 km) model, TaiwanVVM, where critical characteristics of various synoptic flow regimes were carefully selected to focus on the effects of local circulation variations. The VAE was constructed to capture essential representations of local circulation scenarios associated with the lee vortices by training on the ensemble data set. The VAE's latent space effectively captures the synoptic flow regimes as controlling factors, aligning with the physical understanding of Taiwan's local circulation dynamics. The critical transition of flow regimes under the influence of southeasterly synoptic flow regimes is also well represented in the VAE's latent space. This indicates that the VAE can learn the nonlinear characteristics of the multiscale interactions involving the lee vortex. The latent space within VAE can serve as a reduced‐order model for predicting local circulation using synoptic wind speed and direction. This explainable VAE binds the physical reasoning to the predictions of the local circulation that ensures the physical examination of the uncertainty in accelerating the local weather assessments under various climate change scenarios.

Tornado-induced instability assessment of super large hyperbolic reinforced concrete cooling towers

Cooling towers are typical high-rise thin-walled structures which are of hyperbolic rotating shell structure type and significantly sensitive to wind loads. Wind-related local instability is the key control factor in the design of structural geometric shape and tower shell thickness optimization. In fact, this kind of stability analysis has only conducted aiming at normal climate (such as monsoon, etc.) under the guideline of series of national Codes. In order to deal with the issues under disaster climate, physical and numerical investigation to evaluate local stability performance of a super large cooling tower (SLCT) under tornado environments based on Buckling Stress State (BSS) method is implemented. Besides, whole process elastic–plastic collapse simulation of the SLCT exposed to the tornados was also carried out to study the failure mechanism and re-evaluated the reasonability of the well-accepted BSS method for structural wind-resistant design. The results revealed that the tornados would have obvious adverse effects on the structural local stability when the SLCT is located at the tornado vortex core radius compared with those under traditional synoptic winds. The swirl ratios and the central distances between the SLCT and the tornado vortex core have significant effects on the local instability of the SLCT. The extended elastic–plastic collapse simulation discovered that the position of the first crack during SLCT collapse process is basically consistent with the critical position from the elastic local stability analysis of the SLCT, indicating that strengthening measures can be carried out in advance at the critical position for structural local stability improvement under tornado conditions. Besides, the extended elastic–plastic collapse numerical simulation of the SLCT could be as the effective supplement to the structural elastic stability assessment (such as BSS method) in the wind-resistant design of the SLCT.

A nonlinear approach for the simulation of the buffeting response of long span bridges under non-synoptic storm winds

In recent years, extreme atmospheric events are becoming increasingly frequent and unpredictable. These phenomena are often characterized by low-frequency variations of the wind speed and angle of attack, mainly due to large-scale turbulence. These features can be critical for long-span bridges as they can lead the deck in conditions where the nonlinear effects of aerodynamic forces are enhanced. Therefore, it is increasingly important to develop reliable numerical tools to simulate the response of these structures to non-synoptic winds. In this work, a nonlinear rheological model that is able to account for the large variations in wind speed and angle of attack is employed to investigate the dynamic response of two different bridges subjected to two different wind fields. The first scenario is a standard synoptic wind field used as a baseline. On the other hand, the second wind scenario represents an extreme non-synoptic atmospheric event. The results highlight how the nonlinear effects of the aerodynamic forces, in particular those related to the large variation of the angle of attack, could lead to significant changes in the bridges’ response. These effects would not be captured by employing standard linearized methods.

Mixed Convection in an Idealized Coastal Urban Environment With Momentum and Thermal Surface Heterogeneities

AbstractCoastal marine heatwaves (MHWs) modulate coastal climate through ocean‐land‐atmosphere interactions, but little is known about how coastal MHWs interact with coastal cities and modify urban thermal environment. In this study, a representative urban coastal environment under MHWs is simplified to a mixed convection problem. Fourteen large‐eddy simulations (LESs) are conducted to investigate how coastal cities interact with MHWs. We consider the simulations by simple urban roughness setup (Set A) as well as explicit urban roughness representation (Set B). Besides, different MHW intensities, synoptic wind speeds, surface fluxes of urban and sea patches are considered. Results suggest that increasing MHW intensity alters streamwise potential temperature gradient and vertical velocity direction. The magnitude of vertical velocity and urban heat island (UHI) intensity decrease with increasing synoptic wind speed. Changing urban or sea surface heat flux also leads to important differences in flow and temperature fields. Comparison between Set A and B reveals a significant increase of vertical velocity magnitude and UHI intensity. To further understand this phenomenon, a canopy layer UHI model is proposed to show the relationship between UHI intensity and urban canopy, thermal heterogeneity and mean advection. The effect of urban canopy is considered in terms of an additional vertical velocity scale that facilitates heat transport from the heated surface and therefore increases UHI intensity. The model can well explain the trend of the simulated results and implies that overlooking the effect of urban canopy underestimates canopy UHI in urban coastal environment.

Mechanisms of Offshore Solid and Liquid Freshwater Flux from the East Greenland Current

Abstract The mechanisms that control the export of freshwater from the East Greenland Current, in both liquid and solid form, are explored using an idealized numerical model and scaling theory. A regional, coupled ocean–sea ice model is applied to a series of calculations in which key parameters are varied and the scaling theory is used to interpret the model results. The offshore ice flux, occurring in late winter, is driven primarily by internal stresses and is most sensitive to the thickness of sea ice on the shelf coming out of Fram Strait and the strength of alongshore winds over the shelf. The offshore liquid freshwater flux is achieved by eddy fluxes in late summer while there is an onshore liquid freshwater flux in winter due to the ice–ocean stress, resulting in only weak annual mean flux. The scaling theory identifies the key nondimensional parameters that control the behavior and reproduces the general parameter dependence found in the numerical model. Climate models predict that winds will increase and ice export from the Arctic will decrease in the future, both of which will lead to a decrease in the offshore flux of sea ice, while the influence on liquid freshwater may increase or decrease, depending on the relative changes in the onshore Ekman transport and offshore eddy fluxes. Additional processes that have not been considered here, such as more complex topography and synoptic wind events, may also contribute to cross-shelf exchange. Significance Statement The purpose of this study is to provide a basic understanding of what controls the flux of sea ice and low-salinity water from the East Greenland shelf into the interior of the Greenland and Iceland Seas. This is a potentially important process since it has been shown that sufficient freshening of the surface waters in the interior of the Nordic seas can inhibit deep convection and the associated air–sea heat flux and water mass transformation. A combination of idealized computer models and basic theory indicates that the fluxes of liquid and solid freshwater are controlled by different mechanisms and occur at different times of the year. Accurate representation in climate models will require representation of small-scale processes such as mesoscale eddies and gradients of ice thickness across the shelf.

Local Controls on Near‐Surface Glacier Cooling Under Warm Atmospheric Conditions

AbstractThe near‐surface boundary layer can mediate the response of mountain glaciers to external climate, cooling the overlying air and promoting a density‐driven glacier wind. The fundamental processes are conceptually well understood, though the magnitudes of cooling and presence of glacier winds are poorly quantified in space and time, increasing the forcing uncertainty for melt models. We utilize a new data set of on‐glacier meteorological measurements on three neighboring glaciers in the Swiss Alps to explore their distinct response to regional climate under the extreme 2022 summer. We find that synoptic wind origins and local terrain modifications, not only glacier size, play an important role in the ability of a glacier to cool the near‐surface air. Warm air intrusions from valley or synoptically‐driven winds onto the glacier can occur between ∼19% and 64% of the time and contribute between 3% and 81% of the total sensible heat flux to the surface during warm afternoon hours, depending on the fetch of the glacier flowline and its susceptibility to boundary layer erosion. In the context of extreme summer warmth, indicative of future conditions, the boundary layer cooling (up to 6.5°C cooler than its surroundings) and resultant katabatic wind flow are highly heterogeneous between the study glaciers, highlighting the complex and likely non‐linear response of glaciers to an uncertain future.

Two-year wind field measurements near the ground at a site of the Tibetan Plateau

A nearly two-year wind field measurement in the plateau has been conducted in the south of Tibet. High-frequency anemometric data of the distinctive plateau wind field was obtained. Combining the non-stationary model and test, wind samples are classified into three types of 10-min samples based on the level of stationarity. Analysis reveals the strong non-stationarity, turbulence intensity, gust factor, and integral length scale of the synoptic wind in the plateau, which differ from the ones at low altitudes. The stationary samples are recommended to represent the plateau synoptic wind for characterizing the fluctuating wind. At smaller time scales, high-frequency records capture some intense gust events. Based on the different influences of wind on the structures from the perspective of structural wind resistance, the plateau transient intense gust events are divided into thunderstorms and front, and short-rise-time gusts. Representative gust events are defined, sifted, and extracted. With the combination analysis of 10-min fluctuating wind characteristics and intense non-stationary gust events, the measurement data assist the structural wind-resistance design in the plateau.

Water vapour exchange between the atmospheric boundary layer and free troposphere over eastern China: seasonal characteristics and the El Niño–Southern Oscillation anomaly

Abstract. This study develops a quantitative climatology of water vapour exchange between the atmospheric boundary layer (ABL) and free troposphere (FT) over eastern China. The exchange flux is estimated for January, April, July and October over 7 years based on a water vapour budget equation using simulated meteorological data. The spatiotemporal characteristics and occurrence mechanism of ABL–FT water vapour exchange and its relationship with the El Niño–Southern Oscillation (ENSO) are revealed: (1) the vertical exchange flux varies regionally and seasonally, with downward transport to maintain ABL moisture during winter and autumn in the northern region and persistent output to humidify the FT in the southern region, particularly in summer. Additionally, the vertical exchange flux is also topographic dependent. (2) The vertical motion at the ABL top, which is produced by the dynamic forcing of the terrain on synoptic winds, is the dominant mechanism for the water vapour vertical exchange over the long-term average. The evolution of the vertical exchange flux within 1 d scale is driven by the ABL diurnal cycle. (3) The interannual variation of water vapour vertical exchange is correlated with ENSO. A triple antiphase distribution with negative–positive–negative anomalies from north to south exists in La Niña years (and vice versa in El Niño years), which corresponds to the spatial pattern of anomalous precipitation. This phenomenon is mainly due to the alteration of vertical velocity and water vapour content at the ABL top varying with ENSO phases. These results provide new insight into understanding the atmospheric water cycle.

Processes governing the surface ozone over a tropical hill station in the Western Ghats

Tropospheric ozone (O3) plays predominant role in atmospheric chemistry, exacerbates the air quality, and contributes to the climate change. Near the Earth's surface, O3 levels exhibit large heterogeneity due to diverse emissions of precursors and effects of meteorological conditions. Nevertheless, the understanding of key dynamical and photochemical processes governing O3 remains limited in the Western Ghats, a tropical region of immense significance in context of the geosphere-biosphere processes. In this regard, we combined surface O3 measurements at Ponmudi (8.758° N, 77.114° E, ∼1 km above mean sea level–amsl), a high-altitude site in the Western Ghats, with ground- and balloon-borne O3 measurements at western coast of India (Thumba: 8.542° N, 76.858° E, ∼3 m amsl) and photochemical box model simulations. O3 diurnal variation exhibits a small amplitude (3–9 ppbv) with lower values during the daytime, in contrast to substantial urban O3 build-up (25–37 ppbv) at Thumba. The influence of regional pollution from the urban boundary layer, downdraft of O3-rich air during night, and dry deposition processes are suggested to govern the O3 diurnal pattern over Ponmudi. Lower O3/CO and O3/NO2 ratios indicating lower O3 production efficiency, and dominant role of dynamics are consistently seen over the study region. O3 variability between Ponmudi and Thumba are found to be well correlated (r = 0.7–0.8) during pre-monsoon and post-monsoon seasons as the sea breeze circulation transport the airmass from coast to the Western Ghats during the daytime. Mean O3 levels at Ponmudi are typically lower than those above Thumba showing an effective O3 loss towards Ponmudi. Chemistry involving strong natural emissions (e.g., isoprene) as simulated by photochemical box model, and greater dry deposition tend to supress O3 build up over this densely vegetated tropical region. Unlike other high-altitude sites, O3 seasonal cycle at Ponmudi is associated closely with synoptic wind changes, and peaks during the winter owing to the transport from Indo Gangetic Plain/northern India. Our study highlights the roles of regional pollution as well as natural processes including biogenic emissions in governing the surface O3 variability over the Western Ghats.

RETRIEVAL OF SURFACE CURRENT FROM HIMAWARI-8 SEA SURFACE TEMPERATURE DATA AND PARTICLE IMAGE VELOCIMETRY METHOD

As human activity occurs at the surface, which is influenced by surface currents, understanding surface currents is crucial. Ocean currents are not solely caused by wind, but also of other factors, such as sea surface temperature. To obtain surface current data, BMKG used HF radar installed in several places, including Flores Sea. This location is significant because it has large ports and heavy crossing traffic. This study aims to analyse surface current data retrieve from Himawari-8 SST data by applied PIV algorithm. Using the PIV algorithm, a cross-correlation plane is generated by comparing two identically sized interrogation windows obtained from successive images. On 5 December 2022 in the Flores Sea, Himawari-8 SST data was employed to estimate sea surface currents every 10 minutes. Surface current motion varies widely from image to image. Western areas are dominated by westward currents, while central and eastern areas are dominated by eastward currents during daylight hours, and westward currents during the night. Synoptic wind affects surface current movement during those hours. Validation with observational data from the Labuan Bajo HF radar shows that the V component current estimation is better than the U component current estimation. This is particularly prevalent in the south and in areas close to the KAWA radar HF location.
 Keywords: Flores Sea; SST; Himawari-8; PIV; surface current

Field measurement study of intense thunderstorm outflows characteristics based on 356 m high meteorological tower

Based on the wind speed records obtained by 356-m-high Shenzhen meteorological gradient tower (SZMGT) during 2019–2020, 10 sets of typical intense thunderstorm outflow records were obtained by screening. This paper suggests that moving average period T=60s is a suitable choice based on the correlation between time-varying mean wind and fluctuating wind. In order to discuss the wind characteristics of thunderstorm flow more precisely, it is divided into ramp-up stage, peak stage, and dissipation stage, and the average wind characteristics and fluctuating wind characteristics are analyzed in detail. Analysis revealed the change of average wind angle is usually caused by the movement of the downburst. The shape of the downburst flow profile is time-varying and has certain differences from several empirical profiles. The dissipation stage is closer to synoptic wind in terms of the wind profile than the ramp-up and peak stages. The turbulence intensity of downbursts is not significantly related to the height, but it is more significantly related to the average wind speed as well as the gust factor.

Sea-land breezes in the Guangdong- Hong Kong- Macau Greater Bay Area coastal zone from 2013 to 2022

Sea-land breezes (SLBs11SLB, sea-land breeze; GBA, Greater Bay Area) are mesoscale circulation phenomena that significantly affect weather and air quality in coastal regions. The Guangdong–Hong Kong–Macau Greater Bay Area (GBA), one of the most densely populated and economically developed regions in China, experiences frequent SLB intrusion. In this study, we examined the SLB features in the GBA from 2013 to 2022 based on observations, focusing particularly on the influence of synoptic conditions on SLB behaviour and their interplay. The annual average daily sea and land wind speeds ranged from 2.8 to 3.2 m/s and 1.9 to 2.2 m/s, and from 1.8 to 2.2 m/s and 1.6 to 1.9 m/s in the eastern and western GBA, respectively. The start time of sea (land) winds first appeared at 0000 (1100) UTC and finally occurred at 0900 (2000) UTC. Climatologically, SLBs were observed more frequently when southerly synoptic winds prevailed in the GBA. SLBs were stronger under synoptic northerly winds, but weaker when synoptic southerly winds prevailed. The diurnal evolution amplitude of SLB strength was much more significant under the control of synoptic northerly winds. In addition, SLBs modified synoptic winds, leading to the distortion of the observed diurnal wind patterns. A southerly increment in synoptic winds was observed from noon to early night on SLB days, whereas a northerly increment was observed from midnight to morning. Northerly synoptic winds weakened or even transformed into southerly winds in the afternoon, whereas southerly synoptic winds were found to decrease or even turn northerly at night. Our study provides an integrated understanding of SLBs in the GBA, especially regarding the behaviour of SLBs under various synoptic conditions and their modification on synoptic winds that reshape the observed wind patterns. These results provide useful information for weather simulations in coastal areas.

Dynamic properties of an aeroelastic transmission tower subjected to synoptic and downburst-like outflows

Electrical transmission towers can be vulnerable to high intensity non-synoptic wind events such as downbursts. This paper compares the wind-induced response of a single self-supported transmission tower subjected to experimentally produced downburst outflows and synoptic (i.e., atmospheric boundary layer (ABL)) winds. Wind tunnel tests were carried out on a 1:50 aeroelastic model of the tower. A similar mean wind speed was produced at 1/6th of tower height and tower height in the downburst and synoptic simulations, respectively. Lower drag coefficients were observed under downburst winds in comparison to synoptic winds for the case tested. Lower peak base shear and base moments were subsequently observed in the downburst case. However, the results indicate that the base dynamic response of a self-supported tower can be slightly higher under downburst wind loads in comparison to synoptic winds. Higher dynamic amplification factors (DAF) and deviations from the mean were observed in the base dynamic response to downburst winds in comparison to the synoptic case. This indicates that self-supported towers can be subjected to more wind-induced vibrations under downburst winds with similar peak wind speeds as the synoptic winds.

The influence of synoptic wind on land–sea breezes

AbstractParticularly challenging classes of heterogeneous surfaces are ones where strong secondary circulations are generated, potentially dominating the flow dynamics. In this study, we focus on land–sea breeze (LSB) circulations resulting from surface thermal contrasts, in the presence of increasing synoptic pressure forcing. The relative importance and orientation of the thermal and synoptic forcings are measured through two dimensionless parameters: a heterogeneity Richardson number (measuring the relative strength of geostrophic wind and convection induced by buoyancy), and the angle α between the shore and geostrophic wind. Large‐eddy simulations reveal the emergence of various regimes where the dynamics are asymmetric with respect to α. Along‐shore cases result in deep LSBs similar to the scenario with no synoptic background, irrespective of the geostrophic wind strength. Across‐shore simulations exhibit a circulation cell that decreases in height with increasing synoptic forcing. However, at the highest synoptic winds simulated, the circulation cell is advected away with sea‐to‐land winds, while a shallow circulation persists for land‐to‐sea cases. Scaling analysis that relates the internal parameters Qshore (net shore volumetric flux) and qshore (net shore advected kinematic heat flux) to the external input parameters results in a succinct model of the shore fluxes that also helps explain the physical implications of the identified LSBs. Finally, the vertical profiles of the shore‐normal velocity and shore‐advected heat flux are used, with the aid of k‐means clustering, to independently classify the LSBs into four regimes (canonical, sea‐driven, land‐driven, and advected), corroborating our visual categorization.

Design load provisions for simulating the critical effect of downbursts on wind turbines

Wind turbines are among the rapidly growing sources of sustainable energy. The review of design codes for this type of structure shows a lack of procedures for estimating the wind loads on wind turbines due to high-intensity wind events such as downbursts. There is a challenge in the analysis and design of wind turbines under downbursts because of the sudden and localized nature of such events, which makes the forces acting on the tower and blades dependent on the characteristics of the event. As such, the objective of the current study is to develop design load provisions that can simulate the critical effect of downbursts on wind turbines. These provisions are developed in two phases. Identifying the peak effects of the moving mean component of the downburst and determining the associated critical profiles are the aim of the first phase. To achieve this task, a comprehensive parametric study is conducted using the previously developed numerical model, HIW-TUR, on a wide range of wind turbine sizes and airfoil types in order to assess the critical response of wind turbines under the mean component of downbursts. The study takes into account the variations in the downburst size and its location relative to the tower center. Then, dynamic analyses under turbulence are conducted in the second phase using the open-source code, FAST, to determine a downburst gust response factor to magnify the effect of the mean component. The downburst gust response factor is then superimposed with the mean component profiles to present a complete set of design provisions. An example is presented to demonstrate the application of the developed loading provisions on a real wind turbine and to compare with the extreme synoptic wind load cases specified by the International Electro-technical Commission Loading Code.

Atmospheric highs drive asymmetric sea ice drift during lead opening from Point Barrow

Abstract. Throughout winter, the winds of migrating weather systems drive the recurrent opening of sea ice leads from Alaska's northernmost headland, Point Barrow. As leads extend offshore into the Beaufort and Chukchi seas, they produce sea ice velocity discontinuities that are challenging to represent in models. We investigate how synoptic wind patterns form leads originating from Point Barrow and influence patterns of sea ice drift across the Pacific Arctic. We identify 135 leads from satellite thermal infrared imagery between January–April 2000–2020 and generate an ensemble of lead-opening sequences by averaging atmospheric conditions and ice velocity across events. On average, leads open as migrating atmospheric highs drive differing ice–coast interactions across Point Barrow. Northerly winds compress the Beaufort ice pack against the coast over several days, slowing ice drift. As winds west of Point Barrow shift offshore, the ice cover fractures and a lead extends from the headland into the pack interior. Ice west of the lead accelerates as it separates from the coast, drifting twice as fast (relative to winds) as ice east of the lead, which remains coastally bound. Consequently, sea ice drift and its contribution to climatological ice circulation becomes zonally asymmetric across Point Barrow. These findings highlight how coastal boundaries modify the response of the consolidated ice pack to wind forcing in winter, producing spatially varying regimes of ice stress and kinematics. Observed connections between winds, ice drift, and lead opening provide test cases for sea ice models aiming to capture realistic ice transport during these recurrent deformation events.

Thunderstorm gust response factor: A closed-form solution

The Davenport gust factor technique is an efficient approach for the estimate of the wind loading on structures due to synoptic winds and the availability of closed-form solutions favoured its implementation in codes and standards. The gust response factor was generalized for thunderstorm outflows based on the definition of suitable equivalent parameters to account for the nonstationary characteristics of the wind velocity. Its sensitivity to the shape of the slowly-varying mean wind velocity was investigated, showing that it has a significant impact on the gust response factor, especially when the structure is lowly-damped. In order to simplify the derivation of the gust response factor the present paper outlines the derivation of a closed-form solution for the equivalent parameters, starting from the approximation of the time-varying variance of the response. The gust response factor derived through the closed-form solution proposed is compared with numerical solution and the existing formulation from literature. Results show that the proposed solution is very accurate and accounts for the transient dynamic effects neglected by the existing formulation, providing an efficient and handy tool for the structural design.