To improve the representation of non-breaking wave-induced mixing in regional ocean models, this study compares two representative wave-induced mixing schemes during the stratified seasons of 2018 in the northwestern Pacific. One scheme represents non-local mixing induced by Langmuir circulation (LC), while the other represents local mixing by wave orbital motion (OM). Both schemes enhance vertical mixing in the upper 100 m relative to the control experiment without wave-induced mixing (CR). However, the LC scheme improves the simulation of the mixed layer depth and generally shows better agreement with satellite and in-situ observations than CR, whereas the OM scheme overestimates vertical mixing, resulting in an overly deep mixed layer and pronounced sea surface temperature cold bias, particularly in the northern part of the model domain. These results indicate that the LC scheme involving the combined effects of surface waves and local wind forcing provides a more realistic representation of upper ocean mixing under various conditions. In contrast, the OM scheme depending solely on wave parameters tends to overestimate vertical mixing, especially when the mixed layer is shallow. Furthermore, the analysis shows that the wave orbital velocity and turbulent Langmuir number are nearly uncorrelated because the latter incorporates both wave and wind effects. This finding demonstrates that wave parameters alone are insufficient to characterize non-breaking wave-induced mixing and provides a physical explanation for the overestimated mixing by the OM scheme.
In an era marked by rapid coastal infrastructure development and profound climate change impacts, effective planning and sustainable management of coastal areas integrating scientific knowledge is imperative. Depth of Closure (DoC) stands out as a crucial scientific concept, providing valuable insights into coastal stability and facilitating a deeper understanding of coastal vulnerability and sediment budgeting. However, scientific resources on DoC estimates for the Indian coastline which exhibits significant diversity are limited mainly due to the lack of availability of site-specific data, particularly for longer duration. The present study which focuses on the spatial and temporal variability in DoC along a 40 km long, highly dynamic coastal sector located in the southern tip of southwestern coast of India, is an initiation in this direction and lays the groundwork for more extensive research on this important topic in the future. As part of the study, a detailed investigation on the DoC limits for a monsoon dominated high energy sandy coast which has been experiencing significant changes in coastal processes, attributed to both natural and anthropogenic influences is carried out. Using the six-year site-specific wave data available from a Wave Rider Buoy deployed in shallow waters at about 23 m water depth, the monthly, seasonal, annual and multi-year DoC limits are computed using widely adopted empirical formulations viz. the Birkemeier (1985) and the Hallermeier (1981) which are based on wave exceedance heights. Since the adaptability of these methods for the Indian coast with varying morphological features has not been adequately explored, the computed DoC limits were compared with in situ coastal profile measurements to validate their applicability. The annual inner DoC values for this monsoon-dominated coast computed using the Birkemeier (1985) and Hallermeier (1981) formulations ranged from 4.2 to 5.5 m and 5.5–7.3 m respectively, with the Hallermeier method indicating overestimation. The inner DoC ( 5.5 m) derived using the Birkemeier formulation shows reasonable agreement with in-situ profile measurements (2–7 m), establishing the adaptability of this for similar high-energy tropical coasts. The study revealed that significant variations in wave characteristics within the coastal region potentially intensified by indirect and remote extreme events can have considerable influence on the DoC limits across different time scales. The need to consider short-term variations in wave characteristics which is often ignored is highlighted as it is one of the prime factors that provides valuable inputs related to the dominant mode of sediment transport (particularly cross-shore), offshore extent of sediment transport, their spatial and temporal variations with changes in coastal morphology etc. This scientific information is vital for taking decisions by the coastal scientists/engineers during the initial stages of the project for recommending appropriate measures and also for successful implementation of the project once it is finalised.
Floating pumice rafts generated by eruptions of submarine volcanoes can be transported over large distances, yet the role of surface waves in controlling pumice drift remains poorly constrained. Wave-induced transport is often parameterized indirectly in numerical simulations despite limited experimental observations. Here we investigate the wave-induced drift of floating pumice using laboratory wave-tank experiments under controlled wave forcing. Natural pumice and analog cubes with characteristic sizes of 5–10 cm and a range of densities were subjected to regular waves with frequencies of 1.0–1.6 Hz and varying wave steepness. Pumice motion was quantified using video-based tracking. Pumice with positive freeboard consistently drifted in the direction of wave propagation, with velocities increasing with wave frequency and amplitude. When normalized by theoretical Stokes drift, velocities collapsed into a similar range across pumice densities but showed systematic dependence on wave steepness, indicating the importance of nonlinear wave effects. The corresponding Keulegan–Carpenter numbers (KC ≈ 0.3–3.4) indicate that the wave-induced orbital excursion was comparable to the body dimensions, suggesting that finite-size wave–body interactions may influence the drift. In contrast, pumice approaching neutral buoyancy exhibited persistent drift opposite to the wave direction under certain conditions. Velocity and orientation records reveal a subharmonic response with a dominant period approximately twice that of the incident wave. Step-like modulation of the pumice tilt angle at this doubled period produces alternating large and small forward excursions, skipping large drift events every other cycle. These results demonstrate that wave–pumice interactions evolve with buoyancy and size and can alter both the magnitude and direction of drift. During intermediate stages of pumice raft evolution, when fragment size approaches the wave orbital excursion, such interactions play a critical role in transport and should be explicitly considered in pumice dispersal models following eruptions of submarine volcanoes.
The Persian Gulf (PG) is a pronounced inverse estuary characterized by strong evaporation, hypersaline waters, and a reversed asymmetry in water exchange through the Strait of Hormuz, where the annual inflowing volume transport exceeds the corresponding outflow. This study uses a high-resolution three-dimensional hydrodynamic model to quantify wind effects on salinity redistribution, stratification, and high-frequency water exchanges. Wind forcing substantially modifies salinity patterns along the PG’s southern coasts, where downwind (northwesterly Shamal) conditions enhance hypersalinity. The wind-straining response of stratification in an idealized inverse estuary contrasts with that in positive estuaries, showing restratification under upwind and destratification under downwind conditions. In the PG, complex bathymetry and tides obscure this signal. Nevertheless, stronger horizontal density gradients in the wind-forced experiment, particularly under prevailing downwind conditions, promote stronger stratification compared to the no-wind case. This is associated with contrasting stratification responses between the upper and lower estuarine zones of the PG. Under upwind (downwind) wind stress greater than + 0.05 Pa (-0.05 Pa), the Wedderburn number ( W_e ) exceeds + 5 (− 5) in the upper estuarine zone, while its absolute value (| W_e |) remains mostly below 1 in the lower zone. These W_e values indicate wind-controlled residual circulation in the upper PG and density-gradient-driven circulation in the lower PG. Wind forcing more than doubles high-frequency extreme net volume and salt fluxes (exceeding ± 0.6 Sv and ± 22 Sv×psu) compared to no-wind conditions, although the annual mean net fluxes remain nearly unchanged between the wind-forced and no-wind experiments. In both experiments, cross-sectionally averaged horizontal density variance changes in concert with inflowing transport, indicating strong coupling between frontal strength and exchange at the Strait of Hormuz. Furthermore, the annual mean inflowing and outflowing volume transports derived from the high-frequency approach decrease by 70
This study investigates the impact of meridional shifts in the Southern Hemisphere (SH) regional Hadley Cell (HC) in the Indian Ocean (IO) on wave power (WP) variability over the North Indian Ocean (NIO) during the boreal winter from 1980 to 2022. HC expansion and contraction years were identified using an Outgoing Longwave Radiation (OLR) threshold to determine the latitudinal position of the poleward edge of the SH HC in the IO. Composite analyses reveal distinct responses of NIO swell and wind-wave power to HC shifts, with the swell response being more pronounced. The eastern NIO is identified as the hotspot of HC-shift-induced swell variability, characterized by typically enhanced swell power during HC expansion and reduced power during contraction. The associated swell response was examined using composite analysis, regression analysis, and swell-source back-tracing. Back-tracing shows that the swell reaching the eastern NIO during boreal winter predominantly originates from the central-eastern Southern Indian Ocean (SIO), although some interannual spatial variability in the source region is evident. This displacement of swell sources in certain years modifies the typical HC shift-related swell WP anomaly pattern. During HC expansion years, the swell response is further modulated by La Niña conditions, with the HC expansion-swell relationship most clearly expressed when expansion coincides with La Niña. During contraction years, changes in swell power are associated with contrasting wind conditions over distinct source regions. These findings suggest a coherent linkage between HC meridional shifts, remote wind forcing, swell-source displacement, and regional swell variability, highlighting HC variability as a contributing large-scale dynamical control on the NIO swell climate and its potential relevance to regional wave-energy assessment and coastal wave conditions.
