scholarly journals Effect of Depth-Induced Breaking on Wind Wave Simulations in Shallow Nearshore Waters off Northern Taiwan during the Passage of Two Super Typhoons

2021 ◽  
Vol 9 (7) ◽  
pp. 706
Author(s):  
Shih-Chun Hsiao ◽  
Han-Lun Wu ◽  
Wei-Bo Chen ◽  
Wen-Dar Guo ◽  
Chih-Hsin Chang ◽  
...  
Keyword(s):  
Wave Breaking ◽  
Surf Zone ◽  
Circulation Model ◽  
Deep Ocean ◽  
Atmospheric Conditions ◽  
Direct Modification ◽  
Modification Technique ◽  
Maximum Increment ◽  
Northern Taiwan

Super Typhoons Maria (2018) and Lekima (2019) were adopted for this case study, although they only passed the northern offshore waters of Taiwan without making landfall. A direct modification technique was employed to create the atmospheric conditions for a wave-circulation model to hindcast large typhoon-driven waves. The radius of the modified scale (Rtrs) for a hybrid typhoon wind plays an important role in the significant wave height (SWH) simulations during the passage of typhoons. The maximum increment in peak SWH reached 3.0 m and 5.0 m in the deep ocean for Super Typhoons Maria (2018) and Lekima (2019), respectively if the Rtrs was increased from 4 × Rmax (radius of the maximum wind) to 7 × Rmax. The SWHs induced by the typhoon winds in the surf zone were more sensitive to different wave-breaking formulations used in the wave-circulation model. The maximum difference in peak SWH reached 2.5 m and 1.2 m for Super Typhoons Maria (2018) and Lekima (2019), respectively, when the wave-breaking formulations of BJ78 (proposed by Battjes and Janssen in 1978) and CT93 (proposed by Church and Thornton in 1993) were introduced to the wave-circulation model. The SWH simulations in the surf zone were insensitive to the wave-breaking criterion (γ) during the passage of typhoons. In shallow nearshore waters, the utilization of a constant γ for the wave-circulation model always produces peak SWHs that are smaller than those using γ based on local steepness or peak steepness.

Lagrangian Drifter Dispersion in the Surf Zone: Directionally Spread, Normally Incident Waves

2009 ◽  
Vol 39 (4) ◽  
pp. 809-830 ◽  
Author(s):  
Matthew Spydell ◽  
Falk Feddersen
Keyword(s):  
Wave Breaking ◽  
Surf Zone ◽  
Circulation Model ◽  
Particle Dispersion ◽  
Energy Cascade ◽  
Relative Dispersion ◽  
Length Scales ◽  
Inverse Energy Cascade ◽  
Rotational Components ◽  
Lagrangian Drifter

Abstract Lagrangian drifter statistics in a surf zone wave and circulation model are examined and compared to single- and two-particle dispersion statistics observed on an alongshore uniform natural beach with small, normally incident, directionally spread waves. Drifter trajectories are modeled with a time-dependent Boussinesq wave model that resolves individual waves and parameterizes wave breaking. The model reproduces the cross-shore variation in wave statistics observed at three cross-shore locations. In addition, observed and modeled Eulerian binned (means and standard deviations) drifter velocities agree. Modeled surf zone Lagrangian statistics are similar to those observed. The single-particle (absolute) dispersion statistics are well predicted, including nondimensionalized displacement probability density functions (PDFs) and the growth of displacement variance with time. The modeled relative dispersion and scale-dependent diffusivity is consistent with the observed and indicates the presence of a 2D turbulent flow field. The model dispersion is due to the rotational components of the modeled velocity field, indicating the importance of vorticity in driving surf zone dispersion. Modeled irrotational velocities have little dispersive capacity. Surf zone vorticity is generated by finite crest-length wave breaking that results, on the alongshore uniform bathymetry, from a directionally spread wave field. The generated vorticity then cascades to other length scales as in 2D turbulence. Increasing the wave directional spread results in increased surf zone vorticity variability and surf zone dispersion. Eulerian and Lagrangian analysis of the flow indicate that the surf zone is 2D turbulent-like with an enstrophy cascade for length scales between approximately 5 and 10 m and an inverse-energy cascade for scales of 20 to 100 m. The vorticity injection length scale (the transition between enstrophy and inverse-energy cascade) is a function of the wave directional spread.

On the impact of sea ice in a global ocean circulation model

1997 ◽  
Vol 25 ◽  
pp. 111-115 ◽  
Author(s):  
Achim Stössel
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Ocean Circulation ◽  
General Circulation ◽  
Thermohaline Circulation ◽  
Circulation Model ◽  
Deep Ocean ◽  
Global Ocean ◽  
Convective Activity ◽  
The Impact

This paper investigates the long-term impact of sea ice on global climate using a global sea-ice–ocean general circulation model (OGCM). The sea-ice component involves state-of-the-art dynamics; the ocean component consists of a 3.5° × 3.5° × 11 layer primitive-equation model. Depending on the physical description of sea ice, significant changes are detected in the convective activity, in the hydrographic properties and in the thermohaline circulation of the ocean model. Most of these changes originate in the Southern Ocean, emphasizing the crucial role of sea ice in this marginally stably stratified region of the world's oceans. Specifically, if the effect of brine release is neglected, the deep layers of the Southern Ocean warm up considerably; this is associated with a weakening of the Southern Hemisphere overturning cell. The removal of the commonly used “salinity enhancement” leads to a similar effect. The deep-ocean salinity is almost unaffected in both experiments. Introducing explicit new-ice thickness growth in partially ice-covered gridcells leads to a substantial increase in convective activity, especially in the Southern Ocean, with a concomitant significant cooling and salinification of the deep ocean. Possible mechanisms for the resulting interactions between sea-ice processes and deep-ocean characteristics are suggested.

scholarly journals Growth of nucleation mode particles in the summertime Arctic: a case study

2016 ◽  
Vol 16 (12) ◽  
pp. 7663-7679 ◽  
Author(s):  
Megan D. Willis ◽  
Julia Burkart ◽  
Jennie L. Thomas ◽  
Franziska Köllner ◽  
Johannes Schneider ◽  
...  
Keyword(s):  
Cloud Condensation Nuclei ◽  
Methanesulfonic Acid ◽  
Lower Troposphere ◽  
Atmospheric Conditions ◽  
Aerosol Formation ◽  
Radiative Balance ◽  
Nucleation Mode ◽  
Cloud Properties ◽  
Marine Influence

Abstract. The summertime Arctic lower troposphere is a relatively pristine background aerosol environment dominated by nucleation and Aitken mode particles. Understanding the mechanisms that control the formation and growth of aerosol is crucial for our ability to predict cloud properties and therefore radiative balance and climate. We present an analysis of an aerosol growth event observed in the Canadian Arctic Archipelago during summer as part of the NETCARE project. Under stable and clean atmospheric conditions, with low inversion heights, carbon monoxide less than 80 ppbv, and black carbon less than 5 ng m−3, we observe growth of small particles,  <  20 nm in diameter, into sizes above 50 nm. Aerosol growth was correlated with the presence of organic species, trimethylamine, and methanesulfonic acid (MSA) in particles ∼ 80 nm and larger, where the organics are similar to those previously observed in marine settings. MSA-to-sulfate ratios as high as 0.15 were observed during aerosol growth, suggesting an important marine influence. The organic-rich aerosol contributes significantly to particles active as cloud condensation nuclei (CCN, supersaturation  =  0.6 %), which are elevated in concentration during aerosol growth above background levels of ∼ 100 to ∼ 220 cm−3. Results from this case study highlight the potential importance of secondary organic aerosol formation and its role in growing nucleation mode aerosol into CCN-active sizes in this remote marine environment.

scholarly journals Stratosphere-troposphere exchange from the Lagrangian perspective: a case study and method sensitivities

2004 ◽  
Vol 4 (3) ◽  
pp. 3249-3284 ◽  
Author(s):  
M. S. Bourqui
Keyword(s):  
Residence Time ◽  
Wave Breaking ◽  
Temporal Evolution ◽  
Baroclinic Wave ◽  
End Effects ◽  
The Past ◽  
Effective Removal ◽  
Residence Time Distributions ◽  
Temporal And Spatial

Abstract. An important part of extra-tropical stratosphere-to-troposphere transport occurs in association with baroclinic wave breaking and cut-off decay at the tropopause. In the last decade many studies have attempted to estimate stratosphere-troposphere exchange (STE) in such synoptic events with various methods, and more recently efforts have been put on inter-comparing these methods. However, large uncertainties remain on the sensitivities to methods intrinsic parameters, and on the best measure for STE with regard to end effects on chemistry. The goal of the present study is to address these two fundamental issues in the context of the application of a trajectory-based Lagrangian method, which has been applied in the past to climatological studies and has also been involved in inter-comparison studies, to a typical baroclinic wave breaking event. The analysis sheds light on (i) the fine mesoscale temporal and spatial structures that are associated with episodic, rapid inflows of stratospheric air into the troposphere; (ii) the spatial resolution of 1°×1° required to reasonably capture STE fluxes in such a wave breaking event; (iii) the effective removal of spurious exchange events using a threshold residence time; (iv) the relevance of residence time distributions for capturing the effective chemical forcing of STE; (v) the large differences in the temporal evolution and geographical distribution of STE fluxes across the 2 and the 4 potential vorticity unit iso-surface definitions of the tropopause.

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