scholarly journals Impact of the Waves on the Sea Surface Roughness Length under Idealized Like-Hurricane Wind Conditions (Part II)

2015 ◽  
Vol 05 (03) ◽  
pp. 326-335
Author(s):  
José Augusto P. Veiga ◽  
Mônica R. Queiroz
Keyword(s):  
Surface Roughness ◽  
Roughness Length ◽  
Sea Surface ◽  
Hurricane Wind ◽  
Surface Roughness Length ◽  
Sea Surface Roughness ◽  
The Waves

scholarly journals Influence of sea surface roughness length parameterization on Mistral and Tramontane simulations

2016 ◽  
Vol 13 ◽  
pp. 107-112 ◽  
Author(s):  
Anika Obermann ◽  
Benedikt Edelmann ◽  
Bodo Ahrens
Keyword(s):  
Surface Roughness ◽  
Wind Speed ◽  
Wind Direction ◽  
Roughness Length ◽  
Western Mediterranean ◽  
Sea Surface ◽  
Surface Roughness Length ◽  
Sea Surface Roughness ◽  
Simulated Wind ◽  
Simulated Wind Speed

Abstract. The Mistral and Tramontane are mesoscale winds in southern France and above the Western Mediterranean Sea. They are phenomena well suited for studying channeling effects as well as atmosphere–land/ocean processes. This sensitivity study deals with the influence of the sea surface roughness length parameterizations on simulated Mistral and Tramontane wind speed and wind direction. Several simulations with the regional climate model COSMO-CLM were performed for the year 2005 with varying values for the Charnock parameter α. Above the western Mediterranean area, the simulated wind speed and wind direction pattern on Mistral days changes depending on the parameterization used. Higher values of α lead to lower simulated wind speeds. In areas, where the simulated wind speed does not change much, a counterclockwise rotation of the simulated wind direction is observed.

scholarly journals Reduced Sea-Surface Roughness Length at a Coastal Site

Atmosphere ◽  
2021 ◽  
Vol 12 (8) ◽  
pp. 991
Author(s):  
Yuncheng He ◽  
Jiyang Fu ◽  
Pak Wai Chan ◽  
Qiusheng Li ◽  
Zhenru Shu ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Atmospheric Boundary Layer ◽  
Roughness Length ◽  
Sea Surface ◽  
Marine Atmospheric Boundary Layer ◽  
Coastal Site ◽  
Surface Roughness Length ◽  
Sea Surface Roughness ◽  
Roughness Lengths

Sea-surface roughness length is a key parameter for characterizing marine atmospheric boundary layer. Although aerodynamic roughness lengths for homogeneous land and open water surfaces have been examined extensively, the extension of relevant knowledge to the highly inhomogeneous coastal area is problematic due to the complex mechanisms controlling coastal meteorology. This study presented a lidar-based observational analysis of sea-surface roughness length at a coastal site in Hong Kong, in which the wind data recorded from March 2012 to November 2015 were considered and analyzed. The results indicated the turning of wind near the land-sea boundary, leading to a dominative wind direction parallel to the coastline and an acceleration in wind. Moreover, the roughness lengths corresponding to two representative azimuthal sectors were compared, in which the roughness lengths for the onshore wind sector (i.e., 120°–240°) appear to be larger than the constant value (z0 = 0.2 mm) recommended in much existing literature, whereas the values for the alongshore wind sector (i.e., 60°–90°) are significantly smaller, i.e., about two orders of magnitude less than that of a typical sea surface. However, it is to be noted that the effect of atmospheric stability, which is of crucial importance in governing the marine atmospheric boundary layer, is not taken into account in this study.

scholarly journals Effects of Modified Surface Roughness Length over Shallow Waters in a Regional Model Simulation

Atmosphere ◽  
2019 ◽  
Vol 10 (12) ◽  
pp. 818
Author(s):  
So-Young Kim ◽  
Song-You Hong ◽  
Young Cheol Kwon ◽  
Yong Hee Lee ◽  
Da-Eun Kim
Keyword(s):  
Surface Roughness ◽  
Wind Speed ◽  
Roughness Length ◽  
Control Experiment ◽  
Lower Troposphere ◽  
Sea Surface ◽  
Shallow Waters ◽  
Surface Roughness Length ◽  
Sea Surface Roughness ◽  
Modified Surface

The effects of modified sea-surface roughness length over shallow waters are examined in a regional climate simulation over East Asia centered on the Korean Peninsula, using the Advanced Research Weather Research and Forecasting model (WRF-ARW). The control experiment calculates the sea-surface roughness length as a function of friction velocity based on the Charnock relationship. The experiment considering water depth in the sea-surface roughness length over shallow waters is compared with the control experiment. In the experiment considering water depth, the excessive near-surface wind speed over shallow waters is reduced compared to that of the control experiment. Wind speed is reduced also in the lower troposphere. The effects of modified surface roughness over shallow waters are not localized to the lower troposphere but extended into the upper troposphere. Through the vertical interaction between the lower and upper levels, upper tropospheric wind—which is underestimated in the control experiment—is enhanced in the experiment with modified sea-surface roughness length, not only over the shallow waters, but also over the entire domain. As a result, the vertical shear of zonal wind increases, leading to the enhancement of the negative meridional temperature gradient in the mid troposphere.

Development of surface roughness length and drag parameterizations over deep seas

2021 ◽  
Author(s):  
Alberto Rabaneda
Keyword(s):  
Surface Roughness ◽  
Energy Transfer ◽  
Kinetic Energy ◽  
Roughness Length ◽  
Surface Profile ◽  
Sea Surface ◽  
Surface Roughness Length ◽  
Starting Point ◽  
Logarithmic Law ◽  
Kinetic Energy Transfer

<p>Many formulations to determine the sea surface roughness length (z<sub>0</sub>) have been proposed in the past. The well-known Charnock’s equation is applied in most of the previous research. In this study, a different point of view is adopted to develop a new formulation. The starting point is an alternative method for surface roughness length calculation, i.e., the Lettau’s method. This method has already been validated onshore in the presence of obstacles over a domain; for obstacles with a defined cross-section perpendicular to the wind direction plane. Over deep waters, it is expected to find only one type of obstacle, i.e., consecutive waves forming straight lines. Different wave systems and the presence of swell add complexity to determine the sea surface profile. Hence, the adaptation of Lettau’s method seems reasonable, but the demonstrated dependency of z<sub>0</sub> to wave age cannot be neglected.</p><p>Wind-generated waves result from a kinetic energy transfer between the atmosphere and the sea surface. However this physical process is not represented in the well-known logarithmic law. While this effect can be neglected onshore, in offshore environments it can be significant, as 20% of the time z<sub>0</sub> is found to be over the expected range. Therefore, a kinetic energy transfer correction is included into an offshore logarithmic law. With an aerodynamic z<sub>0</sub>, achieved by the adaptation of the Lettau’s equation, and the new offshore logarithmic law, an empirical method for the kinetic energy transfer correction is proposed.</p>

Dynamic modelling of sea-surface roughness for large-eddy simulation of wind over ocean wavefield

2013 ◽  
Vol 726 ◽  
pp. 62-99 ◽  
Author(s):  
Di Yang ◽  
Charles Meneveau ◽  
Lian Shen
Keyword(s):  
Surface Roughness ◽  
Large Eddy Simulation ◽  
Wind Wave ◽  
Dynamic Modelling ◽  
Sea Surface ◽  
Near Surface ◽  
Eddy Simulation ◽  
Sea Surface Roughness ◽  
Large Eddy ◽  
The Waves

AbstractWind blowing over the ocean surface can be treated as a turbulent boundary layer over a multiscale rough surface with moving roughness elements, the waves. Large-eddy simulation (LES) of such flows is challenging because LES resolves wind–wave interactions only down to the grid scale, $\Delta $, while the effects of subgrid-scale (SGS) waves on the wind need to be modelled. Usually, a surface-layer model based on the law of the wall is used; but the surface roughness has been known to depend on the local wind and wave conditions and is difficult to parameterize. In this study, a dynamic model for the SGS sea-surface roughness is developed, with the roughness corresponding to the SGS waves expressed as ${\alpha }_{w} \hspace{0.167em} { \sigma }_{\eta }^{\Delta } $. Here, ${ \sigma }_{\eta }^{\Delta } $ is the effective amplitude of the SGS waves, modelled as a weighted integral of the SGS wave spectrum based on the geometric and kinematic properties of the waves for which five candidate expressions are examined. Moreover, ${\alpha }_{w} $ is an unknown dimensionless model coefficient determined dynamically based on the first-principles constraint that the total surface drag force or average surface stress must be independent of the LES filter scale $\Delta $. The feasibility and consistency of the dynamic sea-surface roughness models are assessed by a priori tests using data from high-resolution LES with near-surface resolution, appropriately filtered. Also, these data are used for a posteriori tests of the dynamic sea-surface roughness models in LES with near-surface modelling. It is found that the dynamic modelling approach can successfully capture the effects of SGS waves on the wind turbulence without ad hoc prescription of the model parameter ${\alpha }_{w} $. Also, for ${ \sigma }_{\eta }^{\Delta } $, a model based on the kinematics of wind–wave relative motion achieves the best performance among the five candidate models.

scholarly journals A Novel Sea Surface Roughness Parameterization Based on Wave State and Sea Foam

2021 ◽  
Vol 9 (3) ◽  
pp. 246
Author(s):  
Difu Sun ◽  
Junqiang Song ◽  
Xiaoyong Li ◽  
Kaijun Ren ◽  
Hongze Leng
Keyword(s):  
Surface Roughness ◽  
Wind Speed ◽  
Drag Coefficient ◽  
Sea Surface ◽  
High Wind Speed ◽  
Wave State ◽  
Wind Speeds ◽  
Sea Surface Roughness ◽  
Extreme Wind ◽  
The Impact

A wave state related sea surface roughness parameterization scheme that takes into account the impact of sea foam is proposed in this study. Using eight observational datasets, the performances of two most widely used wave state related parameterizations are examined under various wave conditions. Based on the different performances of two wave state related parameterizations under different wave state, and by introducing the effect of sea foam, a new sea surface roughness parameterization suitable for low to extreme wind conditions is proposed. The behaviors of drag coefficient predicted by the proposed parameterization match the field and laboratory measurements well. It is shown that the drag coefficient increases with the increasing wind speed under low and moderate wind speed conditions, and then decreases with increasing wind speed, due to the effect of sea foam under high wind speed conditions. The maximum values of the drag coefficient are reached when the 10 m wind speeds are in the range of 30–35 m/s.

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