Impact of currents on surface fluxes computation and their feedback on coastal dynamics

Abstract. A twin numerical experiment was conducted in the seas of Sardinia (Western Mediterranean) to assess the impact, at coastal scales, of the use of relative winds (i.e. taking into account ocean surface currents) in the computation of heat and momentum fluxes through bulk formulas. The model, the Regional Ocean Modeling System (ROMS), was implemented at 2 km of resolution in order to well resolve (sub-)mesoscale dynamics. Small changes (1–2%) in terms of spatially-averaged fluxes correspond to quite large spatial differences of such quantities (up to 15–20%) and to comparably significant differences in terms of mean velocities of the surface currents. Wind power input of the wind stress to the ocean surface P results also reduced by a 15%, especially where surface currents are stronger. Quantitative validation with satellite SST suggests that such a modification on the fluxes improves the model solution especially in areas of cyclonic circulation, where the heat fluxes correction is predominant in respect to the dynamical correction. Surface currents changes above all in their fluctuating part, while the stable part of the flow show changes mainly in magnitude and less in its path. Both total and eddy kinetic energies of the surface current field results reduced in the experiment where fluxes took into account for surface currents. Dynamically, the largest correction is observed in the SW area where anticyclonic eddies approach the continental slope. This reduction also impacts the vertical dynamics and specifically the local upwelling that results diminished both in spatial extension as well in magnitude. Simulations suggest that, even at local scales and in temperate regions, it is preferable to take into account for such a component in fluxes computation. Results also confirm the tight relationship between local coastal upwelling and eddy-slope interactions in the area.

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Impact of currents on surface flux computations and their feedback on dynamics at regional scales

Ocean Science ◽

10.5194/os-11-657-2015 ◽

2015 ◽

Vol 11 (4) ◽

pp. 657-666 ◽

Cited By ~ 9

Author(s):

A. Olita ◽

I. Iermano ◽

L. Fazioli ◽

A. Ribotti ◽

C. Tedesco ◽

...

Keyword(s):

Surface Current ◽

Surface Flux ◽

Power Input ◽

Western Mediterranean ◽

Surface Fluxes ◽

Surface Currents ◽

Qualitative Comparison ◽

Satellite Sst ◽

Ocean Surface Currents ◽

The Impact

Abstract. A twin numerical experiment was conducted in the seas around the island of Sardinia (Western Mediterranean) to assess the impact, at regional and coastal scales, of the use of relative winds (i.e., taking into account ocean surface currents) in the computation of heat and momentum fluxes through standard (Fairall et al., 2003) bulk formulas. The Regional Ocean Modelling System (ROMS) was implemented at 3 km resolution in order to well resolve mesoscale processes, which are known to have a large influence in the dynamics of the area. Small changes (few percent points) in terms of spatially averaged fluxes correspond to quite large differences of such quantities (about 15 %) in spatial terms and in terms of kinetics (more than 20 %). As a consequence, wind power input P is also reduced by ~ 14 % on average. Quantitative validation with satellite SST suggests that such a modification of the fluxes improves the model solution especially in the western side of the domain, where mesoscale activity (as suggested by eddy kinetic energy) is stronger. Surface currents change both in their stable and fluctuating part. In particular, the path and intensity of the Algerian Current and of the Western Sardinia Current (WSC) are impacted by the modification in fluxes. Both total and eddy kinetic energies of the surface current field are reduced in the experiment where fluxes took into account the surface currents. The main dynamical correction is observed in the SW area, where the different location and strength of the eddies influence the path and intensity of the WSC. Our results suggest that, even at local scales and in temperate regions, it would be preferable to take into account such a contribution in flux computations. The modification of the original code, substantially cost-less in terms of numerical computation, improves the model response in terms of surface fluxes (SST validated) and it also likely improves the dynamics as suggested by qualitative comparison with satellite data.

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The Vorticity Balance of the Ocean Surface in Hawaii from a Regional Reanalysis

Journal of Physical Oceanography ◽

10.1175/jpo-d-14-0074.1 ◽

2015 ◽

Vol 45 (2) ◽

pp. 424-440 ◽

Cited By ~ 22

Author(s):

Joao Marcos Azevedo Correia de Souza ◽

Brian Powell ◽

Alma Carolina Castillo-Trujillo ◽

Pierre Flament

Keyword(s):

Ocean Surface ◽

Ocean Modeling ◽

Surface Currents ◽

Regional Ocean Modeling System ◽

The North ◽

System A ◽

Representation Error ◽

Zonal Wavenumber ◽

Ocean Surface Currents ◽

Regional Reanalysis

AbstractThe ocean surface vorticity budget around the Hawaiian Islands is examined using an 18-month model reanalysis generated using four-dimensional variational state estimation with all available observations (satellite, in situ, and high-frequency radio). To better resolve the ocean surface currents and reduce the representation error of the radio-measured surface currents, this study developed a new vertical scheme for the Regional Ocean Modeling System. A new, detailed description of the ocean surface vorticity is created, revealing a region dominated by cyclonic (anticyclonic) vorticity to the north (south) of the mean position of the Hawaii Lee Countercurrent. Advection of vorticity is the primary process that transports the vorticity generated in the lee of the islands by the wind wake. In this island lee, the zonal wavenumber spectra show a cascade of vorticity/energy from the submesoscale toward the larger scales. Latitudinal differences in the advection of vorticity spectra indicate the propagation of a first baroclinic mode Rossby wave in the region dominated by anticyclonic vorticity to the west of the island of Hawaii, while the region dominated by cyclonic vorticity is disrupted by the wake of the smaller islands.

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CYGNSS Observations and Analysis of Low-Latitude Extratropical Cyclones

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-20-0190.1 ◽

2021 ◽

Vol 60 (4) ◽

pp. 527-541

Author(s):

Juan A. Crespo ◽

Catherine M. Naud ◽

Derek J. Posselt

Keyword(s):

Surface Wind ◽

Ocean Surface ◽

Surface Wind Speed ◽

Satellite System ◽

Surface Fluxes ◽

Heat Fluxes ◽

Surface Processes ◽

Extratropical Cyclones ◽

Low Latitude ◽

Reanalysis Dataset

AbstractLatent and sensible heat fluxes over the oceans are believed to play an important role in the genesis and evolution of marine-based extratropical cyclones (ETCs) and affect rapid cyclogenesis. Observations of ocean surface heat fluxes are limited from existing in situ and remote sensing platforms, which may not offer sufficient spatial and temporal resolution. In addition, substantial precipitation frequently veils the ocean surface around ETCs, limiting the capacity of spaceborne instruments to observe the surface processes within maturing ETCs. Although designed as a tropics-focused mission, the Cyclone Global Navigation Satellite System (CYGNSS) can observe ocean surface wind speed and heat fluxes within a notable quantity of low-latitude extratropical fronts and cyclones. These observations can assist in understanding how surface processes may play a role in cyclogenesis and evolution. This paper illustrates CYGNSS’s capability to observe extratropical cyclones manifesting in various ocean basins throughout the globe and shows that the observations provide a robust sample of ETCs winds and surface fluxes, as compared with a reanalysis dataset.

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Intraseasonal Land–Atmosphere Coupling in the West African Monsoon

Journal of Climate ◽

10.1175/2008jcli2475.1 ◽

2008 ◽

Vol 21 (24) ◽

pp. 6636-6648 ◽

Cited By ~ 47

Author(s):

Christopher M. Taylor

Keyword(s):

Soil Moisture ◽

Sensible Heat Flux ◽

West African Monsoon ◽

West African ◽

Surface Fluxes ◽

Heat Fluxes ◽

The West ◽

African Monsoon ◽

Low Level ◽

The Impact

Abstract Via its impact on surface fluxes, subseasonal variability in soil moisture has the potential to feed back on regional atmospheric circulations, and thereby rainfall. An understanding of this feedback mechanism in the climate system has been hindered by the lack of observations at an appropriate scale. In this study, passive microwave data at 10.65 GHz from the Tropical Rainfall Measuring Mission satellite are used to identify soil moisture variability during the West African monsoon. A simple model of surface sensible heat flux is developed from these data and is used, alongside atmospheric analyses from the European Centre for Medium-Range Weather Forecasting (ECMWF), to provide a new interpretation of monsoon variability on time scales of the order of 15 days. During active monsoon periods, the data indicate extensive areas of wet soil in the Sahel. The impact of the resulting weak surface heat fluxes is consistent in space and time with low-level variations in atmospheric heating and vorticity, as depicted in the ECMWF analyses. The surface-induced vorticity structure is similar to previously documented intraseasonal variations in the monsoon flow, notably a westward-propagating vortex at low levels. In those earlier studies, the variability in low-level flow was considered to be the critical factor in producing intraseasonal fluctuations in rainfall. The current analysis shows that this vortex can be regarded as an effect of the rainfall (via surface hydrology) as well as a cause.

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Multi-Physics Ensemble versus Atmosphere–Ocean Coupled Model Simulations for a Tropical-Like Cyclone in the Mediterranean Sea

Atmosphere ◽

10.3390/atmos10040202 ◽

2019 ◽

Vol 10 (4) ◽

pp. 202 ◽

Cited By ~ 9

Author(s):

Antonio Ricchi ◽

Mario Marcello Miglietta ◽

Davide Bonaldo ◽

Guido Cioni ◽

Umberto Rizza ◽

...

Keyword(s):

High Resolution ◽

Mediterranean Sea ◽

Computational Cost ◽

Ocean Model ◽

Surface Fluxes ◽

Ocean Modeling ◽

Sea Surface ◽

Regional Ocean Modeling System ◽

The Mediterranean ◽

Physics Ensemble

Between 19 and 22 January 2014, a baroclinic wave moving eastward from the Atlantic Ocean generated a cut-off low over the Strait of Gibraltar and was responsible for the subsequent intensification of an extra-tropical cyclone. This system exhibited tropical-like features in the following stages of its life cycle and remained active for approximately 80 h, moving along the Mediterranean Sea from west to east, eventually reaching the Adriatic Sea. Two different modeling approaches, which are comparable in terms of computational cost, are analyzed here to represent the cyclone evolution. First, a multi-physics ensemble using different microphysics and turbulence parameterization schemes available in the WRF (weather research and forecasting) model is employed. Second, the COAWST (coupled ocean–atmosphere wave sediment transport modeling system) suite, including WRF as an atmospheric model, ROMS (regional ocean modeling system) as an ocean model, and SWAN (simulating waves in nearshore) as a wave model, is used. The advantage of using a coupled modeling system is evaluated taking into account air–sea interaction processes at growing levels of complexity. First, a high-resolution sea surface temperature (SST) field, updated every 6 h, is used to force a WRF model stand-alone atmospheric simulation. Later, a two-way atmosphere–ocean coupled configuration is employed using COAWST, where SST is updated using consistent sea surface fluxes in the atmospheric and ocean models. Results show that a 1D ocean model is able to reproduce the evolution of the cyclone rather well, given a high-resolution initial SST field produced by ROMS after a long spin-up time. Additionally, coupled simulations reproduce more accurate (less intense) sea surface heat fluxes and a cyclone track and intensity, compared with a multi-physics ensemble of standalone atmospheric simulations.

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Weak and strong constraint data assimilation in the inverse Regional Ocean Modeling System (ROMS): Development and application for a baroclinic coastal upwelling system

Ocean Modelling ◽

10.1016/j.ocemod.2006.08.002 ◽

2007 ◽

Vol 16 (3-4) ◽

pp. 160-187 ◽

Cited By ~ 66

Author(s):

Emanuele Di Lorenzo ◽

Andrew M. Moore ◽

Hernan G. Arango ◽

Bruce D. Cornuelle ◽

Arthur J. Miller ◽

...

Keyword(s):

Data Assimilation ◽

Coastal Upwelling ◽

Ocean Modeling ◽

Regional Ocean Modeling System ◽

Strong Constraint ◽

Upwelling System

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Impacts of Atmospheric Reanalysis Uncertainty on Atlantic Overturning Estimates at 25°N

Journal of Climate ◽

10.1175/jcli-d-18-0241.1 ◽

2018 ◽

Vol 31 (21) ◽

pp. 8719-8744 ◽

Cited By ~ 3

Author(s):

Helen R. Pillar ◽

Helen L. Johnson ◽

David P. Marshall ◽

Patrick Heimbach ◽

So Takao

Keyword(s):

Climate Model ◽

Surface Heat ◽

Surface Fluxes ◽

Heat Fluxes ◽

Labrador Sea ◽

Surface Heat Fluxes ◽

Ensemble Mean ◽

Meridional Overturning ◽

The Impact ◽

Average Uncertainty

Atmospheric reanalyses are commonly used to force numerical ocean models, but despite large discrepancies reported between different products, the impact of reanalysis uncertainty on the simulated ocean state is rarely assessed. In this study, the impact of uncertainty in surface fluxes of buoyancy and momentum on the modeled Atlantic meridional overturning at 25°N is quantified for the period January 1994–December 2011. By using an ocean-only climate model and its adjoint, the space and time origins of overturning uncertainty resulting from air–sea flux uncertainty are fully explored. Uncertainty in overturning induced by prior air–sea flux uncertainty can exceed 4 Sv (where 1 Sv ≡ 106 m3 s−1) within 15 yr, at times exceeding the amplitude of the ensemble-mean overturning anomaly. A key result is that, on average, uncertainty in the overturning at 25°N is dominated by uncertainty in the zonal wind at lags of up to 6.5 yr and by uncertainty in surface heat fluxes thereafter, with winter heat flux uncertainty over the Labrador Sea appearing to play a critically important role.

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Sensible Heat Fluxes in the Nearly Neutral Boundary Layer: The Impact of Frictional Heating within the Surface Layer

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-18-0158.1 ◽

2019 ◽

Vol 76 (4) ◽

pp. 1039-1053

Author(s):

J. M. Edwards

Keyword(s):

Boundary Layer ◽

Surface Layer ◽

Frictional Heating ◽

Sensible Heat Flux ◽

Surface Fluxes ◽

Heat Fluxes ◽

Sensible Heat ◽

Simple Modification ◽

Neutral Boundary Layer ◽

The Impact

Abstract The effect of frictional dissipative heating on the calculation of surface fluxes in the atmospheric boundary layer using bulk flux formulas is considered. Although the importance of frictional dissipation in intense storms has been widely recognized, it is suggested here that its impact is also to be seen at more moderate wind speeds in apparently enhanced heat transfer coefficients and countergradient fluxes in nearly neutral conditions. A simple modification to the bulk flux formula can be made to account for its impact within the surface layer. This modification is consistent with an interpretation of the surface layer as one across which the flux of total energy is constant. The effect of this modification on tropical cyclones is assessed in an idealized model, where it is shown to reduce the predicted maximum wind speed by about 4%. In numerical simulations of three individual storms, the impacts are more subtle but indicate a reduction of the sensible heat flux into the storm and a cooling of the surface layer.

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Uncertainty Estimates for SeaSonde HF Radar Ocean Current Observations

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-18-0104.1 ◽

2019 ◽

Vol 36 (2) ◽

pp. 231-247 ◽

Cited By ~ 4

Author(s):

Brian Emery ◽

Libe Washburn

Keyword(s):

Numerical Models ◽

Surface Current ◽

Ocean Modeling ◽

Hf Radar ◽

Ocean Current ◽

Data Quality Control ◽

Music Algorithm ◽

Regional Ocean Modeling System ◽

Mean Values ◽

Uncertainty Estimates

Abstract HF radars typically produce maps of surface current velocities without estimates of the measurement uncertainties. Many users of HF radar data, including spill response and search and rescue operations, incorporate these observations into models and would thus benefit from quantified uncertainties. Using both simulations and coincident observations from the baseline between two operational SeaSonde HF radars, we demonstrate the utility of expressions for estimating the uncertainty in the direction obtained with the Multiple Signal Classification (MUSIC) algorithm. Simulations of radar backscatter using surface currents from the Regional Ocean Modeling System show a close correspondence between direction of arrival (DOA) errors and estimated uncertainties, with mean values of 15° at 10 dB, falling to less than 3° at 30 dB. Observations from two operational SeaSondes have average DOA uncertainties of 2.7° and 3.8°, with a fraction of the observations (10.5% and 7.1%, respectively) having uncertainties of >10°. Using DOA uncertainties for data quality control improves time series comparison statistics between the two radars, with r2=0.6 increasing to r2=0.75 and RMS difference decreasing from 15 to 12 cm s−1. The analysis illustrates the major sources of error in oceanographic HF radars and suggests that the DOA uncertainties are suitable for assimilation into numerical models.

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Modeling the Pathways and Mean Dynamics of River Plume Dispersal in the New York Bight

Journal of Physical Oceanography ◽

10.1175/2008jpo4082.1 ◽

2009 ◽

Vol 39 (5) ◽

pp. 1167-1183 ◽

Cited By ~ 36

Author(s):

Weifeng G. Zhang ◽

John L. Wilkin ◽

Robert J. Chant

Keyword(s):

New York ◽

New Jersey ◽

Hudson River ◽

Ocean Modeling ◽

Ocean Dynamics ◽

Surface Currents ◽

Regional Ocean Modeling System ◽

New York Bight ◽

York Bight ◽

The Mean

Abstract This study investigates the dispersal of the Hudson River outflow across the New York Bight and the adjacent inner- through midshelf region. Regional Ocean Modeling System (ROMS) simulations were used to examine the mean momentum dynamics; the freshwater dispersal pathways relevant to local biogeochemical processes; and the contribution from wind, remotely forced along-shelf current, tides, and the topographic control of the Hudson River shelf valley. The modeled surface currents showed many similarities to the surface currents measured by high-frequency radar [the Coastal Ocean Dynamics Applications Radar (CODAR)]. Analysis shows that geostrophic balance and Ekman transport dominate the mean surface momentum balance, with most of the geostrophic flow resulting from the large-scale shelf circulation and the rest being locally generated. Subsurface circulation is driven principally by the remotely forced along-shelf current, with the exception of a riverward water intrusion in the Hudson River shelf valley. The following three pathways by which freshwater is dispersed across the shelf were identified: (i) along the New Jersey coast, (ii) along the Long Island coast, and (iii) by a midshelf offshore pathway. Time series of the depth-integrated freshwater transport show strong seasonality in dispersal patterns: the New Jersey pathway dominates the winter–spring seasons when winds are downwelling favorable, while the midshelf pathway dominates summer months when winds are upwelling favorable. A series of reduced physics simulations identifies that wind is the major force for the spreading of freshwater to the mid- and outer shelf, that remotely forced along-shelf currents significantly influence the ultimate fate of the freshwater, and that the Hudson River shelf valley has a modest dynamic effect on the freshwater spreading.

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