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

Ocean Science ◽  
2015 ◽  
Vol 11 (4) ◽  
pp. 657-666 ◽  
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.

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

2015 ◽  
Vol 12 (1) ◽  
pp. 1-30
Author(s):  
A. Olita ◽  
I. Iermano ◽  
L. Fazioli ◽  
A. Ribotti ◽  
C. Tedesco ◽  
...  
Keyword(s):  
Coastal Upwelling ◽  
Surface Current ◽  
Ocean Surface ◽  
Western Mediterranean ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Ocean Modeling ◽  
Surface Currents ◽  
Regional Ocean Modeling System ◽  
The Impact

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.

scholarly journals Nature of the Mesoscale Boundary Layer Height and Water Vapor Variability Observed 14 June 2002 during the IHOP_2002 Campaign

2009 ◽  
Vol 137 (1) ◽  
pp. 414-432 ◽  
Author(s):  
F. Couvreux ◽  
F. Guichard ◽  
P. H. Austin ◽  
F. Chen
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
Mesoscale Model ◽  
Surface Flux ◽  
Early Morning ◽  
Surface Fluxes ◽  
Layer Height ◽  
Horizontal Advection ◽  
Boundary Layer Height ◽  
The Impact

Abstract Mesoscale water vapor heterogeneities in the boundary layer are studied within the context of the International H2O Project (IHOP_2002). A significant portion of the water vapor variability in the IHOP_2002 occurs at the mesoscale, with the spatial pattern and the magnitude of the variability changing from day to day. On 14 June 2002, an atypical mesoscale gradient is observed, which is the reverse of the climatological gradient over this area. The factors causing this water vapor variability are investigated using complementary platforms (e.g., aircraft, satellite, and in situ) and models. The impact of surface flux heterogeneities and atmospheric variability are evaluated separately using a 1D boundary layer model, which uses surface fluxes from the High-Resolution Land Data Assimilation System (HRLDAS) and early-morning atmospheric temperature and moisture profiles from a mesoscale model. This methodology, based on the use of robust modeling components, allows the authors to tackle the question of the nature of the observed mesoscale variability. The impact of horizontal advection is inferred from a careful analysis of available observations. By isolating the individual contributions to mesoscale water vapor variability, it is shown that the observed moisture variability cannot be explained by a single process, but rather involves a combination of different factors: the boundary layer height, which is strongly controlled by the surface buoyancy flux, the surface latent heat flux, the early-morning heterogeneity of the atmosphere, horizontal advection, and the radiative impact of clouds.

scholarly journals Estimating Ocean Vector Winds and Currents Using a Ka-Band Pencil-Beam Doppler Scatterometer

2018 ◽  
Author(s):  
Ernesto Rodriguez ◽  
Alexander Wineteer ◽  
Dragana Perkovic-Martin ◽  
Tamás Gál ◽  
Bryan Stiles ◽  
...  
Keyword(s):  
Wind Speed ◽  
Surface Current ◽  
Surface Currents ◽  
Pencil Beam ◽  
Doppler Measurement ◽  
Ka Band ◽  
Geophysical Model ◽  
Challenges And Opportunities ◽  
Ocean Surface Currents ◽  
Tightly Coupled

Ocean surface currents and winds are tightly coupled essential climate variables, and, given their short time scales, observing them at the same time and resolution is of great interest. DopplerScatt is an airborne Ka-band scatterometer that has been developed under NASA's Instrument Incubator Program (IIP) to provide a proof of concept of the feasability of measuring these variables using pencil-beam scanning Doppler scatterometry. In the first half of this paper, we present the Doppler scatterometer measurement and processing principles, paying particular attention to deriving a complete measurement error budget. Although Doppler radars have been used for the estimation of surface currents, pencil-beam Doppler Scatterometry offers challenges and opportunities that require separate treatment. The calibration of the Doppler measurement to remove platform and instrument biases has been a traditional challenge for Doppler systems, and we introduce several new techniques to mitigate these errors when conical scanning is used. The use of Ka-band for airborne Doppler scatterometry measurements is also new, and, in the second half of the paper, we examine the phenomenology of the mapping from radar cross section and radial velocity measurements to winds and surface currents. To this end, we present new Ka-band Geophysical Model Functions (GMF's) for winds and surface currents obtained from multiple airborne campaigns. We find that the wind Ka-band GMF exhibits similar dependence to wind speed as that for Ku-band scatterometers, such as QuikSCAT, albeit with much greater upwind-crosswind modulation. The surface current GMF at Ka-band is significantly different from that at C-band, and, above 4.5 m/s has a weak dependence on wind speed, although still dependent on wind direction. We examine the effects of Bragg-wave modulation by long waves through a Modululation Transfer Function (MTF), and show that the observed surface current dependence on winds is consistent with past Ka-band MTF observations. Finally, we provide a preliminary validation of our geophysical retrievals, which will be expanded in subsequent publications. Our results indicate that Ka-band Doppler scatterometry could be a feasible method for wide-swath simultaneous measurements of winds and currents from space.

scholarly journals Assimilating realistically simulated wide-swath altimeter observations in a high-resolution shelf-seas forecasting system

Ocean Science ◽  
2021 ◽  
Vol 17 (6) ◽  
pp. 1791-1813
Author(s):  
Robert R. King ◽  
Matthew J. Martin
Keyword(s):  
Mean Squared Error ◽  
Surface Current ◽  
Surface Currents ◽  
Correlated Errors ◽  
North West ◽  
Forecasting System ◽  
Negative Impacts ◽  
Ocean Topography ◽  
The Impact ◽  
Wide Swath

Abstract. The impact of assimilating simulated wide-swath altimetry observations from the upcoming Surface Water and Ocean Topography (SWOT) mission is assessed using observing system simulation experiments (OSSEs). These experiments use the Met Office 1.5 km resolution North West European Shelf analysis and forecasting system. In an effort to understand the importance of future work to account for correlated errors in the data assimilation scheme, we simulate SWOT observations with and without realistic correlated errors. These are assimilated in OSSEs along with simulated observations of the standard observing network, also with realistic errors added. It was found that while the assimilation of SWOT observations without correlated errors reduced the RMSE (root mean squared error) in sea surface height (SSH) and surface current speeds by up to 20 %, the inclusion of correlated errors in the observations degraded both the SSH and surface currents, introduced an erroneous increase in the mean surface currents and degraded the subsurface temperature and salinity. While restricting the SWOT data to the inner half of the swath and applying observation averaging with a 5 km radius negated most of the negative impacts, it also severely limited the positive impacts. To realise the full benefits in the prediction of the ocean mesoscale offered by wide-swath altimetry missions, it is crucial that methods to ameliorate the effects of correlated errors in the processing of the SWOT observations and account for the correlated errors in the assimilation are implemented.

scholarly journals Assimilating realistically simulated wide-swath altimeter observations in a high-resolution shelf-seas forecasting system

2021 ◽  
Author(s):  
Robert R. King ◽  
Matthew J. Martin
Keyword(s):  
Surface Current ◽  
Surface Currents ◽  
Correlated Errors ◽  
North West ◽  
Shelf Seas ◽  
Forecasting System ◽  
Negative Impacts ◽  
Future Work ◽  
The Impact ◽  
Wide Swath

Abstract. The impact of assimilating simulated wide-swath altimetry observations from the upcoming SWOT mission is assessed using Observing System Simulation Experiments (OSSEs). These experiments use the Met Office 1.5 km resolution North-West European Shelf analysis and forecasting system. In an effort to understand the importance of future work to account for correlated errors in the data assimilation scheme, we simulate SWOT observations with and without realistic correlated errors. These are assimilated in OSSEs along with simulated observations of the standard observing network, also with realistic errors added. It was found that while the assimilation of SWOT observations without correlated errors reduced the RMSE in sea surface height (SSH) and surface current speeds by up to 20 %, the inclusion of correlated errors in the observations degraded both the SSH and surface currents, introduced an erroneous increase in the mean surface currents, and degraded the sub-surface temperature and salinity. While restricting the SWOT data to the inner half of the swath and applying observation averaging with a 5 km radius negated most of the negative impacts, it also severely limited the positive impacts. To realise the full benefits in the prediction of the ocean mesoscale offered by wide-swath altimetry missions it is crucial that methods to ameliorate the effects of correlated errors in the processing of the SWOT observations and to account for the correlated errors in the assimilation are implemented.

scholarly journals The Influence of Idealized Heterogeneity on Wet and Dry Planetary Boundary Layers Coupled to the Land Surface

2005 ◽  
Vol 62 (7) ◽  
pp. 2078-2097 ◽  
Author(s):  
Edward G. Patton ◽  
Peter P. Sullivan ◽  
Chin-Hoh Moeng
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Convective Boundary Layer ◽  
Land Surface ◽  
Surface Flux ◽  
Scalar Fields ◽  
Surface Fluxes ◽  
Convective Boundary ◽  
Turbulent Statistics ◽  
The Impact

Abstract This manuscript describes numerical experiments investigating the influence of 2–30-km striplike heterogeneity on wet and dry convective boundary layers coupled to the land surface. The striplike heterogeneity is shown to dramatically alter the structure of the convective boundary layer by inducing significant organized circulations that modify turbulent statistics. The impact, strength, and extent of the organized motions depend critically on the scale of the heterogeneity λ relative to the boundary layer height zi. The coupling with the land surface modifies the surface fluxes and hence the circulations resulting in some differences compared to previous studies using fixed surface forcing. Because of the coupling, surface fluxes in the middle of the patches are small compared to the patch edges. At large heterogeneity scales (λ/zi ∼18) horizontal surface-flux gradients within each patch are strong enough to counter the surface-flux gradients between wet and dry patches allowing the formation of small cells within the patch coexisting with the large-scale patch-induced circulations. The strongest patch-induced motions occur in cases with 4 < λ/zi < 9 because of strong horizontal pressure gradients across the wet and dry patches. Total boundary layer turbulence kinetic energy increases significantly for surface heterogeneity at scales between λ/zi = 4 and 9; however, entrainment rates for all cases are largely unaffected by the striplike heterogeneity. Velocity and scalar fields respond differently to variations of heterogeneity scale. The patch-induced motions have little influence on total vertical scalar flux, but the relative contribution to the flux from organized motions compared to background turbulence varies with heterogeneity scale. Patch-induced motions are shown to dramatically impact point measurements in a free-convective boundary layer. The magnitude and sign of this impact depends on the location of the measurement within the region of heterogeneity.

scholarly journals Velocity Estimation of Ocean Surface Currents in along-Track InSAR System Based on Conditional Generative Adversarial Networks

2021 ◽  
Vol 13 (20) ◽  
pp. 4088
Author(s):  
He Yan ◽  
Qianru Hou ◽  
Guodong Jin ◽  
Xing Xu ◽  
Gong Zhang ◽  
...  
Keyword(s):  
Current Velocity ◽  
Surface Current ◽  
Ocean Surface ◽  
Velocity Estimation ◽  
Training Dataset ◽  
Generative Adversarial Networks ◽  
Surface Currents ◽  
Ocean Surface Currents ◽  
Ocean Surface Current ◽  
Along Track

Velocity estimation of ocean surface currents is of great significance in the fields of the fishery, shipping, sewage discharge, and military affairs. Over the last decade, along-track interferometric synthetic aperture radar (along-track InSAR) has been demonstrated to be one of the important instruments for large-area and high-resolution ocean surface current velocity estimation. The calculation method of the traditional ocean surface current velocity, as influenced by the large-scale wave orbital velocity and the Bragg wave phase velocity, cannot easily separate the current velocity, characterized by large error and low efficiency. In this paper, a novel velocity estimation method of ocean surface currents is proposed based on Conditional Generative Adversarial Networks (CGANs). The main processing steps are as follows: firstly, the known ocean surface current field diagrams and their corresponding interferometric phase diagrams are constructed as the training dataset; secondly, the estimation model of the ocean surface current field is constructed based on the pix2pix algorithm and trained by the training dataset; finally, the interferometric phase diagrams in the test dataset are input into the trained model. In the simulation experiment, processing results of the proposed method are compared with those of traditional ocean surface current velocity estimation methods, which demonstrate the efficiency and effectiveness of the novel method.

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