scholarly journals Characterizing ERA-Interim and ERA5 surface wind biases using ASCAT

Ocean Science ◽  
2019 ◽  
Vol 15 (3) ◽  
pp. 831-852 ◽  
Author(s):  
Maria Belmonte Rivas ◽  
Ad Stoffelen
Keyword(s):  
Large Scale ◽  
Surface Wind ◽  
Atmospheric Stability ◽  
Ocean Current ◽  
Western Boundary ◽  
Boundary Current ◽  
Wind Stress Curl ◽  
Meridional Winds ◽  
Mesoscale Convective ◽  
Transient Wind

Abstract. This paper analyzes the differences between ERA-Interim and ERA5 surface winds fields relative to Advanced Scatterometer (ASCAT) ocean vector wind observations, after adjustment for the effects of atmospheric stability and density, using stress-equivalent winds (U10S) and air–sea relative motion using ocean current velocities. In terms of instantaneous root mean square (rms) wind speed agreement, ERA5 winds show a 20 % improvement relative to ERA-Interim and a performance similar to that of currently operational ECMWF forecasts. ERA5 also performs better than ERA-Interim in terms of mean and transient wind errors, wind divergence and wind stress curl biases. Yet, both ERA products show systematic errors in the partition of the wind kinetic energy into zonal and meridional, mean and transient components. ERA winds are characterized by excessive mean zonal winds (westerlies) with too-weak mean poleward flows in the midlatitudes and too-weak mean meridional winds (trades) in the tropics. ERA stress curl is too cyclonic in midlatitudes and high latitudes, with implications for Ekman upwelling estimates, and lacks detail in the representation of sea surface temperature (SST) gradient effects (along the equatorial cold tongues and Western Boundary Current (WBC) jets) and mesoscale convective airflows (along the Intertropical Convergence Zone and the warm flanks for the WBC jets). It is conjectured that large-scale mean wind biases in ERA are related to their lack of high-frequency (transient wind) variability, which should be promoting residual meridional circulations in the Ferrel and Hadley cells.

scholarly journals Characterizing ERA-interim and ERA5 surface wind biases using ASCAT

2019 ◽  
Author(s):  
Maria Belmonte Rivas ◽  
Ad Stoffelen
Keyword(s):  
Large Scale ◽  
Surface Wind ◽  
Atmospheric Stability ◽  
Ocean Current ◽  
Wind Stress Curl ◽  
Wind Variability ◽  
Meridional Winds ◽  
Mesoscale Convective ◽  
Transient Wind ◽  
The Tropics

Abstract. This paper analyses the differences between ERA-Interim and ERA5 surface winds fields relative to ASCAT ocean vector wind observations, after adjustment for the effects of atmospheric stability and density, using stress equivalent winds (U10S), and air-sea relative motion using ocean current velocities. In terms of instantaneous RMS wind speed agreement, ERA5 winds show a 20 % improvement relative to ERA interim, and a performance similar to that of currently operational ECMWF forecasts. ERA5 also performs better than ERA-interim in terms of mean and transient wind errors, wind divergence and wind stress curl biases. Yet, both ERA products show systematic errors in the partition of the wind kinetic energy into zonal and meridional, mean and transient components. ERA winds are characterized by excessive mean zonal winds (westerlies) with defective mean poleward flows at mid-latitudes, and defective mean meridional winds (trades) in the tropics. ERA stress curl is too cyclonic at mid and high latitudes, with implications for Ekman upwelling estimates, and lack detail in the representation of SST gradient effects (along the equatorial cold tongues and WBC jets) and mesoscale convective airflows (along the ITCZ and the warm flanks for the WBC jets). It is conjectured that large-scale mean wind biases in ERA are related to their lack of high frequency (transient wind) variability, which should be promoting residual meridional circulations in the Ferrell and Hadley cells.

scholarly journals A Coupled Decadal Prediction of the Dynamic State of the Kuroshio Extension System

2014 ◽  
Vol 27 (4) ◽  
pp. 1751-1764 ◽  
Author(s):  
Bo Qiu ◽  
Shuiming Chen ◽  
Niklas Schneider ◽  
Bunmei Taguchi
Keyword(s):  
Wind Stress ◽  
Large Scale ◽  
Current System ◽  
Kuroshio Extension ◽  
Surface Wind ◽  
Storm Tracks ◽  
Dynamic State ◽  
Western Boundary ◽  
Wind Stress Curl ◽  
The Kuroshio

Abstract Being the extension of a wind-driven western boundary current, the Kuroshio Extension (KE) has long been recognized as a turbulent current system rich in large-amplitude meanders and energetic pinched-off eddies. An important feature emerging from recent satellite altimeter measurements and eddy-resolving ocean model simulations is that the KE system exhibits well-defined decadal modulations between a stable and an unstable dynamic state. Here the authors show that the decadally modulating KE dynamic state can be effectively defined by the sea surface height (SSH) anomalies in the 31°–36°N, 140°–165°E region. By utilizing the SSH-based KE index from 1977 to 2012, they demonstrate that the time-varying KE dynamic state can be predicted at lead times of up to ~6 yr. This long-term predictability rests on two dynamic processes: 1) the oceanic adjustment is via baroclinic Rossby waves that carry interior wind-forced anomalies westward into the KE region and 2) the low-frequency KE variability influences the extratropical storm tracks and surface wind stress curl field across the North Pacific basin. By shifting poleward (equatorward) the storm tracks and the large-scale wind stress curl pattern during its stable (unstable) dynamic state, the KE variability induces a delayed negative feedback that can enhance the predictable SSH variance on the decadal time scales.

Topographic Rossby Waves in the Abyssal South China Sea

2021 ◽  
Author(s):  
QI QUAN ◽  
ZHONGYA CAI ◽  
GUANGZHEN JIN ◽  
ZHIQIANG LIU
Keyword(s):  
South China Sea ◽  
Group Velocity ◽  
South China ◽  
Large Scale ◽  
Rossby Waves ◽  
Western Boundary ◽  
Horizontal Shear ◽  
Boundary Current ◽  
China Sea ◽  
Topographic Rossby Waves

AbstractTopographic Rossby waves (TRWs) in the abyssal South China Sea (SCS) are investigated using observations and high-resolution numerical simulations. These energetic waves can account for over 40% of the kinetic energy (KE) variability in the deep western boundary current and seamount region in the central SCS. This proportion can even reach 70% over slopes in the northern and southern SCS. The TRW-induced currents exhibit columnar (i.e., in-phase) structure in which the speed increases downward. Wave properties such as the period (5–60 days), wavelength (100–500 km), and vertical trapping scale (102–103 m) vary significantly depending on environmental parameters of the SCS. The TRW energy propagates along steep topography with phase propagation offshore. TRWs with high frequencies exhibit a stronger climbing effect than low-frequency ones and hence can move further upslope. For TRWs with a certain frequency, the wavelength and trapping scale are dominated by the topographic beta, whereas the group velocity is more sensitive to the internal Rossby deformation radius. Background circulation with horizontal shear can change the wavelength and direction of TRWs if the flow velocity is comparable to the group velocity, particularly in the central, southern, and eastern SCS. A case study suggests two possible energy sources for TRWs: mesoscale perturbation in the upper layer and large-scale background circulation in the deep layer. The former provides KE by pressure work, whereas the latter transfers the available potential energy (APE) through baroclinic instability.

Positive Regional Sea Level Anomalies in Southern Brazil Due to Changes in Austral Atmospheric Circulation

2021 ◽  
Author(s):  
Venisse Schossler ◽  
Francisco Aquino ◽  
Jefferson Simões ◽  
Pedro Reis ◽  
Denilson Viana
Keyword(s):  
Sea Level ◽  
Wind Stress ◽  
Southern Annular Mode ◽  
Altimeter Data ◽  
Western Boundary ◽  
Positive Trend ◽  
Boundary Current ◽  
Wind Stress Curl ◽  
Sea Level Anomalies ◽  
Regional Sea Level

Abstract Pressure gradients and winds play an important role in Southern Hemisphere (SH) sea levels, which are currently associated with the positive trend of the Southern Annular Mode (SAM). This study investigated regional sea level anomalies (SLAs) in the southern coast Brazil using altimeter data (1993–2019), post-processed by the X-TRACK (CTOH/LEGOS). We observed a negative SLA from 1993 to 2009 and a positive SLA from 2010 to 2019, with upward trends throughout the evaluation period. We analyzed wind stress curl, pressure, and wind fields at sea level (FNMOC and ERA 5, respectively) in addition to sea surface temperature and height anomalies (SSTA/SSHA-OISST) in the South Atlantic Ocean (SAO) for 1993–2009 and 2010–2019. In relation to the first period, the second shows the enhancement in Hadley and Walker cells and trade winds, in addition to greater SSTA and SSHA in SAO. The SAO subtropical gyre and zonal winds at 45°S contribute to the intensification of the western boundary current. A greater pressure gradient between the SAO surface and the southeast of South America is noteworthy. Regionally, the positive SAM brings an increase in sea level to the study area, caused by greater wind stress and variability in heat flows.

A three-dimensional model of the wind-driven ocean circulation

1968 ◽  
Vol 34 (4) ◽  
pp. 721-734 ◽  
Author(s):  
J. A. Johnson
Keyword(s):  
Ocean Circulation ◽  
Three Dimensional ◽  
Ekman Layer ◽  
Return Flow ◽  
Western Boundary ◽  
Dimensional Model ◽  
Boundary Current ◽  
Three Dimensional Model ◽  
Wind Stress Curl ◽  
Interior Flow

A linear three-dimensional model of the wind-driven ocean circulation is treated by boundary-layer methods. The interior flow, below the Ekman layer, differs from the classical gyres of Munk (1950). There is a north-eastwards transport of fluid from the western boundary current of the southern gyre across the latitude of zero wind stress curl into the northern gyre. A return flow in the Ekman layer preserves continuity.

Ship Routing Based on the Kuroshio Current

2017 ◽  
Author(s):  
Chen Chen ◽  
Masashi Kashiwagi
Keyword(s):  
North Pacific Ocean ◽  
Kuroshio Current ◽  
Ocean Model ◽  
Ocean Current ◽  
Western Boundary ◽  
Boundary Current ◽  
Ship Maneuvering ◽  
Ship Routing ◽  
Ship Navigation ◽  
The Kuroshio

As a strong western-boundary current, the Kuroshio Current has significant effects on the ship navigation in the East China Sea (ECS). To quantitatively know more about its influence, we present simulations of the ocean current in the North Pacific Ocean using the well-known Princeton Ocean Model (POM). The high-resolution current distributions could be applied to conduct numerical simulations of the ship navigation, which utilized a ship maneuvering model known as the Mathematical Maneuvering Group (MMG). Calculation of a container ship as well as a training ship have been conducted. The simulation results of both ships can show the significant effects of ocean currents on ship’s drifting as well as speed change, which could be used to optimize cost of both fuel and time by properly utilizing the current in ship routing.

scholarly journals Pacific Shallow Meridional Overturning Circulation in a Warming Climate

2011 ◽  
Vol 24 (24) ◽  
pp. 6424-6439 ◽  
Author(s):  
Daiwei Wang ◽  
Mark A. Cane
Keyword(s):  
Surface Layer ◽  
Large Scale ◽  
Climate Model ◽  
Surface Wind ◽  
Meridional Overturning Circulation ◽  
First Century ◽  
Western Boundary ◽  
Warming Climate ◽  
Meridional Overturning ◽  
Twenty First Century

Abstract By analyzing a set of the Coupled Model Intercomparison Project phase 3 (CMIP3) climate model projections of the twenty-first century, it is found that the shallow meridional overturning of the Pacific subtropical cells (STCs) show contrasting trends between two hemispheres in a warming climate. The strength of STCs and equivalently the STC surface-layer transport tend to be weakening (strengthening) in the Northern (Southern) Hemisphere as a response to large-scale surface wind changes over the tropical Pacific. The STC pycnocline transport convergence into the equatorial Pacific Ocean from higher latitudes shows a robust weakening in the twenty-first century. This weakening is mainly through interior pathways consistent with the relaxation of the zonal pycnocline tilt, whereas the transport change through western boundary pathways is small and not consistent across models. It is found that the change of the western boundary pycnocline transport is strongly affected by the shoaling of the pycnocline base. In addition, there is a robust weakening of the Indonesian Throughflow (ITF) transport in a warming climate. In the multimodel ensemble mean, the response to greenhouse warming of the upper-ocean mass balance associated with the STCs is such that the weakening of the equatorward pycnocline transport convergence is balanced by a weakening of the poleward surface-layer transport divergence and the ITF transport of similar amounts.

scholarly journals Interannual to Decadal Variability of the Upper-Ocean Heat Content in the Western North Pacific and Its Relationship to Oceanic and Atmospheric Variability

2018 ◽  
Vol 31 (13) ◽  
pp. 5107-5125 ◽  
Author(s):  
Hanna Na ◽  
Kwang-Yul Kim ◽  
Shoshiro Minobe ◽  
Yoshi N. Sasaki
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Decadal Variability ◽  
Kuroshio Extension ◽  
Heat Content ◽  
Western Boundary ◽  
Delayed Response ◽  
Atmospheric Variability ◽  
Wind Stress Curl

Three-dimensional oceanic thermal structures and variability in the western North Pacific (NP) are examined on the interannual to decadal time scales and their relationship to oceanic and atmospheric variability is discussed by analyzing observation and reanalysis data for 45 years (1964–2008), which is much longer than the satellite-altimetry period. It is shown that the meridional shift of the Kuroshio Extension (KE) and subarctic frontal zone (SAFZ) is associated with the overall cooling/warming over the KE and SAFZ region (KE–SAFZ mode). It appears, however, that changes in KE strength induce different signs of thermal anomalies to the south and north of the KE, not extended to the SAFZ (KE mode), possibly contributing to noncoherent variability between the KE and SAFZ. Thus, the KE and SAFZ are dependent on each other in the context of the KE–SAFZ mode, while the KE is independent of the SAFZ in terms of the KE mode. This intricate relationship is associated with different linkages to atmospheric variability; the KE–SAFZ mode exhibits a relatively fast response to the large-scale wind stress curl forcing in the NP, whereas the KE mode is related to a delayed response to the atmospheric forcing via jet-trapped baroclinic Rossby wave propagation. It is suggested that further knowledge of the underlying mechanisms of the two modes would contribute to understanding ocean–atmosphere feedback as well as potential predictability over the western boundary current region in the NP.

scholarly journals Mixing Nonlocality and Mixing Anisotropy in an Idealized Western Boundary Current Jet

2017 ◽  
Vol 47 (12) ◽  
pp. 3015-3036 ◽  
Author(s):  
Ru Chen ◽  
Stephanie Waterman
Keyword(s):  
Large Scale ◽  
Eddy Diffusivity ◽  
Western Boundary Current ◽  
Wave Radiation ◽  
Western Boundary ◽  
Equilibration Time ◽  
Boundary Current ◽  
Jet Mixing ◽  
Velocity Magnitude ◽  
Axis Length

AbstractMotivated by the key role of western boundary currents in shaping water mass distribution and gyre water exchanges, this study characterizes mixing in an idealized western boundary current jet using a barotropic quasigeostrophic model with numerical particles deployed. Both the nonlocality of mixing, depicted by nonlocality ellipses, and mixing anisotropy, depicted by mixing ellipses, are estimated. Mixing is more nonlocal within the jet compared to the jet flanks. In general, the size of nonlocality ellipses, a metric of the degree of mixing nonlocality, scales with the eddy velocity magnitude and the equilibration time for diffusivity. The tilt and eccentricity of the nonlocality ellipses, a characterization of the anisotropy of mixing nonlocality, agree with those of momentum flux ellipses in the regions where mixing nonlocality is small. Mixing ellipse characteristics are flow regime dependent. In regions dominated by wave radiation, the mixing ellipses align with the contours of the wave streamfunction and are very anisotropic. Inside the recirculations, however, the mixing ellipses are nearly isotropic. Mixing ellipses are zonally elongated in the jet upstream because of the suppression of cross-jet mixing by the jet and the anisotropy of eddy velocity, and they can have negative minor axis length in the jet downstream, indicating negative cross-jet eddy diffusivity, which is consistent with upgradient eddy fluxes there. Thus, despite significant spatial heterogeneity in mixing nonlocality and anisotropy, in this idealized system at least, spatial patterns in these diagnostics tend to be relatively large scale and tied to larger-scale dynamics. The implications of these results to eddy parameterization and jet dynamics are discussed.

scholarly journals The Effects of Mesoscale Ocean–Atmosphere Coupling on the Large-Scale Ocean Circulation

2009 ◽  
Vol 22 (15) ◽  
pp. 4066-4082 ◽  
Author(s):  
Andrew Mc C. Hogg ◽  
William K. Dewar ◽  
Pavel Berloff ◽  
Sergey Kravtsov ◽  
David K. Hutchinson
Keyword(s):  
Spatial Scale ◽  
Ocean Circulation ◽  
Large Scale ◽  
Ocean Model ◽  
Small Scale ◽  
Western Boundary ◽  
Ekman Pumping ◽  
Boundary Current ◽  
Ocean Atmosphere ◽  
Gyre Circulation

Abstract Small-scale variation in wind stress due to ocean–atmosphere interaction within the atmospheric boundary layer alters the temporal and spatial scale of Ekman pumping driving the double-gyre circulation of the ocean. A high-resolution quasigeostrophic (QG) ocean model, coupled to a dynamic atmospheric mixed layer, is used to demonstrate that, despite the small spatial scale of the Ekman-pumping anomalies, this phenomenon significantly modifies the large-scale ocean circulation. The primary effect is to decrease the strength of the nonlinear component of the gyre circulation by approximately 30%–40%. This result is due to the highest transient Ekman-pumping anomalies destabilizing the flow in a dynamically sensitive region close to the western boundary current separation. The instability of the jet produces a flux of potential vorticity between the two gyres that acts to weaken both gyres.

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