The Impact of SST Specification on ECMWF Surface Wind Stress Fields in the Eastern Tropical Pacific

2005 ◽  
Vol 18 (4) ◽  
pp. 530-550 ◽  
Author(s):  
Dudley B. Chelton
Keyword(s):  
Wind Stress ◽  
Weather Prediction ◽  
Surface Wind ◽  
Cold Season ◽  
Numerical Weather Prediction Model ◽  
Tropical Pacific ◽  
Stress Fields ◽  
Eastern Tropical Pacific ◽  
Ocean Atmosphere ◽  
The Impact

Abstract The impact of SST specification on low-level winds in the operational ECMWF numerical weather prediction model is investigated in the eastern tropical Pacific from comparisons of ECMWF wind stress fields with QuikSCAT satellite scatterometer observations of wind stress during the August–December cold seasons of 2000 and 2001. These two time periods bracket the 9 May 2001 change from the Reynolds SST analyses to the Real-Time Global SST (RTG_SST) analyses as the ocean boundary condition in the ECMWF model. The ocean–atmosphere interaction in the eastern tropical Pacific that is clearly evident in QuikSCAT wind stress divergence and curl fields is also evident in the ECMWF winds, but is more than twice as strong in the 2001 cold season as in the 2000 cold season, due primarily to the improved spatial and temporal resolution of the RTG_SST analyses compared with the Reynolds SST analyses. While a significant improvement compared with 2000, the response of the 2001 ECMWF wind stress field to SST is only about half as strong as the coupling inferred from QuikSCAT data and satellite observations of SST from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI). It is concluded that the underrepresentation of the ocean–atmosphere coupling is attributable partly to underrepresentation of SST gradients in the RTG_SST fields and partly to inadequacies of the ECWMF model. The latter may be due to errors in the parameterization of boundary layer processes or to insufficient horizontal or vertical resolution in the model.

scholarly journals Observations of Coupling between Surface Wind Stress and Sea Surface Temperature in the Eastern Tropical Pacific

2001 ◽  
Vol 14 (7) ◽  
pp. 1479-1498 ◽  
Author(s):  
Dudley B. Chelton ◽  
Steven K. Esbensen ◽  
Michael G. Schlax ◽  
Nicolai Thum ◽  
Michael H. Freilich ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Wind Stress ◽  
Surface Wind ◽  
Tropical Pacific ◽  
Sea Surface ◽  
Eastern Tropical Pacific ◽  
Surface Wind Stress

Simulating ENSO SSTAs from TAO/TRITON Winds: The Impacts of 20 Years of Buoy Observations in the Pacific Waveguide and Comparison with Reanalysis Products

2017 ◽  
Vol 30 (3) ◽  
pp. 1041-1059 ◽  
Author(s):  
Andrew M. Chiodi ◽  
D. E. Harrison
Keyword(s):  
Wind Stress ◽  
Southern Oscillation ◽  
Surface Wind ◽  
Major Elements ◽  
Ocean Model ◽  
Tropical Pacific ◽  
Wind Fields ◽  
Enso Events ◽  
The Pacific ◽  
The Impact

Abstract The fundamental importance of near-equatorial zonal wind stress in the evolution of the tropical Pacific Ocean’s seasonal cycle and El Niño–Southern Oscillation (ENSO) events is well known. It has been two decades since the TAO/TRITON buoy array was deployed, in part to provide accurate surface wind observations across the Pacific waveguide. It is timely to revisit the impact of TAO/TRITON winds on our ability to simulate and thereby understand the evolution of sea surface temperature (SST) in this region. This work shows that forced ocean model simulations of SST anomalies (SSTAs) during the periods with a reasonably high buoy data return rate can reproduce the major elements of SSTA variability during ENSO events using a wind stress field computed from TAO/TRITON observations only. This demonstrates that the buoy array usefully fulfills its waveguide-wind-measurement purpose. Comparison of several reanalysis wind fields commonly used in recent ENSO studies with the TAO/TRITON observations reveals substantial biases in the reanalyses that cause substantial errors in the variability and trends of the reanalysis-forced SST simulations. In particular, the negative trend in ERA-Interim is much larger and the NCEP–NCAR Reanalysis-1 and NCEP–DOE Reanalysis-2 variability much less than seen in the TAO/TRITON wind observations. There are also mean biases. Thus, even with the TAO/TRITON observations available for assimilation into these wind products, there remain oceanically important differences. The reanalyses would be much more useful for ENSO and tropical Pacific climate change study if they would more effectively assimilate the TAO/TRITON observations.

scholarly journals Vertical Mixing in the Ocean and Its Impact on the Coupled Ocean–Atmosphere System in the Eastern Tropical Pacific*

2009 ◽  
Vol 22 (13) ◽  
pp. 3703-3719 ◽  
Author(s):  
Kelvin J. Richards ◽  
Shang-Ping Xie ◽  
Toru Miyama
Keyword(s):  
Vertical Mixing ◽  
Tropical Pacific ◽  
Intertropical Convergence Zone ◽  
General Character ◽  
Convergence Zone ◽  
Ocean Mixing ◽  
Cold Tongue ◽  
Eastern Tropical Pacific ◽  
Ocean Atmosphere ◽  
The Impact

Abstract The zonal and meridional asymmetries in the eastern tropical Pacific (the eastern equatorial cold tongue and the northern intertropical convergence zone) are key aspects of the region that are strongly influenced by ocean–atmosphere interactions. Here the authors investigate the impact of vertical mixing in the ocean on these asymmetries, employing a coupled ocean–atmosphere regional model. Results highlight the need to study the impact of processes such as vertical mixing in the context of the coupled system. Changes to the vertical mixing in the ocean are found to produce large changes in the state of the system, which include changes to the surface properties of the ocean, the ocean currents, the surface wind field, and clouds and precipitation in the atmosphere. Much of the strength of the impact is through interactions between the ocean and atmosphere. Increasing ocean mixing has an opposite effect on the zonal and meridional asymmetries. The zonal asymmetry is increased (i.e., a colder eastern equatorial cold tongue and increased easterly winds), whereas the meridional asymmetry is decreased (a reduced north–south temperature difference and reduced southerlies), with the impact being enhanced by the Bjerknes and wind–evaporation–sea surface temperature feedbacks. Water mass transformations are analyzed by consideration of the diapynic fluxes. Although the general character of the diapycnic transport remains relatively unchanged with a change in ocean mixing, there are changes to the magnitude and location of the transport in density space. Oceanic vertical mixing impacts the balance of terms contributing to the heating of the ocean surface mixed layer. With reduced mixing the advection of heat plays an increased role in areas such as the far eastern tropical Pacific and under the intertropical convergence zone.

Reduced Stability of the Atlantic Meridional Overturning Circulation due to Wind Stress Feedback during Glacial Times

2008 ◽  
Vol 21 (23) ◽  
pp. 6260-6282 ◽  
Author(s):  
Olivier Arzel ◽  
Matthew H. England ◽  
Willem P. Sijp
Keyword(s):  
Sea Ice ◽  
Wind Stress ◽  
Surface Wind ◽  
Meridional Overturning Circulation ◽  
Nonlinear Dependence ◽  
Upper Ocean ◽  
Overturning Circulation ◽  
Climate Conditions ◽  
Meridional Overturning ◽  
The Impact

Abstract A previous study by Mikolajewicz suggested that the wind stress feedback stabilizes the Atlantic thermohaline circulation. This result was obtained under modern climate conditions, for which the presence of the massive continental ice sheets characteristic of glacial times is missing. Here a coupled ocean–atmosphere–sea ice model of intermediate complexity, set up in an idealized spherical sector geometry of the Atlantic basin, is used to show that, under glacial climate conditions, wind stress feedback actually reduces the stability of the meridional overturning circulation (MOC). The analysis reveals that the influence of the wind stress feedback on the glacial MOC response to an external source of freshwater applied at high northern latitudes is controlled by the following two distinct processes: 1) the interactions between the wind field and the sea ice export in the Northern Hemisphere (NH), and 2) the northward Ekman transport in the tropics and upward Ekman pumping in the core of the NH subpolar gyre. The former dominates the response of the coupled system; it delays the recovery of the MOC, and in some cases even stabilizes collapsed MOC states achieved during the hosing period. The latter plays a minor role and mitigates the impact of the former process by reducing the upper-ocean freshening in deep-water formation regions. Hence, the wind stress feedback delays the recovery of the glacial MOC, which is the opposite of what occurs under modern climate conditions. Close to the critical transition threshold beyond which the circulation collapses, the glacial MOC appears to be very sensitive to changes in surface wind stress forcing and exhibits, in the aftermath of the freshwater pulse, a nonlinear dependence upon the wind stress feedback magnitude: a complete and irreversible MOC shutdown occurs only for intermediate wind stress feedback magnitudes. This behavior results from the competitive effects of processes 1 and 2 on the midlatitude upper-ocean salinity during the shutdown phase of the MOC. The mechanisms presented here may be relevant to the large meltwater pulses that punctuated the last glacial period.

Regional oceanic and biogeochemical modeling strategy :forced or coupled model ?

2021 ◽  
Author(s):  
Véra Oerder ◽  
Pierre-Amaël Auger ◽  
Joaquim Bento ◽  
Samuel Hormazabal
Keyword(s):  
High Resolution ◽  
Wind Stress ◽  
Coupled Model ◽  
Heat Fluxes ◽  
Atmospheric Conditions ◽  
Coupled Simulation ◽  
Biogeochemical Modeling ◽  
Ocean Atmosphere ◽  
The Impact ◽  
Oceanic Model

<p><span> Regional high resolution biogeochemical modeling studies generaly use an oceanic model forced by prescribed atmospheric conditions. The computational cost of such approach is far lower than using an high resolution ocean-atmosphere coupled model. However, forced oceanic models cannot represent adequately the atmospheric reponse to the oceanic mesoscale (~10-100km) structures and the impact on the oceanic dynamics.</span></p><p><span>To assess the bias introduce by the use of a forced model, we compare here a regional high resolution (1/12º) ocean-atmosphere coupled model with oceanic simulations forced by the outputs of the coupled simulation. Several classical forcing strategies are compared : bulk formulae, prescribed stress, prescribed heat fluxes with or without Sea Surface Temperature (SST) restoring term, .... We study the Chile Eastern Boundary Upwelling System, and the oceanic model includes a biogeochemical component,</span></p><p><span>The coupled model oceanic mesoscale impacts the atmosphere through surface current and SST anomalies. Surface currents mainly affect the wind stress while SST impacts both the wind stress and the heat fluxes. In the forced simulations, mesoscale structures generated by the model internal variability does not correspond to those of the coupled simulation. According to the forcing strategy, the atmospheric conditions are not modified by the forced model mesoscale, or the modifications are not realistic. The regional dynamics (coastal upwelling, mesoscale activity, …) is affected, with impact on the biogeochemical activity.</span></p><p> </p><p> </p><p><em>This work was supported by the FONDECYT project 3180472 (Chile), with computational support of the NLHPC from the Universidad de Chile, the HPC from the Pontificia Universidad Catolica de Valparaiso and the Irene HPC from the GENCI at the CEA (France).</em></p>

An Investigation of the Stability Dependence of SST-Induced Vertical Mixing over the Ocean in the Operational Met Office Model

2017 ◽  
Vol 30 (1) ◽  
pp. 91-107 ◽  
Author(s):  
Qingtao Song ◽  
Dudley B. Chelton ◽  
Steven K. Esbensen ◽  
Andrew R. Brown
Keyword(s):  
Wind Speed ◽  
Weather Prediction ◽  
Surface Wind ◽  
Vertical Mixing ◽  
Surface Wind Speed ◽  
Satellite Observations ◽  
Sea Surface ◽  
Stable Conditions ◽  
Wide Range ◽  
The Impact

This study presents an assessment of the impact of a March 2006 change in the Met Office operational global numerical weather prediction model through the introduction of a nonlocal momentum mixing scheme. From comparisons with satellite observations of surface wind speed and sea surface temperature (SST), it is concluded that the new parameterization had a relatively minor impact on SST-induced changes in sea surface wind speed in the Met Office model in the September and October 2007 monthly averages over the Agulhas Return Current region considered here. The performance of the new parameterization of vertical mixing was evaluated near the surface layer and further through comparisons with results obtained using a wide range of sensitivity of mixing parameterization to stability in the Weather Research and Forecasting (WRF) Model, which is easily adapted to such sensitivity studies. While the new parameterization of vertical mixing improves the Met Office model response to SST in highly unstable (convective) conditions, it is concluded that significantly enhanced vertical mixing in the neutral to moderately unstable conditions (nondimensional stability [Formula: see text] between 0 and −2) typically found over the ocean is required in order for the model surface wind response to SST to match the satellite observations. Likewise, the reduced mixing in stable conditions in the new parameterization is also relatively small; for the range of the gradient Richardson number typically found over the ocean, the mixing was reduced by a maximum of only 10%, which is too small by more than an order of magnitude to be consistent with the satellite observations.

scholarly journals On the effect of model parameters on forecast objects

2018 ◽  
Vol 11 (4) ◽  
pp. 1577-1590 ◽  
Author(s):  
Caren Marzban ◽  
Corinne Jones ◽  
Ning Li ◽  
Scott Sandgathe
Keyword(s):  
Forest Fires ◽  
Eddy Currents ◽  
Numerical Models ◽  
Weather Prediction ◽  
Clustering Algorithms ◽  
Latin Hypercube Sampling ◽  
Numerical Weather Prediction Model ◽  
Model Parameters ◽  
Multiple Model ◽  
The Impact

Abstract. Many physics-based numerical models produce a gridded, spatial field of forecasts, e.g., a temperature map. The field for some quantities generally consists of spatially coherent and disconnected objects. Such objects arise in many problems, including precipitation forecasts in atmospheric models, eddy currents in ocean models, and models of forest fires. Certain features of these objects (e.g., location, size, intensity, and shape) are generally of interest. Here, a methodology is developed for assessing the impact of model parameters on the features of forecast objects. The main ingredients of the methodology include the use of (1) Latin hypercube sampling for varying the values of the model parameters, (2) statistical clustering algorithms for identifying objects, (3) multivariate multiple regression for assessing the impact of multiple model parameters on the distribution (across the forecast domain) of object features, and (4) methods for reducing the number of hypothesis tests and controlling the resulting errors. The final output of the methodology is a series of box plots and confidence intervals that visually display the sensitivities. The methodology is demonstrated on precipitation forecasts from a mesoscale numerical weather prediction model.

scholarly journals Reducing Climatology Bias in an Ocean–Atmosphere CGCM with Improved Coupling Physics

2005 ◽  
Vol 18 (13) ◽  
pp. 2344-2360 ◽  
Author(s):  
Jing-Jia Luo ◽  
Sebastien Masson ◽  
Erich Roeckner ◽  
Gurvan Madec ◽  
Toshio Yamagata
Keyword(s):  
Wind Stress ◽  
Surface Current ◽  
Ocean Surface ◽  
Tropical Pacific ◽  
Equatorial Pacific ◽  
Eastern Pacific ◽  
Cold Tongue ◽  
Easterly Wind ◽  
Ocean Atmosphere ◽  
The Tropical Pacific

Abstract The cold tongue in the tropical Pacific extends too far west in most current ocean–atmosphere coupled GCMs (CGCMs). This bias also exists in the relatively high-resolution SINTEX-F CGCM despite its remarkable performance of simulating ENSO variations. In terms of the importance of air–sea interactions to the climatology formation in the tropical Pacific, several sensitivity experiments with improved coupling physics have been performed in order to reduce the cold-tongue bias in CGCMs. By allowing for momentum transfer of the ocean surface current to the atmosphere [full coupled simulation (FCPL)] or merely reducing the wind stress by taking the surface current into account in the bulk formula [semicoupled simulation (semi-CPL)], the warm-pool/cold-tongue structure in the equatorial Pacific is simulated better than that of the control simulation (CTL) in which the movement of the ocean surface is ignored for wind stress calculation. The reduced surface zonal current and vertical entrainment owing to the reduced easterly wind stress tend to produce a warmer sea surface temperature (SST) in the western equatorial Pacific. Consequently, the dry bias there is much reduced. The warming tendency of the SST in the eastern Pacific, however, is largely suppressed by isopycnal diffusion and meridional advection of colder SST from south of the equator due to enhanced coastal upwelling near Peru. The ENSO signal in the western Pacific and its global teleconnection in the North Pacific are simulated more realistically. The approach as adopted in the FCPL run is able to generate a correct zonal SST slope and efficiently reduce the cold-tongue bias in the equatorial Pacific. The surface easterly wind itself in the FCPL run is weakened, reducing the easterly wind stress further. This is related with a weakened zonal Walker cell in the atmospheric boundary layer over the eastern Pacific and a new global angular momentum balance of the atmosphere associated with reduced westerly wind stress over the southern oceans.

Low-Level Jets, Orographic Effects, and Extreme Events in Nares Strait: A Model-Based Mesoscale Climatology

2008 ◽  
Vol 136 (12) ◽  
pp. 4746-4759 ◽  
Author(s):  
R. M. Samelson ◽  
P. L. Barbour
Keyword(s):  
Time Series ◽  
Wind Stress ◽  
Pressure Difference ◽  
Weather Prediction ◽  
Surface Wind ◽  
Atmospheric Model ◽  
The Arctic ◽  
Baffin Bay ◽  
Low Level ◽  
Nares Strait

Abstract A mesoscale atmospheric model, nested in operational global numerical weather prediction fields, is used to estimate low-level winds and surface wind stress through Nares Strait, between Ellesmere Island and Greenland, during 2 yr from August 2003 to July 2005. During most of the year, the model low-level winds are dominated by intense, southward along-strait flow, with monthly-mean southward 10-m winds reaching 10 m s−1 in winter. Summertime flow is weak and distributions of hourly along-strait winds during the 2-yr period are strongly bimodal. The strong southward low-level winds are associated with ageostrophic, orographically channeled flow down the pressure gradient from the Lincoln Sea to Baffin Bay and are highly correlated with the pressure difference along Nares Strait. The 2-yr means and leading EOFs of monthly-mean 10-m winds and wind stress place the strongest winds and stress in the southern parts of Smith Sound and of Kennedy Channel, at the openings to Baffin Bay and Kane Basin, at known sites of polynya formation, including the North Water polynya in Smith Sound, suggesting that the locally intensified winds may cause these persistent polynyas. An intense wind event observed in Nares Strait by a field camp, with surface winds exceeding 30 m s−1, generally follows the typical pattern of these low-level flows. Based on the model correlation of winds and pressure difference, a 51-yr time series of estimated winds in Nares Strait is reconstructed from historical surface pressure measurements at Thule, Greenland, and Alert, Canada. The pressure difference and reconstructed wind time series are correlated with the Arctic Oscillation at annual and longer periods, but not on monthly periods.

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