scholarly journals Axial Wind Effects on Stratification and Longitudinal Salt Transport in an Idealized, Partially Mixed Estuary*

2009 ◽  
Vol 39 (8) ◽  
pp. 1905-1920 ◽  
Author(s):  
Shih-Nan Chen ◽  
Lawrence P. Sanford
Keyword(s):  
Wind Stress ◽  
Salinity Gradient ◽  
Ocean Model ◽  
Salt Transport ◽  
Salt Flux ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Shear Dispersion ◽  
Wind Events ◽  
Wind Mixing

Abstract A 3D hydrodynamic model [Regional Ocean Model System (ROMS)] is used to investigate how axial wind influences stratification and to explore the associated longitudinal salt transport in partially mixed estuaries. The model is configured to represent a straight estuarine channel connecting to a shelf sea. The results confirm that wind straining of the along-channel salinity gradient exerts an important control on stratification. Two governing parameters are identified: the Wedderburn number (W) defined as the ratio of wind stress to axial baroclinic pressure gradient force, and the ratio of an entrainment depth to water depth (hs/H). Here W controls the effectiveness of wind straining, which promotes increases (decreases) in stratification during down-estuary (up-estuary) wind. The ratio hs/H determines the portion of the water column affected by direct wind mixing. While stratification is always reduced by up-estuary wind, stratification shows an increase-then-decrease transition when down-estuary wind stress increases. Such transition is a result of the competition between wind straining and direct wind mixing. A horizontal Richardson number modified to include wind straining/mixing is shown to reasonably represent the transition, and a regime diagram is proposed to classify the wind’s role on stratification. Mechanisms driving salt flux during axial wind events are also explored. At the onset and end of the wind events, barotropic adjustment drives strong transient salt fluxes. Net salt flux is controlled by the responses of subtidal shear dispersion to wind forcing. Moderate down-estuary winds enhance subtidal shear dispersion, whereas up-estuary winds always reduce it. Supporting observations from upper Chesapeake Bay are presented.

scholarly journals Coastal Trapped Waves, Alongshore Pressure Gradients, and the California Undercurrent*

2014 ◽  
Vol 44 (1) ◽  
pp. 319-342 ◽  
Author(s):  
Thomas P. Connolly ◽  
Barbara M. Hickey ◽  
Igor Shulman ◽  
Richard E. Thomson
Keyword(s):  
Pressure Gradient ◽  
Wind Stress ◽  
West Coast ◽  
Current System ◽  
Ocean Model ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Pressure Gradients ◽  
Transport Pathway ◽  
California Current System

Abstract The California Undercurrent (CUC), a poleward-flowing feature over the continental slope, is a key transport pathway along the west coast of North America and an important component of regional upwelling dynamics. This study examines the poleward undercurrent and alongshore pressure gradients in the northern California Current System (CCS), where local wind stress forcing is relatively weak. The dynamics of the undercurrent are compared in the primitive equation Navy Coastal Ocean Model and a linear coastal trapped wave model. Both models are validated using hydrographic data and current-meter observations in the core of the undercurrent in the northern CCS. In the linear model, variability in the predominantly equatorward wind stress along the U.S. West Coast produces episodic reversals to poleward flow over the northern CCS slope during summer. However, reproducing the persistence of the undercurrent during late summer requires additional incoming energy from sea level variability applied south of the region of the strongest wind forcing. The relative importance of the barotropic and baroclinic components of the modeled alongshore pressure gradient changes with latitude. In contrast to the southern and central portions of the CCS, the baroclinic component of the alongshore pressure gradient provides the primary poleward force at CUC depths over the northern CCS slope. At time scales from weeks to months, the alongshore pressure gradient force is primarily balanced by the Coriolis force associated with onshore flow.

scholarly journals Temporal evolution of the momentum balance terms and frictional adjustment observed over the inner shelf during a storm

Ocean Science ◽  
2016 ◽  
Vol 12 (1) ◽  
pp. 137-151 ◽  
Author(s):  
M. Grifoll ◽  
A. L. Aretxabaleta ◽  
J. L. Pelegrí ◽  
M. Espino
Keyword(s):  
Coriolis Force ◽  
Wind Stress ◽  
Water Depth ◽  
Momentum Balance ◽  
Wave Radiation ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Inner Shelf ◽  
Coastal Waves ◽  
Nw Mediterranean

Abstract. We investigate the rapidly changing equilibrium between the momentum sources and sinks during the passage of a single two-peak storm over the Catalan inner shelf (NW Mediterranean Sea). Velocity measurements at 24 m water depth are taken as representative of the inner shelf, and the cross-shelf variability is explored with measurements at 50 m water depth. During both wind pulses, the flow accelerated at 24 m until shortly after the wind maxima, when the bottom stress was able to compensate for the wind stress. Concurrently, the sea level also responded, with the pressure-gradient force opposing the wind stress. Before, during and after the second wind pulse, there were velocity fluctuations with both super- and sub-inertial periods likely associated with transient coastal waves. Throughout the storm, the Coriolis force and wave radiation stresses were relatively unimportant in the along-shelf momentum balance. The frictional adjustment timescale was around 10 h, consistent with the e-folding time obtained from bottom drag parameterizations. The momentum evolution at 50 m showed a larger influence of the Coriolis force at the expense of a decreased frictional relevance, typical in the transition from the inner to the mid-shelf.

Observed El Niño SSTA Development and the Effects of Easterly and Westerly Wind Events in 2014/15

2017 ◽  
Vol 30 (4) ◽  
pp. 1505-1519 ◽  
Author(s):  
Andrew M. Chiodi ◽  
D. E. Harrison
Keyword(s):  
Wind Stress ◽  
El Niño ◽  
El Nino ◽  
Ocean Model ◽  
Equatorial Pacific ◽  
Westerly Wind ◽  
Easterly Wind ◽  
Model Studies ◽  
Wind Events ◽  
Westerly Wind Events

Abstract The unexpected halt of warm sea surface temperature anomaly (SSTA) growth in 2014 and development of a major El Niño in 2015 has drawn attention to our ability to understand and predict El Niño development. Wind stress–forced ocean model studies have satisfactorily reproduced observed equatorial Pacific SSTAs during periods when data return from the TAO/TRITON buoy network was high. Unfortunately, TAO/TRITON data return in 2014 was poor. To study 2014 SSTA development, the observed wind gaps must be filled. The hypothesis that subseasonal wind events provided the dominant driver of observed waveguide SSTA development in 2014 and 2015 is used along with the available buoy winds to construct an oceanic waveguide-wide surface stress field of westerly wind events (WWEs) and easterly wind surges (EWSs). It is found that the observed Niño-3.4 SSTA development in 2014 and 2015 can thereby be reproduced satisfactorily. Previous 2014 studies used other wind fields and reached differing conclusions about the importance of WWEs and EWSs. Experiment results herein help explain these inconsistencies, and clarify the relative importance of WWEs and EWSs. It is found that the springtime surplus of WWEs and summertime balance between WWEs and EWSs (yielding small net wind stress anomaly) accounts for the early development and midyear reversal of El Niño–like SSTA development in 2014. A strong abundance of WWEs in 2015 accounts for the rapid SSTA warming observed then. Accurately forecasting equatorial Pacific SSTA in years like 2014 and 2015 may require learning to predict WWE and EWS occurrence characteristics.

scholarly journals Seasonal Arctic sea-ice simulations with a prognostic ice-ocean model

1991 ◽  
Vol 15 ◽  
pp. 45-53 ◽  
Author(s):  
Peter H. Ranelli ◽  
William D. Hibler
Keyword(s):  
Arctic Ocean ◽  
Arctic Basin ◽  
Ocean Model ◽  
Arctic Sea Ice ◽  
Salt Transport ◽  
Salt Flux ◽  
The Arctic ◽  
Diagnostic Model ◽  
Quasi Equilibrium ◽  
The Arctic Ocean

A prognostic ice-ocean model of the Arctic, Greenland and Norwegian seas with daily wind and atmospheric forcing is integrated for 30 years to quasi-equilibrium. Three simulations are carried out to investigate the role played by ice deformation and transport in baroclinic adjustment of the Arctic Ocean: a standard run with precipitation and ice transport, a simulation without precipitation and a “thermodynamics only” simulation without ice transport but including precipitation. A diagnostic model is integrated for five years to serve as a comparative control run. Comparison of the vertically integrated stream-function of each of the model runs indicates that the vertical density stratification needed to maintain the circulation of the Arctic Ocean is reduced excessively when precipitation is neglected and artificially enhanced if ice transport out of the basin is ignored. This effect is even more noticeable in the surface currents and is also apparent in a comparison of simulated and observed drifting-buoy tracks. An analysis of the salt budget of the Arctic Ocean indicates that the three main components, salt transport by the ocean, salt flux from the annual cycle of ice, and a fresh-water flux from precipitation and river runoff are approximately of the same magnitude. The main circulation deficiency identified in the simulations is an inadequate flow of Atlantic water into the Arctic Basin through the Fram Strait.

scholarly journals The Deflection of the China Coastal Current over the Taiwan Bank in Winter

2018 ◽  
Vol 48 (7) ◽  
pp. 1433-1450 ◽  
Author(s):  
Enhui Liao ◽  
Lie Yauw Oey ◽  
Xiao-Hai Yan ◽  
Li Li ◽  
Yuwu Jiang
Keyword(s):  
Pressure Gradient ◽  
Wind Stress ◽  
Large Scale ◽  
Numerical Models ◽  
Gradient Force ◽  
Coastal Current ◽  
Pressure Gradient Force ◽  
Bottom Stress ◽  
In Situ Data ◽  
Offshore Flow

AbstractIn winter, an offshore flow of the coastal current can be inferred from satellite and in situ data over the western Taiwan Bank. The dynamics related to this offshore flow are examined here using observations as well as analytical and numerical models. The currents can be classified into three regimes. The downwind (i.e., southward) cold coastal current remains attached to the coast when the northeasterly wind stress is stronger than a critical value depending on the upwind (i.e., northward) large-scale pressure gradient force. By contrast, an upwind warm current appears over the Taiwan Bank when the wind stress is less than the critical pressure gradient force. The downwind coastal current and upwind current converge and the coastal current deflects offshore onto the bank during a moderate wind. Analysis of the vorticity balance shows that the offshore transport is a result of negative bottom stress curl that is triggered by the positive vorticity of the two opposite flows. The negative bottom stress curl is reinforced by the gentle slope over the bank, which enhances the offshore current. Composite analyses using satellite observations show cool waters with high chlorophyll in the offshore current under moderate wind. The results of composite analyses support the model findings and may explain the high productivity over the western bank in winter.

scholarly journals Seasonal Arctic sea-ice simulations with a prognostic ice-ocean model

1991 ◽  
Vol 15 ◽  
pp. 45-53 ◽  
Author(s):  
Peter H. Ranelli ◽  
William D. Hibler
Keyword(s):  
Arctic Ocean ◽  
Arctic Basin ◽  
Ocean Model ◽  
Arctic Sea Ice ◽  
Salt Transport ◽  
Salt Flux ◽  
The Arctic ◽  
Diagnostic Model ◽  
Quasi Equilibrium ◽  
The Arctic Ocean

A prognostic ice-ocean model of the Arctic, Greenland and Norwegian seas with daily wind and atmospheric forcing is integrated for 30 years to quasi-equilibrium. Three simulations are carried out to investigate the role played by ice deformation and transport in baroclinic adjustment of the Arctic Ocean: a standard run with precipitation and ice transport, a simulation without precipitation and a “thermodynamics only” simulation without ice transport but including precipitation. A diagnostic model is integrated for five years to serve as a comparative control run. Comparison of the vertically integrated stream-function of each of the model runs indicates that the vertical density stratification needed to maintain the circulation of the Arctic Ocean is reduced excessively when precipitation is neglected and artificially enhanced if ice transport out of the basin is ignored. This effect is even more noticeable in the surface currents and is also apparent in a comparison of simulated and observed drifting-buoy tracks. An analysis of the salt budget of the Arctic Ocean indicates that the three main components, salt transport by the ocean, salt flux from the annual cycle of ice, and a fresh-water flux from precipitation and river runoff are approximately of the same magnitude. The main circulation deficiency identified in the simulations is an inadequate flow of Atlantic water into the Arctic Basin through the Fram Strait.

scholarly journals A Momentum Budget Analysis of Westerly Wind Events Associated with the Madden–Julian Oscillation during DYNAMO

2015 ◽  
Vol 72 (10) ◽  
pp. 3780-3799 ◽  
Author(s):  
Ji-Hyun Oh ◽  
Xianan Jiang ◽  
Duane E. Waliser ◽  
Mitchell W. Moncrieff ◽  
Richard H. Johnson ◽  
...  
Keyword(s):  
Lower Troposphere ◽  
Active Phase ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Madden Julian Oscillation ◽  
Westerly Wind ◽  
Budget Analysis ◽  
Momentum Budget ◽  
Wind Events ◽  
Westerly Wind Events

Abstract The Dynamics of the Madden–Julian Oscillation (DYNAMO) field campaign was conducted over the Indian Ocean (IO) from October 2011 to February 2012 to investigate the initiation of the Madden–Julian oscillation (MJO). Three MJOs accompanying westerly wind events (WWEs) occurred in late October, late November, and late December 2011. Momentum budget analysis is conducted to understand the contributions of the dynamical processes involved in the wind evolution associated with the MJO over the IO during DYNAMO using European Centre for Medium-Range Weather Forecasts analysis. This analysis shows that westerly acceleration at lower levels associated with the MJO active phase generally appears to be maintained by the pressure gradient force (PGF), which could be partly canceled by meridional advection of the zonal wind. Westerly acceleration in the midtroposphere tends to be mostly attributable to vertical advection. The results herein imply that there is no simple linear dynamic model that can capture the WWEs associated with the MJO and that nonlinear processes have to be considered. In addition, the MJO in November (MJO2), accompanied by two WWEs (WWE1 and WWE2) spaced a few days apart, is diagnosed. Unlike other WWEs during DYNAMO, horizontal advection is more responsible for the westerly acceleration in the lower troposphere for WWE2 than the PGF. Interactions between the MJO2 envelope and convectively coupled waves (CCWs) are analyzed to illuminate the dynamical contribution of these synoptic-scale equatorial waves to the WWEs. The authors suggest that different developing processes among WWEs can be attributed to different types of CCWs.

scholarly journals Shifting momentum balance and frictional adjustment observed over the inner-shelf during a storm

2015 ◽  
Vol 12 (3) ◽  
pp. 897-924
Author(s):  
M. Grifoll ◽  
A. Aretxabaleta ◽  
J. L. Pelegrí ◽  
M. Espino
Keyword(s):  
Wind Stress ◽  
Water Depth ◽  
Momentum Balance ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Inner Shelf ◽  
Bottom Stress ◽  
Nw Mediterranean ◽  
High Kinetic Energy ◽  
Nw Mediterranean Sea

Abstract. We investigate the rapidly changing equilibrium between the momentum sources and sinks during the passage of a two-peak storm over the Catalan inner-shelf (NW Mediterranean Sea). Velocity measurements at 24 m water depth are taken as representative of the inner shelf, and the cross-shelf variability is explored with additional measurements at 50 m water depth. At 24 m, as the storm-related wind stress accelerated the flow, velocity increased throughout the water column, resulting in bottom stress starting to become important. The sea level also responded, with the pressure gradient force opposing the wind stress. In particular, during the second wind pulse, there were rapid oscillations in the acceleration and advective terms, apparently reflecting the incapacity of the bottom stress to dissipate the high kinetic energy of the system. The Coriolis and wave induced terms (via radiation stresses) were less important in the momentum balance. The frictional adjustment time scale was around 10 h, consistent with the e-folding time obtained from bottom drag parameterizations. Estimates of the frictional time and Ekman depth confirm the prevailing frictional response at 24 m. The momentum evolution in deeper parts of the shelf (50 m) showed an increase in the Coriolis force at the expense of the frictional term, typical in the transition from the inner to the mid-shelf.

scholarly journals Sensitivity of Hurricane Intensity Forecast to Convective Momentum Transport Parameterization

2006 ◽  
Vol 134 (2) ◽  
pp. 664-674 ◽  
Author(s):  
Jongil Han ◽  
Hua-Lu Pan
Keyword(s):  
Wind Shear ◽  
Vertical Wind Shear ◽  
Momentum Transport ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Momentum Exchange ◽  
Forecast System ◽  
Hurricane Intensity ◽  
Convective Momentum Transport ◽  
The Many

Abstract A parameterization of the convection-induced pressure gradient force (PGF) in convective momentum transport (CMT) is tested for hurricane intensity forecasting using NCEP's operational Global Forecast System (GFS) and its nested Regional Spectral Model (RSM). In the parameterization the PGF is assumed to be proportional to the product of the cloud mass flux and vertical wind shear. Compared to control forecasts using the present operational GFS and RSM where the PGF effect in CMT is taken into account empirically, the new PGF parameterization helps increase hurricane intensity by reducing the vertical momentum exchange, giving rise to a closer comparison to the observations. In addition, the new PGF parameterization forecasts not only show more realistically organized precipitation patterns with enhanced hurricane intensity but also reduce the forecast track error. Nevertheless, the model forecasts with the new PGF parameterization still largely underpredict the observed intensity. One of the many possible reasons for the large underprediction may be the absence of hurricane initialization in the models.

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