scholarly journals Origin of the Annual to Decadal Peaks of Variability in the Response of Simple Ocean Models to Stochastic Forcing

2007 ◽  
Vol 37 (8) ◽  
pp. 2146-2157 ◽  
Author(s):  
Jérôme Sirven ◽  
Christophe Herbaut ◽  
Julie Deshayes ◽  
Claude Frankignoul
Keyword(s):  
Spatial Pattern ◽  
Analytical Model ◽  
Rossby Waves ◽  
Ocean Model ◽  
Western Boundary ◽  
Ekman Pumping ◽  
Stochastic Forcing ◽  
One Dimensional ◽  
Ocean Models ◽  
Strongly Damped

Abstract The response of the ocean to stochastic forcings is studied in a closed basin, using a simple one-dimensional analytical model. The focus is on the mechanisms that determine the time scales of the response and their possible links with free basin modes. The response may be described as a forced solution plus propagating solutions whose spatial pattern does not depend on the forcing. The propagating solutions are of two types. The first ones propagate eastward and are strongly damped so that their influence remains limited to the western boundary layer. The others are damped long Rossby waves that propagate westward and whose amplitude depends on the spatial extension and the frequency of the forcing. The amplitude increases if the frequency of the forcing is close to the frequency of the basin modes, but the spatial pattern differs from that of the latter; higher frequencies are favored if the zonal extension of the forcing is reduced. The response of a 1.5-layer reduced-gravity ocean model forced by stochastic Ekman pumping confirms the results of the analytical model.

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.

Limitation of One-Dimensional Ocean Models for Coupled Hurricane–Ocean Model Forecasts

2009 ◽  
Vol 137 (12) ◽  
pp. 4410-4419 ◽  
Author(s):  
Richard M. Yablonsky ◽  
Isaac Ginis
Keyword(s):  
North Atlantic Ocean ◽  
Three Dimensional ◽  
Ocean Model ◽  
Sea Surface ◽  
Upper Ocean ◽  
Surface Cooling ◽  
One Dimensional ◽  
Sea Surface Cooling ◽  
Ocean Models ◽  
The One

Abstract Wind stress imposed on the upper ocean by a hurricane can limit the hurricane’s intensity primarily through shear-induced mixing of the upper ocean and subsequent cooling of the sea surface. Since shear-induced mixing is a one-dimensional process, some recent studies suggest that coupling a one-dimensional ocean model to a hurricane model may be sufficient for capturing the storm-induced sea surface temperature cooling in the region providing heat energy to the hurricane. Using both a one-dimensional and a three-dimensional version of the same ocean model, it is shown here that the neglect of upwelling, which can only be captured by a three-dimensional ocean model, underestimates the storm-core sea surface cooling for hurricanes translating at <∼5 m s−1. For hurricanes translating at <2 m s−1, more than half of the storm-core sea surface cooling is neglected by the one-dimensional ocean model. Since the majority of hurricanes in the western tropical North Atlantic Ocean translate at <5 m s−1, the idealized experiments presented here suggest that one-dimensional ocean models may be inadequate for coupled hurricane–ocean model forecasting.

Influence of Midlatitude Winds on the Stratification of the Equatorial Thermocline*

2006 ◽  
Vol 36 (2) ◽  
pp. 222-237 ◽  
Author(s):  
Masami Nonaka ◽  
Julian P. McCreary ◽  
Shang-Ping Xie
Keyword(s):  
Rossby Waves ◽  
Western Boundary ◽  
Thermocline Depth ◽  
Ekman Pumping ◽  
Baroclinic Mode ◽  
Layer Model ◽  
Mode Water ◽  
Equatorial Thermocline ◽  
Sponge Layer ◽  
Small Basin

Abstract The stratification of the equatorial thermocline is a key variable for tropical climate dynamics, through its influence on the temperature of the water that upwells in the eastern equatorial ocean. In this study, two types of ocean models are used, an ocean general circulation model (GCM) and a 1½-layer model, to investigate processes by which changes in the midlatitude winds affect the equatorial stratification. Specifically, the influences of anomalous mode-water formation, Ekman pumping, and entrainment in the subpolar ocean are examined. The effects of a “sponge layer” adjacent to the northern boundary of the basin are also assessed. Solutions are forced by idealized zonal winds with strong or weak midlatitude westerlies, and they are found in rectangular basins that extend from the equator to 36°N (small basin) or to 60°N (large basin). In the GCM solutions, a prominent response to reduced winds is the thinning of the mixed layer in the northwestern region of the subtropical gyre, leading to less subduction of low-potential-vorticity mode water and hence thinning of the upper thermocline in the central-to-eastern subtropics. Almost all of this thinning signal, however, recirculates within the subtropics, and does not extend to the equator. Another midlatitude response is shallowing (deepening) of the thermocline in the subtropical (subpolar) ocean in response to Ekman pumping. This, primarily, first-baroclinic-mode (n = 1) response has the most influence on the equatorial thermocline. First-baroclinic-mode Rossby waves propagate to the western boundary of the basin where they reflect as packets of coastal Kelvin and short-wavelength Rossby waves that carry the midlatitude signal to the equator. Subsequently, equatorial Kelvin waves spread it along the equator, leading to a shoaling and thinning of the equatorial thermocline. The layer-thickness field h in the 1½-layer model corresponds to thermocline depth in the GCM. Both the sponge layer and subpolar Ekman suction are important factors for the 1½-layer model solutions, requiring water upwelled in the interior ocean to be transported into the sponge layer via the western boundary layer. In the small basin, equatorial h thins in response to weakened westerlies when there is a sponge layer, but it thickens when there is not. In the large basin, equatorial h is unaffected by weakened westerlies when there is a sponge layer, but it thins when water is allowed to entrain into the layer in the subpolar gyre. It is concluded that the thinning of the equatorial thermocline in the GCM solutions is caused by the sponge layer in the small basin and by entrainment in the subpolar ocean in the large one.

scholarly journals The Vertical Structure of Large-Scale Unsteady Currents

2015 ◽  
Vol 45 (3) ◽  
pp. 755-777 ◽  
Author(s):  
Antoine Hochet ◽  
Alain Colin de Verdière ◽  
Robert Scott
Keyword(s):  
Linear Model ◽  
Large Scale ◽  
Vertical Structure ◽  
Rossby Waves ◽  
Ocean Model ◽  
Altimeter Data ◽  
Western Boundary ◽  
Mean Flow ◽  
Low Latitudes ◽  
Barotropic Mode

AbstractA linear model based on the quasigeostrophic equations is constructed in order to predict the vertical structure of Rossby waves and, more broadly, of anomalies resolved by altimeter data, roughly with periods longer than 20 days and with wavelengths larger than 100 km. The subsurface field is reconstructed from sea surface height and climatological stratification. The solution is calculated in periodic rectangular regions with a 3D discrete Fourier transform. The effect of the mean flow on Rossby waves is neglected, which the authors believe is a reasonable approximation for low latitudes. The method used has been tested with an idealized double-gyre simulation [performed with the Miami Isopycnal Coordinate Ocean Model (MICOM)]. The linear model is able to give reasonable predictions of subsurface currents at low latitudes (below approximately 30°) and for relatively weak mean flow. However, the predictions degrade with stronger mean flows and higher latitudes. The subsurface velocities calculated with this model using AVISO altimetric data and velocities from current meters have also been compared. Results show that the model gives reasonably accurate results away from the top and bottom boundaries, side boundaries, and far from western boundary currents. This study found, for the regions where the model is valid, an energy partition of the traditional modes of approximately 68% in the barotropic mode and 25% in the first baroclinic mode. Only 20% of the observed kinetic energy can be attributed to free Rossby waves of long periods that propagate energy to the west.

Comparative Dynamics of Atmosphere-Ocean-Models within the Description of the Perturbed Global Carbon Cycle

1981 ◽  
Vol 36 (3) ◽  
pp. 233-250
Author(s):  
E. O. Siré ◽  
G. H. Kohlmaier ◽  
G. Kratz ◽  
U. Fischbach ◽  
H. Brohl
Keyword(s):  
Surface Layer ◽  
Deep Ocean ◽  
Eddy Diffusivity ◽  
Ocean Model ◽  
One Dimensional ◽  
Partial Pressures ◽  
Biogenic Carbon ◽  
Carbon Transfer ◽  
Ocean Models ◽  
Global Carbon

For a certain class of ocean models describing the exchange of inorganic carbon between the atmosphere and the surface layer of the ocean as well as between the surface layer and the deep sea the dynamical airborne fraction is evaluated analytically under the assumption that the growth rate of the atmospheric source term (fossil fuel plus net biogenic carbon input into the atmosphere) is slowly variable with time. Each of these models exhibits a certain uptake capacity of the deep ocean which is quantified. Considerations are made as to whether the terrestrial biota are to be regarded as a source or a sink for additional atmospheric CO2 depending on the modelling of the deep ocean. It is shown that a global one-dimensional box-diffusion ocean model with a depth dependent eddy diffusivity K(z) - K(0) exp[-z/z*], with an adjustable parameter set {K(0), z*}, provides a fairly well fit to the prebomb 14C ocean distribution and to an appreciable net biogenic carbon transfer into the atmosphere. The range of future atmospheric CO2 partial pressures is estimated for a given fossil input

scholarly journals Response of the Kuroshio Extension to Rossby Waves Associated with the 1970s Climate Regime Shift in a High-Resolution Ocean Model*

2005 ◽  
Vol 18 (15) ◽  
pp. 2979-2995 ◽  
Author(s):  
Bunmei Taguchi ◽  
Shang-Ping Xie ◽  
Humio Mitsudera ◽  
Atsushi Kubokawa
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Regime Shift ◽  
Rossby Waves ◽  
Kuroshio Extension ◽  
Ocean Model ◽  
Western Boundary ◽  
Climate Regime ◽  
Climate Regime Shift ◽  
The Kuroshio

Abstract The response of the Kuroshio Extension (KE) to large-scale Rossby waves remotely excited by wind stress changes associated with the 1970s climate regime shift is studied using a high-resolution regional ocean model. Two ensemble simulations are conducted: The control run uses monthly climatological forcing while, in the second ensemble, anomalous forcing is imposed at the model eastern boundary around 165°E derived from a hindcast of decadal changes in subsurface temperature and salinity using a coarser-resolution model of the Pacific basin. Near the KE, ocean adjustment deviates strongly from the linear Rossby wave dynamics. Most notably, the eastward acceleration of the KE is much narrower in meridional extent than that associated with the incoming Rossby waves imposed on the eastern boundary. This KE acceleration is associated with an enhanced potential vorticity (PV) gradient across the front that is consistent with the inertial western boundary layer theory: the arrival of the Rossby waves at the western boundary causes the eastward current to accelerate, leading to enhanced advection of low (high) PV water of subtropical (subarctic) origin along the western boundary layer. The meridional dipole of PV anomalies results in a pair of anomalous recirculations with a narrow eastward jet in between. A three-layer quasigeostrophic model is used to demonstrate this inertial adjustment mechanism. Finally, transient eddy activity increases significantly and the eddy momentum transport acts to strengthen the mean flow response. The result that ocean physical response to broad-scale atmospheric forcing is large near the KE front has important implications for fisheries research.

scholarly journals Ensemble forecasting greatly expands the prediction horizon for ocean mesoscale variability

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Prasad G. Thoppil ◽  
Sergey Frolov ◽  
Clark D. Rowley ◽  
Carolyn A. Reynolds ◽  
Gregg A. Jacobs ◽  
...  
Keyword(s):  
Initial Conditions ◽  
Horizontal Resolution ◽  
Ocean Model ◽  
Mesoscale Dynamics ◽  
Predictive Skill ◽  
Freshwater Transport ◽  
Prediction Horizon ◽  
Initial Location ◽  
Ocean Models ◽  
High Uncertainty

AbstractMesoscale eddies dominate energetics of the ocean, modify mass, heat and freshwater transport and primary production in the upper ocean. However, the forecast skill horizon for ocean mesoscales in current operational models is shorter than 10 days: eddy-resolving ocean models, with horizontal resolution finer than 10 km in mid-latitudes, represent mesoscale dynamics, but mesoscale initial conditions are hard to constrain with available observations. Here we analyze a suite of ocean model simulations at high (1/25°) and lower (1/12.5°) resolution and compare with an ensemble of lower-resolution simulations. We show that the ensemble forecast significantly extends the predictability of the ocean mesoscales to between 20 and 40 days. We find that the lack of predictive skill in data assimilative deterministic ocean models is due to high uncertainty in the initial location and forecast of mesoscale features. Ensemble simulations account for this uncertainty and filter-out unconstrained scales. We suggest that advancements in ensemble analysis and forecasting should complement the current focus on high-resolution modeling of the ocean.

scholarly journals The features of the coastal fronts in the Eastern Guangdong coastal waters during the downwelling-favorable wind period

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Chaoyu Yang ◽  
Haibin Ye
Keyword(s):  
Coastal Waters ◽  
Meteorological Data ◽  
Pearson Correlation ◽  
Ocean Model ◽  
Ekman Pumping ◽  
Zonal Distribution ◽  
Factors Affecting ◽  
China Sea ◽  
Hybrid Coordinate Ocean Model ◽  
The Mean

AbstractA coastal front was detected in the eastern Guangdong (EGD) coastal waters during a downwelling-favorable wind period by using the diffuse attenuation coefficient at 490 nm (Kd(490)). Long-term satellite data, meteorological data and hydrographic data collected from 2003 to 2017 were jointly utilized to analyze the environmental factors affecting coastal fronts. The intensities of the coastal fronts were found to be associated with the downwelling intensity. The monthly mean Kd(490) anomalies in shallow coastal waters less than 25 m deep along the EGD coast and the monthly mean Ekman pumping velocities retrieved by the ERA5 dataset were negatively correlated, with a Pearson correlation of − 0.71. The fronts started in October, became weaker and gradually disappeared after January, extending southwestward from the southeastern coast of Guangdong Province to the Wanshan Archipelago in the South China Sea (SCS). The cross-frontal differences in the mean Kd(490) values could reach 3.7 m−1. Noticeable peaks were found in the meridional distribution of the mean Kd(490) values at 22.5°N and 22.2°N and in the zonal distribution of the mean Kd(490) values at 114.7°E and 114.4°E. The peaks tended to narrow as the latitude increased. The average coastal surface currents obtained from the global Hybrid Coordinate Ocean Model (HYCOM) showed that waters with high nutrient and sediment contents in the Fujian and Zhejiang coastal areas in the southern part of the East China Sea could flow into the SCS. The directions and lengths of the fronts were found to be associated with the flow advection.

Polar Optical Phonon Instability and Intervalley Transfer in Gallium Nitride

1998 ◽  
Vol 512 ◽  
Author(s):  
B. E. Foutz ◽  
S. K. O'leary ◽  
M. S. Shur ◽  
L. F. Eastman ◽  
B. L. Gelmont ◽  
...  
Keyword(s):  
Gallium Nitride ◽  
Analytical Model ◽  
Optical Phonon ◽  
Room Temperature ◽  
Phonon Scattering ◽  
Polar Optical Phonon ◽  
Scattering Mechanism ◽  
Loss Mechanism ◽  
One Dimensional ◽  
Optical Phonon Scattering

ABSTRACTWe develop a simple, one-dimensional, analytical model, which describes electron transport in gallium nitride. We focus on the polar optical phonon scattering mechanism, as this is the dominant energy loss mechanism at room temperature. Equating the power gained from the field with that lost through scattering, we demonstrate that beyond a critical electric field, 114 kV/cm at T = 300 K, the power gained from the field exceeds that lost due to polar optical phonon scattering. This polar optical phonon instability leads to a dramatic increase in the electron energy, this being responsible for the onset of intervalley transitions. The predictions of our analytical model are compared with those of Monte Carlo simulations, and are found to be in satisfactory agreement.

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