Zonal jets in the Southern Ocean: a semi-analytical model based on scale separation

A reduced-order semi-analytic model of multiple zonal jets in the Southern Ocean is proposed based on the statistical approach and scale decomposition. By introducing two dominant scales in the vorticity equation, the model describes the large-scale and mesoscale dynamics using the explicit momentum dissipation in the horizontal and vertical directions. For validation and physical insights, the results of the reduced-order model are compared with solutions of two eddy-resolving ocean models: i) a realistic primitive-equation HYCOM (HYbrid Coordinate Ocean Model) simulation of the Southern Ocean and ii) an idealized quasi-geostrophic model of a shear-driven channel flow

Технологические решения для строительства разведочной вертикальной скважины глубиной 2680 метров на газовом месторождении (ХМАО)

Технологические решения для строительства разведочной вертикальной скважины глубиной 2680 метров на газовом месторождении (ХМАО).Technological solutions for the construction of an exploration vertical well with a depth of 2680 meters at the gas field (KHMAO)

Relationship between air-sea density flux and isopycnal meridional overturning circulation in a warming climate

The article of record as published may be found at http://dx.doi.org/10.1175/JCLI-D-11-00682.1This study aims to explore the relationship between air–sea density flux and isopycnal meridional overturning circulation (MOC), using the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) model projections of the twenty-first-century climate. The focus is on the semiadiabatic component of MOC beneath the mixed layer; this component is described using the concept of the push–pull mode, which represents the combined effects of the adiabatic push into the deep ocean in the Northern Hemisphere and the pull out of the deep ocean in the Southern Hemisphere. The analysis based on the GFDL Climate Model version 2.1 (CM2.1) simulation demonstrates that the push–pull mode and the actual isopycnal MOC at the equator evolve similarly in the deep layers, with their maximum transports decreasing by 4–5 Sv (1 Sv [ 106 m3 s21) during years 2001–2100. In particular, the push–pull mode and actual isopycnal MOC are within approximately 10% of each other at the density layers heavier than 27.55 kg m23, where the reduction in the MOC strength is the strongest. The decrease in the push–pull mode is caused by the direct contribution of the anomalous heat, rather than freshwater, surface fluxes. The agreement between the deep push–pull mode and MOC in the values of linear trend and variability on time scales longer than a decade suggests a largely adiabatic pole-to-pole mechanism for these changes. The robustness of the main conclusions is further explored in additional model simulations

Mechanisms Controlling the Sensitivity of the Atlantic Thermohaline Circulation to the Parameterization of Eddy Transports in Ocean GCMs

The authors identify and describe the important dynamical mechanisms that explain the significant sensitivity of the Atlantic thermohaline circulation to the parameterization of heat and salt transports by mesoscale eddies in numerical models. In particular, the effects of the Gent-McWilliams (GM) scheme, which has a strong flattening effect on isopycnals, and a simple horizontal diffusion scheme are considered and compared. Two control runs, one with each scheme, exhibit very different circulations and density structures. To analyze the dynamical reasons for the differences between the control runs, a number of numerical experiments with regionally varying diffusion coefficients are carried out, emphasizing the effects of different schemes in key regions. The main effect of eddies in the Southern Ocean in nature is to shoal the subsurface isopycnal surfaces, thus increasing the density of the northward inflow of relatively dense intermediate waters into the Atlantic-as will be seen, this is more effectively done by the GM parameterization of the eddies. The resulting increase in the subsurface density at low latitudes decreases the meridional density contrast with the high latitudes of the North Atlantic, shoals the pycnocline, and consequently weakens the meridional overturning. By contrast, the effect of the eddy transports in the western boundary current in the Northern Hemisphere on the strength of the North Atlantic Deep Water (NADW) formation is shown to be smaller. The Northern Hemisphere upwelling and horizontal flow structure is strongly affected by local eddy transports, and the outflow of the NADW is very sensitive to the Northern Hemisphere eddy transports as a result. The original scaling of Gnanadesikan is modified to include the effects of horizontal mixing in low latitudes. The results confirm the leading role of the Southern Ocean eddies in affecting the strength of NADW formation, while the Northern Hemisphere horizontal mixing mostly affects local upwelling. The eddy transports in the Southern Ocean also affect the properties of Antarctic Bottom Water, which influences the vertical penetration of the NADW overturning cell as well as the density of the deep ocean

Comparison of the Observed Mixed Layer Depth in the Lee of the Hawaiian Island to the Modeled Mixed Layer Depth of the Regional Navy Coastal Ocean Model

This study evaluates the ability of the Hawaii Regional Navy Coastal Ocean Model to accurately predict the depth of the surface mixed layer in the lee of the Hawaiian Islands. Accurately modeling the depth of the surface mixed layer in this complex wake island environment is important to naval operations because the area hosts numerous training exercises. The simulated data were compared to CTD data collected from sea gliders, and tests for correlation were conducted. For mixed layer depths that did show correlation, match-paired t tests were used to determine the significance of the correlations. It was determined that the Hawaii Regional Navy Coastal Ocean Model has difficulty accurately predicting the depth of the surface mixed layer. It was also determined that the model has difficulty with unusual oceanographic features such as mode water eddies. These features are too uncommon and short-lived to be depicted in the climatology data. The climatology data are a major component of the synthetic profiles that the model generates, and these profiles tend to smooth out the unusual subsurface isothermal layer. List of Abbreviations BT - bathythermographs CCE - cold core eddy COAMPS - Coupled Ocean/Atmosphere Mesoscale Prediction System CTD - conductivity, temperature, and depth GDEM - Generalized Digital Environmental Model IR - infrared MLD - mixed layer depth MODAS - Modular Ocean Data Assimilation System MOODS - Master Oceanographic Observation Dataset NCODA - Navy Coupled Ocean Data Assimilation NCOM1 - Hawaii Regional Navy Coastal Ocean Model with in situ assimilation NCOM2 - Hawaii Regional Navy Coastal Ocean Model without in situ assimilation PAVE - Profile Analysis and Visualization Environment SSHa - sea surface height anomaly derived from altimetry SST - sea surface temperature WCE - warm core edd

Reducing Errors in Temperature and Salinity in an Ocean Model Forced by Restoring Boundary Conditions

Restoring boundary conditions, wherein the temperature and salinity are restored to surface target fields of temperature and salinity, are traditionally used for studies of the ocean circulation in ocean general circulation models. The canonical problem with these boundary conditions is that, when the target fields are chosen as the observed fields, accurate simulation of the surface fields of temperature and salinity would imply that the surface fluxes and therefore the ocean heat transports approach zero, a clearly unrealistic situation. It is clear that the target fields cannot be chosen as the observed fields. A simple but effective method of modifying conventional restoring boundary conditions is introduced, designed to keep the calculated values of surface temperature and salinity as close to observations as possible. The technique involves calculating the optimal target fields in the restoring boundary conditions by an iterative procedure. The method accounts for oceanic processes, such as advection and eddy mixing in the derivation of the new boundary conditions. A reduced version of this method is introduced that produces comparable results but offers greater simplicity in implementation. The simplicity of the method is particularly attractive in idealized studies, which often employ restoring surface boundary conditions. The success of the new method is, however, limited by several factors that cannot be easily compensated by the adjustment of the target profiles. These factors include inaccurate model dynamics, errors in the observations, and the too-simplified form of restoring surface boundary conditions themselves. The application of the method in this study with a coarse-resolution model leads to considerable improvements of the simulation of sea surface temperature (SST) and sea surface salinity (SSS). Both amplitude and phase of the annual cycle in SST greatly improve. The resulting magnitudes of surface heat and freshwater fluxes increase on average, and the meridional heat transport gets stronger. However, the fluxes in some regions remain unrealistic, notably the too-strong freshwater forcing of the western boundary currents in the Northern Hemisphere. Southern Ocean cooling and freshening are also likely to be too strong. The subsurface values of temperature improve greatly, proving that a large part of errors in the subsurface temperature distribution in our model can be corrected by reducing errors at the surface. In contrast, the reduction of errors in surface salinity fails to improve uniformly the simulated subsurface salinity values