scholarly journals A Model Study of the Spectral Structure of Boundary-Driven Rossby Waves and Related Altimetric Implications

2005 ◽  
Vol 35 (2) ◽  
pp. 218-231 ◽  
Author(s):  
Stefano Pierini
Keyword(s):  
Large Scale ◽  
Rossby Waves ◽  
North Pacific Ocean ◽  
Altimeter Data ◽  
Western Boundary ◽  
Spectral Structure ◽  
The North ◽  
Model Study ◽  
General Aspects ◽  
Coastal Kelvin Waves

Abstract A two-layer primitive equation box model of the North Pacific Ocean is used to highlight and analyze some general aspects of the linear large-scale boundary-driven oceanic variability that are detectable through altimeter observations. The model is forced by a white-noise wind, and a spectral analysis of the zonal and meridional, barotropic and baroclinic velocity components is carried out. Several dynamical features are identified in terms of boundary-driven Rossby waves, and their spatial structure and frequency dependence are examined theoretically and discussed in connection with recent studies based on altimeter data. In particular, the following aspects of the variability are analyzed: 1) beta-refracted baroclinic Rossby waves, which are found to be generated along the eastern boundary of the ocean by the passage of coastal Kelvin waves originating from the equatorial waveguide, and 2) westward-intensified barotropic Rossby waves, which originate from the western boundary of the ocean after reflection of longer waves generated in midocean. In the discussion the stress is put on dynamical aspects not yet fully understood and on the possibility that altimetry can provide further insight into their functioning.

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.

DESIGN AND IMPLEMENTATION OF THE OCEANOGRAPHIC MODELING AND OBSERVATION NETWORK (REMO) FOR PHYSICAL OCEANOGRAPHY STUDIES AND OCEAN FORECASTING

2014 ◽  
Vol 31 (2) ◽  
Author(s):  
Jose Antonio Moreira Lima
Keyword(s):  
Atlantic Ocean ◽  
Large Scale ◽  
North Pacific Ocean ◽  
Integrated Approach ◽  
Sea Surface ◽  
Global Ocean ◽  
Height Anomaly ◽  
The North ◽  
Observation Network ◽  
Ocean Forecasting

This paper is concerned with the planning, implementation and some results of the Oceanographic Modeling and Observation Network, named REMO, for Brazilian regional waters. Ocean forecasting has been an important scientific issue over the last decade due to studies related to climate change as well as applications related to short-range oceanic forecasts. The South Atlantic Ocean has a deficit of oceanographic measurements when compared to other ocean basins such as the North Atlantic Ocean and the North Pacific Ocean. It is a challenge to design an ocean forecasting system for a region with poor observational coverage of in-situ data. Fortunately, most ocean forecasting systems heavily rely on the assimilation of surface fields such as sea surface height anomaly (SSHA) or sea surface temperature (SST), acquired by environmental satellites, that can accurately provide information that constrain major surface current systems and their mesoscale activity. An integrated approach is proposed here in which the large scale circulation in the Atlantic Ocean is modeled in a first step, and gradually nested into higher resolution regional models that are able to resolve important processes such as the Brazil Current and associated mesoscale variability, continental shelf waves, local and remote wind forcing, and others. This article presents the overall strategy to develop the models using a network of Brazilian institutions and their related expertise along with international collaboration. This work has some similarity with goals of the international project Global Ocean Data Assimilation Experiment OceanView (GODAE OceanView).

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.

Using Satellite Altimeter and SST Observations of the 1997-1998 El Nino to Check the Key Ocean Processes Involved in a Strong El Nino.

2021 ◽  
Author(s):  
David Webb ◽  
Andrew Coward ◽  
Helen Snaith
Keyword(s):  
El Niño ◽  
Large Scale ◽  
El Nino ◽  
Ocean Model ◽  
Satellite Altimeter ◽  
The North ◽  
Satellite Sst ◽  
Model Study ◽  
North Equatorial Counter Current ◽  
Equatorial Current

<p>A recent high-resolution ocean model study of the strong El Ninos of 1982-1983 and 1997-1998 highlighted a previously neglected ocean mechanism which was active during their growth.   The mechanism involved a weakening of both the Equatorial Current and the tropical instability eddies in mid-ocean.  It also involved an increase in the strength of the North Equatorial Counter Current due to the passage of the annual Rossby wave.</p><p>      This presentation reports how satellite altimeter and satellite SST data was used to validate the model results the key areas, confirming the changes in the current and eddy fields and the resulting eastward extension of the region of highest SST values.  The SST changes were sufficient to trigger new regions deep-atmospheric convection and so had the potential to have a significant impact on the development of the El Nino and the resulting changes in the large scale atmospheric circulation.</p>

scholarly journals Internal tide energy flux over a ridge measured by a co-located ocean glider and moored ADCP

2019 ◽  
Author(s):  
Rob Hall ◽  
Barbara Berx ◽  
Gillian Damerell
Keyword(s):  
Energy Flux ◽  
Large Scale ◽  
Low Frequency ◽  
Internal Tide ◽  
Small Scale ◽  
Potential Density ◽  
The North ◽  
Model Study ◽  
Continental Shelves ◽  
Alternative Approach

Abstract. Internal tide energy flux is an important diagnostic for the study of energy pathways in the ocean, from large-scale input by the surface tide, to small-scale dissipation by turbulent mixing. Accurate calculation of energy flux requires repeated full-depth measurements of both potential density (ρ) and horizontal current velocity (u) over at least a tidal cycle and over several weeks to resolve the internal spring-neap cycle. Typically, these observations are made using full-depth oceanographic moorings that are vulnerable to being fished-out by commercial trawlers when deployed on continental shelves and slopes. Here we test an alternative approach to minimise these risks, with u measured by a low-frequency ADCP moored near the seabed and ρ measured by an autonomous ocean glider holding station by the ADCP. The method is used to measure the M2 internal tide radiating from the Wyville Thompson Ridge in the North Atlantic. The observed energy flux (4.2 ± 0.2 kW m−1) compares favourably with historic observations and a previous numerical model study. Error in the energy flux calculation due to imperfect co-location of the glider and ADCP is estimated by sub-sampling potential density in an idealised internal tide field along pseudorandomly distributed glider paths. The error is considered acceptable (

scholarly journals The pulsating nature of large-scale Saharan dust transport as a result of interplays between mid-latitude Rossby waves and the North African Dipole Intensity

2017 ◽  
Vol 167 ◽  
pp. 586-602 ◽  
Author(s):  
E. Cuevas ◽  
A.J. Gómez-Peláez ◽  
S. Rodríguez ◽  
E. Terradellas ◽  
S. Basart ◽  
...  
Keyword(s):  
Large Scale ◽  
Rossby Waves ◽  
Saharan Dust ◽  
North African ◽  
Dust Transport ◽  
The North

scholarly journals On the Crucial Role of Basin Geometry in Double-Gyre Models of the Kuroshio Extension

2008 ◽  
Vol 38 (6) ◽  
pp. 1327-1333 ◽  
Author(s):  
Stefano Pierini
Keyword(s):  
Crucial Role ◽  
North Pacific Ocean ◽  
Kuroshio Extension ◽  
Low Frequency ◽  
Altimeter Data ◽  
Western Boundary ◽  
Low Frequency Variability ◽  
Basin Geometry ◽  
The Kuroshio ◽  
Double Gyre

Abstract The decadal chaotic relaxation oscillation obtained in a recent double-gyre model study of the Kuroshio Extension intrinsic low-frequency variability was found to compare surprisingly well with the real variability of the jet as revealed by altimeter data, despite the high degree of idealization of the model. In this note it is shown that elements of realism in the basin geometry, present in that study and absent in previous double-gyre models applied to the Kuroshio Extension, play a crucial role in shaping the low-frequency variability of the jet, and can explain the good performance of the model. A series of numerical experiments with different basin geometries of increasing degrees of simplicity are analyzed. If the schematic western boundary representing the coastline south of Japan is removed, the strong decadal variability completely disappears and only a very weak periodic oscillation about an elongated state of the jet is found. If the large zonal width of the basin (representing correctly the extension of the North Pacific Ocean) is reduced by a half, then the total meridional Sverdrup transport is reduced by the same factor, and so is the intensity of the Kuroshio and Oyashio western boundary currents: as a result, the modeled Kuroshio Extension is totally unrealistic in shape and is steady. If both simplifications are introduced the resulting jet is, again, totally unrealistic, yielding a weak periodic bimodal cycle. On the basis of these results, two main conclusions are drawn: (i) the introduction of appropriate geometrical elements of realism in double-gyre model studies of the Kuroshio Extension is essential, and (ii) the Kuroshio Extension intrinsic low-frequency variability would be dramatically different if the southwestern coastline of Japan were more meridionally oriented.

Kīlauea lava fuels phytoplankton bloom in the North Pacific Ocean

Science ◽  
2019 ◽  
Vol 365 (6457) ◽  
pp. 1040-1044 ◽  
Author(s):  
Samuel T. Wilson ◽  
Nicholas J. Hawco ◽  
E. Virginia Armbrust ◽  
Benedetto Barone ◽  
Karin M. Björkman ◽  
...  
Keyword(s):  
North Pacific ◽  
Large Scale ◽  
Phytoplankton Bloom ◽  
North Pacific Ocean ◽  
Biological Response ◽  
Molecular Evidence ◽  
North Pacific Subtropical Gyre ◽  
The North ◽  
High Concentrations ◽  
The North Pacific

From June to August 2018, the eruption of Kīlauea volcano on the island of Hawai‘i injected millions of cubic meters of molten lava into the nutrient-poor waters of the North Pacific Subtropical Gyre. The lava-impacted seawater was characterized by high concentrations of metals and nutrients that stimulated phytoplankton growth, resulting in an extensive plume of chlorophyll a that was detectable by satellite. Chemical and molecular evidence revealed that this biological response hinged on unexpectedly high concentrations of nitrate, despite the negligible quantities of nitrogen in basaltic lava. We hypothesize that the high nitrate was caused by buoyant plumes of nutrient-rich deep waters created by the substantial input of lava into the ocean. This large-scale ocean fertilization was therefore a unique perturbation event that revealed how marine ecosystems respond to exogenous inputs of nutrients.

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