Global Observations of Oceanic Rossby Waves
12 Apr 1996-Science (American Association for the Advancement of Science)-Vol. 272, Iss: 5259, pp 234-238
TL;DR: The TOPEX/POSEIDON satellite altimeter has detected Rossby waves throughout much of the world ocean from sea level signals with ≲10-centimeter amplitude and ≳500-kilometer wavelength.
Abstract: Rossby waves play a critical role in the transient adjustment of ocean circulation to changes in large-scale atmospheric forcing. The TOPEX/POSEIDON satellite altimeter has detected Rossby waves throughout much of the world ocean from sea level signals with ≲10-centimeter amplitude and ≳500-kilometer wavelength. Outside of the tropics, Rossby waves are abruptly amplified by major topographic features. Analysis of 3 years of data reveals discrepancies between observed and theoretical Rossby wave phase speeds that indicate that the standard theory for free, linear Rossby waves is an incomplete description of the observed waves.
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TL;DR: In this paper, an automated procedure for identifying and tracking mesoscale features based on their SSH signatures yields 35,891 eddies with average lifetime of 32 weeks and an average propagation distance of 550 km.
1,744 citations
Cites background from "Global Observations of Oceanic Ross..."
...17) is qualitatively similar to those of the advective and QG nonlinearity parameters U/c and U/( Ls 2 ) over most of the World Ocean....
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...High-resolution sea surface height (SSH) fields constructed by merging measurements from two simultaneously operating altimeters (Ducet et al., 2000; Le Traon et al., 2003) have revealed that SSH variability is dominated by westward-propagating nonlinear mesoscale eddies throughout most of the World Ocean (Chelton et al., 2007)....
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...Close scrutiny reveals that the propagation speeds outside of the tropics are somewhat faster than predicted by the classical theory for Rossby waves (Chelton and Schlax, 1996; Fu and Chelton, 2001, and references therein; Osychny and Cornillon, 2004, and numerous subsequent studies; see also Fig....
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...Analogous patterns of preference for eddy polarity are found in association with other major meandering currents in the World Ocean....
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...It was evident from the first few years of the sea-surface height (SSH) fields from T/P that westward propagation is nearly ubiquitous in the World Ocean (Chelton and Schlax, 1996), confirming the conclusions from previous analyses of upper-ocean thermal observations in the North Pacific during the 1970s and 1980s (see Fig....
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TL;DR: In this article, the authors review observations, theory and model results on the monsoon circulation of the Indian Ocean and discuss possible physical mechanisms behind seasonal variability of the meridional overturning streamfunction and heat flux.
1,437 citations
TL;DR: In this paper, the first baroclinic gravity-wave phase speed c1 and the Rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles.
Abstract: Global 1 83 18 climatologies of the first baroclinic gravity-wave phase speed c1 and the Rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles. These new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the Northern Hemisphere and the South Atlantic and with a 1 83 18 fine-resolution map of c1 for the tropical Pacific. It is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5%‐15% owing to seemingly minor computational errors. Geographical variations in the new high-resolution maps of c1 and l1 are discussed in terms of a WKB approximation that elucidates the effects of earth rotation, stratification, and water depth on these quantities. It is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the World Ocean. This is rationalized from consideration of the WKB approximation.
1,290 citations
Cites background or result from "Global Observations of Oceanic Ross..."
...This study was also motivated by a recent analysis of altimeter data (Chelton and Schlax 1996), which showed large-scale, low-frequency sea level signals propagating westward throughout much of the World Ocean....
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...…radius could account for the apparent factor-of-2 discrepancy between the westward propagation speeds of midlatitude sea level signals observed in TOPEX/POSEIDON altimeter data by Chelton and Schlax (1996) and the phase speeds predicted from the standard theory for nondispersive Rossby waves....
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...Oceanogr.) have shown that latitudinally varying increases in phase speed very comparable to those observed by Kessler (1990) and Chelton and Schlax (1996) can be obtained for purely free waves when the effects of vertical shear on the potential vorticity field are included in the eigenvalue…...
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TL;DR: In this article, 10 years of sea-surface height (SSH) fields constructed from the merged TOPEX/Poseidon (T/P) and ERS-1/2 altimeter datasets are analyzed to investigate mesoscale variability in the global ocean.
Abstract: [1] Ten years of sea-surface height (SSH) fields constructed from the merged TOPEX/Poseidon (T/P) and ERS-1/2 altimeter datasets are analyzed to investigate mesoscale variability in the global ocean. The higher resolution of the merged dataset reveals that more than 50% of the variability over much of the World Ocean is accounted for by eddies with amplitudes of 5–25 cm and diameters of 100–200 km. These eddies propagate nearly due west at approximately the phase speed of nondispersive baroclinic Rossby waves with preferences for slight poleward and equatorward deflection of cyclonic and anticyclonic eddies, respectively. The vast majority of the eddies are found to be nonlinear.
894 citations
University of Hawaii1, United States Naval Research Laboratory2, National Oceanic and Atmospheric Administration3, Oregon State University4, University of California, Los Angeles5, Scripps Institution of Oceanography6, University of Rhode Island7, Woods Hole Oceanographic Institution8, Hokkaido University9
TL;DR: In this paper, the physical processes that lie behind the interaction of sharp SST gradients and the overlying marine atmospheric boundary layer and deeper atmosphere, using high-resolution satellite data, field data and numerical models, are examined.
600 citations
Cites background from "Global Observations of Oceanic Ross..."
...These anomalies are referred to here as eddies for simplicity: but note the considerable debate over whether these features are Rossby waves (Chelton and Schlax, 1996) or closed vortices (such as those observed by Kennan and Flament, 2000, see also Chelton et al., 2007b)....
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References
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TL;DR: The Journal of Marine Research (JMR) as mentioned in this paper is an online peer-reviewed journal that publishes original research on a broad array of topics in physical, biological, and chemical oceanography.
Abstract: PO Box 208118, New Haven, CT 06520-8118 USA (203) 432-3154 fax (203) 432-5872 jmr@yale.edu www.journalofmarineresearch.org The Journal of Marine Research is an online peer-reviewed journal that publishes original research on a broad array of topics in physical, biological, and chemical oceanography. In publication since 1937, it is one of the oldest journals in American marine science and occupies a unique niche within the ocean sciences, with a rich tradition and distinguished history as part of the Sears Foundation for Marine Research at Yale University.
1,044 citations
TL;DR: In this article, the authors carried out several statisticaJ tests to assess the likelihood that the recent behavior of the Southern Oscillation (SO) is part of a natural decadal timescae variation.
Abstract: The tendency for more frequent E1 Nifio events America to the International Dateline. It is the basin-scale and fewer La Nifia events since the late 1970's has been phenomenon, however, that is linked to globaJ atmospheric linked to decadl changes in climate throughout the Pacific circulation and associated weather anomalies. The primary basin. Aspects of the most recent warming in the tropical response in the atmosphere coupled to EN is the SO and, Pacific from 1990 to 1995, which are connected to but not together, the tropical Pacific warm events are often referred synonymous with E1 Nifio, are unprecedented in the climate to as ENSO events. record of the past 113 years. There is a distinction between E1 Nifio (EN), the Southern Oscillation (SO)in the atmo- sphere, and ENSO, where the two are strongly linked, that emerges clearly on decadal time scaJes. In the traditional E1 Nifio region, sea surface temperature anomalies (SSTAs) have waxed and waned, while SSTAs in the centraequatorial Pa- cific, which are better linked to the SO, remained positive from 1990 to June 1995. We carry out several statisticaJ tests to assess the likelihood that the recent behavior of the SO is part of a natural decadal-timescae variation. One test fits an autoregressive-moving average (ARMA) model to a measure of the SO given by the first hundred years of the pressures at Darwin, Australia, beginning in 1882. Both the recent trend for more ENSO events since 1976 and the prolonged 1990- 1995 ENSO event are unexpected given the previous record, with a probability of occurrence about once in 2,000 years. This opens up the possibility that the ENSO changes may be partly caused by the observed increases in greenhouse gases.
801 citations
TL;DR: The TOPEX/POSEIDON satellite as mentioned in this paper is the first space mission specifically designed and conducted for studying the circulation of the world's oceans and has been making observations of the global oceans with unprecedented accuracy since late September 1992.
Abstract: TOPEX/POSEIDON is the first space mission specifically designed and conducted for studying the circulation of the world's oceans. A state-of-the-art radar altimetry system is used to measure the precise height of sea level, from which information on the ocean circulation is obtained. The satellite, launched on August 10, 1992, has been making observations of the global oceans with unprecedented accuracy since late September 1992. To meet the stringent measurement accuracy required for ocean circulation studies, a number of innovative improvements have been made to the mission design, including the first dual-frequency space-borne radar altimeter capable of retrieving the ionospheric delay of the radar signal, a three-frequency microwave radiometer for retrieving the signal delay caused by the water vapor in the troposphere, an optimal model of the Earth's gravity field and multiple satellite tracking systems for precision orbit determination. Additionally, the satellite also carries two experimental instruments to demonstrate new technologies: a single-frequency solid-state altimeter for the technology of low-power, low-weight altimeter and a Global Positioning System receiver for continuous,precise satellite tracking. The performance of the mission's measurement system has been tested by numerous verification studies. The results indicate that the root-sum-square accuracy of a single-pass sea level measurement is 4.7 cm for the TOPEX system and 5.1 cm for the POSEIDON system; both are more than a factor of 2 better than the requirement of 13.7 cm. This global data set is being analyzed to improve understanding of the global ocean circulation as well as the ocean tides, geodesy, and geodynamics, and ocean wind and waves. The mission is designed to last for at least 3 years with a possible extension to 6 years. The multiyear global data set will go a long way toward understanding the ocean circulation and its variability in relation to climate change. A summary of the mission's systems and their performance as well as the mission's science team is presented.
698 citations
TL;DR: In this article, a model was proposed that suggests an ocean-atmosphere coupling by which zonal advection of SST feeds back to the atmosphere; the model duplicates the steplike advance of warm water and westerly winds across the equatorial Pacific at the onset of the El Nino of 1991-1992.
Abstract: Ten-year time series of sea surface temperature (SST), 20°C depth, and zonal winds measured by moored buoys across the equatorial Pacific are used to define the intraseasonal (30- to 90-day period) Kelvin waves. The Kelvin waves are observed to be forced west of the date line and propagate at a speed of 2.4 m s−1, with high zonal coherence over at least 10,000 km. They form a major component of thermocline depth variability in the east-central Pacific. The intraseasonal-band variance has a low-frequency modulation both at the annual and interannual frequencies; higher amplitudes are observed in boreal fall/winter and during the onset phase of El Nino warm events. The oceanic intraseasonal variability and its low-frequency modulation are coherent with atmospheric intraseasonal variations (the Madden-Julian Oscillation (MJO)), which are known to propagate eastward into the Pacific from the Indian Ocean as part of a planetary-scale signal. The life cycle of an individual or series of MJOs is determined by a combination of factors including tropical SSTs over the warm pool regions of the Indian and Pacific Oceans and interaction with the planetary-scale atmospheric circulation. Thus the intraseasonal Kelvin waves should be taken as an aspect of a global phenomenon, not simply internal to the Pacific. The oceanic intraseasonal variability peaks at periods near 60–75 days, while the corresponding atmospheric variations have somewhat higher frequencies (35- to 60-day periods). We show that this period offset is potentially related to the zonal fetch of the wind compared to the frequency-dependent zonal wavelength of the Kelvin wave response. A simple model is formulated that suggests an ocean-atmosphere coupling by which zonal advection of SST feeds back to the atmosphere; the model duplicates the steplike advance of warm water and westerly winds across the Pacific at the onset of the El Nino of 1991–1992. The key dynamics of the model is that the atmosphere responds rapidly to the state of the ocean, but the ocean's response to the atmosphere is lagged because it is an integral over the entire wind forcing history felt by the wave. This results in a nonlinear ordinary differential equation that allows a net nonzero lowfrequency ocean signal to develop from zero-mean sinusoidal forcing at intraseasonal frequencies.
393 citations
TL;DR: In this paper, the surface pressure reformulation of the Bryan-Cox-Semtner global ocean model was further improved by eliminating the rigid-lid approximation in favor of an implicit free-surface method for the barotropic mode.
Abstract: The surface pressure reformulation of the Bryan-Cox-Semtner global ocean model, which we developed recently, has been further improved by eliminating the rigid-lid approximation in favor of an implicit free-surface method for the barotropic mode. This retains the advantages of the surface pressure formulation and in addition (1) substantially improves the computational efficiency of the barotropic mode; (2) computes surface height directly, allowing comparison with and assimilation of altimetry data (with a rigid-lid case the surface height is accurately computed only in the limit of a steady state); (3) improves accuracy in the computation of long-wavelength Rossby waves and includes the effects of long-wavelength surface gravity waves; (4) provides robustness by selectively damping computational modes; (5) simplifies satisfying global energetic balances required for energetic consistency; and (6) alleviates “checkerboarding” in the surface height or pressure fields. A variable thickness top-layer model is developed to account for the free surface, and a generalized form of implicit time discretization of the barotropic equations is introduced. This discretization is analyzed in detail from the point of view of accuracy, stability, and damping properties, and certain cases are selected for their advantageous properties. The performance of the method is demonstrated on the Connection Machine, CM-200, and the results of numerical simulations are compared using the stream function, rigid-lid surface pressure, and free-surface formulations.
392 citations