On long baroclinic Rossby waves in the tropical North Atlantic observed from profiling floats

Chu, Peter C.; Ivanov, Leonid M.; Melnichenko, Oleg; Wells, N. C.

doi:10.1029/2006jc003698

Cited by 39 publications

(34 citation statements)

References 58 publications

(91 reference statements)

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“…The vertical structure found by Chu et al (2007) used temperature data from ARGO floats in the North Atlantic and as a result is quite different to those found here with a pronounced sub-surface maximum at 1500 m and zero ampli- tude at the surface. Their findings showed a large contribution from the second baroclinic mode in the structure, but did display a similarity to the U -BPD profile with an inversion seen in the top 200 m, which is not seen in the model profiles here.…”

Section: Discussioncontrasting

confidence: 92%

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The vertical structure of oceanic Rossby waves: a comparison of high-resolution model data to theoretical vertical structures

2012

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Abstract. Tests of the new Rossby wave theories that have been developed over the past decade to account for discrepancies between theoretical wave speeds and those observed by satellite altimeters have focused primarily on the surface signature of such waves. It appears, however, that the surface signature of the waves acts only as a rather weak constraint, and that information on the vertical structure of the waves is required to better discriminate between competing theories.Due to the lack of 3-D observations, this paper uses highresolution model data to construct realistic vertical structures of Rossby waves and compares these to structures predicted by theory. The meridional velocity of a section at 24 • S in the Atlantic Ocean is pre-processed using the Radon transform to select the dominant westward signal. Normalized profiles are then constructed using three complementary methods based respectively on: (1) averaging vertical profiles of velocity, (2) diagnosing the amplitude of the Radon transform of the westward propagating signal at different depths, and (3) EOF analysis. These profiles are compared to profiles calculated using four different Rossby wave theories: standard linear theory (SLT), SLT plus mean flow, SLT plus topographic effects, and theory including mean flow and topographic effects. Our results support the classical theoretical assumption that westward propagating signals have a well-defined vertical modal structure associated with a phase speed independent of depth, in contrast with the conclusions of a recent study using the same model but for different locations in the North Atlantic. The model structures are in general surface intensified, with a sign reversal at depth in some regions, notably occurring at shallower depths in the East Atlantic. SLT provides a good fit to the model structures in the top 300 m, but grossly overestimates the sign reversal at depth. The addition of mean flow slightly improves the latter issue, but is too surface intensified. SLT plus topography rectifies the overestimation of the sign reversal, but overestimates the amplitude of the structure for much of the layer above the sign reversal. Combining the effects of mean flow and topography provided the best fit for the mean model profiles, although small errors at the surface and mid-depths are carried over from the individual effects of mean flow and topography respectively. Across the section the best fitting theory varies between SLT plus topography and topography with mean flow, with, in general, SLT plus topography performing better in the east where the sign reversal is less pronounced. None of the theories could accurately reproduce the deeper sign reversals in the west. All theories performed badly at the boundaries. The generalization of this method to other latitudes, oceans, models and baroclinic modes would provide greater insight into the variability in the ocean, while better observational data would allow verification of the model findings.

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Section: Discussioncontrasting

confidence: 92%

“…Chu et al (2007) used data from ARGO floats in the North Atlantic to extract vertical profiles of Rossby waves. They found that the second baroclinic mode was always dominant, with the contributions of other modes geographically variable.…”

Section: F K Hunt Et Al: the Vertical Structure Of Oceanic Rossby mentioning

confidence: 99%

The vertical structure of oceanic Rossby waves: a comparison of high-resolution model data to theoretical vertical structures

2012

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“…This slow signal transfer across the North Atlantic is in the same order as the magnitude of Rossby Wave propagation. With a typical wave speed of 10-15 cm·s −1 [42] the NAO induced SST pattern in the region of the AF needs one to two years to reach the west coast of the Atlantic where the drift of the Gulf Stream is observed. Much lower wave speeds have been quantified by ref.…”

Section: The Front's Impact On the Gulf Streammentioning

confidence: 99%

Impact of the azores front propagation on deep ocean particle flux

Fründt

Waniek

2012

Open Geosciences

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Abstract:The Azores Current originating as a branch of the Gulf Stream is a highly dynamic system in the subtropical North Atlantic. The associated front forms the northeastern boundary of the North Atlantic Subtropical Gyre. In this study we analyzed 42 years of assimilated modeled temperature fields to localize the position of the Azores Front at 22 • W and observed a fast north-and southward propagation between 30 • N and 37 • N on monthly to decadal time scales. The North Atlantic Oscillation with correlated changes of the wind direction was identified as one driving mechanism. As the front is acting as a guide for Rossby waves, the signal of the front's propagation is transferred to the western Atlantic and, among other atmospheric forcing mechanisms, induces a shifting of the Northern Wall of the Gulf Stream with one year delay. Shallower mixed layer depths in the northern frontal region of the Azores Current caused by the rise of the isotherms lead to nutrient supply and primary production different from those found in the southern frontal region of the current system. A high interannual variability is manifested in deep ocean particle flux, derived from a sediment trap in 2000 m water depth at the mooring site KIEL276 (33 • N, 22 • W) from 1993 to 2008, which is directly related to the phytoplankton bloom in the euphotic zone. This variability is explained by the propagation of the front and strong variations in the catchment areas of the sediment trap due to the associated eddy activity in the frontal region.

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“…Applications of Argo data have included analysis of ocean Rossby waves (Chu et al 2007) and deep seasonal temperature variations (Hosoda et al 2006). Recently, the high temporal resolution of the Argo data was used to show that the temperature structure of an equatorial Kelvin wave in the Pacific, forced by a particular MJO event, extended down to at least 1500 m depth (Matthews et al 2007), deeper than expected from theoretical considerations (Johnson and McPhaden 1993).…”

Section: Introductionmentioning

confidence: 99%

Ocean temperature and salinity components of the Madden–Julian oscillation observed by Argo floats

2009

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New diagnostics of the Madden-Julian oscillation (MJO) cycle in ocean temperature and, for the first time, salinity are presented. The MJO composites are based on 4 years of gridded Argo float data from [2003][2004][2005][2006], and extend from the surface to 1400 m depth in the tropical Indian and Pacific Oceans. The MJO surface salinity anomalies are consistent with precipitation minus evaporation fluxes in the Indian Ocean, and with anomalous zonal advection in the Pacific. The Argo sea surface temperature and thermocline depth anomalies are consistent with previous studies using other data sets. The near-surface density changes due to salinity are comparable to, and partially offset, those due to temperature, emphasising the importance of including salinity as well as temperature changes in mixedlayer modelling of tropical intraseasonal processes. The MJO-forced equatorial Kelvin wave that propagates along the thermocline in the Pacific extends down into the deep ocean, to at least 1400 m. Coherent, statistically significant, MJO temperature and salinity anomalies are also present in the deep Indian Ocean.

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On long baroclinic Rossby waves in the tropical North Atlantic observed from profiling floats

Cited by 39 publications

References 58 publications

The vertical structure of oceanic Rossby waves: a comparison of high-resolution model data to theoretical vertical structures

The vertical structure of oceanic Rossby waves: a comparison of high-resolution model data to theoretical vertical structures

Impact of the azores front propagation on deep ocean particle flux

Ocean temperature and salinity components of the Madden–Julian oscillation observed by Argo floats

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