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Gary T Mitchum - One of the best experts on this subject based on the ideXlab platform.
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climate change driven accelerated sea level rise detected in the altimeter era
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: R. Steven Nerem, B D Beckley, John T Fasullo, B D Hamlington, D Masters, Gary T MitchumAbstract:Using a 25-y time series of precision satellite altimeter data from TOPEX/Poseidon, Jason-1, Jason-2, and Jason-3, we estimate the climate-change-driven acceleration of global mean sea level over the last 25 y to be 0.084 ± 0.025 mm/y2 Coupled with the average climate-change-driven rate of sea level rise over these same 25 y of 2.9 mm/y, simple extrapolation of the quadratic implies global mean sea level could rise 65 ± 12 cm by 2100 compared with 2005, roughly in agreement with the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report (AR5) model projections.
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climate change driven accelerated sea level rise detected in the altimeter era
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: R. Steven Nerem, B D Beckley, John T Fasullo, B D Hamlington, D Masters, Gary T MitchumAbstract:Using a 25-y time series of precision satellite altimeter data from TOPEX/Poseidon, Jason-1, Jason-2, and Jason-3, we estimate the climate-change–driven acceleration of global mean sea level over the last 25 y to be 0.084 ± 0.025 mm/y 2 . Coupled with the average climate-change–driven rate of sea level rise over these same 25 y of 2.9 mm/y, simple extrapolation of the quadratic implies global mean sea level could rise 65 ± 12 cm by 2100 compared with 2005, roughly in agreement with the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report (AR5) model projections.
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calibration of topex poseidon and jason altimeter data to construct a continuous record of mean sea level change
Marine Geodesy, 2004Co-Authors: Eric Leuliette, Steven R Nerem, Gary T MitchumAbstract:Jason, the successor to the TOPEX/POSEIDON (T/P) mission, has been designed to continue seamlessly the decade-long altimetric sea level record initiated by T/P. Intersatellite calibration has determined the relative bias to an accuracy of 1.6 mm rms. Tide gauge calibration of the T/P record during its original mission shows a drift of −0.1 ± 0.4 mm/year. The tide gauge calibration of 20 months of nominal Jason data indicates a drift of −5.7 ± 1.0 mm/year, which may be attributable to errors in the orbit ephemeris and the Jason Microwave Radiometer. The analysis of T/P and Jason altimeter data over the past decade has resulted in a determination of global mean sea level change of +2.8 ± 0.4 mm/year.
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surface manifestation of internal tides generated near hawaii
Geophysical Research Letters, 1996Co-Authors: Richard D. Ray, Gary T MitchumAbstract:Analysis of Topex/Poseidon satellite altimetry reveals short-wavelength fluctuations in the ocean surface tide that are attributable to internal tides. A significant fraction of the semidiurnal internal tide generated at the Hawaiian Ridge is evidently phase-locked to the astronomical potential and can modulate the amplitude of the surface tide by ∼5 cm. The internal tide is thus easily mapped along satellite groundtracks, and it is found to be spatially coherent over great distances, with waves propagating well over 1000 km from the Hawaiian Ridge before decaying below noise level. Both first and second baroclinic modes are observed in both the M 2 (lunar) and S 2 (solar) tides. The high space-time coherence is in sharp contrast to what is often inferred from current-meter observations, but it confirms recent speculations from an acoustic experiment north of Hawaii.
R. Steven Nerem - One of the best experts on this subject based on the ideXlab platform.
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climate change driven accelerated sea level rise detected in the altimeter era
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: R. Steven Nerem, B D Beckley, John T Fasullo, B D Hamlington, D Masters, Gary T MitchumAbstract:Using a 25-y time series of precision satellite altimeter data from TOPEX/Poseidon, Jason-1, Jason-2, and Jason-3, we estimate the climate-change–driven acceleration of global mean sea level over the last 25 y to be 0.084 ± 0.025 mm/y 2 . Coupled with the average climate-change–driven rate of sea level rise over these same 25 y of 2.9 mm/y, simple extrapolation of the quadratic implies global mean sea level could rise 65 ± 12 cm by 2100 compared with 2005, roughly in agreement with the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report (AR5) model projections.
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climate change driven accelerated sea level rise detected in the altimeter era
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: R. Steven Nerem, B D Beckley, John T Fasullo, B D Hamlington, D Masters, Gary T MitchumAbstract:Using a 25-y time series of precision satellite altimeter data from TOPEX/Poseidon, Jason-1, Jason-2, and Jason-3, we estimate the climate-change-driven acceleration of global mean sea level over the last 25 y to be 0.084 ± 0.025 mm/y2 Coupled with the average climate-change-driven rate of sea level rise over these same 25 y of 2.9 mm/y, simple extrapolation of the quadratic implies global mean sea level could rise 65 ± 12 cm by 2100 compared with 2005, roughly in agreement with the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report (AR5) model projections.
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present day sea level change observations and causes
Reviews of Geophysics, 2004Co-Authors: Anny Cazenave, R. Steven NeremAbstract:We investigate climate-related processes causing variations of the global mean sea level on interannual to decadal time scale. Wc focus on thermal expansion of the oceans and continental water mass balance. We show that during the 1990s where global mean sea level change has been measured by Topex/Poseidon satellite altimetry. thermal expansion is the dominant contribution to the observed 2.5 mm/yr sea level rise. For the past decades, exchange of water between continental reservoirs and oceans had a small, but not totally negligible contribution (about 0.2 mm/yr) to sea level rise. For the last four decades, thermal contribution is estimated to about 0.5 mm/yr, with a possible accelerated rale of thermosteric rise during the 1990s. Topex/Posei don shows an increase in mean sea level of 2.5 mm/yr over the last decade, a value about two times larger than reported by historical tide gauges. This would suggest that there has been significant acceleration of sea level rise in the recent past, possibly related to ocean warming.
Richard D. Ray - One of the best experts on this subject based on the ideXlab platform.
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constraints on energy dissipation in the earth s body tide from satellite tracking and altimetry
2013Co-Authors: Richard D. Ray, R J Eanes, F G LemoineAbstract:The phase lag by which the earth's body tide follows the tidal potential is estimated for the principal lunar semidiurnal tide M(sub 2). The estimate results from combining recent tidal solutions from satellite tracking data and from Topex/Poseidon satellite altimeter data. Each data type is sensitive to the body-tide lag: gravitationally for the tracking data, geometrically for the altimetry. Allowance is made for the lunar atmospheric tide. For the tidal potential Love number kappa(sub 2) we obtain a lag epsilon of 0.20 deg +/- 0.05 deg, implying an effective body-tide Q of 280 and body-tide energy dissipation of 110 +/- 25 gigawatts.
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non stationary internal tides observed with satellite altimetry
Geophysical Research Letters, 2011Co-Authors: Richard D. Ray, Edward D ZaronAbstract:[1] Temporal variability of the internal tide is inferred from a 17-year combined record of Topex/Poseidon and Jason satellite altimeters. A global sampling of along-track sea-surface height wavenumber spectra finds that non-stationary variance is generally 25% or less of the average variance at wavenumbers characteristic of mode-1 tidal internal waves. With some exceptions the non-stationary variance does not exceed 0.25 cm2. The mode-2 signal, where detectable, contains a larger fraction of non-stationary variance, typically 50% or more. Temporal subsetting of the data reveals interannual variability barely significant compared with tidal estimation error from 3-year records. Comparison of summer vs. winter conditions shows only one region of noteworthy seasonal changes, the northern South China Sea. Implications for the anticipated SWOT altimeter mission are briefly discussed.
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estimates of m2 tidal energy dissipation from topex poseidon altimeter data
Journal of Geophysical Research, 2001Co-Authors: Gary D Egbert, Richard D. RayAbstract:Most of the tidal energy dissipation in the ocean occurs in shallow seas, as has long been recognized. However, recent work has suggested that a significant fraction of the dissipation, perhaps 1 TW or more, occurs in the deep ocean. This paper builds further evidence for that conclusion. More than 6 years of data from the TOPEX/Poseidon satellite altimeter are used to map the tidal dissipation rate throughout the world ocean. The dissipation rate is estimated as a balance between the rate of working by tidal forces and the energy flux divergence, computed using currents derived by least squares fitting of the altimeter data and the shallow water equations. Such calculations require dynamical assumptions, in particular about the nature of dissipation. To assess sensitivity of dissipation estimates to input assumptions, a large suite of tidal inversions based on a wide range of drag parameterizations and employing both real and synthetic altimeter data are compared. These experiments and Monte Carlo error fields from a generalized inverse model are used to establish error uncertainties for the dissipation estimates. Owing to the tight constraints on tidal elevation fields provided by the altimeter, area integrals of the energy balance are remarkably insensitive to required dynamical assumptions. Tidal energy dissipation is estimated for all major shallow seas (excluding individual polar seas) and compared with previous model and data-based estimates. Dissipation in the open ocean is significantly enhanced around major bathymetric features, in a manner consistent with simple theories for the generation of baroclinic tides.
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estimates of internal tide energy fluxes from topex poseidon altimetry central north pacific
Geophysical Research Letters, 2001Co-Authors: Richard D. Ray, D E CartwrightAbstract:Energy fluxes for first-mode M2 internal tides are deduced throughout the central North Pacific Ocean from Topex/Poseidon satellite altimeter data. Temporally coherent internal tide signals in the altimetry, combined with climatological hydrographic data, determine the tidal displacements, pressures, and currents at depth, which yield power transmission rates. For a variety of reasons the deduced rates should be considered lower bounds. Internal tides are found to emanate from several large bathymetric structures, especially the Hawaiian Ridge, where the integrated flux amounts to about 6 gigawatts. Internal tides are generated at the Aleutian Trench near 172°W and propagate southwards nearly 2000 km.
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error spectrum for the global m2 ocean tide
Geophysical Research Letters, 2001Co-Authors: Richard D. Ray, Gary D Egbert, R J Eanes, N K PavlisAbstract:The most accurate determinations of the global ocean tides are currently based on altimeter measurements made by the Topex/Poseidon satellite. The error spectrum corresponding to the M2 tidal solution is here estimated, primarily by inverse methods and secondarily by simple differencing of several of the best tidal models. The tidal error spectrum is flatter than the tidal signal spectrum, and it exceeds 10% of the signal at spherical harmonic degree 15 and above. The tide errors also exceed the anticipated sensitivity of the upcoming Grace satellite gravity mission for all degrees below 40, and possibly below 50.
Anny Cazenave - One of the best experts on this subject based on the ideXlab platform.
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reconstruction of past decades sea level using thermosteric sea level tide gauge satellite altimetry and ocean reanalysis data
Global and Planetary Change, 2008Co-Authors: Muriel Ergenguye, W Llovel, Anny Cazenave, A Lombard, J Viarre, Jeanfrancois CretauAbstract:Abstract This study investigates past sea level reconstruction (over 1950–2003) based on tide gauge records and EOF spatial patterns from different 2-D fields. In a first step, we test the influence on the reconstructed signal of the 2-D fields temporal coverage. For that purpose we use global grids of thermosteric sea level data, available over 1950–2003. Different time spans (in the range 10–50 yr) for the EOF spatial patterns, and different geographical distributions for the 1-D thermosteric sea level time series (interpolated at specific locations from the 2-D grids), are successively used to reconstruct the 54-year long thermosteric sea level signal. In each case we compare the reconstructed trend map with the reference. The simulation indicates that the longer the time span covered by the spatial EOFs, the closer to the reference the reconstructed thermosteric sea level trends. In a second step, we apply the method to reconstructing 2-D sea level data over 1950–2003, combining sparse tide gauge records available since 1950, with EOF spatial patterns from different sources: (1) thermosteric sea level grids over 1955–2003, (2) sea level grids from Topex/Poseidon satellite altimetry over 1993–2003, and (3) dynamic height grids from the SODA reanalysis over 1958–2001. The reconstructed global mean sea level trend based on thermosteric EOFs (case 1) is significantly lower than the observed trend, while the interannual/decadal sea level fluctuations are well reproduced. Case 2 (Topex/Poseidon EOFs over 1993–2003) leads to a global mean sea level trend over the 54-year time interval very close to the observed trend. But the spatial trends of the reconstruction over 1950–2003 are significantly different from those obtained with thermosteric EOFs. Case 3 (SODA EOFs over 1958–2001) provides a reconstruction trend map over 1950–2003 that differs significantly from the previous two cases. We discuss possible causes for such differences. For the three cases, on the other hand, reconstructed spatial trends over 1993–2003 agree well with the regional sea level trends observed by Topex/Poseidon.
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ob river discharge from topex poseidon satellite altimetry 1992 2002
Remote Sensing of Environment, 2004Co-Authors: A. Kouraev, O. Samain, Elena Zakharova, N M Mognard, Anny CazenaveAbstract:The paper discusses an application of the TOPEX/Poseidon (T/P) altimetry data to estimate the discharge of one of the largest Arctic rivers—the Ob' river. We first discuss the methodology to select and retrieve the altimeter water levels during the various phases of the hydrological regime. Then we establish the relationships between the satellite-derived water levels and the in situ river discharge measurements at the Salekhard gauging station near the Ob' estuary. The comparison of in situ and satellite-derived estimations of the Ob' discharge at Salekhard shows that the T/P data can successfully be used for hydrological studies of this river. We address the problems affecting the accuracy of the discharge estimations from altimeter measurements, identify potential solutions and suggest how satellite altimetry data may benefit hydrological studies of Arctic rivers.
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present day sea level change observations and causes
Reviews of Geophysics, 2004Co-Authors: Anny Cazenave, R. Steven NeremAbstract:We investigate climate-related processes causing variations of the global mean sea level on interannual to decadal time scale. Wc focus on thermal expansion of the oceans and continental water mass balance. We show that during the 1990s where global mean sea level change has been measured by Topex/Poseidon satellite altimetry. thermal expansion is the dominant contribution to the observed 2.5 mm/yr sea level rise. For the past decades, exchange of water between continental reservoirs and oceans had a small, but not totally negligible contribution (about 0.2 mm/yr) to sea level rise. For the last four decades, thermal contribution is estimated to about 0.5 mm/yr, with a possible accelerated rale of thermosteric rise during the 1990s. Topex/Posei don shows an increase in mean sea level of 2.5 mm/yr over the last decade, a value about two times larger than reported by historical tide gauges. This would suggest that there has been significant acceleration of sea level rise in the recent past, possibly related to ocean warming.
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ice cover variability in the caspian and aral seas from active and passive microwave satellite data
Polar Research, 2003Co-Authors: Anny Cazenave, Fabrice Papa, Alexei V Kouraev, P I Buharizin, Jeanfrancois Cretaux, Julia Dozortseva, Frederique RemyAbstract:The paper discusses time and space variations of ice extent in the Caspian and Aral seas during the last decade (1992–2002). It uses synergy of data from active (radar altimeter) and passive (radiometer) microwave nadirlooking instruments onboard the TOPEX/Poseidon satellite. The proposed approach is substantiated and validated using both in situ and satellite imagery data for the Caspian Sea. The results indicate significant spatial and temporal variability of ice conditions, with a significant decrease of both the duration of ice season and ice extent during the last four winters (1998–2002). The TOPEX/Poseidon-derived time series of sea ice extent are very valuable in view of the fragmentary and mostly unpublished data on ice conditions on the Caspian and Aral seas since the mid-1980s.
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water level fluctuations in the plata basin south america from topex poseidon satellite altimetry
AGU Fall Meeting Abstracts, 2002Co-Authors: Caroline Maheu, Anny Cazenave, Carlos R MechosoAbstract:[1] Time series of water level in major rivers of the Plata basin are examined using altimetry data from the Topex/Poseidon satellite over the period 1993–2001. Ten sites are selected on the Parana, three on the Paraguay, one the Uruguay and seven on wetlands. It is confirmed that the seasonal cycle of river levels decreases in amplitude with increasing latitude of the site. The normalized time series for sites along the same river differ mainly by a time-lag corresponding to propagation speeds of about 0.1 ms−1. The interannual variability of the Lower Parana, with a strong peak in early 1998 and minima in early 1996 and 2000, shows the remote effects of El Nino/Southern Oscillation (ENSO). The variability of the Upper Parana and Paraguay shows similar ENSO impacts with smaller amplitudes after 1995, and the effects of regional features climate variability before that date (e.g. the South American monsoon). The results support the usefulness of satellite altimetry for a dense and continuous monitoring of river water levels.
Neil J Holbrook - One of the best experts on this subject based on the ideXlab platform.
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observed variability of the south pacific westward sea level anomaly signal in the presence of bottom topography
Geophysical Research Letters, 2005Co-Authors: A M Maharaj, Paolo Cipollini, Neil J HolbrookAbstract:This study investigates the behavior of westward propagating sea level anomalies across the South Pacific Ocean, with a focus on the long Rossby wave signal determined from filtered TOPEX/Poseidon and ERS satellite altimeter data. An evaluation of the energy variability of the signal using a two-dimensional Radon Transform analysis suggests that Rossby waves interact with both ridges and seamounts at various locations across the basin. Anomalously slow Rossby wave phase speeds are found over steep, isolated bathymetric features in the tropical South Pacific and over the plateau around New Zealand. Interaction with ridges increases the energetic variability, range of dominant propagation speeds, and meridional deviations in the Rossby wave signal.
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observed variability of the south pacific westward sea level anomaly signal in the presence of bottom topography
Geophysical Research Letters, 2005Co-Authors: A M Maharaj, Paolo Cipollini, Neil J HolbrookAbstract:This study investigates the behavior of westward propagating sea level anomalies across the South Pacific Ocean, with a focus on the long Rossby wave signal determined from filtered TOPEX/Poseidon and ERS satellite altimeter data. An evaluation of the energy variability of the signal using a two-dimensional Radon Transform analysis suggests that Rossby waves interact with both ridges and seamounts at various locations across the basin. Anomalously slow Rossby wave phase speeds are found over steep, isolated bathymetric features in the tropical South Pacific and over the plateau around New Zealand. Interaction with ridges increases the energetic variability, range of dominant propagation speeds, and meridional deviations in the Rossby wave signal.