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Stammer D.,University of Hamburg | Cazenave A.,CNRS Geophysical Research and Oceanographic Laboratory | Ponte R.M.,Atmospheric and Environmental Research Inc. | Tamisiea M.E.,National Oceanographic Center
Annual Review of Marine Science | Year: 2013

Regional sea level changes can deviate substantially from those of the global mean, can vary on a broad range of timescales, and in some regions can even lead to a reversal of long-term global mean sea level trends. The underlying causes are associated with dynamic variations in the ocean circulation as part of climate modes of variability and with an isostatic adjustment of Earth's crust to past and ongoing changes in polar ice masses and continental water storage. Relative to the coastline, sea level is also affected by processes such as earthquakes and anthropogenically induced subsidence. Present-day regional sea level changes appear to be caused primarily by natural climate variability. However, the imprint of anthropogenic effects on regional sea level-whether due to changes in the atmospheric forcing or to mass variations in the system-will grow with time as climate change progresses, and toward the end of the twenty-first century, regional sea level patterns will be a superposition of climate variability modes and natural and anthropogenically induced static sea level patterns. Attribution and predictions of ongoing and future sea level changes require an expanded and sustained climate observing system. © 2013 by Annual Reviews. All rights reserved.

Cazenave A.,CNRS Geophysical Research and Oceanographic Laboratory | Dieng H.-B.,CNRS Geophysical Research and Oceanographic Laboratory | Meyssignac B.,CNRS Geophysical Research and Oceanographic Laboratory | Von Schuckmann K.,avenue deUniversite | And 2 more authors.
Nature Climate Change | Year: 2014

Present-day sea-level rise is a major indicator of climate change. Since the early 1990s, sea level rose at a mean rate of a ̂1/43.1 mm yr a ̂'1 (refs,). However, over the last decade a slowdown of this rate, of about 30%, has been recorded. It coincides with a plateau in Earths mean surface temperature evolution, known as the recent pause in warming. Here we present an analysis based on sea-level data from the altimetry record of the past a ̂1/420 years that separates interannual natural variability in sea level from the longer-term change probably related to anthropogenic global warming. The most prominent signature in the global mean sea level interannual variability is caused by El Niño-Southern Oscillation, through its impact on the global water cycle. We find that when correcting for interannual variability, the past decades slowdown of the global mean sea level disappears, leading to a similar rate of sea-level rise (of 3.3 ± 0.4 mm yr a ̂'1) during the first and second decade of the altimetry era. Our results confirm the need for quantifying and further removing from the climate records the short-term natural climate variability if one wants to extract the global warming signal. © 2014 Macmillan Publishers Limited. All rights reserved.

Birol F.,CNRS Geophysical Research and Oceanographic Laboratory | Cancet M.,CNRS Laboratory for Aerology | Estournel C.,CNRS Laboratory for Aerology
Journal of Marine Systems | Year: 2010

Altimetry has become a powerful tool to understand the dynamics of the deep-sea ocean circulation. Despite the technical problems encountered in the coastal zone by this observational technique, resulting in large data gaps in those areas, solutions already exist to mitigate this issue and to allow the retrieval of coastal information from existing altimetric data. Using some of these solutions, we have reprocessed a new set of 14.5 years of the TOPEX/Poseidon and Jason-1 satellite altimeter data over the Northwestern Mediterranean Sea, leading to a significant increase in the quantity of available data near coastlines. Time series of geostrophic surface velocity anomalies have been computed from the along-track altimeter sea level anomalies. In this paper, we evaluate the ability of these altimeter-derived currents to capture the main surface circulation features and the associated seasonal variability in the area of interest. In-situ ADCP current measurements are used to estimate the accuracy of altimeter geostrophic surface velocity anomalies at different locations on the shelf edge. The results indicate good qualitative altimeter performances at seasonal time scales, confirming that altimetry is reliable to observe synoptic variations of the Liguro-Provençal-Catalan Current System. The seasonal evolution of the shelf edge flow is then documented using results from satellite altimetry and from sea surface temperature (SST). The regional picture of the shelf edge circulation that emerges agrees fairly well with previous knowledge (the flow is much stronger during winter than during summer) but also reveals interesting aspects of the coastal current system: (1) the characteristics of the seasonal cycle observed appear highly consistent along the Northwestern Mediterranean shelf break, suggesting a continuous current from the Tyrrhenian to the Balearic Seas, (2) the relationship with the Balearic Current appears somewhat more complex and suggests that its evolution is controlled by another inflow contribution, at least in spring, (3) the seasonal variations of the shelf edge flow over a particular year can show large discrepancies with the averaged picture presented in this study, since large year to year differences are observed. © 2010 Elsevier B.V. All rights reserved.

Rahmstorf S.,Potsdam Institute for Climate Impact Research | Foster G.,Tempo Analytics | Cazenave A.,CNRS Geophysical Research and Oceanographic Laboratory
Environmental Research Letters | Year: 2012

We analyse global temperature and sea-level data for the past few decades and compare them to projections published in the third and fourth assessment reports of the Intergovernmental Panel on Climate Change (IPCC). The results show that global temperature continues to increase in good agreement with the best estimates of the IPCC, especially if we account for the effects of short-term variability due to the El Niño/Southern Oscillation, volcanic activity and solar variability. The rate of sea-level rise of the past few decades, on the other hand, is greater than projected by the IPCC models. This suggests that IPCC sea-level projections for the future may also be biased low. © 2012 IOP Publishing Ltd.

Fiolleau T.,French National Center for Scientific Research | Roca R.,CNRS Geophysical Research and Oceanographic Laboratory
Quarterly Journal of the Royal Meteorological Society | Year: 2013

The ability of the current and upcoming space-borne microwave observing systems to document precipitation processes during the life cycle of tropical convective systems is investigated with emphasis on sampling considerations. A composite technique is introduced that will serve as a Day 1 algorithm for the Megha-Tropiques mission. It is exemplified using the Tropical Rainfall Measurement Mission (TRMM) satellite observations from the TRMM Microwave Imager (TMI) instrument and the fleet of operational geostationary infrared images for the boreal summer 2009 over the whole intertropical belt. At the system scale, over both land and oceanic regions, rainfall is overall strong at the beginning (the first third) of the life cycle and then smoothly decreases as the system shrinks and dissipates. Larger rain yields are observed for the land systems (~6 mm h-1 maximum) compared to the systems over ocean (~4 mm h-1 maximum). An in-depth analysis of the sensitivity of the results to various aspects of the sampling is performed using simulated observations. The benefit of using various platforms is discussed, including considerations of constellation configuration. The entire Tropics as well as regional scales are explored, revealing the expected improvements from the inclusion of the Megha-Tropiques observations. The sampling results are also strongly supportive of the use of multiple-platform microwave observations from the upcoming Global Precipitation Mission constellation to build a mesoscale convective system precipitation composite life cycle, although the merging of the parameters derived from various resolution radiometers would deserve further investigations. © 2013 Royal Meteorological Society.

Qu T.,University of Hawaii at Manoa | Song Y.T.,California Institute of Technology | Maes C.,CNRS Geophysical Research and Oceanographic Laboratory
Journal of Geophysical Research: Oceans | Year: 2014

This study investigates the sea surface salinity (SSS) and barrier layer variability in the equatorial Pacific using recently available Aquarius and Argo data. Comparison between the two data sets indicates that Aquarius is able to capture most of the SSS features identified by Argo. Despite some discrepancies in the mean value, the SSS from the two data sets shows essentially the same seasonal cycle in both magnitude and phase. For the period of observation between August 2011 and July 2013 Aquarius nicely resolved the zonal displacement of the SSS front along the equator, showing its observing capacity of the western Pacific warm pool. Analysis of the Argo data provides further information on surface stratification. A thick barrier layer is present on the western side of the SSS front during all the period of observation, moving back and forth along the equator with its correlation with the Southern Oscillation Index exceeding 0.80. Generally, the thick barrier layer moves eastward during El Niño and westward during La Niña. The mechanisms responsible for this zonal displacement are discussed. © 2013. American Geophysical Union. All Rights Reserved.

Cazenave A.,CNRS Geophysical Research and Oceanographic Laboratory | Llovel W.,CNRS Geophysical Research and Oceanographic Laboratory
Annual Review of Marine Science | Year: 2010

Measuring sea level change and understanding its causes has considerably improved in the recent years, essentially because new in situ and remote sensing observations have become available. Here we report on most recent results on contemporary sea level rise. We first present sea level observations from tide gauges over the twentieth century and from satellite altimetry since the early 1990s. We next discuss the most recent progress made in quantifying the processes causing sea level change on timescales ranging from years to decades, i.e., thermal expansion of the oceans, land ice mass loss, and land water-storage change. We show that for the 1993-2007 time span, the sum of climate-related contributions (2.85 ± 0.35 mm year ?1) is only slightly less than altimetry-based sea level rise (3.3 ± 0.4 mm year ?1): ?30% of the observed rate of rise is due to ocean thermal expansion and ?55% results from land ice melt. Recent acceleration in glacier melting and ice mass loss from the ice sheets increases the latter contribution up to 80% for the past five years. We also review the main causes of regional variability in sea level trends: The dominant contribution results from nonuniform changes in ocean thermal expansion. © 2010 by Annual Reviews.

Dewitte B.,CNRS Geophysical Research and Oceanographic Laboratory | Yeh S.-W.,Hanyang University | Thual S.,CNRS Geophysical Research and Oceanographic Laboratory
Climate Dynamics | Year: 2013

Vertical stratification changes at low frequency over the last decades are the largest in the western-central Pacific and have the potential to modify the balance between ENSO feedback processes. Here we show evidence of an increase in thermocline feedback in the western-central equatorial Pacific over the last 50 years, and in particular after the climate shift of 1976. It is demonstrated that the thermocline feedback becomes more effective due to the increased stratification in the vicinity of the mean thermocline. This leads to an increase in vertical advection variability twice as large as the increase resulting from the stronger ENSO amplitude (positive asymmetry) in the eastern Pacific that connects to the thermocline in the western-central Pacific through the basin-scale 'tilt' mode. Although the zonal advective feedback is dominant over the western-central equatorial Pacific, the more effective thermocline feedback allows for counteracting its warming (cooling) effect during warm (cold) events, leading to the reduced covariability between SST and thermocline depth anomalies in the NINO4 (160°E-150°W; 5°S-5°N) region after the 1976 climate shift. This counter-intuitive relationship between thermocline feedback strength as derived from the linear relationship between SST and thermocline fluctuations and stratification changes is also investigated in a long-term general circulation coupled model simulation. It is suggested that an increase in ENSO amplitude may lead to the decoupling between eastern and central equatorial Pacific sea surface temperature anomalies through its effect on stratification and thermocline feedback in the central-western Pacific. © 2012 Springer-Verlag.

Gille S.T.,University of California at San Diego | Gille S.T.,CNRS Geophysical Research and Oceanographic Laboratory
Journal of Geophysical Research: Oceans | Year: 2012

Diurnal temperature variability in the top 50m of the ocean is assessed by pairing Argo temperature profiles with geographically colocated Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) sea surface temperatures (SSTs) collected within 24 h of each other. Data pairs with time separations of up to 3 h are used to evaluate systematic differences between the two data sets. Daytime SSTs are warmer than Argo 5m temperatures in low-wind conditions, as expected due to diurnal surface warming effects. SSTs also tend to be warmer than Argo 5m temperatures when columnar water vapor is less than ∼7 mm. These effects are removed empirically. For Argo data collected within 24 h of satellite overpass times, temperature differences between Argo and AMSR-E show evidence of a diurnal cycle detectable at 5m depth and below. The diurnal amplitude decreases with increasing latitude and increasing depth to the base of the mixed layer and is stronger in summer than in winter. At 5m depth, the amplitude of the summer diurnal cycle ranges from about 0.1C at the equator to 0.05C near 60 latitude. At latitudes where the diurnal amplitude exceeds about 0.04C, maximum temperatures occur at about 16:50 0:40 local time, and minimum temperatures occur at about 07:50 0:40 local time. Above the base of the mixed layer, the time of the diurnal maximum increases with depth, consistent with downward propagation of the diurnal signal, while the time of the minimum implies an upward propagation. © 2012. American Geophysical Union. All Rights Reserved.

Nicholls R.J.,University of Southampton | Cazenave A.,CNRS Geophysical Research and Oceanographic Laboratory
Science | Year: 2010

Global sea levels have risen through the 20th century. These rises will almost certainly accelerate through the 21st century and beyond because of global warming, but their magnitude remains uncertain. Key uncertainties include the possible role of the Greenland and West Antarctic ice sheets and the amplitude of regional changes in sea level. In many areas, nonclimatic components of relative sealevel change (mainly subsidence) can also be locally appreciable. Although the impacts of sea-level rise are potentially large, the application and success of adaptation are large uncertainties that require more assessment and consideration. Copyright Science 2010 by the American Association for the Advancement of Science; all rights reserved.

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