ORCID Profile
0000-0002-3017-6993
Current Organisations
The Superior University
,
Magellium
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Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-8001
Abstract: We investigate the performances of GRACE and GRACE Follow-On satellite gravimetry missions in assessing the ocean mass budget at global scale over 2005-2020. For that purpose, we focus on the last years of the record (2015-2020) when GRACE and GRACE Follow-On faced instrumental problems. We compare the global mean ocean mass estimates from GRACE and GRACE Follow-On to the sum of its contributions from Greenland, Antarctica, land glaciers, terrestrial water storage and atmospheric water content estimated with independent observations. Significant residuals are observed in the global mean ocean mass budget at interannual time scales. Our analyses suggest that the terrestrial water storage variations based on global hydrological model likely contributes to a large part to the misclosure of the global mean ocean mass budget at interannual time scales. We also compare the GRACE-based global mean ocean mass with the altimetry-based global mean sea level corrected for the Argo-based thermosteric contribution (an equivalent of global mean ocean mass). After correcting for the wet troposphere drift of the radiometer on-board the Jason-3 altimeter satellite, we find that mass budget misclosure is reduced but still significant. However, replacing the Argo-based thermosteric component by the ORAS5 ocean reanlaysis or from CERES top of the atmosphere observations leads to closure of the mass budget over the 2015-2020 time span. We conclude that the two most likely sources of error in the global mean ocean mass budget are the thermosteric component based on Argo and the terrestrial water storage contribution based on global hydrological models. The GRACE and GRACE Follow-On data are unlikely to be responsible on their own for the non-closure of the global mean ocean mass budget.
Publisher: Copernicus GmbH
Date: 26-09-2022
DOI: 10.5194/GSTM2022-25
Abstract: & & The GRACE (Gravity Recovery And Climate Experiment) and GRACE Follow-On (FO) satellite gravity missions enable global monitoring of the mass transport within the Earth& #8217 s system, leading to unprecedented advances in our understanding of the global water cycle in a changing climate. This study focuses on the quantification of changes in terrestrial water storage based on an ensemble of GRACE and GRACE-FO solutions and two global hydrological models. Significant changes in terrestrial water storage are detected at pluriannual and decadal time-scales in GRACE and GRACE-FO satellite gravity data, that are considerably underestimated by global hydrological models. The largest differences (more than 20 cm in equivalent water height) are observed in South America (Amazon, Sao Francisco and Parana river basins) and tropical Africa (Congo, Zambezi and Okavango river basins). Significant differences (a few cm) are observed worldwide at similar time-scales, and are generally well correlated with precipitation. While the origin of such differences is unknown, part of it is likely to be climate-related and at least partially due to inaccurate predictions of hydrological models. Slow changes in the terrestrial water cycle may indeed be overlooked in global hydrological models due to inaccurate meteorological forcing (e.g., precipitation), unresolved groundwater processes, anthropogenic influences, changing vegetation cover and limited calibration/validation datasets. Significant differences between GRACE satellite measurements and hydrological model predictions have been identified, quantified and characterised in the present study. Efforts must be made to better understand the gap between both methods at pluriannual and decadal time-scales, which challenges the use of global hydrological models for the prediction of the evolution of water resources in changing climate conditions.& &
Publisher: Copernicus GmbH
Date: 23-03-2023
Abstract: Abstract. We investigate the performances of Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) satellite gravimetry missions in assessing the ocean mass budget at the global scale over 2005–2020. For that purpose, we focus on the last years of the record (2015–2020) when GRACE and GRACE Follow-On faced instrumental problems. We compare the global mean ocean mass estimates from GRACE and GRACE Follow-On to the sum of its contributions from Greenland, Antarctica, land glaciers, terrestrial water storage and atmospheric water content estimated with independent observations. Significant residuals are observed in the global mean ocean mass budget at interannual timescales. Our analyses suggest that the terrestrial water storage variations based on global hydrological models likely contribute in large part to the misclosure of the global mean ocean mass budget at interannual timescales. We also compare the GRACE-based global mean ocean mass with the altimetry-based global mean sea level corrected for the Argo-based thermosteric contribution (an equivalent of global mean ocean mass). After correcting for the wet troposphere drift of the radiometer on board the Jason-3 altimeter satellite, we find that mass budget misclosure is reduced but still significant. However, replacing the Argo-based thermosteric component by the Ocean Reanalysis System 5 (ORAS5) or from the Clouds and the Earth's Radiant Energy System (CERES) top of the atmosphere observations significantly reduces the residuals of the mass budget over the 2015–2020 time span. We conclude that the two most likely sources of error in the global mean ocean mass budget are the thermosteric component based on Argo and the terrestrial water storage contribution based on global hydrological models. The GRACE and GRACE Follow-On data are unlikely to be responsible on their own for the non-closure of the global mean ocean mass budget.
Publisher: Elsevier BV
Date: 09-2020
Publisher: Copernicus GmbH
Date: 29-08-2023
DOI: 10.5194/SP-2023-28
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-14931
Abstract: The Earth energy imbalance (EEI) at the top of the atmosphere is responsible for the accumulation of energy in the climate system. While necessary to better understand the Earth& #8217 s warming climate, measuring the EEI is challenging as it is a globally integrated variable whose variations are small (0.5-1 W.m& #8722 ) compared to the amount of energy entering and leaving the climate system (~ 340 W.m-2). Accuracies better than 0.1 W.m& #8722 are needed to evaluate the temporal variations of the EEI at decadal and longer time-scales. The CERES experiment provides EEI time variations with a typical uncertainty of & #177 0.1 W.m& #8722 and shows a trend in EEI of 0.50 +/- 0.47 W.m& #8722 per decade over the period 2005-2019. The combination of space altimetry and space gravimetry measurements provides an estimate of the ocean heat content (OHC) change which is an accurate proxy of EEI (because % of the excess of energy stored by the planet in response to the EEI is accumulated in the ocean in the form of heat).& In Marti et al. (2021), the global OHC was estimated at global scales based on the combination of space altimetry and space gravimetry measurements over 2002-2016. Changes in the EEI were then derived with realistic estimates of its uncertainty. Here we present the improvements brought to the global OGC and EEI over an extended period (2002-2021), such as the calculation of the expansion efficiency of heat over the total water column, the improvement of ocean mass solution, the empirical correction of the wet tropospheric correction of Jason-3 altimeter measurements (Barnoud et al., 2022). The space geodetic GOHC-EEI product based on space altimetry and space gravimetry is available on the AVSIO website at 0.24400/527896/a01-2020.003. & References: Barnoud A., Picard B., Meyssignac B., Marti F., Ablain M., Roca R. Reducing the uncertainty in the satellite altimetry estimates of global mean sea level trends using highly stable water vapour climate data records. Submitted to JGR: Oceans. Marti, F., Blazquez, A., Meyssignac, B., Ablain, M., Barnoud, A., Fraudeau, R., Jugier, R., Chenal, J., Larnicol, G., Pfeffer, J., Restano, M., and Benveniste, J.: Monitoring the ocean heat content change and the Earth energy imbalance from space altimetry and space gravimetry, Earth Syst. Sci. Data, 14, 229& #8211 , 0.5194/essd-14-229-2022, 2022.
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-7746
Abstract: A cycle of about 6 years has long been observed in the Earth& #8217 s magnetic field, length of day, dynamic oblateness, polar motions and surface displacements and attributed to dynamical processes occurring in the core and at the core mantle boundary. Recently, a 6-year cycle has also been detected in the rate of change of the global mean sea level and the ice-mass contributions from Greenland and continental glaciers. In this study, we report new observations of a 6-year cycle in the terrestrial water storage estimates based on the satellite gravity missions GRACE and GRACE-FO, consistent with precipitation and global hydrological models. The causes for such oscillations in the climate system are still unexplained, but raise the question of the respective contributions of the Earth& #8217 s deep interior and external surface fluid envelopes to the 6-year cycles reported in many geodetic variables. Indeed, while some of these 6-year fluctuations are convincingly attributed to Earth& #8217 s deep interior processes, for some other variables, climate-related processes occurring in the surface fluid envelopes or at the Earth& #8217 s surface may be more likely. This issue is exacerbated by an opposition of phase discovered between the angular momentum of the atmosphere and the length of day at around 6 years, suggesting that dynamical processes occurring in the Earth& #8217 s core induce a rotation of the solid Earth and the atmosphere as a single system. An overview of the 6-yr cycle observed in different variables of the Earth System may therefore help to better understand potential links between the solid Earth and climate.
Publisher: Copernicus GmbH
Date: 16-12-2022
DOI: 10.5194/EGUSPHERE-2022-1032
Abstract: Abstract. The GRACE (Gravity Recovery And Climate Experiment) and GRACE Follow-On (FO) satellite gravity missions enable global monitoring of the mass transport within the Earth’s system, leading to unprecedented advances in our understanding of the global water cycle in a changing climate. This study focuses on the quantification of changes in terrestrial water storage based on an ensemble of GRACE and GRACE-FO solutions and two global hydrological models. Significant changes in terrestrial water storage are detected at pluriannual and decadal time -scales in GRACE and GRACE-FO satellite gravity data, that are generally underestimated by global hydrological models. The largest differences (more than 20 cm in equivalent water height) are observed in South America (Amazon, Sao Francisco and Parana river basins) and tropical Africa (Congo, Zambezi and Okavango river basins). Significant differences (a few cm) are observed worldwide at similar timescales, and are generally well correlated with precipitation. While the origin of such differences is unknown, pa rt of it is likely to be climate-related and at least partially due to inaccurate predictions of hydrological models. Slow changes in the terrestrial water cycle may indeed be overlooked in global hydrological models due to inaccurate meteorological forcin g (e.g., precipitation), unresolved groundwater processes, anthropogenic influences, changing vegetation cover and limited calibration/validation datasets. Significant differences between GRACE satellite measurements and hydrological model predictions have been identified, quantified and characterised in the present study. Efforts must be made to better understand the gap between both methods at pluriannual and decadal time-scales, which challenges the use of global hydrological models for the prediction of the evolution of water resources in changing climate conditions.
Publisher: Copernicus GmbH
Date: 08-08-2022
Publisher: Copernicus GmbH
Date: 08-08-2022
DOI: 10.5194/EGUSPHERE-2022-716
Abstract: Abstract. We investigate the continuity and stability of GRACE and GRACE Follow-On satellite gravimetric missions by assessing the ocean mass budget at global scale over 2005–2020, focusing on the last years of the record (2015–2020) when GRACE and GRACE Follow-On faced instrumental problems. For that purpose, we compare the global mean ocean mass estimates from GRACE and GRACE Follow-On to the sum of its contributions from Greenland, Antarctica, land glaciers and terrestrial water storage estimated with independent observations. A significant residual trend of -1.60 ± 0.36 mm/yr over 2015–2018 is observed. We also compare the gravimetry-based global mean ocean mass with the altimetry-based global mean sea level corrected for the thermosteric contribution. We estimate and correct for the drift of the wet tropospheric correction of the Jason-3 altimetry mission computed from the on-board radiometer. It accounts for about 40 % of the budget residual trend beyond 2015. After correction, the remaining residual trend amounts to -0.90 ± 0.78 mm/yr over 2015–2018 and -0.96 ± 0.48 mm/yr over 2015–2020. GRACE and GRACE Follow-On data might be responsible for part of the observed non-closure of the ocean mass budgets since 2015. However, we show that significant interannual variability is not well accounted for by the data used for the other components of the budget, including the thermosteric sea level and the terrestrial water storage. Besides, missing contributions from the evolution of the deep ocean or the atmospheric water vapour may also contribute.
Publisher: Copernicus GmbH
Date: 26-09-2022
DOI: 10.5194/GSTM2022-50
Abstract: & & & We investigate the continuity and stability of GRACE and GRACE Follow-On satellite gravimetric missions by assessing the ocean mass budget at global scale over 2005& #8211 , focusing on the last years of the record (2015& #8211 ) when GRACE and GRACE Follow-On faced instrumental problems. For that purpose, we compare the global mean ocean mass estimates from GRACE and GRACE Follow-On to the sum of its contributions from Greenland, Antarctica, land glaciers and terrestrial water storage estimated with independent observations. A significant residual trend of -1.60 & #177 0.36 mm/yr over 2015& #8211 is observed. We also compare the gravimetry-based global mean ocean mass with the altimetry-based global mean sea level corrected for the thermosteric contribution. We estimate and correct for the drift of the wet tropospheric correction of the Jason-3 altimetry mission computed from the on-board radiometer. It accounts for about 40 % of the budget residual trend beyond 2015. After correction, the remaining residual trend amounts to -0.90 & #177 0.78 mm/yr over 2015& #8211 and -0.96 & #177 0.48 mm/yr over 2015& #8211 . GRACE and GRACE Follow-On data might be responsible for part of the observed non-closure of the ocean mass budgets since 2015. However, we show that significant interannual variability is not well accounted for by the data used for the other components of the budget, including the thermosteric sea level and the terrestrial water storage. Besides, missing contributions from the evolution of the deep ocean or the atmospheric water vapour may also contribute.& & &
Location: France
Location: Italy
Location: France
Location: France
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Syed Abdul Qadir Shah.