Ocean Circulation from the synergy of altimeter-derived and oceanic tracers observations

2021 ◽  
Author(s):  
Daniele Ciani ◽  
Marie-Hélène Rio ◽  
Bruno Buongiorno Nardelli ◽  
Stéphanie Guinehut ◽  
Elodie Charles ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Time Window ◽  
Ocean Surface ◽  
Global Scale ◽  
Surface Currents ◽  
Sensitivity Experiment ◽  
Daily Data ◽  
Basin Scale ◽  
Ocean Surface Currents ◽  
Spatio Temporal

<p>Measuring the ocean surface currents at high spatio-temporal resolutions is crucial for scientific and socio-economic applications. Since the early 1990s, the synoptic and global-scale monitoring of the ocean surface currents has been provided by constellations of Radar Altimeters. The Altimeter observations enable to derive the geostrophic component of the surface currents with effective spatial-temporal resolutions O(100 km) and O(10 days), respectively. Therefore, only the largest mesoscale oceanic features can be accurately resolved. In order to enhance the altimeter system capabilities, we propose a synergistic use of high resolution, satellite-derived Sea Surface Temperature (SST), Chlorophyll concentrations (Chl) and Altimeter-derived currents. Our approach is tested in both global-scale and regional contexts.<br>At global scale, relying on past numerical studies, we perform a sensitivity experiment based on several gap-free SST datasets, emphasizing strengths and weaknesses in ocean currents applications. Overall, the comparison with in-situ measured currents shows that our synergistic method can improve the altimeter estimates up to 30% locally.<br>Then, our method is also implemented with Chl data in the  Mediterranean Sea, where the most energetic variable signals are found at spatio-temporal scales up to 10 km and few days. We test the method feasibility in an Observing System Simulation Experiment relying on model outputs of the European Copernicus Marine Service. Statistical analyses based on the 2017 daily data show that our approach can improve the altimeter-derived currents accuracy up to 50% at the basin scale, also enhancing the effective spatial-temporal resolutions up to 30 km and less than 10 days, respectively. The method efficiency decreases when the surface Chl patterns are dominated by the biological activity rather than the currents advection, which mostly occurs in the mid-February to mid-March time window. Preliminary tests on the method applicability to satellite-derived data are also presented and discussed.</p>

scholarly journals Ocean Currents Reconstruction from a Combination of Altimeter and Ocean Colour Data: A Feasibility Study

2021 ◽  
Vol 13 (12) ◽  
pp. 2389
Author(s):  
Daniele Ciani ◽  
Elodie Charles ◽  
Bruno Buongiorno Buongiorno Nardelli ◽  
Marie-Hélène Rio ◽  
Rosalia Santoleri
Keyword(s):  
Mediterranean Sea ◽  
Time Window ◽  
Ocean Surface ◽  
Global Scale ◽  
Biogeochemical Model ◽  
Surface Currents ◽  
Ocean Surface Currents ◽  
Marine Surface ◽  
The Mediterranean ◽  
Spatio Temporal

Measuring the ocean surface currents at high spatio-temporal resolutions is crucial for scientific and socio-economic applications. Since the early 1990s, the synoptic and global-scale monitoring of the ocean surface currents has been provided by constellations of radar altimeters. By construction, altimeter constellations provide only the geostrophic component of the marine surface currents. In addition, given the effective spatial-temporal resolution of the altimeter-derived products (O (100 km) and O (10 days), respectively), only the largest ocean mesoscale features can be resolved. In order to enhance the altimeter system capabilities, we propose a synergistic use of high resolution sea surface Chlorophyll observations (Chl) and altimeter-derived currents’ estimates. The study is focused on the Mediterranean Sea, where the most energetic signals are found at spatio-temporal scales up to 10 km and a few days. The proposed method allows for inferring the marine surface currents from the evolution of the Chl field, relying on altimeter-derived currents as a first-guess estimate. The feasibility of this approach is tested through an Observing System Simulation Experiment, starting from biogeochemical model outputs distributed by the European Copernicus Marine Service. Statistical analyses based on the 2017 daily data showed that our approach can improve the altimeter-derived currents accuracy up to 50%, also enhancing their effective spatial resolution up to 30 km. Moreover, the retrieved currents exhibit larger temporal variability than the altimeter estimates over annual to weekly timescales. Our method is mainly limited to areas/time periods where/when Chl gradients are larger and are modulated by the marine currents’ advection. Its application is thus more efficient when the surface Chl evolution is not dominated by the biological activity, mostly occurring in the mid-February to mid-March time window in the Mediterranean Sea. Preliminary tests on the method applicability to satellite-derived data are also presented and discussed.

scholarly journals Improving the Altimeter-Derived Surface Currents Using High-Resolution Sea Surface Temperature Data: A Feasability Study Based on Model Outputs

2016 ◽  
Vol 33 (12) ◽  
pp. 2769-2784 ◽  
Author(s):  
M.-H. Rio ◽  
R. Santoleri ◽  
R. Bourdalle-Badie ◽  
A. Griffa ◽  
L. Piterbarg ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Ocean Circulation ◽  
Large Scale ◽  
Spatial Scales ◽  
Ocean Surface ◽  
Sea Surface ◽  
High Temporal Resolution ◽  
Surface Currents ◽  
Ocean Surface Currents

AbstractAccurate knowledge of ocean surface currents at high spatial and temporal resolutions is crucial for a gamut of applications. The altimeter observing system, by providing repeated global measurements of the sea surface height, has been by far the most exploited system to estimate ocean surface currents over the past 20 years. However, it neither permits the observation of currents moving away from the geostrophic balance nor is it capable of resolving the shortest spatial and temporal scales of the currents. Therefore, to overcome these limitations, in this study the ways in which the high-spatial-resolution and high-temporal-resolution information from sea surface temperature (SST) images can improve the altimeter current estimates are investigated. The method involves inverting the SST evolution equation for the velocity by prescribing the source and sink terms and employing the altimeter currents as the large-scale background flow. The method feasibility is tested using modeled data from the Mercator Ocean system. This study shows that the methodology may improve the altimeter velocities at spatial scales not resolved by the altimeter system (i.e., below 150 km) but also at larger scales, where the geostrophic equilibrium might not be the unique or dominant process of the ocean circulation. In particular, the major improvements (more than 30% on the meridional component) are obtained in the equatorial band, where the geostrophic assumption is not valid. Finally, the main issues anticipated when this method is applied using real datasets are investigated and discussed.

scholarly journals Ocean Surface Currents Reconstruction: Spectral Characterization of the Transfer Function Between SST and SSH

2020 ◽  
Vol 125 (10) ◽  
Author(s):  
Cristina González‐Haro ◽  
Jordi Isern‐Fontanet ◽  
Pierre Tandeo ◽  
René Garello
Keyword(s):  
Transfer Function ◽  
Ocean Surface ◽  
Spectral Characterization ◽  
Surface Currents ◽  
Ocean Surface Currents

Ocean surface currents from satellite data

2017 ◽  
Vol 122 (4) ◽  
pp. 2647-2651 ◽  
Author(s):  
Kathleen Dohan
Keyword(s):  
Satellite Data ◽  
Ocean Surface ◽  
Surface Currents ◽  
Ocean Surface Currents

The spatio-temporal evolution of groundwater dependent precipitation

2021 ◽  
Author(s):  
Cristina Passet ◽  
Lan Wang-Erlandsson ◽  
Yoshihide Wada ◽  
Agnes Pranindita ◽  
Agatha De Boer
Keyword(s):  
Temporal Evolution ◽  
Groundwater Resources ◽  
Terrestrial Ecosystems ◽  
Global Scale ◽  
Groundwater Abstraction ◽  
Groundwater Availability ◽  
Basin Scale ◽  
The Usa ◽  
Spatio Temporal ◽  
Selection Of

<div><span>A<strong> </strong>substantial portion of groundwater abstracted from aquifers is used for irrigation and evaporated to the atmosphere, potentially contributing towards downwind precipitation. While the fate of evaporation fluxes from land have been analysed, the atmospheric pathways of evaporation originating from groundwater have not yet been globally quantified. This study analysed the geographical distribution, the seasonality and the magnitude of groundwater-dependent precipitation (Pgw) </span><span>at a global scale and for a selection of countries and river basins. The Eulerian moisture tracking WAM-2layers model was used to process meteorological and groundwater abstraction input data from 1980 to 2010.  Results show considerable contributions of groundwater to precipitation downwind of the most heavily irrigated areas, leading to net groundwater losses over these areas. Globally, 40% of the Pgw </span><span>precipitates directly in the oceans, and do not contribute to biomass production in terrestrial ecosystems. Some of the countries with the highest rates of groundwater abstraction (India, the USA, Pakistan and Iran), receive low volumes of Pgw </span><span>and are net losers of groundwater resources. The countries with the highest net gain of groundwater are China, Canada and Russia. At river basin scale, the Indus, Ganges and Mississippi basins are net losers of groundwater to downwind Pgw</span><span>, while the Yangtze, Tarim and Brahmaputra basins receive more Pgw </span><span>than their groundwater withdrawals. The share of precipitation that originates from groundwater varies considerably with seasons, and can be especially high when low local precipitation levels occur in combination with high upwind groundwater abstraction. Furthermore, precipitation dependence on </span><span>groundwater (ρgw)</span><span>, has steadily increased between 1980 to 2010 in all studied areas and globally. Our study suggests that the countries and basins with a high and increasing dependency on ρgw </span><span>to support their precipitation can be vulnerable to groundwater availability upwind.</span></div>

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