Revisiting non-tidal ocean loading corrections for high precision terrestrial gravimetry

Mapping Intimacies ◽

10.5194/egusphere-egu21-5308 ◽

2021 ◽

Author(s):

Ezequiel D. Antokoletz ◽

Hartmut Wziontek ◽

Henryk Dobslaw ◽

Claudia N. Tocho

Keyword(s):

Time Series ◽

High Precision ◽

Ocean Circulation ◽

Ocean Dynamics ◽

Atmospheric Effects ◽

Satellite Gravity ◽

Simple Assumption ◽

Superconducting Gravimeters ◽

Loading Effects ◽

Ocean Loading

In modelling of atmospheric loading effects in terrestrial gravimetry by numerical weather models, often the Inverse Barometer (IB) hypothesis is applied over oceans. This simple assumption implies an isostatic compensation of the oceans to atmospheric pressure changes, causing no net deformation of the seafloor. However, the IB hypothesis is in general not valid for periods shorter than a few weeks and, consequently, the ocean dynamics cannot be neglected. In particular, for the correction of high precision gravity time series as e.g. obtained from superconducting gravimeters, it is essential to model even small contributions in order to separate different effects. When including non-tidal ocean loading effects from ocean circulation models into atmospheric models, special care has to be taken of the interface between the atmosphere and the oceans in order not to account contributions twice.The established approach for modelling non-tidal ocean loading effects is revised in this study. When combining it with the modelling of atmospheric effects for terrestrial gravimetry, it is shown that Newtonian attraction contributions from the atmosphere may be accounted twice. To solve this problem, an alternative is proposed and tested which further reduces the variability of the gravity residuals, as shown for a set of four superconducting gravity meters globally distributed.The improvement is achieved by a different treatment of the Newtonian attraction component related to the IB effect. Discrepancies up to the &#956;Gal level are demonstrated, depending on the location of the station. With several simplifications, the approach can be made operational and included in existing services, further improving the compatibility of terrestrial gravity time series with satellite gravity observations.

Sea Ice Concentration Products over Polar Regions with Chinese FY3C/MWRI Data

Remote Sensing ◽

10.3390/rs13112174 ◽

2021 ◽

Vol 13 (11) ◽

pp. 2174

Author(s):

Lijian Shi ◽

Sen Liu ◽

Yingni Shi ◽

Xue Ao ◽

Bin Zou ◽

...

Keyword(s):

Time Series ◽

Sea Ice ◽

Ocean Circulation ◽

The Arctic ◽

Retrieval Algorithm ◽

Atmospheric Effects ◽

Observation Data ◽

Long Time Series ◽

Ice Concentration ◽

Long Time

Polar sea ice affects atmospheric and ocean circulation and plays an important role in global climate change. Long time series sea ice concentrations (SIC) are an important parameter for climate research. This study presents an SIC retrieval algorithm based on brightness temperature (Tb) data from the FY3C Microwave Radiation Imager (MWRI) over the polar region. With the Tb data of Special Sensor Microwave Imager/Sounder (SSMIS) as a reference, monthly calibration models were established based on time–space matching and linear regression. After calibration, the correlation between the Tb of F17/SSMIS and FY3C/MWRI at different channels was improved. Then, SIC products over the Arctic and Antarctic in 2016–2019 were retrieved with the NASA team (NT) method. Atmospheric effects were reduced using two weather filters and a sea ice mask. A minimum ice concentration array used in the procedure reduced the land-to-ocean spillover effect. Compared with the SIC product of National Snow and Ice Data Center (NSIDC), the average relative difference of sea ice extent of the Arctic and Antarctic was found to be acceptable, with values of −0.27 ± 1.85 and 0.53 ± 1.50, respectively. To decrease the SIC error with fixed tie points (FTPs), the SIC was retrieved by the NT method with dynamic tie points (DTPs) based on the original Tb of FY3C/MWRI. The different SIC products were evaluated with ship observation data, synthetic aperture radar (SAR) sea ice cover products, and the Round Robin Data Package (RRDP). In comparison with the ship observation data, the SIC bias of FY3C with DTP is 4% and is much better than that of FY3C with FTP (9%). Evaluation results with SAR SIC data and closed ice data from RRDP show a similar trend between FY3C SIC with FTPs and FY3C SIC with DTPs. Using DTPs to present the Tb seasonal change of different types of sea ice improved the SIC accuracy, especially for the sea ice melting season. This study lays a foundation for the release of long time series operational SIC products with Chinese FY3 series satellites.

A multi-year time series of observation-based 3D horizontal and vertical quasi-geostrophic global ocean currents

Earth System Science Data ◽

10.5194/essd-12-1711-2020 ◽

2020 ◽

Vol 12 (3) ◽

pp. 1711-1723

Author(s):

Bruno Buongiorno Nardelli

Keyword(s):

Time Series ◽

Ocean Circulation ◽

General Circulation ◽

Numerical Models ◽

Ocean Currents ◽

Ocean Dynamics ◽

Global Ocean ◽

Diagnostic Model ◽

Geostrophic Balance ◽

Consiglio Nazionale Delle Ricerche

Abstract. Estimates of 3D ocean circulation are needed to improve our understanding of ocean dynamics and to assess their impact on marine ecosystems and Earth climate. Here we present the OMEGA3D product, an observation-based time series of (quasi-)global 3D ocean currents covering the 1993–2018 period, developed by the Italian Consiglio Nazionale delle Ricerche within the European Copernicus Marine Environment Monitoring Service (CMEMS). This dataset was obtained by applying a diabatic quasi-geostrophic (QG) diagnostic model to the data-driven CMEMS-ARMOR3D weekly reconstruction of temperature and salinity as well as ERA Interim fluxes. Outside the equatorial band, vertical velocities were retrieved in the upper 1500 m at 1∕4∘ nominal resolution and successively used to compute the horizontal ageostrophic components. Root mean square differences between OMEGA3D total horizontal velocities and totally independent drifter observations at two different depths (15 and 1000 m) decrease with respect to corresponding estimates obtained from zero-order geostrophic balance, meaning that estimated vertical velocities can also be deemed reliable. OMEGA3D horizontal velocities are also closer to drifter observations than velocities provided by a set of reanalyses spanning a comparable time period but based on data assimilation in ocean general circulation numerical models. The full OMEGA3D product (released on 31 March 2020) is available upon free registration at https://doi.org/10.25423/cmcc/multiobs_glo_phy_w_rep_015_007 (Buongiorno Nardelli, 2020a). The reduced subset used here for validation and review purposes is openly available at https://doi.org/10.5281/zenodo.3696885 (Buongiorno Nardelli, 2020b).

Observation of gravity fluctuations due to tide-induced groundwater table fluctuations with two superconducting gravimeters

10.5194/egusphere-egu2020-19014 ◽

2020 ◽

Author(s):

Hiroki Goto ◽

Mituhiko Sugihara ◽

Yuji Nishi ◽

Hiroshi Ikeda

Keyword(s):

Groundwater Level ◽

Hydraulic Properties ◽

Groundwater Resources ◽

Groundwater Table ◽

Surface Gravity ◽

Superconducting Gravimeters ◽

Loading Effects ◽

Ocean Loading ◽

Aquifer Properties ◽

The Difference

Estimation of aquifer hydraulic properties is necessary for predicting groundwater flow and hence managing groundwater resources. Analysis of tide-induced groundwater table fluctuations in unconfined aquifers is one of the methods to estimate aquifer properties. Changes in groundwater level affect surface gravity. Consequently, surface gravity in coastal regions is expected to fluctuate due to the groundwater table fluctuations and is potentially useful for estimating aquifer properties. Moreover, gravity measurements are sensitive to mass redistribution around the observation location and therefore are useful for estimating the storage coefficient of an aquifer. In this study, surface gravity and unconfined groundwater level were measured continuously near the coast of Japan to observe gravity fluctuations due to the tide-induced groundwater table fluctuations. Groundwater level measured in two wells at 60 and 90 m distances from the coastline fluctuated in response to ocean tides. Two superconducting gravimeters (SGs) were installed at 70 and 80 m distances from the coastline and at an elevation of 8 m. After taking the difference between gravity values recorded with the two SGs and then correcting the gravity difference for ocean loading effects, diurnal and semi-diurnal gravity fluctuations, which are possibly due to tide-induced groundwater table fluctuations, were recognized. These results suggest that gravity monitoring with two SGs at different distances from the coastline can be useful for observing gravity fluctuations due to tide-induced groundwater table fluctuations and possibly for estimating aquifer hydraulic properties.

A Time History of Pre- and Post-Bomb Radiocarbon in the Barents Sea Derived from Arcto-Norwegian Cod Otoliths

Radiocarbon ◽

10.1017/s0033822200041515 ◽

2001 ◽

Vol 43 (2B) ◽

pp. 843-855 ◽

Cited By ~ 30

Author(s):

John M Kalish ◽

Reidar Nydal ◽

Kjell H Nedreaas ◽

George S Burr ◽

Gro L Eine

Keyword(s):

Time Series ◽

Ocean Circulation ◽

General Circulation ◽

Barents Sea ◽

Dissolved Inorganic Carbon ◽

Time History ◽

General Circulation Models ◽

Fine Tuning ◽

Birth Date ◽

The Barents Sea

Radiocarbon measured in seawater dissolved inorganic carbon (DIC) can be used to investigate ocean circulation, atmosphere/ocean carbon flux, and provide powerful constraints for the fine-tuning of general circulation models (GCMs). Time series of 14C in seawater are derived most frequently from annual bands of hermatypic corals. However, this proxy is unavailable in temperate and polar oceans. Fish otoliths, calcium carbonate auditory, and gravity receptors in the membranous labyrinths of teleost fishes, can act as proxies for 14C in most oceans and at most depths. Arcto-Norwegian cod otoliths are suited to this application due to the well-defined distribution of this species in the Barents Sea, the ability to determine ages of individual Arcto-Norwegian cod with a high level of accuracy, and the availability of archived otoliths collected for fisheries research over the past 60 years. Using measurements of 14C derived from Arcto-Norwegian cod otoliths, we present the first pre- and post-bomb time series (1919–1992) of 14C from polar seas and consider the significance of these data in relation to ocean circulation and atmosphere/ocean flux of 14C. The data provide evidence for a minor Suess effect of only 0.2‰ per year between 1919 and 1950. Bomb 14C was evident in the Barents Sea as early as 1957 and the highest 14C value was measured in an otolith core from a cod with a birth date of 1967. The otolith 14C data display key features common to records of 14C obtained from a Georges Bank mollusc and corals from the tropical and subtropical North Atlantic.

Ocean Convection

Fluids ◽

10.3390/fluids6100360 ◽

2021 ◽

Vol 6 (10) ◽

pp. 360

Author(s):

Catherine Vreugdenhil ◽

Bishakhdatta Gayen

Keyword(s):

Climate Change ◽

Ocean Circulation ◽

Mixed Layer ◽

Water Mass ◽

Current Knowledge ◽

Open Ocean ◽

Meridional Overturning Circulation ◽

Ocean Dynamics ◽

Global Circulation Models ◽

Ocean Convection

Ocean convection is a key mechanism that regulates heat uptake, water-mass transformation, CO2 exchange, and nutrient transport with crucial implications for ocean dynamics and climate change. Both cooling to the atmosphere and salinification, from evaporation or sea-ice formation, cause surface waters to become dense and down-well as turbulent convective plumes. The upper mixed layer in the ocean is significantly deepened and sustained by convection. In the tropics and subtropics, night-time cooling is a main driver of mixed layer convection, while in the mid- and high-latitude regions, winter cooling is key to mixed layer convection. Additionally, at higher latitudes, and particularly in the sub-polar North Atlantic Ocean, the extensive surface heat loss during winter drives open-ocean convection that can reach thousands of meters in depth. On the Antarctic continental shelf, polynya convection regulates the formation of dense bottom slope currents. These strong convection events help to drive the immense water-mass transport of the globally-spanning meridional overturning circulation (MOC). However, convection is often highly localised in time and space, making it extremely difficult to accurately measure in field observations. Ocean models such as global circulation models (GCMs) are unable to resolve convection and turbulence and, instead, rely on simple convective parameterizations that result in a poor representation of convective processes and their impact on ocean circulation, air–sea exchange, and ocean biology. In the past few decades there has been markedly more observations, advancements in high-resolution numerical simulations, continued innovation in laboratory experiments and improvement of theory for ocean convection. The impacts of anthropogenic climate change on ocean convection are beginning to be observed, but key questions remain regarding future climate scenarios. Here, we review the current knowledge and future direction of ocean convection arising from sea–surface interactions, with a focus on mixed layer, open-ocean, and polynya convection.

Multi-grid algorithm for passive tracer transport in the NEMO ocean circulation model: a case study with the NEMO OGCM (version 3.6)

Geoscientific Model Development ◽

10.5194/gmd-13-5465-2020 ◽

2020 ◽

Vol 13 (11) ◽

pp. 5465-5483

Author(s):

Clément Bricaud ◽

Julien Le Sommer ◽

Gurvan Madec ◽

Christophe Calone ◽

Julie Deshayes ◽

...

Keyword(s):

Spatial Resolution ◽

Ocean Circulation ◽

Circulation Model ◽

Ocean Model ◽

Ocean Dynamics ◽

Global Ocean ◽

Passive Tracer ◽

Tracer Transport ◽

Ocean Circulation Model ◽

Grid Algorithm

Abstract. Ocean biogeochemical models are key tools for both scientific and operational applications. Nevertheless the cost of these models is often expensive because of the large number of biogeochemical tracers. This has motivated the development of multi-grid approaches where ocean dynamics and tracer transport are computed on grids of different spatial resolution. However, existing multi-grid approaches to tracer transport in ocean modelling do not allow the computation of ocean dynamics and tracer transport simultaneously. This paper describes a new multi-grid approach developed for accelerating the computation of passive tracer transport in the Nucleus for European Modelling of the Ocean (NEMO) ocean circulation model. In practice, passive tracer transport is computed at runtime on a grid with coarser spatial resolution than the hydrodynamics, which reduces the CPU cost of computing the evolution of tracers. We describe the multi-grid algorithm, its practical implementation in the NEMO ocean model, and discuss its performance on the basis of a series of sensitivity experiments with global ocean model configurations. Our experiments confirm that the spatial resolution of hydrodynamical fields can be coarsened by a factor of 3 in both horizontal directions without significantly affecting the resolved passive tracer fields. Overall, the proposed algorithm yields a reduction by a factor of 7 of the overhead associated with running a full biogeochemical model like PISCES (with 24 passive tracers). Propositions for further reducing this cost without affecting the resolved solution are discussed.

Last Glacial Maximum (LGM) climate forcing and ocean dynamical feedback and their implications for estimating climate sensitivity

Climate of the Past ◽

10.5194/cp-17-253-2021 ◽

2021 ◽

Vol 17 (1) ◽

pp. 253-267

Author(s):

Jiang Zhu ◽

Christopher J. Poulsen

Keyword(s):

Last Glacial Maximum ◽

Ocean Circulation ◽

Climate Sensitivity ◽

Radiative Forcing ◽

Ice Sheets ◽

Glacial Maximum ◽

Ocean Dynamics ◽

Last Glacial ◽

True Value ◽

Climate Forcings

Abstract. Equilibrium climate sensitivity (ECS) has been directly estimated using reconstructions of past climates that are different than today's. A challenge to this approach is that temperature proxies integrate over the timescales of the fast feedback processes (e.g., changes in water vapor, snow, and clouds) that are captured in ECS as well as the slower feedback processes (e.g., changes in ice sheets and ocean circulation) that are not. A way around this issue is to treat the slow feedbacks as climate forcings and independently account for their impact on global temperature. Here we conduct a suite of Last Glacial Maximum (LGM) simulations using the Community Earth System Model version 1.2 (CESM1.2) to quantify the forcing and efficacy of land ice sheets (LISs) and greenhouse gases (GHGs) in order to estimate ECS. Our forcing and efficacy quantification adopts the effective radiative forcing (ERF) and adjustment framework and provides a complete accounting for the radiative, topographic, and dynamical impacts of LIS on surface temperatures. ERF and efficacy of LGM LIS are −3.2 W m−2 and 1.1, respectively. The larger-than-unity efficacy is caused by the temperature changes over land and the Northern Hemisphere subtropical oceans which are relatively larger than those in response to a doubling of atmospheric CO2. The subtropical sea-surface temperature (SST) response is linked to LIS-induced wind changes and feedbacks in ocean–atmosphere coupling and clouds. ERF and efficacy of LGM GHG are −2.8 W m−2 and 0.9, respectively. The lower efficacy is primarily attributed to a smaller cloud feedback at colder temperatures. Our simulations further demonstrate that the direct ECS calculation using the forcing, efficacy, and temperature response in CESM1.2 overestimates the true value in the model by approximately 25 % due to the neglect of slow ocean dynamical feedback. This is supported by the greater cooling (6.8 ∘C) in a fully coupled LGM simulation than that (5.3 ∘C) in a slab ocean model simulation with ocean dynamics disabled. The majority (67 %) of the ocean dynamical feedback is attributed to dynamical changes in the Southern Ocean, where interactions between upper-ocean stratification, heat transport, and sea-ice cover are found to amplify the LGM cooling. Our study demonstrates the value of climate models in the quantification of climate forcings and the ocean dynamical feedback, which is necessary for an accurate direct ECS estimation.

Accuracy Analysis of Gravity Field Changes from Grace RL06 and RL05 Data Compared to in Situ Gravimetric Measurements in the Context of Choosing Optimal Filtering Type

Artificial Satellites ◽

10.2478/arsa-2020-0008 ◽

2020 ◽

Vol 55 (3) ◽

pp. 100-117

Author(s):

Viktor Szabó ◽

Dorota Marjańska

Keyword(s):

Gravity Field ◽

Ocean Circulation ◽

Gravity Data ◽

The Other ◽

Subsurface Water ◽

Satellite Gravity ◽

Absolute Gravimetry ◽

The Earth ◽

Gravity Measurements ◽

Gravity Recovery

AbstractGlobal satellite gravity measurements provide unique information regarding gravity field distribution and its variability on the Earth. The main cause of gravity changes is the mass transportation within the Earth, appearing as, e.g. dynamic fluctuations in hydrology, glaciology, oceanology, meteorology and the lithosphere. This phenomenon has become more comprehensible thanks to the dedicated gravimetric missions such as Gravity Recovery and Climate Experiment (GRACE), Challenging Minisatellite Payload (CHAMP) and Gravity Field and Steady-State Ocean Circulation Explorer (GOCE). From among these missions, GRACE seems to be the most dominating source of gravity data, sharing a unique set of observations from over 15 years. The results of this experiment are often of interest to geodesists and geophysicists due to its high compatibility with the other methods of gravity measurements, especially absolute gravimetry. Direct validation of gravity field solutions is crucial as it can provide conclusions concerning forecasts of subsurface water changes. The aim of this work is to present the issue of selection of filtration parameters for monthly gravity field solutions in RL06 and RL05 releases and then to compare them to a time series of absolute gravimetric data conducted in quasi-monthly measurements in Astro-Geodetic Observatory in Józefosław (Poland). The other purpose of this study is to estimate the accuracy of GRACE temporal solutions in comparison with absolute terrestrial gravimetry data and making an attempt to indicate the significance of differences between solutions using various types of filtration (DDK, Gaussian) from selected research centres.

The Role of Oceanic Feedback in the Climate Response to Doubling CO2

Journal of Climate ◽

10.1175/jcli-d-11-00712.1 ◽

2012 ◽

Vol 25 (21) ◽

pp. 7544-7563 ◽

Cited By ~ 49

Author(s):

Jian Lu ◽

Bin Zhao

Keyword(s):

Ocean Circulation ◽

Global Climate ◽

Coupled Model ◽

Southern Annular Mode ◽

Ocean Dynamics ◽

Climate Response ◽

Tropical Precipitation ◽

Fluctuation Dissipation ◽

Wes Feedback ◽

Partial Coupling

Two suites of partial coupling experiments are devised with the upper-ocean dynamics version (UOM) of the CCSM3 to isolate the effects of the feedbacks from the change of the wind-driven ocean circulation and air–sea heat flux in the global climate response to the forcing of doubling CO2. The partial coupling is achieved by implementing a so-called overriding technique, which helps quantitatively partition the total response in the fully coupled model to the feedback component in question and the response to external forcing in the absence of the former. By overriding the wind stress seen by the ocean and the wind speed through the bulk formula for evaporation, the experiments help to reveal that (i) the wind–evaporation–SST (WES) feedback is the main formation mechanism for the tropical SST pattern under the CO2 forcing, verifying the hypothesis proposed by Xie et al.; (ii) the weakened tropical Pacific wind is shown in this UOM model not to be the cause for the enhanced equatorial Pacific warming, as one might expect from the thermocline and Bjerknes feedbacks; (iii) WES is also the leading mechanism for shaping the tropical precipitation response in the ocean; and (iv) both the wind-driven ocean dynamical feedback and the WES feedback act to increase the persistence of the southern annular mode (SAM) and the increased time scale of the SAM due to these feedbacks manifests itself in the response of the jet shift to an identical CO2 forcing, in a manner conforming to the fluctuation–dissipation theorem.

Geochronology - a suitable tool to discern causality from temporal coincidence?

10.5194/egusphere-egu21-896 ◽

2021 ◽

Author(s):

Urs Schaltegger

Keyword(s):

Time Series ◽

High Precision ◽

Age Determination ◽

System Behavior ◽

Large Igneous Provinces ◽

Igneous Provinces ◽

Volcanic Plumbing System ◽

Non Linear ◽

Age Variation ◽

Non Linear System

Geoscientists tend to subdivide the system Earth into different subsystems (geosphere, hydrosphere, atmosphere, biosphere), which are interacting with each other in a non-linear way. The quantitative understanding of this interaction is essential to make reconstructions of the geological past. This is mostly done by a linear approach of establishing time-series of chemical and physical proxies, calibrating their contemporaneity through geochronology, and eventually invoke causality. A good example is the comparison of carbon or oxygen isotope time series to the paleo-biodiversity in ancient sedimentary sections, temporally correlated using astrochronology or high-precision U-Pb dating of volcanic zircon in interlayered ash beds. While highly accurate and precise data are necessary to form the basis for linear and non-linear models, we have to be aware that any analysis is the result of an experiment &#8211; an isotope-chemical analysis in the U-Pb example - introducing random and non-random noise, which can mimic, disturb, distort or mask non-linear system behavior. High-precision/high-accuracy U-Pb age determination using the mineral zircon (ZrSiO4) and application of the techniques of isotope dilution, thermal ionization mass spectrometry is a good example of such an experiment we apply to the geological history of our planet.Two examples where precise U-Pb dating methods are used to link disparate processes are (1) using the duration and the tempo of zircon growth in a magmatic system as a measure for modeling magma flux in space and time, and apply these to infer potential eruptibility and volcanic hazard of a plutonic-volcanic plumbing system; (2) establish absolute age and duration of magma emplacement in large igneous provinces, feed these data into models of volatile injection into and residence of volatile species in the atmosphere, estimate their influence on the inherent parameters of Earth&#8217;s climate, and infer causality with climatic, environmental and biotic crises. Both of these are outstanding scientific questions that attract and deserve significant attention by a general as well as academic public. However, insufficient attention is drawn onto the questions of the nature and importance of the noise we add through isotopic age determination.There are two prominent issues to be discussed in this context, (1) to what extent (at what precision) can we distinguish natural age variation among zircon grains from random scatter produced by analytical techniques and the complexity of the U-Pb isotopic system in zircon, and (2) how can we correlate the U-Pb dates established for crystallization of zircon in residual and/or assimilated melt portions of mafic magmatic rocks from large igneous provinces to the release and injection of magmatic and contact-metamorphic volatiles into the atmosphere? This contribution intends to demonstrate that analytical scatter and complex system behavior are often confounded with age variation (and vice versa) and will outline new approaches and insights how to quantify their respective contributions.