bluuebunny/crossref_metadata_2025 huggingface dataset:
Contemporary biodiversity pattern is affected by climate change at multiple temporal scales in steppe on the Mongolian Plateau
Authors: Li Zijing , Li Zhiyong , Tong Xuze , Dong Lei , Zheng Ying , Zhang Jinghui , Miao Bailing , Wang Lixin , Zhao Liqing , Wen Lu , Han Guodong , Li Frank Yonghong , Liang Cunzhu
Published: September 2022

Abstract. Present and historical climate conditions jointly determine contemporary biodiversity patterns and ecosystem functions. However, it remains unclear how contemporary climate and paleoclimate changes together affect the three dimensions of biodiversity (i.e., taxonomic diversity, functional diversity and phylogenetic diversity) and their relationship with ecosystem functions. Here, we assess the impact of current climate, paleoclimate and its anomalies on contemporary biodiversity and ecosystem functions. We estimated the taxonomic diversity, functional diversity and phylogenetic diversity of grassland on the Mongolian Plateau using vegetation survey data and trait information. We then used Random Forest models and Structural Equation models to assess the relative importance of the present climate, the Mid Holocene climate, the Last-Glacial Maximum climate and paleoclimate changes as determinants of diversity and aboveground biomass. Our results showed that paleoclimate changes and modern climate jointly determined contemporary biodiversity patterns, while community biomass was mainly affected by modern climate, namely the aridity index. Modern aridity and temperature were two major influences on all three dimensions of biodiversity. Mid-Holocene climate anomalies had a strong effect on species richness and phylogenetic diversity, while functional diversity was mainly affected by temperature anomalies since the Last Glacial Maximum. These findings suggest that contemporary biodiversity patterns may be affected by processes at divergent temporal scales. Our results show that simultaneously exploring the response of the three dimensions of biodiversity in different periods of climate change and the theoretical framework for its impact on community biomass is helpful to provide a more comprehensive understanding of patterns of biodiversity and its relationship with ecosystem functions.
Recently fixed carbon fuels microbial activity several meters below the soil surface
Authors: Scheibe Andrea , Sierra Carlos , Spohn Marie
Published: September 2022

Abstract. The deep soil, >1 meter, harbors a substantial share of the global microbial biomass. Currently, it is not known whether microbial activity several meters below the surface is fueled by recently fixed carbon or by old carbon that persisted in soil for several hundred years. Understanding the carbon source of microbial activity in deep soil is important to identify the drivers of biotic processes in the critical zone. Therefore, we explored carbon cycling in soils in three climate zones (arid, mediterranean, and humid) of the Coastal Cordillera of Chile down to a depth of six meters, using carbon isotopes. Specifically, we determined the 13C : 12C ratio (δ13C) of soil and roots, and the 14C : 12C ratio (Δ14C) of soil and CO2 respired by microorganisms. We found that the Δ14C of the respired CO2-C was higher than of the soil organic carbon in all soils (except for two topsoils). Further, we found that the δ13C of the soil organic carbon changed only in the upper decimeters (by less than 6 ‰). Our results show that microbial activity several meters below the soil surface is mostly fueled by recently fixed carbon that is on average much younger than the total soil organic carbon present in the respective soil depth increments, in all three climate zones. Further, our results indicate that strong microbial decomposition of the soil organic matter only occurs in the upper decimeters of the soils, which is likely due to stabilization of organic carbon in the deep soil. In conclusion, our results demonstrate that microbial processes in the deep soil several meters below the surface are closely tied to primary production aboveground.
Microphysics of liquid water in sub-10 nm ultrafine aerosol particles
Authors: Li Xiaohan , Bourg Ian C.
Published: September 2022

Abstract. Ultrafine aerosol particles with sizes smaller than 50 nm have been shown in recent studies to serve as a large source of cloud condensation nuclei (CCN) that can promote additional cloud droplet formation under supersaturation conditions. Knowledge of the microphysics of liquid water in these droplets remains limited, particularly in the sub-10 nm particle size range, due to experimental and theoretical challenges associated with the complexity of aerosol components and the small length scales of interest (e.g., difficulty of precisely sampling the liquid-air interface, questionable validity of mean-field theoretical representations). Here, we carried out molecular dynamics (MD) simulations of aerosol particles with diameters between 1 and 10 nm and characterized atomistic-level structure and water dynamics in well-mixed and phase-separated system with different particle sizes, NaCl salinities, and organic surface loadings as a function of distance from the time-averaged Gibbs dividing interface or instantaneous water-air interface. We define a sphericity factor (Φ) that can shed light on the phase-mixing state of nanodroplets, and we reveal an unexpected dependence of mixing state on droplet size. Our results also evidence an ion concentration enhancement in ultrafine aerosols, which should modulate salt nucleation kinetics in ultrafine sea salt aerosols, and provide detailed characterization of the influence of droplet size on surface tension and on water self-diffusivity near the interface. Analysis of water evaporation free energy and water activity demonstrates the validity of the Kelvin equation and Köhler theory at droplet sizes larger than 4 nm under moderate salinities and organic loadings and the need for further extension to account for ion concentration enhancement in sub-10 nm aerosols, droplet-size-dependent phase separation effects, and a sharp decrease in the cohesiveness of liquid water in sub-4 nm droplets. Finally, we show that an idealized fractional surface coating factor (fs) can be used to categorize and reconcile water accommodation coefficients (α*) observed in MD simulations and experimental results in the presence of organic coatings, and we resolve the droplet-size dependence of α*.
High-resolution maps of above- and belowground woody biomass in China from 2003 to 2020
Authors: Chen Yongzhe , Feng Xiaoming , Fu Bojie , Ma Haozhi , Zohner Constantin M. , Crowther Thomas W. , Huang Yuanyuan , Wu Xutong , Wei Fangli
Published: September 2022

Abstract. To quantify the ecological consequences of recent nation wide restoration efforts in China, spatially explicit information on woody biomass changes over the 21st century is critical However, long term biomass tracking at the national scale remains challenging as it requires continuous and high resolution monitoring . Here, we mapped above and belowground biomass (AGB and BGB) for woody vegetation in China between 2003 and 2020 at 1 km spatial resolution by integrating multiple types of remote sensing observations with intensive field plot measurements through machine learning and mixed pixel decomposition methods On average, 11.0 ± 0.7 and 2.8 ± 0.2 PgC are stored in above and belowground live woody biomass in China. Over the last 18 years , the total woody biomass carbon in China has increased at a rate of 163.8 TgC yr-1 (0.5 % yr-1). T he most pronounced biomass gains occurred in central to south ern China, including the southern Loess Plateau, Qinling Mountains, southwest karst and southeast forest s . T he combined use of low frequency (L-band , microwaves and laser remote sensing data provides a powerful tool to minimize under or overestimation of biomass variation in space and time Future research is needed to explore the drivers of the observed woody biomass trends , and to evaluate the degree to which biomass gains will translate into biodiverse, healthy ecosystems and thus are sustainable.
Deep-water red shrimp fishery in the Eastern-Central Mediterranean Sea: AIS-observed monthly fishing effort and frequency over four years
Authors: Pulcinella Jacopo , Armelloni Enrico Nicola , Ferrà Carmen , Scarcella Giuseppe , Tassetti Anna Nora
Published: September 2022

Abstract. Deep-sea fishery in the Mediterranean Sea was historically driven by the commercial profitability of deepwater red shrimps and understanding spatio-temporal dynamics of fishing is key to comprehensively evaluate the status of these profitable resources and prevent stock collapse. A four-year time series of AIS-based observed monthly patterns and related frequency of trawling disturbance are provided with a resolution of 0.01°*0.01°, accounting for the spatial extent and temporal variability in deep water bottom contact fisheries during the period 2015–2018. The dataset was estimated from 370 fishing vessels that were found to perform trawling in deep water (400 m–800 m) during the study period, and they represent a significant part of the real fleet exploiting this fishing grounds in the study area. The reconstructed deep-water trawling effort dataset is available at: https://doi.org/10.17882/89150 (Pulcinella et al., 2022). This large-scale and high-resolution dataset may help researchers of many scientific fields, as well as those involved in fishery management and in the update of existing management plans for deep-water red shrimp fisheries as foreseen in relevant General Fisheries Commission for the Mediterranean (GFCM) recommendations.
 Reduction of aliasing errors in gravity field recovery by means of covariance information for ocean tide models
Authors: Wilms Josefine , Panafidina Natalia , Hauk Markus , Dahle Christoph , Sulzbach Roman , Flechtner Frank
Published: September 2022

The GRACE and GRACE-FO missions are fundamental in establishing a near-continuous time series of global mass transport since 2002. However, monthly gravity field recovery using these mission data includes errors limiting the spatial and temporal resolution of the estimated gravity field solutions. The major error contributions, besides the noise of the accelerometer instruments, arise from temporal aliasing errors due to undersampling of signals to be recovered (e.g. hydrology), uncertainties in the de-aliasing models (e.g., non-tidal atmosphere and ocean) and imperfect ocean tide models. Especially the latter will also remain one of the most limiting factors in determining high-resolution temporal gravity fields from Next-Generation Gravity Missions (NGGM).

In this context, recent developments have been made within the Research Unit NEROGRAV (New Refined Observations of Climate Change from Spaceborne Gravity Missions) funded by the German Research Foundation DFG. One of the projects within NEROGRAV deals with the stochastic modeling regarding ocean tide background models by the utilization of covariance information for eight major tidal constituents. The repeatable pattern of the tidal signal enables the extraction of uncertainty information by an ensemble of different ocean tide models. This information can be introduced into the gravity field recovery process in terms of a covariance matrix while expanding the parameter space by additional tidal parameters to be estimated.

This presentation provides an overview of the recovered monthly gravity fields from GRACE/GRACE-FO when applying covariance information of ocean tide errors. Furthermore, results from simulations representing a GRACE-FO type mission as well as an NGGM double-pair scenario (polar plus inclined pair) are presented. The results show reduced tidal aliasing errors as well as more realistic formal uncertainties.
Improving groundwater loss estimates using a combination of GNSS, GRACE-FO, and InSAR: Case study of California’s recent 2020-2021 drought
Authors: Carlson Grace , Werth Susanna , Shirzaei Manoochehr
Published: September 2022

Over the last two decades, California, USA has undergone three multi-year intense periods of drought, with the most recent still ongoing as of August 2022. Low precipitation and unusually warm temperatures, yielding high evapotranspiration rates, low snowpack, and early snowmelt, have led to record low surface water levels in reservoirs across the state and an increased reliance on groundwater resources, resulting in widespread groundwater overdraft. Extreme states in the water cycle such as drought can be measured directly and indirectly using several geodetic remote sensing tools, including observations from the GRACE and GRACE-FO satellites and deformation recorded by Global Navigation Satellite System (GNSS) stations measuring the elastic response of Earth’s crust to changes in mass loading. In California’s Central Valley, a large, elongate sedimentary basin between the Coastal Ranges and Sierra Nevada Mountains, groundwater overdraft during drought has caused widespread subsidence. This subsidence is a poroelastic response to aquifer overdraft and has been observed using interferometric synthetic aperture radar (InSAR) and GNSS station displacements. This presentation proposes a unified geophysical model incorporating observations from GRACE, which provides regional closure of the water budget at impressive accuracy but a low spatial resolution, and indirect measurements of poroelastic and elastic deformation from GNSS and InSAR, to derive improved estimates of terrestrial water storage change (∆TWS) at a higher spatial resolution. Using a joint inversion framework that combines GRACE-FO ∆TWS with elastic deformation from GNSS station displacements and InSAR-derived vertical land motion showing poroelastic aquifer deformation over the Central Valley aquifer, we produce high-resolution maps of ∆TWS over California and Nevada and groundwater loss over the Central Valley during the 2020-2021 drought period. We find that the largest water loss occurs over the southern Central Valley, with groundwater loss of more than two meters equivalent water height. Outside of the southern Central Valley, we find that the largest TWS declines occur in the northern Sierra Nevada Mountains and northern Central Valley, with ∆TWS of ~0.5-1 meter equivalent water height. We also show that groundwater loss estimates determined using our joint inversion framework are larger, but mainly in agreement with GRACE-derived groundwater loss estimates when considering underlying processes and uncertainties.
Prospects of Satellite Gravimetry to Monitor Atmospheric Mass, Water Vapor Partial Pressure, and/or Atmospheric Net-Water Fluxes
Authors: Balidakis Kyriakos , Dobslaw Henryk , Zus Florian , Eicker Annette , Dill Robert , Wickert Jens
Published: September 2022

Global Atmospheric re-analysis efforts aim at the realistic reproduction of the time-variable atmospheric state and associated diagnostic quantities by assimilating a wide range of different types of observations into a numerical model. Satellite gravimetry as realized with GRACE and GRACE-FO is on the one hand sensitive to the three-dimensional distribution of mass in the atmosphere and on the other hand also to (rapid) variations in terrestrial water storage, that largely represent the time-integrated effect of precipitation and evapotranspiration. By means of an ensemble of three global atmospheric reanalyses (ERA5, MERRA2, JRA-55) and two operational numerical weather prediction models (IFS from ECMWF, ICON from the German Meteorological Service) we will discuss the current level of agreement among the atmospheric models for (i) hydrostatic surface pressure, (ii) water vapor partial pressure, and (iii) atmospheric net-water fluxes obtained from summing precipitation and evapotranspiration. For time-scales between a few days and several weeks, we find that atmospheric net-water fluxes show the highest spread among the different models, thereby indicating a need for additional observations of both precipitation and/or evapotranspiration that are not yet routinely assimilated. We also find that water vapor partial pressure is quite uncertain, but note that tropospheric products from dense GNSS station networks are promising to constrain the moisture distribution. Finally, we demonstrate that atmospheric mass is already well constrained in weather models due to the abundant availability of in situ barometers at the Earth’s surface so that utilizing a priori information from global atmospheric model data in satellite gravity data processing via the Atmosphere and Ocean De-Aliasing Level-1B Model is very well justified. In terms of meteorologic applications of future satellite gravity missions currently under consideration by both NASA and ESA, we thus recommend to further refine methodologies aiming at isolating signals of atmospheric net-water fluxes out of the time-variable gravity signatures instead of attempting to map any direct signatures of the atmospheric mass distribution.
Scale Factor Determination for the GRACE-FO LRI and Thermal Coupling in KBR-LRI Residuals
Authors: Misfeldt Malte , Müller Vitali , Müller Laura , Bekal Pallavi , Bähre Simon , Heinzel Gerhard
Published: September 2022

The GRACE-FO missions hosts two ranging instruments, namely the prime K-Band Ranging (KBR) and the Laser Ranging Interferometer (LRI) as a technology demonstrator.

The LRI scale factor and a time-tag bias are currently estimated on a daily basis in post-processing through cross-calibrating KBR and LRI range, assuming that the KBR range is accurate enough to estimate these parameters. However, this might not hold, and errors of the KBR might get imprinted onto the LRI measurement. Prominent errors in the inter-satellite ranging data are so-called tone errors, which have a sinusoidal form and appear mainly at 1/rev and 2/rev frequencies. These errors have a significant influence on the estimated scale and time shift.

In this talk, we present a model for the LRI scale factor when GF-1 satellite is in the reference role, i.e., a model for the resonance frequency of the optical reference cavity of GF-1. The model was derived based on four years of flight data. Moreover, we show that the seasonal or beta-angle-related variations in the daily scale and time-shift estimates can be described by a thermal coupling, which produces mainly ranging tone errors proportional to the temperature of specific thermistors. We considered two possible coupling mechanisms, temperature-induced changes to the phase and to the frequency. The dominant coupling term is proportional to the temperature at the zenith-pointing solar array and produces range variations of up to +/- 8 µm at 1/rev frequency in the KBR-LRI residuals. These results can be used to improve the LRI1B data product and have relevance for the development of future LRI-like instruments for upcoming missions.
Interannual TWS Trends in the East-African Rift Region 
Authors: Boergens Eva , Güntner Andreas , Sips Mike , Schwatke Christian , Dobslaw Henryk
Published: September 2022

The German-American satellite missions GRACE (Gravity Recovery and Climate Experiment, 2002-2017) and its successor GRACE-Follow-On (GRACE-FO, since 2018) observed terrestrial water storage (TWS) variations over the continents. With 20 years of data, we can now study interannual trends and variations in water storage beyond the strong declining trends of ice sheets or glaciers. Africa is the only continent which exhibits an overall positive trend in TWS for the GRACE/GRACE-FO period. In this contribution, we analyse the interannual TWS variations in Africa and focus on the East-African Rift region around Lake Victoria, Lake Tanganyika, and Lake Turkana, where the long-term TWS increase is most pronounced.

As TWS trends are not monotonous over time, a signal decomposition into linear trend and sinusoidal annual and semiannual seasonality is insufficient to investigate interannual variability. Hence, we employ the STL method (Seasonal Trend decomposition based on Loess) to separate the TWS signals into an interannual trend signal, which is not a linear trend, a seasonal signal, and residuals. These interannual trend signals are used in a subsequent cluster algorithm to identify regions with similar interannual variability. We found complex interannual TWS signals in East Africa and many African regions. In the East African Rift region, we can observe a decrease in TWS until around 2006, after which an increasing trend started. Finally, in the last few years, the trend has further accelerated.

To better understand the origin of the observed interannual signal, we compare the TWS time series with precipitation and evaporation data and SWS data derived from satellite altimetry. The interannual variations of precipitation are insufficient to explain the strong interannual variations visible in the TWS data in Eastern Africa. SWS variations, in contrast, are highly correlated with TWS, explaining nearly 50% of the TWS variations. Among the surface water bodies, we study the influence of Lake Victoria in particular, as it is the largest lake in the region, and its water balance is also governed by a dam at its outlet. SWS of this lake is heavily affected by man-made decisions and is visible in the GRACE/GRACE-FO observations.
150 km ANU mascon solutions
Authors: Tregoning Paul , McGirr Rebecca , Purcell Anthony , Allgeyer Sebastien
Published: September 2022

We present updated mascon solutions of the temporal gravity field, derived from the analysis of Level-1B GRACE and GRACE-FO data using the range acceleration observable. Our previous solutions contained significant noise in particular regions of high mass loss (e.g. West Antarctica), which was caused by inappropriate levels of regularisation. Here we show a new approach of both iteration and regularisation of the solutions which generates more reliable estimates of the mass variations across the whole Earth, with both temporal and spatial consistency despite not applying any temporal or spatial inter-mascon constraints. We compare mascon solutions at spatial resolutions from 300 km to 100 km, show estimates of ocean mass increase and mass loss in ice-covered regions as well as assess the C20 time series estimated directly from GRACE data alone. Our new mascon estimates, at ~200 km x 200 km spatial resolution, are now publicly available.
 Absolute Laser Frequency Readout of Cavity for Next Generation Geodesy Mission
Authors: Rees Emily Rose , Wade Andrew , Sutton Andrew , McKenzie Kirk
Published: September 2022

We demonstrate the absolute frequency calibration of a laser using a free spectral range cavity readout designed for next generation geodesy missions.

The Gravity Recovery and Climate Experiment (GRACE) missions rely on inter-satellite interferometry to measure changes in the local gravity of the Earth. These measurements are compared over seasons and years, providing a critical tool for the understanding of large-scale mass transport, in particular the movement of water and ice.  The GRACE Follow-On mission launched in 2018 and included a Laser Ranging Instrument (LRI) as a technology demonstration. The LRI demonstrated performance two orders of magnitude better than the equivalent Microwave Instrument (MWI). As such, laser interferometry is expected to be relied upon as the primary instrument for the next generation of GRACE-like missions.

To enable the use of laser interferometry as the primary science measurement, laser frequency stability is important at two time scales; short timescales (10-1000 seconds) to measure the local gravity, and long timescales (months and years) to enable the comparison of these gravity measurements over time.

Short term laser frequency stability is provided by stabilizing the laser to an optical cavity using the Pound-Drever-Hall method, however, a new technique will be required to provide long term laser frequency stability.

We have previously demonstrated a simple phase modulation scheme that is able to measure laser frequency change over long timescales using measurements of the optical cavity's free spectral range [1]. More recently we have calibrated the technique to absolute frequency by comparing with an atomic reference and have also validated an approach for on-ground calibration to allow the absolute frequency to be determined in orbit [2].

[1] E.R. Rees, A. R. Wade, A. J. Sutton, R. E. Spero, D. A. Shaddock, and K. Mckenzie, ‘Absolute frequency readout derived from ULE cavity for next generation geodesy missions’, Opt. Express, OE, vol. 29, no. 16, pp. 26014–26027, Aug. 2021, doi: 10.1364/OE.434483.

[2] E.R. Rees, A. R. Wade, A. J. Sutton, and K. McKenzie, ‘Absolute Frequency Readout of Cavity against Atomic Reference’, Remote Sensing, vol. 14, no. 11, p. 2689, Jun. 2022, doi: 10.3390/rs14112689.
The global land water storage data set release 2 (GLWS2.0) derived via assimilating GRACE and GRACE-FO data into the WaterGAP global hydrological model
Authors: Kusche Juergen , Gerdener Helena , Schulze Kerstin , Fupeng Li , Döll Petra , Ackermann Sebastian , Müller Schmied Hannes , Hosseini Moghari Seyed Mohammad , van Dam Tonie , klos Anna
Published: September 2022

We describe the new Global Land Water Storage data set (GLWS2.0), which contains total water storage anomalies (TWSA) over the global land with a spatial resolution of 0.5°, covering the time frame 2003 to 2019 without gaps, and including an uncertainty quantification.

 

GLWS is produced by assimilating 4° gridded GRACE and GRACE-FO-derived TWSA into the WaterGAP global hydrological model using the Parallel Data Assimilation Framework (PDAF). The resulting data set represents thus an optimal synthesis of GRACE data, the hydrological model and implicitly all data sets that went into the model. This synthesis seeks to fit GRACE and GRACE-FO TWSA grids within error bars (from propagating full level-2 error variance covariance matrices), and at the same time it solves the horizontal and vertical water balances as represented in the hydrological model, again within error bars. To this end, the uncertainty of the hydrological model simulation is represented via a 32-member ensemble, where we account for the uncertainty of the precipitation and temperature data and for the uncertainty of some model calibration parameters. As a result, when no GRACE (-FO) data is available, GLWS represents the mean of an ensemble where each member is dynamically consistent with the model. It is important to understand that this mean depends on the ensemble and the previous GRACE estimates, and thus differs from published WaterGAP standard runs even if there is no GRACE data within a particular month. Due to the dynamical constraints, the assimilation-derived GLWS data set does not represent a simple downscaling of the GRACE data, i.e. spatial smoothing of GLWS does not necessarily correspond to GRACE (-FO) TWSA. GLWS indeed contains all water storages that are represented in WaterGAP (e.g. groundwater), but here we will focus only on TWSA.

 

The main updates with respect to the release 1 were the use of an updated version of WaterGAP as well as minor bug fixes in the assimilation. GLWS1.0 and GLWS2.0 have already been provided to several research groups within the DFG GlobalCDA research unit and beyond for evaluation purposes.

 

In this presentation we describe the methods and data sets that went into GLWS2.0, and the validation of the resulting 0.5° TWSA grids from a geodesy applications perspective, including comparisons to GRACE and GRACE-FO data and to GNSS-derived site displacements. We will also show some extended experiments with jointly assimilating river discharge data, model parameter estimation, and the integration of machine-learning based model prediction in our assimilation approach.
Enhanced near-real time gravity field retrieval for NGGM
Authors: Abrykosov Petro , Pail Roland
Published: September 2022

The main goal of a next generation gravity mission (NGGM) is to improve the observation of mass transport processes primarily through an enhanced sampling with respect to space and time. Thus, high-resolution gravity products can be retrieved over short time periods which are highly valuable for geophysical applications like the monitoring and forecast of extreme climate events such as e.g. floods and droughts.

In this regard, a near-real-time (NRT) processing strategy was proposed in Purkhauser et al. (2020) where the so-called Wiese approach (co-parametrization of short-periodic low-resolution gravity fields and a long-period high-resolution one) was combined with a sliding window averaging. However, in recent studies some drawbacks of the Wiese scheme could be identified and partially rectified by a so-called data-driven multi-step self-de-aliasing approach (DMD).

In this contribution, the original NRT scheme is revised and re-run on the basis of the DMD method within numerical closed-loop simulations. The added value of DMD over the Wiese approach within the NRT processing is quantified and presented, and drawbacks and advantages of either methodology are discussed.
Closed Loop Simulations Evaluating the Resolvability of Climate-Related Mass Transport Signal in Current and Next-Generation Satellite Gravity Missions
Authors: Schlaak Marius , Pail Roland , Eicker Annette
Published: September 2022

The existing observation record of satellite gravity missions spans more than two decades and is already closing in on the minimum time series of 30 years needed to decouple natural and anthropogenic forcing mechanisms according to the Global Climate Observing System (GCOS). Next Generation Gravity Missions (NGGMs) are expected to be launched within this decade, setting high anticipation for an enhanced monitoring capability that will improve the spatial and temporal resolutions of gravity observations significantly. They will allow an evaluation of long-term trends in the Terrestrial Water Storage (TWS) signal. The observations might therefore be used to verify climate projections and give additional inputs to the climate modelling community. This contribution shows numerical closed-loop simulation results of a GRACE-type in-line single-pair missions and Bender double-pair missions with realistic noise assumptions for the key payload and ocean-tide background model errors. The gravity signal in the simulations is based on modeled mass transport time series of components of the TWS, obtained from future climate projections until the year 2100 following the shared socio-economic pathway scenario 5-8.5 (SSP5-8.5). It evaluates different parameter models, among them the recoverability of long-term climate trends, annual amplitude, and phase of the TWS employing closed-loop numerical simulations of different current and NGGM concepts. Special emphasis shall be given on the robustness of the estimated TWS long-term-trend for different parameter models applied in different simulation scenarios, systematic changes, as well as on the methodology of the simulation themselves.
High-Resolution Atmospheric-hydrological Background Modelling for GRACE/GRACE-FO – regional refinement and validation
Authors: Mielke Christian , Dixit Shashi , Kracheletz Magdalena , Friederichs Petra , Kusche Jürgen , Springer Anne , Hense Andreas
Published: September 2022

We will give an insight into the atmospheric physics contribution to the New Refined Observations of Climate Change from Spaceborne Gravity Missions (NEROGRAV) research group, which is funded by the German Research Foundation (DFG). Since May 2019, NEROGRAV develops new analysis methods and modeling approaches to improve data analysis of the GRACE and GRACE-FO mission. Our contribution to this research unit is the High-Resolution Atmospheric-hydrological Background Modelling for GRACE/GRACE-FO – regional refinement and validation (HIRABAM). One of our goals in this individual project (IP) is the development of improved Atmospheric Ocean Dealiasing (AOD) products by integrating high-resolution regional atmospheric modeling. Furthermore, we are interested in whether and how extreme hydrometeorological events map into GRACE L1/2 data.

The 1995-2019 COSMO-REA6 regional reanalysis and the July 2021 ICON-EU/D2 analysis are non-hydrostatic regional atmospheric models with 3D fields on grid sizes below 10 km, with mass densities of dry air and all water phases (gaseous, liquid clouds and rain, icy snow, sleet, and hail) available in each of their 40-50 vertical layers. By integrating over all layers, the total local and column-by-column atmospheric mass density can be calculated without using the hydrostatic assumption. Unfortunately, such high-resolution atmospheric model data is currently only available within the EURO-CORDEX domain, which covers the European continent. Nevertheless, to compute global spherical coefficients for our AOD products that benefit from the high resolution of the regional models, we nested COSMO-REA6 in a lower-resolution but global model. Here we want to answer the question: does high-resolution mass variability leaves a significant fingerprint in the global loading coefficients? The heavy rainfall observed in the Ruhr/Ahr/Erft/Maas basin in July 2021 are clearly visible in ICON-EU/D2 atmospheric data. The question to be answered here is: are mass variations of such extreme weather events visible in GRACE/GRACE-FO data and do they exceed typical uncertainties?
Progress Toward Creating GRACE and GRACE-FO Mascons for Studying Ocean Dynamics
Authors: Tamisiea Mark , Chambers Don , Pie Nadège , Save Himanshu , Bonin Jennifer
Published: September 2022

We are developing a specialized set of CSR mascons for ocean dynamics studies. The standard GRACE/GRACE-FO mascon solutions contain both the barystatic (global mean) mass change and the geographically variable redistribution of mass caused by gravitation, rotation, and deformation (GRD) changes, neither of which drive ocean dynamics on monthly scales.  In addition, misassignment of mass loss of the major ice sheets to the nearby oceans (leakage) affects the ability to use the mascons to measure adjacent deep currents. Here, we present preliminary results for mascons utilizing different background models and regularization from the standard release. We also demonstrate barystatic-GRD fingerprint calculations consistent with the mascons' estimate of continental mass changes as well as the modeled atmospheric and dynamic ocean changes.  These results are evaluated for improvement by comparison with ocean bottom pressure recorders, tide gauges, and ocean state estimates
Merging GRACE Follow-On gravity fields with various approaches
Authors: Lenczuk Artur , Klos Anna , Bogusz Janusz
Published: September 2022

For the 2002–2017 period, an essential information about global monthly gravity variations was provided by the Gravity Recovery and Climate Experiment (GRACE) mission. Gravimetric mission have given a new opportunities to analyze fluctuations in the Earth's system, so GRACE observations is widely used in various fields of science. After a gap of almost a year, in May 2018, the GRACE mission successor, i.e., the GRACE Follow-On (GRACE-FO) mission was launched. Both mission observations are processed and supplied by various centers. Therefore, in the following research, we determine a monthly homogenous gravity fields for GRACE-FO mission based on recent Science Data System (SDS) solutions. We use all available 44 months (June 2018 to March 2022) of GRACE-FO monthly data in spherical harmonics form up to degree and order 96. Data is provided by SDS centers, i.e., the Center for Space Research (CSR; the United States), the German Research Center for Geosciences (GFZ) and the NASA’s Jet Propulsion Laboratory (JPL; the United States). To obtain merged gravity fields, we test algorithms based on non-iterative: (1) coefficient-wise and (2) field-wise weighting methods, and iterative: (3) variance component estimation (VCE) method, which help to eliminate signal noise left from each data sets after Gaussian spatial smoothing. In a case of weights, we obtained similar magnitude of them for three selected datasets for non-iterative methods, but CSR weights dominate for the VCE method. In the study, our solution was analyzed in spectral and spatial domain of gravity signal (spherical harmonics case) and land hydrology (total water storage case; TWS). The analysis of signal information contained in each degree and order of spherical harmonic coefficients notice that largest amount of information is contained up to 60 degree and order for SDS and weighted solutions. Above degree and order 60 is more than two times less information. The greatest signal differences between our and SDS solutions occur for the sectorial coefficients up to 40. We also show that the applied field-wise weights much more effectively remove remaining noise after spatial averaging than per-order/degree weighting. Moreover, the obtained values of signals variance for our solutions concur with the geophysical models. In case of land hydrology, the used weighting approaches reduce root mean square scatter of TWS by 5-15% for continental areas. The largest differences occur mainly in high latitudes for both hemispheres. Regional analyses (e.g. Amazon, Zambezi, Murray Darling river basins) show good agreement of monthly TWS series between original GRACE-FO (from SDS centers) and our solutions. We received the extreme TWS differences up to 15% depending on the data center (CSR, GFZ or JPL) and weighting method.
Global-scale random bottom pressure anomalies from oceanic intrinsic variability
Authors: Zhao Mengnan , Ponte Rui , Penduff Thierry
Published: September 2022

Effective interpretations of ocean bottom pressure (OBP) data from GRACE and GRACE-FO missions are essential for the proper assimilation of GRACE measurements in ocean models and more generally to better understand changes in sea level, ocean circulation and climate. Random variations in OBP driven by chaotic intrinsic processes, associated with non-linear mesoscale turbulence such as eddies, have recently been proved as important as those driven directly by atmospheric forcing. The two types of OBP variability can be separated using eddy-permitting ocean large ensemble simulations such as those from the OceaniC Chaos — ImPacts, strUcture, predicTability (OCCIPUT) project. Our published OCCIPUT analysis has shown that the chaotic intrinsic processes can lead to OBP variations on scales larger than the mesoscale. Previous studies attribute this behavior to an energy inverse cascade, in which mesoscale processes may cascade towards larger scales through non-linear interactions. Here, our analysis of the OCCIPUT ensemble reveals a new mechanism that can lead to truly global-scale intrinsic OBP variability. The leading Empirical Orthogonal Function (EOF) of the monthly chaotic intrinsic OBP variations, which explains approximately a quarter of the total intrinsic variance, shows a global-scale spatial pattern that follows H/f contours, where H is water depth and f is Coriolis parameter (Figure 1). Analyses of the EOF pattern indicate that the associated OBP anomalies on timescales from months to years conserve potential vorticity in most of the ocean except for eddy active regions. A consistent interpretation is that, in response to the OBP anomalies generated by eddies, OBP field in the rest of the ocean evolves freely along H/f contours on a global scale. Southern Ocean eddies in areas such as Drake Passage are likely to be a main source of excitation of the global EOF, leading to the opposite polarity between the Southern Ocean and the Atlantic/Arctic basins. Over most of the oceans, we find that adding intrinsic OBP from the leading EOF to the atmospherically driven OBP brings the variances simulated by OCCIPUT closer to those estimated from GRACE. This is consistent with the existence of such global-scale OBP associated with chaotic intrinsic variability in the GRACE measurements. Our results highlight the importance of chaotic intrinsic OBP variability over global scales when interpreting GRACE data.

Figure 1: Standard deviation of the leading EOF mode of chaotic intrinsic OBP field [cm] overlaid by H/f contours [ms].
COST-G: towards a new GRACE and GRACE-FO combination
Authors: Meyer Ulrich , Lasser Martin , Darbeheshti Neda , Jäggi Adrian , Flechtner Frank , Dahle Christoph , Förste Christoph , Güntner Andreas , Mayer-Gürr Torsten , Kvas Andreas , Behzadpour Saniya , Lemoine Jean-Michel , Koch Igor , Flury Jakob , Bourgogne Stephane , Feng Wei
Published: September 2022

The combination service for time-variable gravity fields (COST-G) provides the full time-series of monthly GRACE gravity fields: COST-G GRACE RL01, combined in reprocessing mode, and a steadily growing time-series of monthly GRACE-FO gravity fields: COST-G GRACE-FO RL01 OP, combined on an operational basis. Both time-series are currently considered for re-combination. In case of GRACE, new high-quality time-series from Chinese analysis centers are available for combination. In case of GRACE-FO, a revision of the weighting scheme, developed in the frame of the Horizon2020 project Global Gravity-based Groundwater Product (G3P), and the availability of reprocessed GRACE-FO time-series from AIUB, CSR, GFZ, and JPL, lead to a significant improvement of the combined gravity fields.

We present the preliminary re-combined GRACE and GRACE-FO time-series and quantify the differences with respect to the COST-G RL01 series in terms of signal and noise content.
Analysis of recent LUH GRACE / GRACE-FO gravity field processing results
Authors: Flury Jakob , Koch Igor , Duwe Mathias , Fletling Nina
Published: September 2022

We show results of both the LUH operational GRACE-FO gravity field processing and of our recent reprocessing of the full GRACE mission. Since 2021, the LUH group at IfE is recognized as Analysis Center in the IAG Combination Service for Time Variable Gravity Fields (COST-G). Quality measures demonstrate that the LUH solutions are close to those of other analysis centers in COST-G and in the GRACE / GRACE-FO Science Data System (SDS). We discuss the current standards and strategy of our processing. We have studied range-rate residuals for the two complete missions, with a focus on specific spatial and temporal patterns. This helps to identify and analyze detailed signatures of anomalous systematic effects, such as shadow transition anomalies, star camera stray light effects, and KBR signal to noise ratio drops. Results could be used to reassess the system integration of the satellite-to-satellite tracking sensor system. We discuss the validation of our spherical harmonic solutions using specific geophysical signals, and we also show and discuss recent LUH LRI-based gravity solutions. 
Multi-scale total water storage variations from fusion of GRACE and GLDAS Noah data using wavelet analysis
Authors: Ghobadi-Far Khosro , Werth Susanna , Shirzaei Manoochehr
Published: September 2022

The observations of total water storage variations (TWSV) from GRACE satellites have a coarse spatial resolution of ~300 km. Hydrological and land surface models, providing TWSV with higher spatial resolutions like 50 km, offer an opportunity to improve the coarse spatial resolution of GRACE data. We present a fusion approach based on wavelet multiresolution analysis to combine TWSV data from GRACE and GLDAS Noah model. We first decompose the TWSV maps from GRACE and GLDAS into their building blocks at various spatial scales, examine their signal characteristics, and then combine complementary spatial features at the wavelet coefficient level. The spectral nature of our approach enables us to easily combine the large-scale components from GRACE with small-scales information from GLDAS Noah and produce a unified, multi-scale TWVS dataset which has the advantages of both input datasets. We show that the spatial signal frequency spectrum of the fusion dataset matches that of GRACE data at low spatial frequencies, but that of GLDAS data at high spatial frequencies, indicating that the algorithm provides a shrinkage free combination of both input datasets. For a case study in contiguous United States, we inspect fused TWSV dataset in the spatial domain. Despite having detailed features originating from GLDAS, the fused dataset accurately quantifies the water budget and its long-term trend, when averaged over large basins during 2003–2015 similar to GRACE. We use the high-resolution surface soil moisture from SMOS satellite and snow water equivalent from SNODAS to demonstrate the improvement in representation of small-scale features associated with soil moisture and snow (i.e., the two water storage components that GLDAS Noah TWS is comprised of) in our fused dataset. In both cases, our fused TWSV dataset shows notable higher correlations with these independent data compared to GLDAS.
Sub-monthly Antarctica surface mass changes from GRACE Follow-On Laser Ranging Interferometer measurements
Authors: Feizi Mohsen , Roofian Naeeni Mehdi , Han Shin-Chan
Published: September 2022

We present our on-going study of regional gravity field and surface mass change recovery with an example of Antarctica.  We use new parameterization based on spherical cap harmonic (SCH) functions that is suitable for modelling gravitational potential over a spherical cap region.  There are a few advantages of efficiency and flexibility in this approach.  (1) The nearly identical potential field based on spherical harmonic (SH) functions can be expressed with a substantially less number of parameters in terms of SCH functions.  (2) The region-specific constraints can be implemented.  (3) Temporal resolution of the gravity recovery can be flexible and adjusted depending of the satellite coverage.  We use the instantaneous gravitational data along the satellite orbit such as Line-of-sight Gravity Difference (LGD) time series that are computed directly from the laser ranging interferometer (LRI) measurements of range change between two satellites.  We will discuss the methodology and show initial inversion results every 10 days over the Antarctica and discuss possible sub-monthly surface mass variability that we can find from our 10-daily regional surface mass solutions from 2019.
Signals of geophysical nature in GRACE and GRACE-FO post-fit range-rate residuals
Authors: Koch Igor , Duwe Mathias , Flury Jakob , Fletling Nina
Published: September 2022

Post-fit residuals of satellite-to-satellite tracking measurements of the GRACE and GRACE-FO missions obtained after a common estimation of orbit and gravity field parameters should ideally contain measurement noise with a behavior that meets expectations for the involved sensors. In reality, obtained GRACE and GRACE-FO post-fit range-rate residuals represent a complex superposition of different effects, e.g. of instrumental, environmental and geophysical nature. In this contribution, we focus on the geophysical signals in the post-fit residuals of the LUH GRACE and GRACE-FO time series. We apply band-pass filtering to extract the geophysical signal buried in the residuals and analyze the most distinctive signatures for their spatial and temporal behavior.