1,721,274 research outputs found
Mary Grace Grace
No full textPortrait of Mary Grace Grace, R.S.M. Date of photograph is unknown.https://www.exhibit.xavier.edu/edgecliff_presidents/1002/thumbnail.jp
Greenland Ice Sheet mass balance GRACE/GRACE-FO (2003-2019) and SMB-D (1948-2019)
No full textData underlying figures 1, 2, 3 and 5.
Figure 1: Monthly mass changes of the Greenland Ice Sheet from GRACE/GRACE-FO and SMB-D (2003-2019)
Figure 2: Biennial mass balance and its components from GRACE/GRACE-FO and SMB-D (2003-2018) for the Greenland Ice Sheet, along with regional estimates for 2017-2018 for East and West.
Figure 3: Rate of mass change for year 2019 from GRACE/GRACE-FO and SMB-D
Figure 5: Annual mass balance and its main components from SMB-D (1948-2019) and GRACE/GRACE-FO (2003-2019
The Assessment of Hydrologic- and Flood-Induced Land Deformation in Data-Sparse Regions Using GRACE/GRACE-FO Data Assimilation
No full textThe vertical motion of the Earth’s surface is dominated by the hydrologic cycle on a seasonal scale. Accurate land deformation measurements can provide constructive insight into the regional geophysical process. Although the Global Positioning System (GPS) delivers relatively accurate measurements, GPS networks are not uniformly distributed across the globe, posing a challenge to obtaining accurate deformation information in data-sparse regions, e.g., Central South-East Asia (CSEA). Model simulations and gravity data (from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO)) have been successfully used to improve the spatial coverage. While combining model estimates and GRACE/GRACE-FO data via the GRACE/GRACE-FO data assimilation (DA) framework can potentially improve the accuracy and resolution of deformation estimates, the approach has rarely been considered or investigated thus far. This study assesses the performance of vertical displacement estimates from GRACE/GRACE-FO, the PCRaster Global Water Balance (PCR-GLOBWB) hydrology model, and the GRACE/GRACE-FO DA approach (assimilating GRACE/GRACE-FO into PCR-GLOBWB) in CSEA, where measurements from six GPS sites are available for validation. The results show that GRACE/GRACE-FO, PCRGLOBWB, and GRACE/GRACE-FO DA accurately capture regional-scale hydrologic- and flood induced vertical displacements, with the correlation value and RMS reduction relative to GPS measurements up to 0.89 and 53%, respectively. The analyses also confirm the GRACE/GRACE-FO DA’s effectiveness in providing vertical displacement estimates consistent with GRACE/GRACE-FO data while maintaining high-spatial details of the PCR-GLOBWB model, highlighting the benefits of GRACE/GRACE-FO DA in data-sparse regions
Grace, Grace, By the Side of the Road
Full text linkGrace, Grace, By the Side of the Road is a collection of poetry and creative nonfiction that contemplates the messiness of growing up and the events, relationships, and environments that shape a person’s identity. This collection traces my experiences from early childhood to college and maintains a particular interest in the landscape of the Midwest as being as integral to my sense of self as family, friendships, and the body. The text itself is an attempt to wrestle with the question: what does love look like amid hardship, change, and imperfection? In “Grace, Grace, By the Side of the Road,” I work through what it means to express grace for both the mundane and the ugly as an act of love
Hydroclimatic Extremes Evaluation Using GRACE/GRACE-FO and Multidecadal Climatic Variables over the Nile River Basin
No full textHydroclimatic extremes such as droughts and floods triggered by human-induced climate change are causing severe damage in the Nile River Basin (NRB). These hydroclimatic extremes are not well studied in a holistic approach in NRB. In this study, the Gravity Recovery and Climate Experiment (GRACE) mission and its Follow on mission (GRACE-FO) derived indices and other standardized hydroclimatic indices are computed for developing monitoring and evaluation methods of flood and drought. We evaluated extreme hydroclimatic conditions by using GRACE/GRACE-FO derived indices such as water storage deficits Index (WSDI); and standardized hydroclimatic indices (i.e., Palmer Drought Severity Index (PDSI) and others). This study showed that during 1950–2019, eight major floods and ten droughts events were identified based on standardized-indices and GRACE/GRACE-FO-derived indices. Standardized-indices mostly underestimated the drought and flood severity level compared to GRACE/GRACE-FO derived indices. Among standardized indices PDSI show highest correlation (r2 = 0.72) with WSDI. GRACE-/GRACE-FO-derived indices can capture all major flood and drought events; hence, it may be an ideal substitute for data-scarce hydro-meteorological sites. Therefore, the proposed framework can serve as a useful tool for flood and drought monitoring and a better understanding of extreme hydroclimatic conditions in NRB and other similar climatic regions
Validation of GRACE/GRACE-FO Solutions Using Caspian Sea Level Change
No full textInternational audienceTo validate gravity recovery and climate experiment (GRACE)/ GRACE follow-on (GRACE-FO) gravity solutions, we compare satellite altimetry observations of Caspian Sea level (CSL) change with CSL estimates from satellite gravity from April 2002 to December 2020. We use GRACE/GRACE-FO Release 6 GSM fields [spherical harmonics (SH)] from the three processing centers [Center for Space Research (CSR), Jet Propulsion Laboratory (JPL), and Geoscience Research Center (GFZ)] and three mascon solutions from CSR, JPL, and Goddard Space Flight Center (GSFC). CSL change is a regional scale signal that should be reasonably well resolved by satellite gravity measurements, but spatial leakage and other corrections are still required. We computed an average of smoothed SH solutions and those that are both smoothed and decorrelation filtered (to remove north–south stripe noise). Averaging mitigates attenuating effects of decorrelation filtering on the north–south oriented Caspian Sea Signal. After spatial leakage, terrestrial water storage, and steric corrections, most GRACE/GRACE-FO CSL estimates agree remarkably well with the altimetry series over a range of time scales as measured by trend and seasonal components and at other frequencies. The linear CSL trend from altimetry is −7.55 ± 0.17 cm/yr, while GRACE/GRACE-FO values range from −7.30 ± 0.17 to −8.66 ± 0.20 cm/yr. Annual amplitudes from altimetry are (17.75 ± 1.28 cm) with GRACE/GRACE-FO values in the range 17.05 ± 1.49 to 19.16 ± 1.55 cm, with good phase agreement. The GSFC mascon solution shows substantially smaller annual amplitude (11.62 ± 1.04 cm) than others. We found no bias between GRACE and GRACE-FO, but GRACE-FO shows larger root-mean-square differences from altimetry. Among the three standard SH solutions, those from CSR show the best agreement with altimetry
Assessment of reduced-dynamic GRACE/GRACE-FO oribt co-estimated with monthly gravity fields
Full text linkWe study the orbits co-estimated in gravity field determination applying the Celestial Mechanics Approach (CMA) developed at the Astronomical Institute, University of Bern (AIUB) using kinematic positions derived from high-low GPS satellite-to-satellite tracking, and low-low K-band-satellite-to-satellite tracking data from GRACE/GRACE-FO. Gravity field coefficients and arc-specific parameters describing a reduced-dynamic orbit are jointly estimated in a common least squares adjustment. We show the influence of using undifferenced integer-ambiguity-fixed kinematic orbits on the co-estimated orbits compared to the use of an undifferenced float solution, especially in view of their stochastic behaviour. We also discuss a commonly observed discrepancy between GPS and K-band observations, which usually asks to additionally (artificially) down-weight the GPS observations with respect to the K-band observations. We validate the derived orbits, by analysing the residuals of combined orbits calculated using both kinematic positions and K-band data, and by analysing the quality of the estimated gravity field solutions
Exploiting the Combined GRACE/GRACE-FO Solutions to Determine Gravimetric Excitations of Polar Motion
No full textObservations from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) missions can be used to estimate gravimetric excitation of polar motion (PM), which reflects the contribution of mass changes in continental hydrosphere and cryosphere to PM variation. Many solutions for Earth’s gravity field variations have been developed by institutes around the world based on GRACE/GRACE-FO data; however, it remains inconclusive which of them is the most reliable for the determination of PM excitation. In this study, we present a combined series of GRACE/GRACE-FO-based gravimetric excitation of PM computed using the three-cornered-hat (TCH) method, wherein the internal noise level in a combined solution is reduced to a minimum. We compare the combined series with results obtained from the combined GRACE/GRACE-FO solution provided by COST-G (International Combination Service for Time-variable Gravity Fields) and from the single solution elaborated by the Center for Space Research (CSR). All the gravimetric excitation series are evaluated by comparison with the sum of hydrological and cryospheric signals in geodetically observed PM excitation (called GAO). The results show that by minimizing the internal noise level in the combined excitation series using the TCH method, we can receive higher consistency with GAO than in the case of COST-G and CSR solutions, especially for the non-seasonal oscillations. For this spectral band, we obtained correlations between GAO and the best-combined series as high as 0.65 and 0.72 for the χ1 and χ2 equatorial components of PM excitation, respectively. The corresponding values for seasonal oscillation were 0.91 for χ1 and 0.89 for χ2. The combined series developed in this study explain up to 68% and 60% of overall GAO variability for χ1 and χ2, respectively
Impact of hydrological mass loading using GRACE/GRACE-FO gravity products and GNSS data over Egypt
No full textThis study investigates the impact of hydrological mass loading on the Egyptian Permanent GNSS Network (EPGN) stations. Initially, GRACE and GRACE-FO products are evaluated, resulting in selecting the CSR center’s DDK5 monthly solutions for estimating terrestrial total water storage (TWS) in terms of equivalent water height (EWH). Monthly vertical displacements (VD) rates are calculated using GNSS data from EPGN stations, while TWS in terms of EWH is derived from GRACE/GRACE-FO data and WGHM model at the same locations. The findings from GRACE show that the mean monthly EWH values exhibit a negative trend of −2.36 mm/year from 2002 to 2012, followed by a positive trend of 3.94 mm/year from early 2013 until mid-2017. For GRACE-FO solutions, EWH shows a positive trend of 5.69 mm/year from mid-2018 to early 2024. A comparison of mean monthly EWH variations from GRACE/GRACE-FO and WGHM with GNSS-derived VD demonstrates a negative correlation at most GNSS stations, particularly in areas with significant hydrological signals, such as the Egyptian Delta and Lake Nasser. This emphasizes the impact of hydrological mass changes on these stations. Finally, mean monthly EWHs from GRACE are evaluated against the WGHM over Egypt. In addition, water level heights are compared to the EWHs from GRACE and WGHM at the ABSM station near Lake Nasser. Results show good agreement between EWHs estimated from GRACE and the WGHM over Egypt. At ABSM station, the water level heights of Lake Nasser provide robustness of our findings
Comparison of GRACE/GRACE-FO Spherical Harmonic and Mascon Products in Interpreting GNSS Vertical Loading Deformations over the Amazon Basin
No full textWe compute the vertical displacements in the Amazon Basin using the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) observations, including both the gravity spherical harmonic (SH) solutions from the Center for Space Research (CSR), GeoForschungsZentrum (GFZ) and Jet Propulsion Laboratory (JPL) and mascons from CSR, JPL and Goddard Space Flight Center (GSFC). The correlation coefficients, annual amplitude and root mean squares (RMS) reductions are calculated to assess the agreements between the GRACE/GRACE-FO and Global Navigation Satellite System (GNSS) vertical displacements at 22 selected GNSS stations. For the six GRACE/GRACE-FO products (i.e., CSR SH, GFZ SH, JPL SH, CSR mascon, GSFC mascon and JPL mascon), the mean annual amplitude reductions are 77.6%, 76.4%, 76.3%, 78.6%, 78.5% and 76.6%, respectively, the corresponding mean RMS reductions are 63.2%, 61.7%, 62.3%, 64.9%, 65.3% and 63.8%, respectively, and the mean correlation coefficients are all over 0.93. On the whole, mascon solutions agree slightly better with GNSS solutions than SH solutions do. The CSR SH and the GSFC mascon solutions show the best agreements with the GNSS solution among the 3 SH and 3 mascon products, respectively. We estimate GRACE/GRACE-FO noises using the three-cornered hat (TCH) method and find that the CSR SH and GSFC mascons also have the smallest noise variances among the SH and mascon products, respectively. By analyzing the GNSS stations from the central and southern Amazon Basin, we find that: (1) the RMS reductions when the mascon solutions are removed from GNSS height series are slightly larger than those using the SH solutions in the center, while in south all the RMS reductions are fairly close; (2) for both SH solutions and mascon solutions, the correlation coefficients in the center are slightly larger than those in the south, but conversely, the mean annual amplitude reductions in the center are much smaller than those in the south
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