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  • English  (28)
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  • 11
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    Multi-spacecraft Current Estimates at Swarm (2020)
    In:  Ionospheric Multi-Spacecraft Analysis Tools
    Details
    Publication Date: 2022-02-10
    Description: In this chapter the application of the curlometer technique to various regions of the inner magnetosphere and upper ionosphere and for special circumstances of sampling is described. The basic technique is first outlined, together with the caveats of use, covering: the four-spacecraft technique, its quality factor and limitations; the lessons learnt from Cluster data, together with issues of implementation, scale size and stationarity, and description of the key regions covered by related methodology. Secondly, the application to the Earth’s ring current region is outlined, covering: the application of Cluster crossings to survey the ring current; the use of the MRA (magnetic rotation analysis) method for field curvature analysis; the use of THEMIS (Time History of Events and Macroscale Interactions during Sub-storms mission) three-spacecraft configurations to sample the ring current, and future use of MMS (Magnetospheric MultiScale mission) and Swarm data, i.e. the case of small separations. Thirdly, the application of the technique to the low altitude regions covered by Swarm is outlined, covering: the extension of the method to stationary signals; the use of special configurations and adjacent times to achieve 2, 3, 4, 5 point analysis; the use of the extended ‘curlometer’ with Swarm close configurations to compute 3-D current density, and a brief indication of the computation of current sheet orientation implied by 2-spacecraft correlations. Fourthly, the direct coordination of Cluster and Swarm to check the scaling and coherence of field-aligned currents (FACs) is outlined.
    Language: English
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  • 12
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    Natural Allanite Reference Materials forIn SituU‐Th‐Pb and Sm‐Nd Isotopic Measurements by LA‐(MC)‐ICP‐MS (2022)
    In:  Geostandards and Geoanalytical Research
    Details
    Publication Date: 2022-06-01
    Description: Allanite is a common accessory mineral that generally incorporates considerable amounts of Th, U and light rare Earth elements in its structure, making it a useful mineral for in situ U-Th-Pb geochronology and Sm-Nd isotope measurements. Here, we present in situ U-Th-Pb ages and Sm-Nd isotopic compositions for nine allanite samples considered as potential reference materials (CAPb, Tara, Daibosatsu, LE40010, LE2808, A007, A011, A012 and SQ-51), with ages ranging from ~ 2650 Ma to ~ 12 Ma. Our study indicates that Daibosatsu and LE40010 have relatively homogeneous 147Sm/144Nd and 143Nd/144Nd isotopic compositions (147Sm/144Nd ratio variation is less than 2%) and, thus, can serve as primary reference materials for Sm-Nd microanalysis. In contrast, CAPb, Tara, LE2808, A007, A011 and A012 all show homogeneous calculated initial 143Nd/144Nd isotopic compositions, but with variable 147Sm/144Nd compositions, and thus can be used only as secondary reference materials for Sm-Nd microanalysis. Of these materials, LE40010 allanite can serve as a suitable primary reference material for in situ U-Pb dating, CAPb allanite can serve as a suitable primary reference material for in situ Th-Pb dating, and LE2808, LE40010, A007, A011 and A012 can serve as suitable secondary reference materials for in situ U-Pb geochronology. In addition, Daibosatsu is suitable as a secondary reference material for Cenozoic Th-Pb dating to monitor data reproducibility.
    Language: English
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  • 13
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    International Geomagnetic Reference Field: the thirteenth generation. (2021)
    In:  Earth Planets and Space
    Details
    Publication Date: 2021-06-15
    Description: In December 2019, the International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group (V-MOD) adopted the thirteenth generation of the International Geomagnetic Reference Field (IGRF). This IGRF updates the previous generation with a definitive main field model for epoch 2015.0, a main field model for epoch 2020.0, and a predictive linear secular variation for 2020.0 to 2025.0. This letter provides the equations defining the IGRF, the spherical harmonic coefficients for this thirteenth generation model, maps of magnetic declination, inclination and total field intensity for the epoch 2020.0, and maps of their predicted rate of change for the 2020.0 to 2025.0 time period.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 14
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    Ambient noise surface wave tomography of the Iberian Peninsula: Implications for shallow seismic structure (2007)
    In:  Geophysical Research Letters
    Details
    Publication Date: 2020-02-12
    Description: We have obtained high resolution group velocity maps of Rayleigh waves at periods from 8 to 25 seconds across the Iberian Peninsula by cross-correlating four months of ambient noise data recorded by 40 permanent broadband stations. Group velocity maps accurately image the main structural elements of the Iberian upper crust, including the Iberian Massif, Alpine orogens and major sedimentary basins. The Pyrenees and the Iberian Chain are imaged as relatively high group velocities, in contrast with the Betic Cordillera, which is characterized by low velocities. We explain these low velocities in the Betics by the presence of widespread intramontane basins created in an extensional episode simultaneous with north–south convergence between the African and Eurasian plates. The most prominent low velocity anomalies in the Iberian Peninsula are related to the Guadalquivir Basin, the flysch units of the Campo de Gibraltar, and the sediments of the Gulf of Cadiz.
    Language: English
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  • 15
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    Runoff Response to Climate Change in Urumqi Glacier No. 1 Catchment over the Past 60 Years, Eastern Tianshan, Central Asia (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-06-01
    Description: Glaciers are vital to water resources in the arid land of central Asia. Long-term runoff records in the glacierized area are particularly valuable in terms of evaluating glacier recession and water resource change on both a regional and global scale. The runoff records of streams draining basins with 46% current glacier cover, located at the Urumqi Glacier No. 1 in the source area of the Urumqi River in eastern Tianshan, central Asia, were examined for the purpose of assessing climatic and glacial influences on temporal patterns of streamflow for the period 1959–2019. This study has introduced a glacio-hydrologic degree-day model to separate the different hydrologic components in glacier-fed streamflow. Results suggest that runoff from the catchment correlates well with temperature and associated precipitation data. The different ways that the glacier melts in response to temperature versus precipitation in a diurnal scale by changing glacier mass balance can effectively stabilize streamflow, showing a strong capacity of the glacier to naturally adjust streamflow in a beneficial manner to water utilization by those downstream. Based on long-term in-situ observation, we found that the “peak water” of ice melt appeared during the period 1996~2019, which verified the modelling results from previous studies.
    Language: English
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  • 16
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    Influence of spatial dipole pattern in Asian aerosol changes on East Asian summer monsoon (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-06-16
    Description: Since China implemented the air pollution prevention and control action in 2013, the aerosol emissions in East Asia have been greatly reduced, while emissions in South Asia have continued to increase. This has led to a dipole pattern of aerosol emissions between South Asia and East Asia. Here, the East Asian summer monsoon (EASM) responses to the dipole changes in aerosol emissions during 2013–2017 are investigated using the atmosphere model of Community Earth System Model version 2 (CESM2). We show that decreases in East Asian emissions alone lead to a 0.09 °C warming in summer during 2013–2017. The warming intensified the land-sea thermal contrast and increased the rainfall by 0.32 mm day〈sup〉-1〈/sup〉. When considering both the emission reductions in East Asia and increases in South Asia, the warming is enhanced to 0.20 °C over central-eastern China, while the rainfall insignificant decreased by 0.07 mm day〈sup〉-1〈/sup〉. It is due to the westward shift of the strengthened western Pacific subtropical high, linked to the increase in black carbon in South Asia. Based on multiple EASM indices, the reductions in aerosol emissions from East Asia alone increased the EASM strength by almost 5%. Considering the effect of westward shift of WPSH, the dipole changes in emissions together increased the EASM by 5–15% during 2013–2017, revealing an important role of South Asian aerosols in changing the East Asian climate. As the enhanced EASM in the recent decade, we also found that the EASM circulation intensified the ozone pollution in China.
    Language: English
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  • 17
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    Seismic potential of Main Recent Fault (Iran): Insights from interseismic fault locking, slip rate, and earthquake recurrence interval (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-06-21
    Description: The Main Recent Fault (MRF) is an important boundary fault that accommodates the oblique convergence motion between the Arabian and Eurasian plates. Several large earthquakes including the 1909 mb 7.4, 1958-1963 three events with magnitude larger than Mw 6.0, and the 2006 Mw 6.1 earthquake had ruptured the central segment of MRF. However, there is no large earthquakes occurred in the northwest segment in the past hundred years. In this study, the interseismic surface deformation along the northwest segment of the MRF has been firstly mapped from the Synthetic Aperture Radar (SAR) images observed by the Sentinel-1 satellite. Then, the ununiformed fault slip rate, locking and deficit are estimated based on the measured interseismic surface deformation. The results show that the fault slip rate varies from 1.0 mm/yr to 4.0 mm/yr in the northwest segment of MRF. In addition, the fault locking pattern is very complex in this segment, and 13 sub-segments could be divided based on the fault locking distribution and historical earthquakes. A seismicity gab is identified from the historical earthquakes, which has a good space consistency with the transition between the significant shallow locking and deep free creeping zones. According to the potential seismic magnitude and estimated recurrence interval, it is found that five segments are approaching the end of their interseismic recurrence interval.
    Language: English
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  • 18
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    Magnetic reconnection in the shock transition region: Electron heating (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-08-09
    Description: The shock transition region is rich of waves and instabilities, forming a turbulent environment where kinetic structures like magnetic reconnection develop. Reconnection is potentially important for contributing energy dissipation at the shock, but its exact role on this aspect is not yet clear. We perform a 2D particle-in-cell simulation starting from the ion-ion instability to simulate the foreshock region, which excites the ULF wave, develops current sheets and eventually leads to reconnection. The probability distribution of T〈sub〉e〈/sub〉 exhibits a shift to higher values near reconnection X-lines compared to elsewhere. By examining T〈sub〉e〈/sub〉 evolution using the superposed epoch analysis, we find that T〈sub〉e〈/sub〉 is higher in reconnection than in non-reconnecting current sheets, and T〈sub〉e〈/sub〉 increases over the ion cyclotron time scale. The heating rate of T〈sub〉e〈/sub〉 is 10%-40% m〈sub〉i〈/sub〉V〈sub〉A〈/sub〉〈sup〉2〈/sup〉, where V〈sub〉A〈/sub〉 is the average ion Alfvén speed in reconnection regions. These results demonstrate the importance of reconnection in heating electrons. We further investigate the bulk electron energization mechanisms by decomposing  under guiding center approximations. Parallel electric field, Fermi and magnetization terms contribute to electron heating and their importance at different reconnection stages are evaluated. The reconnection structures can be complicated due to flows originated from the ion-scale waves, and interactions between multiple reconnection sites, etc. Our simulation results may assist future analysis of observation data.
    Language: English
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  • 19
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    Deformation monitoring using daily repeated GNSS-R data (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-08-09
    Description: GNSS reflectometry has been proved to possess the capabilities for deformation monitoring by observing the carrier phase difference between the direct and reflected signals. This approach does not need to install GNSS receivers on the slopes and can be used to remote monitoring the slope deformation. However, to obtain the carrier phase measurement, the requirements to signal quality and monitoring geometry is relatively high, and the application of this method is limited because of the requirement of continuous observation and the involvement of a software defined radio (SDR) receiver. We present an innovative deformation monitoring method of observing signal-to-noise ratio (SNR) oscillation pattern of the interference of direct and reflected signals, by using daily repeated GNSS-R data. The direct and reflected signals were merged by radio frequency combiner, then fed into an out-of-shelve commercial GNSS receiver. The SNR of the interference signal can be directly outputted and recorded, and the oscillation pattern between observation days have been aligned by a geometry model, and the phase shift of the oscillation pattern can be analyzed for deformation monitoring. The field experiment results show sub-centimeter level accuracy with more than 300 meters monitoring range. This new method possesses the advantages of robust, low data size and computational burden, and long monitoring range. Especially, without need of continuous observation and applicable for a commercial GNSS receiver make this method more practical for long-term quasi-static deformation monitoring.
    Language: English
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  • 20
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    Insights into runoff changes in the source region of Yellow River under frozen ground degradation (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-05-03
    Description: The source region of the Yellow River (SRYR) in the northeastern Tibetan Plateau is critical for supplying water resources to downstream areas. However, streamflow in the SRYR declined despite a slight increase in precipitation during the past few decades. The SRYR experienced significant frozen ground degradation with climate warming, but how frozen ground degradation influences runoff remains unclear. This study investigated the changes of the precipitation-runoff relationship using the double-mass curve method and examined the impact of long-term spatiotemporal changes in frozen ground on the water balance components using the geomorphology-based eco-hydrological model (GBEHM). The results showed that the precipitation-runoff relationship changed significantly since 1989 in the SRYR from 1960 to 2019. In the same period, the areal mean value of the maximum thickness of seasonally frozen ground (MTSFG) decreased by 0.10 m/10a and the areal mean active layer thickness (ALT) of permafrost increased by 0.06 m/10a. Besides, 21.0% of the entire SRYR has degraded from permafrost to seasonally frozen ground (SFG). The total water storage increased by 2.9 mm/a in the permafrost region due to the increase in active layer thickness and by 5.7 mm/a in the degradation region where permafrost completely thawed during 1960-2019. The runoff seasonality was also altered, being indicated as an increase in winter runoff. These findings help provide a better understanding of the runoff change under climate warming in permafrost-affected regions and provide insights into future water resources management in the Yellow River basin under the climate warming.
    Language: English
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