Earth and Space Science
ISSN / EISSN : 2333-5084 / 2333-5084
Published by: American Geophysical Union (AGU) (10.1029)
Total articles ≅ 959
Latest articles in this journal
Earth and Space Science; https://doi.org/10.1029/2021ea001879
The severe drought of 1983-1984 in the Sahel region, and its socio-economic impacts for people relying on farming had for consequence the first major gold rush at Koma Bangou in the southwestern part of Niger. Initiated in 1984, the gold panning activities were interrupted from 1989 to 1999 with exploration permits assigned to the mining industry. The site was reclassified at the year-end 1999 as a gold panning site and artisanal mining resumed until present-day. Gold panning activies such as ore extraction and cyanide processing produced mining waste including rocks, mine tailings, and treatment residues. Mining waste is a serious environmental, health and safety problem. Multispectral Landsat images (TM4-5, ETM7+, OLI/TIRS) acquired between 1984 and 2020 were used to map the spatial evolution of waste generated by gold panning activities at Koma Bangou. Different processing methods were tested, including Minimum Noise Fraction (MNF) transform, Band Ratio (BR) and Feature Oriented Principal Component Selection (FPCS). The FPCS applied to hydroxyl-bearing minerals appears to be most efficient to map gold extraction and cyanidation waste areas. The waste surface associated with ore extraction has increased from 9.43 ha in 1984 to 234.20 ha in 2020, with continuous expansion during the period of clandestine activity (1989-1999). The waste surface associated with cyanidation has increased from 5.56 ha in 2009 (the year of cyanide treatment introduction) to 99.53 ha in 2020. Landsat multispectral imagery proved a suitable data source for monitoring the evolution of gold mining waste and consequences of public policies at Koma Bangou.
Earth and Space Science; https://doi.org/10.1029/2021ea001912
The shortwave infrared (SWIR) channels commonly accommodated in satellite-borne passive sensors contain information on cloud thermodynamic phase as well as cloud optical thickness (COT) and cloud effective radius (CER). This study develops algorithms for simultaneous retrieval of COT, CER, and cloud thermodynamic phase to estimate the fractional probability of the cloud phase as an alternative to discrete discrimination into liquid and ice typical of operational cloud retrievals. Two algorithms were developed and applied to the SWIR channels centered at 1.05, 1.63, and 2.21 µm of Second-generation Global Imager (SGLI). The first algorithm retrieves COT, CER, and ice COT fractions relative to the total COT, which is a continuous quantity representing the partitioning into liquid and ice phases. The second represents the cloud phase partitioning in the form of differences between radiances observed and simulated under the assumptions of either liquid or ice clouds when retrieving COT and CER. The cloud phases from these algorithms agreed quantitatively with each other, and were able to characterize the phase occurrence on a global scale. The two types of cloud phase characterization were further compared against CALIPSO to find that the zonal-mean occurrences of the cloud phase from the first algorithm were broadly consistent with those from CALIPSO, except for significantly smaller occurrences of supercooled water clouds in SGLI than in CALIPSO over middle-to-high latitude oceans. The cloud phase occurrences were also found to systematically vary with CER and cloud-top temperature on a global scale in a manner significantly different between SGLI and CALIPSO.
Earth and Space Science; https://doi.org/10.1029/2021ea001903
The Chemistry and Camera (ChemCam) instrument on board the Mars Science Laboratory (MSL) rover Curiosity has collected a very large and unique dataset of in-situ spectra and images of Mars since landing in August 2012. More than 800 000 single shot LIBS (laser-induced breakdown spectroscopy) spectra measured on more than 2 500 individual targets were returned so far by ChemCam. Such a dataset is ideally suited for the application of statistical methods for the recognition of patterns that are difficult to observe by humans. In this work, we develop an approach relying on the feature extraction method Non-Negative Matrix Factorization (NMF) and the repetition of k-means clustering to classify ChemCam spectra. A strong consistency of the clustering results among the repetitions were found, which allowed us to identify six clusters representing the dominant compositions measured by ChemCam in Gale crater so far. By tracking clusters across the rover traverse from landing to sol 2756, we are able to provide a chemostratigraphic overview of Gale crater from the ChemCam perspective. Transitions between major geologic groups (such as the Bradbury and the Mt. Sharp groups) are identifiable demonstrating that they are compositionally distinct, consistent with previous work. Compositional differences between their members also appear in the results. Furthermore, a first approach in which a random forest classifier was trained and validated with the obtained cluster assignments, reveals promising results for predicting cluster memberships of new ChemCam LIBS data acquired after sol 2756.
Earth and Space Science; https://doi.org/10.1029/2021ea001894
Infrasound (low frequency acoustic waves) has proven useful to detect and characterize subaerial volcanic activity, but understanding the infrasonic source during sustained eruptions is still an area of active research. Preliminary comparison between acoustic eruption spectra and the jet noise similarity spectra suggests that volcanoes can produce an infrasonic form of jet noise from turbulence. The jet noise similarity spectra, empirically derived from audible laboratory jets, consist of two noise sources: large scale turbulence (LST) and fine scale turbulence (FST). We fit the similarity spectra quantitatively to eruptions of Mount St. Helens in 2005; Tungurahua in 2006, and Kilauea in 2018 using nonlinear least squares fitting. By fitting over a wide infrasonic frequency band (0.05 - 10 Hz) and restricting the peak frequency above 0.15 Hz, we observe a better fit during times of eruption versus non-eruptive background noise. Fitting smaller overlapping frequency bands highlights changes in the fit of LST and FST spectra, which aligns with observed changes in eruption dynamics. Our results indicate that future quantitative spectral fitting of eruption data will help identify changes in eruption source parameters such as velocity, jet diameter and ash content which are critical for effective hazard monitoring and response.
Earth and Space Science; https://doi.org/10.1029/2021ea001711
Gas hydrate filled fractures and veins readily occur in fine-grained deep water marine sediments that increase sediment strength and restrict sediment consolidation. Subsequent hydrate destabilization can dramatically reduce sediment strength, which may lead to slope failures. To investigate the undrained behaviour a series of consolidated undrained (CU) triaxial tests were carried out on fine-grained soils containing cylindrical THF hydrate veins of varying diameter to mimic naturally occurring hydrate-bearing clays. Axial compressions tests on stand-alone hydrate veins showed brittle failure with axial stresses reasonably independent of vein diameter and confining stress and thought related to development of bending stresses and tensile cracking. Reduced axial strain rates led to ductile behavior, potentially suppressing tensile crack development, resulting in slightly higher failure stresses. CU shear tests on hydrate-bearing specimens showed increasing strength and stiffness with increasing vein diameter and confining stress, although the impact of confining stresses reduced for the largest diameter veins. Using a Mohr-Coulomb failure criteria, increased strength was associated with increase in cohesion and reduction in friction angle. The enhanced strength would reduce consolidation processes that would lead to sediment instabilities if the hydrate was destabilized. However, for larger diameter veins, increasing lateral stresses from the soil reduced buckling stresses with significant plastic deformation of the THF veins being observed at the end of tests, suggesting a strain rate dependent behavior. Further research is required to fully understand this behavior and its impact on sediment consolidation to fully consider the relationship between hydrate dissociation and sediment instability.
Earth and Space Science; https://doi.org/10.1029/2021ea001819
As an important indicator of solar activity, the long-term total solar irradiance (TSI) observations are needed to uncover the impact of solar activity on Earth’s climate. In this paper, the periodic variation of TSI and its relationships with sunspot number and Ca II K index are analyzed by using the satellite observation data from 1979 to 2015 and the wavelet method. The results of continuous wavelet analysis show that TSI, sunspot number and Ca II K index all have significant and stable oscillation periods of 9∼13 years and intermittent oscillation periods of 2∼6 months only during the time of intense solar activity. Moreover, the results of cross wavelet analysis indicate that the effect of sunspot number and Ca II K index on TSI is mainly reflected in the period of 9∼13 years with one month phase lag, and sunspot number and Ca II K index cannot explain the TSI variation in the period of 3∼6 months. Under the condition of considering the phase relationship and the model order, the TSI reconstruction model is established and the monthly TSI time series from 1907 to 1978 is restored.
Earth and Space Science; https://doi.org/10.1029/2021ea001695
We present a method to determine local gravity fields for the Moon using Gravity Recovery and Interior Laboratory (GRAIL) data. We express gravity as gridded gravity anomalies on a sphere, and we estimate adjustments to a background global start model expressed in spherical harmonics. We processed GRAIL Ka-band range-rate data with a short-arc approach, using only data over the area of interest. We determine our gravity solutions using neighbor smoothing constraints. We divided the entire Moon into twelve regions and two polar caps, with a resolution of (which is equivalent to degree and order 1199 in spherical harmonics), and determined the optimal smoothing parameter for each area by comparing localized correlations between gravity and topography for each solution set. Our selected areas share nodes with surrounding areas and they are overlapping. To mitigate boundary effects, we patch the solutions together by symmetrically omitting the boundary parts of overlapping solutions. Our new solution has been iterated, and it has improved correlations with topography when compared to a fully iterated global model. Our method requires fewer resources, and can easily handle regionally varying resolution or constraints. The smooth model describes small-scale features clearly, and can be used in local studies of the structure of the lunar crust.
Earth and Space Science; https://doi.org/10.1029/2021ea001852
This study examines the diurnal variation of the aerosol optical depth (AOD) at 355 nm observed by Raman lidar (RL) at the Atmospheric Radiation Measurement Program (ARM) Southern Great Plains (SGP) site under both clear and cloudy-sky conditions. Here only cloudy-skies when the lidar signal is not fully attenuated are considered. The daytime AOD and its variation from the RL showed an excellent agreement with the Aerosol Robotic Network, demonstrating that the RL-retrieved AOD is not affected by solar background contamination. The climatological annual-mean daytime-mean AOD is only slightly larger than the nighttime-mean AOD (by 1-3%). However, day-to-day variations are observed such that the daytime- and nighttime-mean AOD difference for a given day can be large (about 95% of days have differences within 0.2). The seasonal AOD diurnal range (i.e., the difference between the maximum and minimum values) relative to the mean was 10-15% except in the winter when it was 44%. The seasonal-mean cloudy-sky AOD diurnal variation is similar to that for clear-sky, except that the AODs are larger (the annual-mean cloudy-sky AOD is larger than the clear-sky by 24%). The aerosol lidar ratio diurnal variations are also examined, which are 10-20% for all seasons with a minimum near 9 am to 15 pm for all seasons except winter. Also presented is the annual-mean AOD from the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite at SGP site: its daytime AOD is about 0.1 smaller than nighttime AOD because of daytime solar background contamination.
Earth and Space Science, Volume 8; https://doi.org/10.1029/2020ea001607
The Anninghe fault (ANHF) and the Zemuhe fault (ZMHF), located in the southeast of the Tibetan Plateau, have a high level of seismic hazard and are among the most active faults in China. This study performed the first measurements of soil gas CO2 at three sites across the ANHF and the ZMHF. The fault locking (FL) depth and extent of different segments of the ANHF and the ZMHF were inverted using the negative dislocation model based on global positioning system velocity data acquired during 2009–2015. Results showed that the degassing intensity of CO2 in the ZMHF is substantially higher than in the ANHF, which is spatially consistent with the degree of inverted FL. The inversion results revealed that the level of coupling, including the locking depth and extent, along the southern segment of the ANHF is markedly greater than in the northern segment of the ZMHF. Soil gas CO2 geochemistry yielded different spatially anomalous features, indicating that the faults have different properties and permeability. The intensive locking of the ANHF and ZMHF segments has reduced permeability through self-sealing processes, which has restricted the escape of gas from the deep crust. Correspondingly, a creeping fault with a low level of coupling could maintain high permeability, which would be favorable for CO2 migration.
Earth and Space Science, Volume 8; https://doi.org/10.1029/2021ea001839
Remote sensing from Earth-observing satellites is now providing valuable information about ocean phytoplankton distributions. This paper presents the new ocean subsurface optical properties obtained from two space-based lidars: the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations satellite and the Advanced Topographic Laser Altimeter System (ATLAS) aboard the Ice, Cloud, and land Elevation Satellite-2 satellite. Obtaining reliable estimates of subsurface biomass necessitates removing instrument artifacts peculiar to each sensor, that is, polarization crosstalk artifacts in the CALIOP signals and after pulsing effects arising from the ATLAS photodetectors. We validate the optical properties derived from the corrected lidar backscatter signals using MODerate-resolution Imaging Spectroradiometer ocean color measurements and autonomous biogeochemical Argo float profiles. Our results support the continued use of present and future spaceborne lidars to study the global plankton system and characterize its vertical structures in the upper ocean.