Mapping rainstorm erosion associated with an individual storm from InSAR coherence loss validated by field evidence for the Atacama Desert

Extreme high-magnitude and low-frequency storm events in arid zones provide the necessary runoff to entrain sediments from source areas and therefore dictate the linkages between hillslopes and channels. Nevertheless, the erosive impact of large storms remains difficult to predict. Most of the uncertainty lies in the lack of topographic change maps associated with single hydro-meteorological events. Consequently, event-based erosion models are poorly constrained and their extrapolation over long time periods remains uncertain. In this study, a 15-month Sentinel-1A coherence time series, optical and field data are used to map the spatial patterns of erosion after the 5-day storm occurred on March 2015, in the Atacama Desert. The coherence change detection (CCD) analysis suggests that temporal loss of coherence is related to variations in soil moisture, while permanent loss of coherence is related to modification of soil texture by erosion and sedimentation. Importantly, permanent loss of coherence is more apparent on gentle rather than steeper slopes, likely reflecting differences in regolith cover and thickness. These findings can contradict the landscape models predicting higher erosion on steeper hillslopes. The CCD technique represents a promising tool for analysing and modelling sediment connectivity in arid areas, giving a clear picture of the relation between sediment sources and sink pathways. © 2020 John Wiley & Sons, Ltd.     

Probabilistic evaluation of the physical impact of future tephra fallout events for the Island of Vulcano,Italy

A first probabilistic scenario-based hazard assessment for tephra fallout is presented for La Fossa volcano (Vulcano Island, Italy) and subsequently used to assess the impact on the built environment. Eruption scenarios are based upon the stratigraphy produced by the last 1000 years of activity at Vulcano and include long–lasting Vulcanian and sub-Plinian eruptions. A new method is proposed to quantify the evolution through time of the hazard associated with pulsatory Vulcanian eruptions lasting from weeks to years, and the increase in hazard related to typical rainfall events around Sicily is also accounted for. The impact assessment on the roofs is performed by combining a field characterization of the buildings with the composite European vulnerability curves for typical roofing stocks. Results show that a sub-Plinian eruption of VEI 2 is not likely to affect buildings, whereas a sub-Plinian eruption of VEI 3 results in 90 % of the building stock having a ≥12 % probability of collapse. The hazard related to long-lasting Vulcanian eruptions evolves through time, and our analysis shows that the town of Il Piano, located downwind of the preferential wind patterns, is likely to reach critical tephra accumulations for roof collapse 5–9 months after the onset of the eruption. If no cleaning measures are taken, half of the building stock has a probability >20 % of suffering roof collapse.     

Compositional characteristics and geodynamic significance of late Miocene volcanic rocks associated with the Chah Zard epithermal gold–silver deposit,southwest Yazd,Iran

Whole‐rock geochemical and Sr–Nd isotopic data are presented for late Miocene volcanic rocks associated with the Chah Zard epithermal Au–Ag deposit in the Urumieh‐Dokhtar Magmatic Arc (UDMA), Iran, to investigate the magma source, petrogenesis and the geodynamic evolution of the study area. The Chah Zard andesitic to rhyolitic volcanic rocks are characterized by significant Large Ion Lithophile Element (LILE) and Light Rare Earth Element (LREE) enrichment coupled with High Field Strength Element (HFSE) depletion. Our geochemical data indicate an adakitic‐like signature for the volcanic rocks (e.g. SiO₂ > 62 wt%, Al₂O₃ > 15 wt%, MgO < 1.5 wt%, Sr/Y > 70, La/Yb > 35, Yb < 1 ppm, and Y < 18 ppm, and no significant Eu anomalies), distinguishing them from the other volcanic rocks of the UDMA. The Chah Zard volcanic rocks have similar Sr and Nd isotopic compositions; the ⁸⁷Sr/⁸⁶Sr(i) ratios range from 0.704 902 to 0.705 093 and the ε_Nd(i) values are from +2.33 to +2.70. However, the rhyolite porphyry represents the final stage of magmatism in the area and has a relatively high ⁸⁷Sr/⁸⁶Sr ratio (0.705 811). Our data suggest that the andesitic magmas are from a heterogeneous source and likely to result from partial melting of a metasomatized mantle wedge associated with a mixture of subducted oceanic crust and sediment. These melts subsequently underwent fractional crystallization along with minor amounts of crustal assimilation. Our study is consistent with the model that the volcanic host rocks to epithermal gold mineralization in the UDMA are genetically related to late Miocene Neo‐Tethyan slab break‐off beneath Central Iran.     

Pb‐isotope compositions of the Tasik Chini volcanic‐hosted massive sulfide deposit,Central Belt of Peninsular Malaysia: Implication for source region and tectonic setting

Lead isotope data of sulfides and host volcanic rocks from the Bukit Botol and Bukit Ketaya deposits, the two representative deposits of the Tasik Chini volcanic‐hosted massive sulfide (VHMS) deposit, Central Belt of Peninsular Malaysia, are reported. Lead isotope compositions of the associated sulfide minerals and volcanic rocks from the Bukit Botol deposit exhibit homogeneous and less radiogenic values (²⁰⁶Pb/²⁰⁴Pb showing a range of composition from 18.14 to 18.20, ²⁰⁷Pb/²⁰⁴Pb between 15.52 and 15.59 and ²⁰⁸Pb/²⁰⁴Pb from 37.96 to 38.35). Similarly, the Pb isotopic compositions of the host volcanic rocks from the Bukit Ketaya deposit yielded a narrow range to those of the sulfide samples (²⁰⁶Pb/²⁰⁴Pb from 18.04 to 18.20, ²⁰⁷Pb/²⁰⁴Pb between 15.43 and 15.57 and ²⁰⁸Pb/²⁰⁴Pb of 37.96 to 38.30). The uniform Pb‐isotope compositions of the sulfides in the ore horizon and the host volcanic rocks from both deposits suggest a derivation from a similar source reservoir and mineralization processes. In the framework of the tectonic model for the Central Belt of Peninsular Malaysia, both deposits display a range of lead isotopic compositions originated from mixing of bulk crust/juvenile arc and minor mantle sources, which are typical for VHMS deposits in an island arc–back arc setting.     

EUREC<Superscript>4</Superscript>A: A Field Campaign to Elucidate the Couplings Between Clouds,Convection and Circulation

Trade-wind cumuli constitute the cloud type with the highest frequency of occurrence on Earth, and it has been shown that their sensitivity to changing environmental conditions will critically influence the magnitude and pace of future global warming. Research over the last decade has pointed out the importance of the interplay between clouds, convection and circulation in controling this sensitivity. Numerical models represent this interplay in diverse ways, which translates into different responses of trade-cumuli to climate perturbations. Climate models predict that the area covered by shallow cumuli at cloud base is very sensitive to changes in environmental conditions, while process models suggest the opposite. To understand and resolve this contradiction, we propose to organize a field campaign aimed at quantifying the physical properties of trade-cumuli (e.g., cloud fraction and water content) as a function of the large-scale environment. Beyond a better understanding of clouds-circulation coupling processes, the campaign will provide a reference data set that may be used as a benchmark for advancing the modelling and the satellite remote sensing of clouds and circulation. It will also be an opportunity for complementary investigations such as evaluating model convective parameterizations or studying the role of ocean mesoscale eddies in air–sea interactions and convective organization.     

Pan-African metamorphic evolution in the southern Yaounde Group (Oubanguide Complex,Cameroon) as revealed by EMP-monazite dating and thermobarometry of garnet metapelites

Garnet-bearing micaschists and paragneisses of the Yaounde Group in the Pan-African Central African Orogenic Belt in Cameroon underwent a polyphase structural evolution with the deformation stages D₁–D₂, D₃ and D₄. The garnet-bearing assemblages crystallized in course of the deformation stage D₁–D₂ which led to the formation of the regional main foliation S₂. In X_Ca–X_Mg coordinates one can distinguish several zonation trends in the garnet porphyroblasts. Zonation trends with increasing X_Mg and variably decreasing X_Ca signalize a garnet growth during prograde metamorphism. Intermineral microstructures provided criteria for local equilibria and a structurally controlled application of geothermobarometers based on cation exchange and net transfer reactions. The syndeformational P–T path sections calculated from cores and rims of garnets in individual samples partly overlap and align along clockwise P–T trends. The P–T evolution started at ～450 °C/7 kbar, passed high-pressure conditions at 11–12 kbar at variable temperatures (600–700 °C) and involved a marked decompression toward 6–7 kbar at high temperatures (700–750 °C). Th–U–Pb dating of metamorphic monazite by electron microprobe (EMP-CHIME method) in eight samples revealed a single period of crystallization between 613 ± 33 Ma and 586 ± 15 Ma. The EMP-monazite age populations between 613 ± 33 Ma enclosed in garnet and 605 ± 12 Ma in the matrix apparently bracket the high temperature–intermediate pressure stage at the end of the prograde P–T path. The younger monazites crystallized still at amphibolite-facies conditions during subsequent retrogression. The Pan-African overall clockwise P–T evolution in the Yaounde Group with its syndeformational high pressure stages and marked pressure variations is typical of the parts of orogens which underwent contractional crustal thickening by stacking of nappe units during continental collision and/or during subduction-related accretionary processes.     

In-flight calibration of the Cassini imaging science sub-system cameras

We describe in-flight calibration of the Cassini Imaging Science Sub-system narrow- and wide-angle cameras using data from 2004 to 2009. We report on the photometric performance of the cameras including the use of polarization filters, point spread functions over a dynamic range greater than 10⁷, gain and loss of hot pixels, changes in flat fields, and an analysis of charge transfer efficiency. Hot pixel behavior is more complicated than can be understood by a process of activation by cosmic ray damage and deactivation by annealing. Point spread function (PSF) analysis revealed a ghost feature associated with the narrow-angle camera Green filter. More generally, the observed PSFs do not fall off with distance as rapidly as expected if diffraction were the primary contributor. Stray light produces significant signal far from the center of the PSF. Our photometric analysis made use of calibrated spectra from eighteen stars and the spectral shape of the satellite Enceladus. The analysis revealed a shutter offset that differed from pre-launch calibration. It affects the shortest exposures. Star photometry results are reproducible to a few percent in most filters. No degradation in charge transfer efficiency has been detected although uncertainties are large. The results of this work have been digitally archived and incorporated into our calibration software CISSCAL available online.     

Tidal mixing in the Indonesian Seas and its effect on the tropical climate system

The sensitivity of the tropical climate to tidal mixing in the Indonesian Archipelago (IA) is investigated using a coupled general circulation model. It is shown that the introduction of tidal mixing considerably improves water masses properties in the IA, generating fresh and cold anomalies in the thermocline and salty and cold anomalies at the surface. The subsurface fresh anomalies are advected in the Indian Ocean thermocline and ultimately surface to freshen the western part of the basin whereas surface salty anomalies are advected in the Leuwin current to salt waters along the Australian coast. The ~0.5°C surface cooling in the IA reduces by 20% the overlying deep convection. This improves both the amount and structure of the rainfall and weakens the wind convergence over the IA, relaxes the equatorial Pacific trade winds and strengthens the winds along Java coast. These wind changes causes the thermocline to be deeper in the eastern equatorial Pacific and shallower in the eastern Indian Ocean. The El Nino Southern Oscillation (ENSO) amplitude is therefore slightly reduced while the Indian Ocean Dipole/Zonal Mode (IODZM) variability increases. IODZM precursors, related to ENSO events the preceding winter in this model, are also shown to be more efficient in promoting an IODZM thanks to an enhanced wind/thermocline coupling. Changes in the coupled system in response tidal mixing are as large as those found when closing the Indonesian Throughflow, emphasizing the key role of IA on the Indo-Pacific climate.     

Impact of the LMDZ atmospheric grid configuration on the climate and sensitivity of the IPSL-CM5A coupled model

The IPSL-CM5A climate model was used to perform a large number of control, historical and climate change simulations in the frame of CMIP5. The refined horizontal and vertical grid of the atmospheric component, LMDZ, constitutes a major difference compared to the previous IPSL-CM4 version used for CMIP3. From imposed-SST (Sea Surface Temperature) and coupled numerical experiments, we systematically analyze the impact of the horizontal and vertical grid resolution on the simulated climate. The refinement of the horizontal grid results in a systematic reduction of major biases in the mean tropospheric structures and SST. The mid-latitude jets, located too close to the equator with the coarsest grids, move poleward. This robust feature, is accompanied by a drying at mid-latitudes and a reduction of cold biases in mid-latitudes relative to the equator. The model was also extended to the stratosphere by increasing the number of layers on the vertical from 19 to 39 (15 in the stratosphere) and adding relevant parameterizations. The 39-layer version captures the dominant modes of the stratospheric variability and exhibits stratospheric sudden warmings. Changing either the vertical or horizontal resolution modifies the global energy balance in imposed-SST simulations by typically several W/m² which translates in the coupled atmosphere-ocean simulations into a different global-mean SST. The sensitivity is of about 1.2 K per 1 W/m² when varying the horizontal grid. A re-tuning of model parameters was thus required to restore this energy balance in the imposed-SST simulations and reduce the biases in the simulated mean surface temperature and, to some extent, latitudinal SST variations in the coupled experiments for the modern climate. The tuning hardly compensates, however, for robust biases of the coupled model. Despite the wide range of grid configurations explored and their significant impact on the present-day climate, the climate sensitivity remains essentially unchanged.     

Climate change under aggressive mitigation: the ENSEMBLES multi-model experiment

We present results from multiple comprehensive models used to simulate an aggressive mitigation scenario based on detailed results of an Integrated Assessment Model. The experiment employs ten global climate and Earth System models (GCMs and ESMs) and pioneers elements of the long-term experimental design for the forthcoming 5th Intergovernmental Panel on Climate Change assessment. Atmospheric carbon-dioxide concentrations pathways rather than carbon emissions are specified in all models, including five ESMs that contain interactive carbon cycles. Specified forcings also include minor greenhouse gas concentration pathways, ozone concentration, aerosols (via concentrations or precursor emissions) and land use change (in five models). The new aggressive mitigation scenario (E1), constructed using an integrated assessment model (IMAGE?2.4) with reduced fossil fuel use for energy production aimed at stabilizing global warming below 2?K, is studied alongside the medium-high non-mitigation scenario SRES A1B. Resulting twenty-first century global mean warming and precipitation changes for A1B are broadly consistent with previous studies. In E1 twenty-first century global warming remains below 2?K in most models, but global mean precipitation changes are higher than in A1B up to 2065 and consistently higher per degree of warming. The spread in global temperature and precipitation responses is partly attributable to inter-model variations in aerosol loading and representations of aerosol-related radiative forcing effects. Our study illustrates that the benefits of mitigation will not be realised in temperature terms until several decades after emissions reductions begin, and may vary considerably between regions. A subset of the models containing integrated carbon cycles agree that land and ocean sinks remove roughly half of present day anthropogenic carbon emissions from the atmosphere, and that anthropogenic carbon emissions must decrease by at least 50% by 2050 relative to 1990, with further large reductions needed beyond that to achieve the E1 concentrations pathway. Negative allowable anthropogenic carbon emissions at and beyond 2100 cannot be ruled out for the E1 scenario. There is self-consistency between the multi-model ensemble of allowable anthropogenic carbon emissions and the E1 scenario emissions from IMAGE?2.4.