bluuebunny/crossref_metadata_2025 huggingface dataset:
Atmospheric mechanisms controlling extreme winter precipitation in the Altiplano
Authors: Segura Hans , Espinoza Jhan Carlo , Junquas Clementine , Lebel Thierry , Vuille Mathias , Sicart Jean-Emmanuel , Condom Thomas
Published: March 2020

During the austral winter (June-August, JJA), precipitation events in the Altiplano (20°S-15°S, > 3000 m.a.s.l.) are uncommon. These events are responsible for damaging road infrastructure and devastating entire crop fields, loss of cattle, and even for the loss of human lives. Thus, an analysis of these events and the understanding of their precursory atmospheric mechanisms are of high importance to diminish their negative impacts. In this study, using 90 rain-gauge stations in the northern Altiplano, we identified days with a precipitation value above the percentile 90 (P90) for the 1979-2014 period. These days were considered as extreme precipitation events. If consecutive single events are separated by a gap of 5 days, we decided to consider those as a new single event. Thus, it was cataloged 129 extreme precipitation events over the northern Altiplano. Moreover, we found that 56 events lasted only for one day (EV1), 28 events for 2 days (EV2), and 45 events for at least 3 days and a maximum of 12 days (EV3). In order to understand the atmospheric mechanisms associated with these extreme events, we used the K-means cluster analysis in the geopotential height at 500 hPa (ERA-Interim) for days inside EV1, EV2 and EV3, respectively. Then, composite analyses of atmospheric circulation at 850, 500 and 200 hPa were done for each cluster group. We observe that two cluster groups in EV1, EV2, and EV3, respectively (98 events in total), are characterized by anomalies of winds, temperature and geopotential height resembling a cutoff low system over the eastern Pacific between 30°S-10°S at 200 and 500 hPa. Over South America, we observed that these events are also associated with southerly cold air intrusions arriving at 20°S and a moistened lower troposphere over the western Amazon. Indeed, the lower troposphere moistening over the western Amazon in previous days seems to be necessary to sustain long-lasting events. One cluster group in EV1 (8 events) and EV2 (6 events), respectively, is associated with southerly cold air intrusions to the east of the Andes originating at high latitudes, and arriving in equatorial regions. In addition, 17 events belonging to EV3 are associated with an anomalous South American Low-Level Jet at 850 hPa and atmospheric anomalies at 200, 500 and 850 hPa, resembling the cutoff low system over the eastern Pacific between 30°S and 10°S.
Assessing the role of internal variability in the carbon budgets framework
Authors: Tokarska Katarzyna , Gillett Nathan P. , Arora Vivek K. , Séférian Roland
Published: March 2020

Carbon budgets are a policy-relevant tool that provides a cap on global total CO2 emissions to limit global mean warming at the desired level, for example, to meet the Paris Agreement target. Internal variability due to natural fluctuations of the climate system affects the temperature and carbon uptake on land and in the ocean. However, uncertainties arising from internal variability have not been quantified in the Transient Climate Response on Cumulative Emissions (TCRE) framework and related carbon budgets. Here we show that even though land carbon uptake exhibits the highest internal variability, most of the uncertainty in TCRE and carbon budgets arises from the temperature component, in concentration-driven simulations. Resulting remaining carbon budgets for 1.5 and 2.0 °C temperature targets differ even up to ±10 PgC (± 36.7 GtCO2; 5-95% range), due to internal variability, which is approximately equivalent to one year of global annual CO2 emissions. Our results suggest that calculating carbon budgets directly from climate models’ output does not introduce significant biases in TCRE and remaining carbon budgets due to internal variability. 
Experimental Study on the Impact of Slope and Silt-laden inflow Conditions on Vegetation Sediment Trapping Process
Authors: Luo Mingjie , Pan Chengzhong , Liu Chunlei
Published: March 2020

Vegetation-restored hillslope surfaces not only reduce erosion but they also remove sediment from upslope silt-laden inflow. To investigate the sediment trapping effect of grassland, this study conducted a series of crossed sediment trapping experiments that examined various factors, such as slope (5°–20°), sediment concentration (40–160 g L−1), and unit flow rate (7.5–45.0 L min−1 m−1). The duration of each experiment was longer than required to reach the stable state of sediment trapping, so we measured and verified the individual sediment trapping capacity (Rm) by experiments. The results showed that gentler slopes generated higher instantaneous sediment trapping efficiency (ISTE) and greater Rm. As the sediment concentration of the silt-laden inflow increased, the impact of slope on Rm increased. Higher sediment concentration led to lower ISTE but greater Rm. Similar to the effect of sediment concentration, a larger unit flow rate led to lower ISTE and greater Rm. Thus, it is evident that interaction among these factors affects sediment trapping process. The experiments revealed the greatest sediment trapping effect of grass strips was concentrated mainly in the first 2-m width, and that 90% of sediment deposition occurred within half the time needed to reach the stable state. Slope and flow rate were found to have an effect on sediment trapping in each section of grass strips, whereas the effect of sediment concentration was concentrated primarily in the first 5-m width. Standard regression coefficients of a comprehensive regression analysis showed that the intensities of the influencing factors on Rm were as follows: slope (0.736) > grassland width (0.498) > unit flow rate (0.398) > sediment concentration (0.240). It was established that slope is the strongest influencing factor, and that sediment concentration and unit flow rate mainly affect Rm by changing the rate of sediment delivery. These results will help expand the theoretical basis regarding the effects of vegetation restoration on watersheds in soil erosion research.
Tsunami hazard in Cascadia from M7--9 earthquake ruptures
Authors: Salaree Amir , Huang Yihe , Ramos Marlon
Published: March 2020

The Cascadia Subduction Zone (CSZ) is a 1,200 km plate boundary that poses the greatest seismic hazard in the Pacific Northwest United States. Cascadia tsunamis have been the primary subject of studies on tsunami scenarios along the United States west coast. However, the geographic extent as well as the final size of potential future ruptures in Cascadia are poorly known. This has caused the result of previous studies to remain mostly hypothetical and simply serve as “worst-case scenarios”.

In this study, we calculate the hazard of M7-9 earthquakes using more realistic models that systematically vary both the geographic extent and slip of the rupture. To achieve this goal, we use rupture simulations derived from locking models to provide estimates of coseismic deformation at the ocean floor, and design several rupture scenarios with variable hypocenters and rupture propagation. We then apply shallow water approximation to simulate the full tsunami waveforms and generate tsunami amplitude profiles along the Cascadia coastline. By varying the seismic moment thresholds of the rupture models, we find that regional maximum coastal amplitudes are not unique for a given rupture size. This phenomenon is mostly due to the special coastal geometry as well as the particular slip partitioning of the elongated north-south rupture. In fact, our simulations reveal that beyond a magnitude of Mw≈8.5, increasing the rupture size will not significantly vary the tsunami hazard, especially in southern Cascadia, with the central segments playing the most crucial role. This result has significant implications in identifying the main sources of tsunami hazard along the US west coast, especially as the worst-case rupture scenario does not uniquely correspond to the worst-case tsunami scenario at a given location.
Using a statistical model to verify warm conveyor belts in ECMWF’s sub-seasonal forecasts
Authors: Quinting Julian F. , Wandel Jan , Büeler Dominik , Grams Christian M.
Published: March 2020

Rapidly ascending air streams in midlatitude cyclones – so-called warm conveyor belts (WCBs) – affect the lifecycle of blocking anticyclones. WCBs are usually identified by selecting coherent bundles of rapidly ascending trajectories. Their calculation, however, requires data at a high spatio-temporal resolution and is computationally expensive. To identify WCBs in expansive data sets such as ensemble reforecasts or climate model projections, alternative approaches are necessary. 

In this study we introduce a logistic regression model which is capable of identifying the inflow, ascent, and outflow phase of WCBs based on Eulerian input parameters. Validation against a Lagrangian-based dataset confirms that the logistic model is reliable in replicating the climatological frequency of WCBs as well as the footprints of WCBs at instantaneous time steps. 

Second, we employ the statistical model to verify the representation of WCBs in ECMWF’s sub-seasonal reforecasts. Overall the reforecasts depict frequencies of WCBs across seasons relatively well at all lead times. A correction of biases in the meteorological parameters for the logistic model partly removes existing biases in the reforecast WCB climatology. However, the bias-corrected  forecast skill still rapidly decays leaving useful skill only up to around day 8. These results corroborate that synoptic-scale activity might hinder accurate forecasts into sub-seasonal time scales for the extratropical large-scale circulation. Future work will elucidate if and in which situation poor skill for WCBs dilutes skill for Atlantic-European weather regimes on sub-seasonal time scales.
Tracking the evolution of the Merapi volcano crater area by high-resolution satellite imagery
Authors: Pinel Virginie , Putra Raditya , Solikhin Akhmad , Beauducel François , Santoso Agus Budi , Humaida Hanik
Published: March 2020

Located about 30 km north of the city of Yogyakarta, Merapi is considered as one of the most dangerous volcano of Indonesia with 3000 to 5000 fatalities since 1672 and about two million people living at less than 30 km from the crater. The recent eruptive history of Merapi is characterized by two eruptive styles: 1) recurrent effusive growth of viscous lava domes, with gravitational collapses producing pyroclastic flows known as « Merapi-type nuées ardentes » (VEI 2); 2) more exceptional explosive eruptions of relatively large size (VEI 3-4), associated with column collapse pyroclastic flows reaching distances larger than 15 km from the summit. The eruptive periodicity is 4 to 5 years for the effusive events and 50 to 100 years for the explosive ones. The last explosive events (VEI 3-4) occurred in November 2010 and opened a 500m wide and 250m deep crater. After the 2010 eruption, the activity has been reduced. We used TerraSAR-X data to characterize eruptive deposits emplaced during the 2010 event as well as sudden destabilization of crater walls. The activity increased significantly during the spring of 2018 when several phreatic eruptions were recorded with ash emission reaching an elevation of more than 5 kilometers. The 11th of August 2018 a new dome was observed inside the summit crater, thus marking the start of a new phase of effusive activity. It is essential to be able to quantitatively follow the temporal evolution of the dome shape and volume through time as its potential destabilisation would produce pyroclastic flow on the volcano flank. A time series of five tri-stereo Pleiades optical images, acquired between February and September 2019, is used to produce High Resolution DEMs of Merapi summit area with a spatial resolution of 3 m and a vertical precision of 1 m. By using a DEM derived from Pleiades stereo images acquired in April 2013 as a reference, the dome volume evolution through time is estimated. We show that the dome had already reached a volume around 0.5 Mm3 (+- 0.02Mm3) end of February 2019 corresponding to a mean effusive rate of 3000 m3/day during 6 months and that its size remained constant after February 2019. These results are consistent with volume estimations derived from drone measurements. However DEMs derived from Pleiades images enable to monitor a larger area and reveal accumulation of eruptive deposits due to dome destabilization a few hundreds of meters below the dome. The magma effusive rate thus remained significant but was reduced to 250 m3/day from February to September 2019.
Königshafen Submarine Groundwater Discharge Network (KiSNet)
Authors: Mallast Ulf , Waska Hannelore , Moosdorf Nils
Published: March 2020

Submarine groundwater discharge (SGD) as a pathway for water and chemical constituents between land and ocean is a rather young topic. For a long time it has been neglected by the scientific community and coastal managers. However, it has increasingly attracted attention since the turn of the millennium. Yet, SGD is mostly investigated either by terrestrial or marine disciplines although a broader, interdisciplinary approach would benefit SGD research. Moreover, so far reported SGD flux data at local to regional scale are a) hardly comparable as, to our best knowledge, only a few, mostly isolated studies directly compared available SGD methods in a quantitative fashion and b) flux data contain large uncertainties, either because they were up-scaled from local discrete (point) measurements to regional scales or because they were derived from modelling/ budgeting of regional or even global matter fluxes despite the known high spatial and temporal variability. 

In order to pave the way for a more standardized and interdisciplinary SGD research that would reduce inherited measurement/ extrapolation uncertainties, the Königshafen Submarine Groundwater Discharge Network (KiSNet)  seeks to contribute through three concrete aims:  

forming an interdisciplinary group of SGD experts to initiate and intensify collaborative ties across disciplines

improving individual methodologies by groundtruthing through interdisciplinary intercomparison, which includes a focus on spatial and temporal variability, and

providing a method catalogue which outlines optimal combinations for qualitative and quantitative SGD investigations that may serve as basis for future standardized SGD research.

The network will convene at the bay of Königshafen on Sylt, Germany, during two different points in time. Each time, all members of the network will apply qualitative (remote sensing, marine and terrestrial ground-based geophysics, biological indicators and socio-scientific methods) and quantitative (seepage meters, temperature rods, natural tracers, numerical simulation) methods from terrestrial and marine disciplines to investigate SGD synchronously and provide a robust basis to tackle above mentioned aims. 

Here, we will outline exact procedures, methods and anticipated results the network will produce and provide an overview on future actions the network anticipates.
Electron density and temperature over Jupiter’s main auroral emission
Authors: Allegrini Frederic , Kurth William , Saur Joachim , Gladstone Randy , Bagenal Fran , Bolton Scott , Clark George , Connerney Jack , Ebert Rob , Hospodarsky George , Hue Vincent , Imai Masafumi , Levin Steve , Louarn Philippe , Mauk Barry , McComas Dave , Sulaiman Ali , Szalay Jamey , Valek Philip W. , Wilson Rob J.
Published: March 2020

Jupiter’s ultraviolet (UV) aurora, the most powerful and intense in the solar system, is caused by energetic electrons precipitating from the magnetosphere into the atmosphere where they excite the molecular hydrogen. Electrons from ~50 eV to ~100 keV are characterized over the auroral regions by the Jovian Auroral Distributions Experiment (JADE) on Juno. Investigating the characteristics of electron distributions at these energies is critical for understanding the source population for the electrons that produce Jupiter’s UV aurora and the mechanisms that accelerated them to keV and MeV energies. In this study, we present a survey of electron distributions and moments derived from JADE in Jupiter’s polar magnetosphere. We quantify the electron properties (e.g. density and temperature) and explore similarities and differences in their distributions over several Juno perijove passes, focusing on regions near the main emission.
Adjustment mechanism of the sand bars in the jingjiang reach after the impounding the three gorges
Authors: Yang Xuhai
Published: March 2020

After the application of the large reservoirs, the conditions of discharge and sediment are changed. Based on a large number of measured hydrological and topographic data, this paper studies the deformation characteristics of sandbars micro-geomorphology in sandy reach of jingjiang river after the impounding of the three gorges reservoir(TGD), and discusses the adjustment mechanism of sandbars. The result shows that the sandy bars showed the head scoured and the shrink of area, and the sandbars in the reach with revetment project was relatively stable.The evolution of the sandbars was mainly influenced by riverbed composition, discharge and sediment process and revetment project. The composition of the riverbed determined the scour resistance of the sandbars, while the change of flow process determined the location and property of scour and silting, and the amount of incoming sediment determined the extent of scour and silting, the implementation of revetment project was beneficial to sandbars stability. After the TGD operation, the erosion of the bars in the Jingjiang reach ranked the strongest when the discharges fall in 15000 m³/s~25000 m³/s. The duration of this flow range increased after the TGD operation in 2003, and the bars presented an erosion state. Due to the impacts of river bed armoring and the significantly reduced sediment, there existed certain interactive relationships between the adjustment in the erosion and deposition of bars and the changes in the percentage of the grain size belonging to 0.125<d<0.25mm. The reduction of the fine sand had a negative impact on the sedimentation of bars after erosion. The layout of the revetment project had a certain control effect on the sandy reach, but the unguarded sandy bars presented scour and deposition with the fluctuation of discharge and sediment process between years.
Sensitivity of Atmosphere-Ocean Interactions during Cold Air Outbreaks to Characteristics of the Sea-Ice Edge
Authors: Spengler Thomas , Spensberger Clemens
Published: March 2020

Cold air outbreaks play a crucial role in the air-sea heat exchange in the higher latitudes. However, we still lack some basic understanding about the sensitivities of these phenomena to latent heating and the role of coupling to the ocean. Despite increasing model resolution, reliable forecasts of these events remain a challenge because of the vast range of scales and physical processes involved. To further explore these sensitivities and dependence on model representation, we couple a moist convective atmospheric boundary layer model with an ocean mixed layer model to investigate the response of moist convection as well as ocean mixing during cold air outbreaks. In addition, we perform sensitivity experiments based on the PolarWRF model in an idealised configuration to represent cold air outbreaks.

Varying sea ice concentration and resolution alters the distribution and intensity of the air-sea heat exchange with ramifications for mixed layer depths in both the atmosphere and ocean. Furthermore, integrated and local sensible and latent heat fluxes depend on the model resolution as well as the distribution of the sea-ice concentration in the marginal ice zone. While surface sensible heat fluxes appear to be rather consistent across different model resolutions, surface latent heat fluxes respond to the organisation of convection at higher resolutions, a feature that is absent for coarser model grids. Different geometries replacing a straight sea-ice edge with various simple geometrical shapes are also tested. Our results have implications for numerical weather prediction and climate models, in particular regarding model resolution and the degree of coupling for the representation of air-sea interaction during cold air outbreaks.
How to treat the seismic compression instability in seismic Microzonation studies
Authors: Fabozzi Stefania , Porchia Attilio , Fierro Tony , Peronace Edoardo , Pagliaroli Alessandro , Moscatelli Massimiliano
Published: March 2020

The identification of areas susceptible to different co-seismic instabilities is an important issue of the seismic zonation at urban scale finalized to the territory planning and its protection. Among the co-seismic permanent deformations caused by seismic shaking, the fractures, the landslides, the settlements due to liquefaction or compression/densification can be recognized.

The seismic compression or densification is a phenomenon producing permanent ground settlements in dry cohesionless soils (clean sands and sands with fine content) inducing damages to structures, infrastructures and lifelines, accordingly with well documented post-earthquake damages of past events.

 The susceptibility to this co-seismic instability in presence of dry clean sand, silty sand and sandy silty has been evaluated in the present work through the evaluation of the expected permanent ground settlements by means of non-simplified uncoupled methods computing volumetric strains from cyclic shear strains evaluated by means of site response analyses. This procedure was integrated into a parametric study of 1D seismic site response analyses varying relative density (or shear wave velocity) and thickness of compressible layers, intensity of input ground motion, depth of the seismic bedrock. The results have been then processed to define simplified charts differentiated for three different levels of input peak ground acceleration values and for the three considered lithologies (clean sands, silty sands and sandy silts).

These latter are mainly finalized to be used at urban scale, in the perspective of Seismic Microzonation (SM) studies requiring input-data commonly available in level 2 and 3 studies that have a strategic application in land use planning in the perspective of the territory protection.

A specific methodology was proposed by means of guideline based on a procedure with increasing complexity: 1) preliminary screening; 2) level 1 analyses; 3) level 3 analyses. The areas potentially susceptible to seismic compression identified in this preliminary phase are to be studied in the level 1 of SM, that identifies attention zones by checking the presence of predisposing conditions to the phenomenon. In the level 3 of SM, the susceptible zones and respect zones are identified through the estimation of the settlements by means of the charts proposed in the present work and the seismic site response analysis, respectively.
Using the CAMELS-GB large-sample dataset to investigate controls on baseflow (BFI)
Authors: Bloomfield John , Addor Nans , Coxon Gemma , Gong Mengyi , Marchant Ben
Published: March 2020

Over the last decade or so many studies of the hydrologic characteristics of basins have been driven by the desire to develop models that enable prediction of particular signatures, such as baseflow and Base Flow Index (BFI), in ungauged basins (PUB). These studies typically focus on understanding how readily available mapped or remotely sensed data can be used to infer hydrologic signals. However, in the specific case of baseflow, there is a recognition that we still have a poor understanding of the relative influences of underlying hydrological processes at appropriate scales, particularly in anthropogenically impacted catchments. New opportunities are being offered to better understand relationships between BFI and various controls on baseflow through the production of large sample catchment datasets. Here we present the results of an analysis of one such large-sample dataset, CAMELS-GB, investigating the relative importance of different hydrogeological controls on baseflow, including factors such as: climatology; hydrogeology; geophysical catchment characteristics, e.g. soil characteristics and land cover; and, anthropogenic influences, e.g. discharge from reservoirs and from sewage treatment works (STWs), abstraction, and mains leakage.

CAMELS-GB consists of daily hydrometerorological time series for the period 1970-2015 and landscape, catchment and hydrogeological attributes for 671 catchments in Great Britain. Machine learning approaches, including random forest algorithms, are used to investigate the influence of catchment characteristics on BFI and to inform the selection of hydrologically reasonable parameters to quantify relationships using linear regression models. We describe how the regression models can be used to investigate and characterise the sensitivity of estimates of BFI to: i.) the underlying hydrogeological mapping; ii.) the spatial support scale of the analysis; and iii.) anthropogenic influences.   
Land use effects on the geochemical soil properties and their control on organic carbon in volcanic soils, near Bandung area (Indonesia)
Authors: Anindita Sastrika , Finke Peter , Sleutel Steven
Published: March 2020

Land use change can significantly influence both mineralogy and chemical soil properties. This conversion, particularly from forest to agricultural system occurs often in volcanic soils due to their favorable properties for food production. Under agriculture, minerals can weather faster than in natural vegetation and this also impacts soil functioning. We aim to assess the impact of land use on geochemical soil properties and soil organic carbon across soils of different age. This study was conducted in Mt. Tangkuban Perahu and Mt. Burangrang where the soils were derived from similar andesitic parent material and have different ages based on their lithology. Five sites were selected representing land uses that have been converted (pine forest and agricultural land) and one site of natural forest as the origin of land use. The results showed that land use management enhances the mineral transformation. Pine forest and agricultural sites displayed higher weathering degree than natural forests as indicated by higher clay content, iron crystallinity index and the presence of gibbsite. The weathering degree of soils in agricultural sites might result from the length of cultivation period and soil age. Land use conversion also altered chemical properties such as pH, CEC, basic cations, and the proportion of amorphous materials. Non-crystalline Al and Fe minerals as indicated by Alo+1/2Feo were highly correlated with organic carbon and specific surface area (SSA) in the subsoils of all land uses. However, we did not see the accumulation of organic carbon in subsoils compared to topsoils as the amount of non-crystalline Al and Fe minerals increases with depth, especially in agricultural lands where the organic fertilizer input is very high. In addition, a significant proportion of carbon was stored in sand aggregate fractions in agricultural land which have longer cultivation period, while it was more readily found in silt and clay fractions in the site with shorter period.

 
Antarctic Uncertainty: Learning more about past ice sheet shapes with Bayesian methods
Authors: Turner Fiona , Wilkinson Richard , Buck Caitlin , Jones Julie M. , Sime Louise
Published: March 2020

Understanding the effect warming has on ice sheets is vital for accurate projections of climate change. A better understanding of how the Antarctic ice sheets have changed size and shape in the past would allow us to improve our predictions of how they may adapt in the future; this is of particular relevance in predicting future global sea level changes. This research makes use of previous reconstructions of the ice sheets, ice core data and Bayesian methods to create a model of the Antarctic ice sheet at the Last Glacial Maximum (LGM). We do this by finding the relationship between the ice sheet shape and water isotope values. 

We developed a prior model which describes the variation between a set of ice sheet reconstructions at the LGM. A set of ice sheet shapes formed using this model was determined by a consultation with experts and run through the general circulation model HadCM3, providing us with paired data sets of ice sheet shapes and water isotope estimates. The relationship between ice sheet shape and water isotopes is explored using a Gaussian process emulator of HadCM3, building a statistical distribution describing the shape of the ice sheets given the isotope values outputted by the climate model. We then use MCMC to sample from the posterior distribution of the ice sheet shape and attempt to find a shape that creates isotopic values matching as closely as possible to the observations collected from ice cores. This allows us to quantify the uncertainty in the shape and incorporate expert beliefs about the Antarctic ice sheet during this time period. Our results suggests that there may have been a thicker West Antarctic ice sheet at the LGM than previously estimated.
Planetary and synoptic-scale dynamic control of extreme cold wave patterns over the United States
Authors: Xie Zuowei , Black Robert , Deng Yi
Published: March 2020

The roles of planetary and synoptic-scale waves in extreme cold wave (ECW) events over the southeastern (SE) and northwestern (NW) United States (US) are studied using a spherical harmonic decomposition in conjunction with piecewise tendency diagnosis (PTD). Planetary waves and synoptic waves jointly work together to initiate ECW events. Notably, the planetary waves not only provide a direct contribution to circulation field enacting ECW events but also alter the background circulation field in such a manner that promotes synoptic waves growth via increases in regional barotropic deformation. The SE-ECW events, concurrent with the Northern Hemisphere annular mode (NAM) negative phase, feature high latitude intensification and subsequent southeastward movement of cold surface air temperature (SAT) anomalies. The planetary-scale pattern provides a sizable contribution to the total wave pattern on both sea level pressure (SLP) and upper level. Moreover, the negative NAM planetary anomaly acts to displace the jet equatorward and thereby increases the barotropic deformation of the synoptic-scale anomaly over southeastern US. PTD confirms that the planetary-scale barotropic deformation plays a key role in deepening the negative height anomaly with a secondary contribution from baroclinic growth. In contrast, NW-ECW events feature a regional SAT cold anomaly that intensified in situ in association with a quasi-stationary positive SLP anomaly with a substantial planetary-scale wave component. The upper level circulation is characterized by a pronounced anomalous ridge over the Gulf of Alaska and a northeast-southwest tilted negative height anomaly to its east. The negative height anomaly axis is orthogonal to the planetary-scale dilatation, result in a stronger planetary barotropic deformation of the incipient negative height anomaly.
A new instrument in earthquake early warning system by detection and modeling of prompt gravity signals
Authors: Juhel Kevin , Montagner Jean-Paul , Ampuero Jean-Paul , Barsuglia Matteo , Bernard Pascal , Losurdo Giovanni , Vallée Martin
Published: March 2020

The recent finding of prompt elastogravity signals (PEGS) before the arrival of P-waves, associated with the M9.1 2011 Tohoku earthquake (Montagner et al., Nat. Comm., 2016; Vallée et al., Science, 2017) and a few earthquakes of magnitude larger than 8.5  (Vallée and Juhel, JGR, 2019) opens the new field of speed-of-light seismology.  The systematic detection of PEGS on real-time might help saving a few seconds before the arrival of destructive seismic waves and to obtain an accurate determination of the magnitude of the earthquake at the end of rupture. So the potential application to earthquake early warning is obvious.

However, the use of classical broadband seismometers for detecting PEGS has severe limitations for detecting earthquakes of magnitude smaller than 8.5: first of all, the background seismic noise and second of all, the partial cancellation of the gravitational perturbation by the inertial induced acceleration recorded by seismometers (Heaton, Nature Comm., 2017). Two different approaches can be explored for detecting for earthquakes of magnitude smaller than 8.5. Either, by using a dense array of broadband seismometers  (more than 100 receivers) or by designing completely new instruments such as gravity strainmeters. These new detectors must be able to measure the difference in gravity acceleration between two masses, making this instrument isolated from the seismic noise. A sensitivity of 10-15 Hz-1/2 at 0.1 Hz is required for detecting earthquakes of M>7 (Juhel et al., JGR, 2019) and the technology developed by the gravitational wave physicists can be used for reaching such a sensitivity. The simulation of the expected gravity strain signals based on analytical model of gravity perturbations associated with a network-based matched filter approach show that a network of 3 gravity strainmeters might make it possible to reach such a challenging goal. Gravity strainmeters could therefore open new ways to investigate the first seconds of the earthquake rupture, speed up the estimate of earthquake magnitude, enhance tsunami warning systems and  complement other EEWS in the future.

 

 
Semidiurnal current dynamics in the Arctic Ocean's eastern Eurasian Basin
Authors: Baumann Till , Polyakov Igor , Padman Laurie , Danielson Seth , Fer Ilker , Howard Susan , Hutchings Jenny , Janout Markus , Nguyen An , Pnyushkov Andrey
Published: March 2020

In the Arctic Ocean, semidiurnal-band processes including tides and wind-forced inertial oscillations are significant drivers of ice motion, ocean currents and shear contributing to mixing. Two years (2013-2015) of current measurements from seven moorings deployed along 125°E from the Laptev Sea shelf (~50 m) down the continental slope into the deep Eurasian Basin (~3900 m) are analyzed and compared with models of baroclinic tides and inertial motion to identify the primary components of semidiurnal-band current (SBC) energy in this region. The strongest SBCs, exceeding 30 cm/s, are observed during summer in the upper ~30 m throughout the mooring array. The largest upper-ocean SBC signal consists of wind-forced oscillations during the ice-free summer. Strong barotropic tidal currents are only observed on the shallow shelf.  Baroclinic tidal currents, generated along the upper continental slope, can be significant. Their radiation away from source regions is governed by critical latitude effects: the S2 baroclinic tide (period = 12.000 h) can radiate northwards into deep water but the M2 (~12.421 h) baroclinic tide is trapped to the continental slope. Baroclinic upper-ocean tidal currents are sensitive to varying stratification, mean flows and sea ice cover.  This time-dependence of baroclinic tides complicates our ability to separate wind-forced inertial oscillations from tidal currents. Since the shear from both sources contributes to upper-ocean mixing that affects the seasonal cycle of the surface mixed layer properties, a better understanding of both, inertial motion and baroclinic tides is needed for projections of mixing and ice-ocean interactions in future Arctic climate states.
Seismic reflection imaging of the low-angle Panamint Valley normal fault system, eastern California, USA
Authors: Gold Ryan , Stephenson William , Briggs Richard , DuRoss Christopher , Kirby Eric , Woolery Edward , Odum Jack , Delano Jaime
Published: March 2020

A fundamental question in seismic hazard analysis is whether <30º-dipping low-angle normal faults (LANFs) slip seismogenically. In comparison to more steeply dipping (45-60º) normal faults, LANFs have the potential to produce stronger shaking given increased potential rupture area in the seismogenic crust and increased proximity to manmade structures built on the hanging wall. While inactive LANFs have been documented globally, examples of seismogenically active LANFs are limited. The western margin of the Panamint Range in eastern California is defined by an archetype LANF that dips west beneath Panamint Valley and has evidence of Quaternary motion. In addition, high-angle dextral-oblique normal faults displace mid-to-late Quaternary alluvial fans near the range front. To image shallow (<1 km depth), crosscutting relationships between the low- and high-angle faults along the range front, we acquired two high-resolution P-wave seismic reflection profiles. The northern ~4.7-km profile crosses the 2-km-wide Wildrose Graben and the southern ~1.1-km profile extends onto the Panamint Valley playa, ~7.5 km S of Ballarat, CA. The profile across the Wildrose Graben reveals a robust, low-angle reflector that likely represents the LANF separating Plio-Pleistocene alluvial fanglomerate and pre-Cambrian meta-sedimentary deposits. High-angle faults interpreted in the seismic profile correspond to fault scarps on Quaternary alluvial fan surfaces. Interpretation of the reflection data suggests that the high-angle faults vertically displace the LANF up to 70 m within the Wildrose Graben. Similarly, the profile south of Ballarat reveals a low-angle reflector, which appears both rotated and displaced up to 260 m by high-angle faults. These results suggest that near the Panamint range front, the high-angle faults are the dominant late Quaternary structures. We conclude that, at least at shallow (<1 km) depths, the LANF we imaged is not seismogenically active today.
Increasing Strength of Compound Hot-Wet Dynamical Extremes Over the Mediterranean
Authors: De Luca Paolo , Messori Gabriele , Faranda Davide , Coumou Dim
Published: March 2020

The Mediterranean (MED) basin is a hot-spot for climate change impacts. We present recently developed techniques derived from Dynamical System Theory to investigate long-term changes in compound hot-wet extremes over the MED. We use three reanalysis products, spanning a 40-year period from 1979 to 2018: ERA5, ERA-Interim and ERA5 10-member ensemble. From these datasets, we extract daily maximum temperature (degC) and total precipitation (mm), which we then use in the dynamical systems analysis.

Results show that the strength of the dynamical coupling between hot and wet extremes increased significantly at both annual and summer (June-August) timescales during the reanalysis period. This means that, regardless of changes in the occurrence of individual hot or wet extremes, joint occurrences may be becoming more frequent.

Compound hot-wet extremes mostly occur during July and August, and correspond to a low-pressure core over the Aegean Sea and the eastern MED. The increasing trends in compound extremes may be associated with surface MED warming. Such enhanced warming can therefore drive compound hot-wet extremes especially during the summer, when localised convection or mesoscale systems such as medicanes are responsible for extreme precipitation events.
Methane from the LGM to the present: The Natural methane cycle
Authors: Kleinen Thomas , Gromov Sergey , Steil Benedikt , Brovkin Victor
Published: March 2020

The time between the last glacial maximum (LGM) and the present is highly interesting with regard to atmospheric methane. Between the LGM and 10 ka BP atmospheric CH4, as reconstructed from ice cores, nearly doubled, with very rapid concentration changes of about 200 ppb occurring during the Bølling Allerød (BA) and Younger Dryas (YD) transitions. During the Holocene, atmospheric CH4 is very similar for 10 ka BP and PI, but CH4 is about 15% lower in between at 5 ka BP.

We use a methane-enabled version of MPI-ESM, the Max Planck Institute Earth System Model, to investigate changes in methane cycling in a transient ESM experiment from the LGM to the present. The model is driven by prescribed orbit, greenhouse gases and ice sheets, with all other changes to the climate system determined internally. Methane cycling is modelled by modules representing the atmospheric transport and sink of methane, as well as terrestrial sources and sinks from soils, termites, and fires. Thus, the full natural methane cycle – with the exception of geological and animal emissions – is represented in the model.

Model results are compared to methane concentrations from ice cores, and key periods in climate/methane evolution are highlighted by detailed analyses. Methane concentrations can mainly be explained by emission changes, with LGM emissions substantially reduced in comparison to the early Holocene and preindustrial states due to lower temperature, CO2, and soil carbon. For the large transitions during the deglaciation, such as the transitions from Older Dryas to BA, BA to YD, and YD to Holocene, ocean circulation changes are required to obtain atmospheric methane changes of sufficient magnitude and rapidity.
The presence of silty mantles in Northcentral Appalachian, USA soils and their relevance to pedology
Authors: Drohan Patrick , Raab Thomas , Hirsch Florian
Published: March 2020

Across the northcentral Appalachians, USA, high silt content soils are found as silty mantles or deep, high silt content pedons. The origin of such soils can be attributed to additions of wind-blown dust deposits (WBD) or local parent materials (i.e. shales or siltstone lithology). Previous research on silt soils originating specifically from WBD attributed to late marine isotope stage (MIS) 2 loess has often been isolated to drainageways receiving outwash from deglaciation. We hypothesize that thin (<25-50 cm) silty mantles, and some deep silt soils occurring farther from outwash systems, are also indicative of post MIS 2 WBD and their extent is widespread. To test this hypothesis, we evaluated over 900 pedons from an ~119,280 km2 area of the northcentral Appalachians, USA to: (i) develop a particle size signature indicative of soils largely derived from WBD versus local parent materials, (ii) determine the potential depth of WBD additions to soils, and (iii) document the spatial extent of WBD versus deep, high-silt content soils across part of the region. Results suggest that silty mantles are prevalent across the study area and have a particle size signature indicative of loess and the mean depth of WBD additions to soils is ~50 cm.  Below 50 cm, local lithology or pedogenesis more influences particle size trends.  Pedon results were applied in a spatial modeling effort using the USA Soil Survey Geographic Database (SSURGO) to document the extent of silty mantles (over non-silt sourced parent materials) and deep, high silt content soils.  Model results indicate silty mantles are common on stable landscape positions or positions that accumulate sediments (depressions or valleys). Aspect dependent deposition appears tied to sources of WBD deposits, and deposits correspond strongly to regional studies of WBD deposits derived from loess. Last, proximity to topography, which can act as a trap for WBD, appears to be a key variable explaining silty mantle and deep, high-silt content soil occurrence. 
Temperature, strain rates, and rheology: the key parameters controling strength variations in the Australian lithosphere
Authors: Tesauro Magdala , Kaban Mikhail , Petrunin Alexey , Aitken Alan
Published: March 2020

The Australian plate is composed of tectonic features showing progression of the age from dominantly Phanerozoic in the east, Proterozoic in the centre, and Archean in the west. These tectonic structures have been investigated in the last three decades using a variety of geophysical methods, but it is still a matter of debates of how temperature and strength are distributed within the lithosphere. We construct a thermal crustal model assuming steady state variations and using surface heat flow data, provided by regional and global database, and heat generation values, calculated from existing empirical relations with seismic velocity variations, which are provided by AusREM seismic tomography model. The lowest crustal temperatures are observed in the eastern part of the WAC and the Officer basin, while Central and South Australia are regions with anomalously elevated heat flow values and temperatures caused by high heat production in the crustal rocks. On the other hand, the mantle temperatures, estimated in a previous study, applying a joint interpretation of the seismic tomography and gravity data, show that the Precambrian West and North Australian Craton (WAC and NAC) are characterized by thick and relatively cold lithosphere that has depleted composition (Mg# > 90). The depletion is stronger in the older WAC than the younger NAC. Substantially hotter and less dense lithosphere is seen fringing the eastern and southeastern margin of the continent. Both crustal and mantle thermal models are used as input for the lithospheric strength calculation. Another input parameter is the crustal rheology, which has been determined based on the seismic velocity distribution, assuming that low (high) velocities reflect more sialic (mafic) compositions and thus weaker (stiffer) rheologies. Furthermore, we use strain rate values obtained from a global mantle flow model constrained by seismic and gravity data. The combination of the values of the different parameters produce a large variability of the rigidity of the plate within the cratonic areas, reflecting the long tectonic history of the Australian plate. The sharp lateral strength variations are coincident with intraplate earthquakes location. The strength variations in the crust and upper mantle is also not uniformly distributed: In the Archean WAC most of the strength is concentrated in the mantle, while the Proterozoic Officer basin shows the largest values of the crustal strength. On the other hand, the younger eastern terranes are uniformly weak, due to the high temperatures.
Seasonal to interannual variability of observed temperatures in the equatorial Pacific
Authors: Rubino Angelo , Zanchettin Davide , de Rovere Francesco , McPhaden Michael J.
Published: March 2020

On large (global and hemispheric) scales, sea surface temperature (SST) anomalies are considered to be good surrogates for marine air temperature (MAT) anomalies. Here we investigate how MAT and SST anomalies from instrumental measurements compare regarding a few crucial aspects of their variability including seasonality and multiannual trends. We make use of MAT and SST data acquired by moored buoys constituting the Tropical Atmosphere Ocean (TAO) array. Buoys are managed by the Pacific Marine Environmental Laboratory (PMEL), which is part of the National Oceanic and Atmospheric Administration (NOAA) agency of the United States of America. We  aim at answering the following questions: How do the monthly average anomalies of SST and MAT compare? Do observed MAT and SST data contain significantly different multiannual trends?