The Dobi graben is a NW-trending, Quaternary continental rift found within the East-Central Block (ECB) of the Afar Depression (AD) in northeastern Ethiopia. Extension occurs on steeply dipping faults, where the ratio of maximum displacement to traced fault length extends to four orders of magnitude. We conducted fault population analysis in the Dobi graben using a 30 m resolution Shuttle Rader Topography Mission (SRTM) Digital Elevation Model (DEM). We traced a total of 953 faults. We used the fault displacement length profiles’ tapering directions and the different types of fault propagations’ termination styles to characterize the fault kinematics pattern. Our population analysis results show that ~45% of the normal faults in the Dobi graben are tapering towards the southeast in a manner similar to the Red Sea Rift (RSR) regional strain gradient. On the other hand, our analysis showed that ~40% of the faults in the Dobi graben are tapering towards the northwest direction in a manner similar to the Gulf of Aden Rift (GAR) regional strain gradient. We found the statistical regression correlation coefficients (R-square value) for both the southeast and the northwest tapering faults to be ~0.7. Therefore, we suggest that ~85% of the lateral propagation of the 953 faults in the Dobi graben is highly influenced by the regional strain transfer of the RSR and GAR. Additionally, based on the fault propagation termination styles, our faults population analysis shows that faults which exhibit the half-restricted termination style account for 85% of the 953 faults. The maximum displacement over the maximum length (Dmax/Lmax) ratio of these faults is 0.03, which is in accord with the constant displacement length fault growth model.

This study presents the novel application of tidal gravimetric data in the determination of phase-velocity dispersion curves of Rayleigh surface waves. Tidal gravimeters are capable to detect surface waves of periods even up to 500−600 s, while a typical broad-band seismic sensor can detect them up to the periods of 200−300 s due to its mechanical limitation. The capability of using tidal gravimeters as long period seismometers has already been analyzed since the late ’90s. These researches were mainly focused on the comparison of the power spectral density of noise level of gravimeters and seismometers and the analysis of normal modes of the largest earthquakes recorded by gravimeters. The first steps in the calculation of group velocity dispersion curves of Rayleigh surface waves were carried out lately. The Wiener deconvolution technique was used to calculate the phase-velocity dispersion curve by a two-stations method, from two pre-processed traces recorded in two different stations, located at the same great circle that the epicentre. The Incorporated Research Institutions for Seismology (IRIS) database were searched in terms of availability of at least 1 Hz data recorded by a co-located broad-band seismometer and tidal gravimeter. Additionally, the IRIS database provides the information about the transfer function of instruments, what is necessary in the two-stations method. Only, three sites met the above conditions: Black Forest, Membach and Rochfort, all located in Western and Central Europe. The compatibility of gravimetric and seismic data in the period range of 20-100 s are shown. Tidal gravimeters, because of their higher sensitivity, can better detect weaker earthquakes, which results in a higher number of recordings. However, to explore all advantages of gravimetric recordings of earthquakes, especially up to the periods of 500-600 s, above analysis must be applied to tidal gravimeters with higher inter-station distances and evaluated transfer functions. This work was done in the research project No. 2017/27/B/ST10/01600 financed from the funds of the Polish National Science Centre.

Supershear earthquakes are rare compared to their subshear counterparts, but the cause for their paucity remains to be understood. We investigate for the first time the prevalence of supershear ruptures across multiple earthquake cycles on long faults using rate-and-state friction and a 2.5D approximation that accounts for the finite seismogenic width W. We find supershear events occur only in a narrow range of friction parameters that is not commonly observed in laboratory experiments, which may explain its rarity in nature. Particularly, the ratio between direct and evolution effects of rate-and-state friction needs to be low (a/b<0.4) and the nucleation length has to be sufficiently large compared to W, but not too large that it causes a transition from seismic to aseismic slip. Our numerical and analytical developments contribute fundamentally to understanding the state of stress on long faults over multiple earthquake cycles and their potential for hosting supershear earthquakes.

Some aspects of the dynamics of aeolian transport over a flat sediment bed have been thoroughly investigated and are relatively well understood. The interactions between grains in transport and the wind give rise to well-known dynamical scaling laws for the fluxes and concentrations of grains in most of the transport layer. However, recent work has revealed a sudden shift in these scaling laws near the granular surface and below. While the vertical flux of grains in the transport layer scale linearly with excess wind shear stress, the vertical flux near the granular surface—the ‘erosion rate’—scales linearly with wind speed. Analysis of numerical modeling results reveal that near-surface horizontal and vertical fluxes are important for the instability that leads to wind ripple growth and stabilization as well as ripple propagation. A few main open questions are: What are the physical mechanisms behind the scaling of the erosion rate with wind speed? Could they arise from the small subpopulation of high-energy grains, who’s characteristics scale differently than the average grain in transport? As these grains move downward from the free-wind layer, do they tend to retain their properties as they pass through the feedback layer, delivering their energy, momentum and scaling directly to the bed? Do collisions between grains near and within the bed, which redistribute energy and momentum from high-energy impacts, play a key role in determining the scaling of near-bed fluxes? How important are potential collective effects that can occur when impacts with sufficient energy to excite the bed occur close together in time and space? An answer to these questions would help complete our understanding of the physics of aeolian transport, with repercussions that shed light onto the emergence and propagation of wind ripples. Using a detailed grain scale numerical model, we are investigating the dynamics of grains near the granular bed, and what saltation properties drive these dynamics. Preliminary results, including velocity distributions near the bed, indicate that the signal from high-energy grains that traverse the feedback layer from above reaches the bed surface, consistent with the hypothesis that the surface erosion rate is related to this small population of grains who’s characteristics scale with the free-wind speed.

Cheniers are ridges consisting of coarse-grained sediments, resting on top of the fine sediment that forms the otherwise muddy coast. In this paper, we use Delft3D to explore how cheniers are formed through wave winnowing. We identify three phases of chenier development: (1) a winnowing phase, during which mud is washed out of the seabed initially consisting of a mixture of sand and mud, (2) a sand transport phase, when the sand in the upper layer is transported onshore, and (3) a crest formation phase, during which a chenier crest rapidly develops at the landward limit of onshore sediment transport. The main mechanism driving onshore sand transport is wave asymmetry. During calm conditions, sand transport takes place within a narrow band limiting the volume of sand delivered nearshore, and therefore no chenier develops. In contrast, average storm conditions mobilise sufficient sand for a crest to develop. Our results thus reveal that chenier formation through wave winnowing does not require extreme storm conditions. Furthermore, our study showed that chenier formation through wave winnowing is a relatively slow process, with the largest time scales associated with the winnowing and sand transport. Once sufficient sand is available nearshore, the crest develops rapidly.

Deltas and fluvial fans are two fan-shaped landforms with complex channel networks. Deltas always occur where rivers enter a standing body of water, such as lakes or oceans. Fluvial fans are inland terrestrial landforms that may form thousands of kilometers from shorelines. Fluvial fans may however also reach lakes and oceans. The current state of knowledge lacks understanding of their morphometric differences or recognition criteria, despite their socioeconomic significance, vulnerability to natural hazards, and important differences in how these landforms respond to global climate change. Moreover, numerous fan-shaped landforms with channel networks have been identified on other planetary bodies, such as Mars and the Saturn's moon Titan, where deltas are important indicators of paleo-shorelines and offer attractive targets for mission sites due to their habitability and high biosignature preservation potential. Here we review the known morphometrics of delta and fluvial fan channel networks, and the differences in their formative processes, and develop morphometric criteria for distinguishing deltas and fluvial fans. We present an ensemble of quantitative metrics that distinguish deltas and fluvial fans and test these criteria on 80 modern channel networks on Earth. Our results improve mechanistic understanding of the fluvial record and delta evolution, provide criteria for accurate recognition of these landforms on planetary bodies and in the sedimentary record, and explain differences in their vulnerabilities to global change.

Climate modeling studies and observations do not fully agree on the implications of anthropogenic warming for evapotranspiration (ET), a major component of the water cycle and driver of irrigation water demand. Here we use California as a testbed to assess the ET impacts of changing atmospheric conditions induced by climate change on irrigated systems. Our analysis of irrigated agricultural and urban regions shows that warmer atmospheric temperatures have minimal implications for ET rates and irrigation water demands-about one percent change per degree Celsius warming (~1 %°C-1). By explicitly modeling irrigation, we control for the confounding effect of climate-driven soil moisture changes and directly estimate water demand implications. Our attribution analysis of the drivers of ET response to global anthropogenic warming shows that as the atmospheric temperature and vapor pressure deficit depart from the ideal conditions for transpiration, regulation of stomata resistance by stressed vegetation almost completely offsets the expected increase in ET rates that would otherwise result from abiotic processes alone. We further show that anthropogenic warming of the atmosphere has minimal implications for mean relative humidity (<1.7%°C-1) and the surface energy budget (<0.2%°C-1), which are critical drivers of ET. This study corroborates the growing evidence that plant physiological changes moderate the degree to which changes in potential ET are realized as actual ET.

We develop an algorithm to integrate GPS and InSAR data for a 3-dimensional crustal deformation field at the Earth’s surface. In the algorithm discrete GPS data points are interpolated to obtain a 3-dimensional continuous velocity field, which is then combined with the InSAR line-of-sight (LOS) velocity data pixel by pixel using the least-squares method. Advantages of our method over previous ones are that: 1) The GPS data points are optimally interpolated by balancing a trade-off between spatial resolution and solution stability. 2) A new algorithm is developed to estimate realistic uncertainties for the interpolated GPS velocities, to be used as weights for GPS data in GPS-InSAR combination. 3) Realistic uncertainties for the InSAR LOS rate data are estimated and used as weights for InSAR data in GPS-InSAR combination. 4) The ramps and/or offsets of the InSAR data are globally estimated for all the images to minimize data misfit, particularly at regions where the data overlaps. Application of this method to real data from southern California shows its capability of successfully restoring 3-dimensional continuous deformation field from spatially limited GPS and dimensionally limited InSAR data. The deformation field reveals water withdrawal induced subsidence and drought caused uplift at various regions in southern California.

For the first time to our knowledge, the aim of this study is to investigate the spatial variation of atmospheric particulate matter concentrations in Abidjan and Korhogo (Cote d’Ivoire), as well as the relative contribution of PM2.5 to PM10 concentrations from measurement campaigns conducted in dry season in Abidjan and Korhogo. During these campaigns, twenty and fourteen sites were sampled respectively in Abidjan and Korhogo during two working days and one week-end day using portable active analysers. Spatial variations obtained by the IDW interpolation method show that PM10 concentrations are the highest in neighbourhoods without paved roads both in Abidjan and Korhogo whereas the highest PM2.5 concentrations are measured at sites influenced by traffic or wood in domestic fires. PM10 is composed of more than 50% PM2.5 particles in Abidjan, but less than 40% in Korhogo. These proportions are partly due to desert dust and road dust resuspension, which are higher in Korhogo than in Abidjan. The results also show the link between particulate concentrations and living standards in the neighbourhoods. Mean daily profiles of PM10 and PM2.5 concentrations are generally similar in Abidjan and Korhogo from site to site, with peaks in morning and in afternoon. However, in Abidjan, some sites have higher morning peaks than evening peaks, while in Korhogo, all concentration peaks are of the same amplitude. In Abidjan, such a difference may be explained by the fact that road traffic intensity is less spread out in the morning than in the evening. In Korhogo, both the use of firewood and dust resuspension increases aerosol concentrations, especially in the evening. In those conditions, a serious public health problem may be expected in both cities, an impact that we have evaluated by measuring PM2.5 oxidative capacity from DTT (Dithiothreitol) analyses in a few sites.

In celestial bodies with collisionless atmospheres, such as Mercury, the spatial distribution of the exosphere is expected to reflect the surface composition. In this study, we discuss whether the distribution of Mg, Ca, and Na, the primary exospheric components on Mercury, have exosphere-surface correlation (ESC) by analyzing the observation data of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) onboard the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. As a result, it was found that Mg has strong ESC, Ca has weak ESC and Na has little ESC. The Monte Carlo simulations of trajectory in the exosphere show that the weak ESC of Ca is due to the relatively large solar radiation acceleration. Na has ESC only in high-temperature regions around 0°E. This can be explained well by considering that the weakly physisorbed Na layer on the surface is depleted under high temperature and that the distribution of strongly chemisorbed Na atoms is reflected in the exosphere. Based on these results, the conditions for components with ESC in celestial bodies with thin atmospheres include low volatility and little solar radiation acceleration.

Hadal trenches act as depocenters for organic material, although pathways for hadal material transport and deposition rates are poorly constrained. Here we assess, focusing, deposition and accumulation, of material and organic carbon in four hadal trench systems underlying provinces of different net primary productivity in the surface ocean – from the eutrophic Atacama and Kuril-Kamchatka trenches, and the mesotrophic Kermadec Trench, to the oligotrophic Mariana Trench. The study is based on the distributions of 210Pbex, 137Cs and total organic carbon from recovered sediment cores and by applying previously quantified benthic mineralization rates. Periods of steady deposition and discreet mass-wasting deposits were identified from the profiles and the latter were associated with historic recorded seismic events in the respective regions. During periods without mass wasting, the estimated focusing factors along trench axes were elevated, suggesting continuous downslope focusing of material towards the interior of the trenches. The estimated accumulation rates of organic carbon during these periods exhibited extensive site-specific variability but were generally similar to values encountered at much shallower settings such as continental slopes and margins. Organic carbon deposition and accumulation rates during periods of steady deposition was not mirrored by surface ocean productivity, but appeared confounded by local bathymetry. Seismic driven mass wasting events markedly enhanced the accumulation of sediment and organic carbon by factors from 20 to 400. Thus, hadal trenches are important sites for deposition and sequestration of organic carbon in the deep-sea partly due to intensified downslope focusing of material but mainly due to mass-wasting events.

Understanding the near-surface roughness is paramount for the evolution of surface features and its contribution to the ice sheet dynamics. In regions experiencing the transition from dry snow to melt conditions, the surface becomes rough which along with liquid water content influences the radar backscatter. Such surfaces are driven by wind resulting in the formation of features oriented at different azimuth directions, ranging from ripples to dunes. Different scales of roughness also induce depolarisation in the radar signal, thereby making it difficult to infer the effective contribution of densification process on total backscatter. Here, we present a physical understanding of a wind-induced snow surface having anisotropic roughness from the modelled radar backscatter. As part of the approach, we propose to model the horizontal component of roughness (autocorrelation length) as a function of azimuth direction in the surface scattering model, i.e. Integral Equation Model. We performed our experiments for strongly anisotropic (a < 0.2), weakly anisotropic (a > 0.7), and isotropic (a = 1) surfaces, where a is the anisotropy, tuned for C-band frequency. Also, the minima of backscatter intensity varied over entire range of azimuth angles at a particular incidence angle is derived for retrieving the most dominant wind direction. From our analysis, significant azimuth modulation occurs in the radar backscatter at low incidence angles. Moreover, we found that the most dominant wind direction at 30-deg incidence angle changes from a strongly anisotropic surface (i.e. 0-deg) to a weakly anisotropic surface (i.e. 90-deg), however it remains unaltered for 45-deg and 60-deg incidence angles (i.e. 90-deg). Our modelled results are in strong agreement with wind scatterometer data of ice sheets and further show the potential of 30-deg incidence angle for tracking the changes in wind flow pattern based on directionality of roughness. In this regard, we foresee the importance of azimuth modulation for understanding the properties and orientation of surface features in the ice sheets, with particular application to wind flow. As a future scope, we plan to apply our model on radar images for the retrieval of wind directions and compare the directionality of roughness with the katabatic wind flow patterns and AWS measurements.

Many biases in global climate models (GCMs) have been associated with the poor representation of unresolved variability due to organised convection in the tropics by the underlying cumulus parameterizations (CP). Many researchers have suggested that the quasi-equilibrium assumption (QEA) on which these CP’s are based is to blame. This is even more problematic with the recent and future increases in grid resolutions as the cloud large ensemble requirement for QEA breaks down. The stochastic multi-cloud model (SMCM) of Khouider et al. 2010 was proposed as a cheap alternative of overcoming this QEA dilemma by emulating the variability of the three cloud types which characterize tropical convection via a Markov jump birth-death process. The SMCM has proven to be very successful in terms of the simulation of the main modes of tropical variability when used as a simple alternative CP in a GCM. Here, we propose to incorporate the SMCM directly into the Zhang-McFarlane scheme (ZMS; Zhang and McFarlane 1995) to break the QEA dead end by using instead a stochastic plume ensemble and generalise the SMCM framework to cumulus schemes. The new stochastic ZMS (SZMS) uses a random number of plumes that are launched for each one of the three cloud types, shallow, congestus and deep, and that detrain at random levels, according to the SMCM. The new approach somehow combines the idea of Cohen and Craig (2006) of assuming a Poisson process for the number of plumes and that of Gentine et al. (2013) of prescribing a distribution of plume detrainment levels. Here we shall show the results of our experiment, for the single column version of the Community Earth System Model. Bibliography: Cohen BG, Craig GC. Fluctuations in an equilibrium convective ensemble. Part II: Numerical experiments. J. Atmos. Sci. 2006;63(8) Gentine P, Betts AK, Lintner BR, Findell KL, Van Heerwaarden CC, D’andrea F. A probabilistic bulk model of coupled mixed layer and convection. Part II: Shallow convection case. J. Atmos. Sci. 2013;70(6) Khouider B, Biello J, Majda AJ. A stochastic multicloud model for tropical convection. Comm. Math. Sci. 2010;8(1) Zhang GJ, McFarlane NA. Sensitivity of climate simulations to the parameterization of cumulus convection in the Canadian Climate Centre general circulation model. Atmos-ocean. 1995;33(3)

This study aims to quantify the impacts of ocean coupling on simulated and projected tropical cyclone (TC) precipitationin the Northern Hemisphere. We used global climate model (GCM) simulations over 1950-2050 from the High Resolution Model Intercomparison Project (HighResMIP) and compared its fully coupled atmosphere-ocean GCMs (AOGCMs) with atmosphere-only GCMs (AGCMs). We find that ocean coupling generally leads to decreased TC precipitation over ocean and land. Large-scale sea surface temperature (SST) biases are critical drivers of the precipitation difference, with secondary contributions from local TC-ocean feedbacks via SST cold wakes. The two driving factors, attributed to ocean coupling in the AOGCMs, influence TC precipitation in association with decreased TC intensity and specific humidity. The AOGCMs and AGCMs consistently project TC precipitation increases in 2015-2050 relative to 1950-2014 over ocean for all basins, and for landfalling TCs in the North Atlantic and western North Pacific.

Earthquake-triggered landslides are a severe hazard and contribute to landscape evolution. To understand their process and controlling factors, we model the onset of seismically-triggered slip on pre-existing slip surfaces governed by laboratory-based rate-and-state friction, including wave propagation effects. Through numerical simulations and theoretical analysis, we identify how friction properties, landslide thickness and incident wave attributes (frequency, duration, amplitude) control slope stability. We find that the frictional state variable tracks the cyclic fatigue of the slip surface, its progressive weakening with each wave cycle. Wave propagation effects introduce two regimes depending on frequency relative to the two-way travel time across the landslide thickness: the stability criterion is well approximated by a threshold on incident peak acceleration at low frequencies, and on peak velocity at high frequencies. We derive analytical approximations, validated by simulations, suitable to apply the model to evaluate landslide stability under arbitrary input motions.

The temporal behaviour of the Martian ionosphere is highly variable due to various dynamic processes including space weather events. Here, we study the effect of two solar flares and coronal mass ejections (CMEs) on the Martian ionosphere for two selected solar events in 2011 and 2015, using the publicly available Mars EXpress (MEX) radio occultation (RO) data (MaRS). We developed a data processing software that converts the calibrated Radio Occultation (RO) Doppler data to scientifically valuable atmospheric profiles. Using this software and previously unexplored MaRS observations, the variations in ionospheric parameters (electron density profiles and total electron content (TEC)) are calculated in order to evaluate the ionospheric changes due to solar flares and CMEs. The RO measurements mostly available 1 to 4 days apart from the peak events, showed no evident change in the TEC nor in the shape of electron density profiles except for a possible gradual decrease in altitude of M2 (main layer) peak density following the arrival of CMEs. To better quantify the effect of solar events on electron density profiles, RO observations near the time of arrival of solar flares and CMEs are crucial. This can be achieved by frequent RO measurements by various Mars orbiters including spacecraft-to-spacecraft measurements assisted by multi-instrument monitoring of the ionosphere.

Temperature and water vapor are known to fluctuate on multiple scales. In this study 27 years of airborne measurements of temperature and relative humidity from IAGOS (In-service Aircraft for a Global Observing System) are used to parameterize the distribution of water vapor in the upper troposphere and lower stratosphere (UTLS). The parameterization is designed to simulate water vapor fluctuations within gridboxes of atmospheric general circulation models (AGCMs) with typical size of a few tens to a few hundreds kilometers. The distributions currently used in such models are often not supported by observations at high altitude. More sophisticated distributions are key to represent ice supersaturation, a physical phenomenon that plays a major role in the formation of natural cirrus and contrail cirrus. Here the observed distributions are fitted with a beta law whose parameters are adjusted from the gridbox mean variables. More specifically the standard deviation and skewness of the distributions are expressed as empirical functions of the average temperature and specific humidity, two typical prognostic variables of AGCMs. Thus, the distribution of water vapor is fully parameterized for a use in these models. The new parameterization simulates the observed distributions with a determination coefficient always greater than 0.917, with a mean value of 0.997. Moreover, the ice supersaturation fraction in a model gridbox is well simulated with a determination coefficient of 0.983. The parameterization is robust to a selection of various geographical subsets of data and to gridbox sizes varying between 25 to 300 km.

We formulate an expression for the turbulent kinetic energy dissipation rate, $\epsilon$, associated with shear–generated turbulence in terms of readily measured properties of the flow or easily derived quantities in models. The expression depends on the turbulent vertical length scale, $\ell_v$, the inverse time scale $N$ and the Richardson number $Ri=N^2/S^2$, where $S$ is the vertical shear, with $\ell_v$ scaled in a way consistent with theories and observations of stratified turbulence. Unlike previous studies the focus is not so much on the functional form of $Ri$, but the vertical variation of the length scale $\ell_v$. Using data from two $\sim$7 day time series in the western equatorial Pacific the scaling is compared with the observed $\epsilon$. The scaling works well with the estimated $\epsilon$ capturing the differences in amplitude and vertical distribution of the observed $\epsilon$ between the two times series. Much of those differences are attributable to changes in the vertical distribution of the length scale $\ell_v$, and in particular the associated turbulent velocity scale, $u_t$. We relate $u_t$ to a measure of the fine-scale variations in velocity, $\tilde{u}$. Our study highlights the need to consider the length scale and its estimation in environmental flows. The implications for the vertical variation of the associated turbulent diffusivity are discussed.