Fracture geometry, density, and distribution control fluid and thermal transport in low porosity rocks, as well as their seismic attributes. The creation of cracks throughout the matrix can result in large and disparate reductions in P- and S-wave velocities with negligible porosity development, which breaks the classic velocity-porosity relationship. Properly interpreting these signatures in seismic surveys from stimulated geothermal, oil, and gas reservoirs or seismogenic areas requires a rock physics model that uses realistic elastic properties of fractures. Conventional models for cracked rocks employ specific inclusion shapes such as spheroids with small aspect ratios. However, all these exhibit the same normal-to-shear compliance ratio -- regardless of aspect ratio -- and therefore impact the bulk and shear moduli in the same qualitative way. As such they are inadequate for describing many of the complementary evolutions of P- and S-wave velocities that transpire with the generation of cracks. Using a differential model of decoupled compliances, we analyze published velocities for granite, basalt, and limestone to quantify typical compliance ratios and find that it is often different from that assumed in conventional crack models, which then affects crack density estimates. We also investigate how the normal and shear compliances change due to certain thermo-hydro-chemo-mechanical processes that generate large crack densities, and conclude that the final compliance ratios often still deviate from that of conventional models. Finally, we demonstrate how the model can be used to describe scatter in both P- and S-wave velocity-porosity trends. Implications for energy extraction and seismic monitoring are discussed.

We propose two new methods to calibrate the parameters of the epidemic-type aftershock sequence (ETAS) model based on expectation maximization (EM) while accounting for temporal variation of catalog completeness. The first method allows for model calibration on earthquake catalogs with long history, featuring temporal variation of the magnitude of completeness, mc. This extended calibration technique is beneficial for long-term probabilistic seismic hazard assessment (PSHA), which is often based on a mixture of instrumental and historical catalogs. The second method jointly estimates ETAS parameters and high-frequency detection incompleteness to address the potential biases in parameter calibration due to short-term aftershock incompleteness. For this, we generalize the concept of completeness magnitude and consider a rate- and magnitude-dependent detection probability – embracing incompleteness instead of avoiding it. Using synthetic tests, we show that both methods can accurately invert the parameters of simulated catalogs. We then use them to estimate ETAS parameters for California using the earthquake catalog since 1932. To explore how the newly gained information from the second method affects earthquakes’ predictability, we conduct pseudo-prospective forecasting experiments for California. Our proposed model significantly outperforms the base ETAS model, and we find that the ability to include small earthquakes for simulation of future scenarios is the main driver of the improvement. Our results point towards a preference of earthquakes to trigger similarly sized aftershocks, which has potentially major implications for our understanding of earthquake interaction mechanisms and for the future of seismicity forecasting.

A document by Saman Aryana. Click on the document to view its contents.

A document by Lukas Bohsung. Click on the document to view its contents.

The Atlantic meridional overturning circulation (AMOC) in many CMIP6 models has been shown to be overly-sensitive to anthropogenic aerosol forcing, and it has been speculated that this is due to the inclusion of aerosol indirect effects for the first time in many models of that generation. We analyze the AMOC response in a newly-released ensemble of historic simulations performed with CESM2 and forced by the older CMIP5 input datasets (CESM2-CMIP5). This AMOC response is then compared to the CESM1 large ensemble (CESM1-LE, forced by the older CMIP5 inputs) and the CESM2 large ensemble (CESM2-LE, forced by the newer CMIP6 inputs). A key conclusion, only made possible by this experimental setup, is that changes in modeled aerosol-indirect effects cannot explain the differences in turbulent fluxes between CESM1-LE and CESM2-LE. Instead, differences in surface turbulent heat fluxes from changes in model inputs likely drive the different AMOC responses.

Key Points:  The HRRR model surface thermodynamic biases are seasonally dependent, presenting a systematic warm and dry bias during the warm season.  The primary locations of the summer warm and dry biases are over farmland, on days with optically thick clouds.  A hydrological bias underestimating of spring snow melt is consistent with subsequent summer warm and dry biases over farmland.

The solar wind protons are accelerated to supersonic velocities within the distance of 10 solar radii from the Sun, as a consequence of a complex physical mechanism including particle kinetic effects as well as the field-particle energy and momentum exchange. We use a numerical kinetic model of the solar wind, accounting for Coulomb collisions (BiCoP), and model a solar wind accelerated only by the \emph{ambipolar} electrostatic filed ($E$) arising due to the difference in mass between electron and proton, and assuring quasi-neutrality and zero current. We study the effect $E$, which was found to be on the order of Dreicer electric field ($E_D$) \cite{Dreicer1959}, has on the resulting electron velocity distribution functions (VDF). The strahl electron radial evolution is represented by means of its \emph{pitch-angle width} (PAW), and the \emph{strahl parallel temperature} ($T_{s,\parallel}$). A continuous transition between collisional and weakly collisional regime results in broader PAW, compared to the single-exobase prediction imposed by the exospheric models. Collisions were found to scatter strahl electrons below 250 eV, which in turn has an effect on the measured $T_{s,\parallel}$. A slight increase was found in $T_{s,\parallel}$ with radial distance, and was stronger for the more collisional run. We estimate that the coronal electron temperature inferred from the observations of $T_{s,\parallel}$ in the solar wind, would be overestimated for between 8 and 15\%.

In order to study sensitivity of physical parameterization schemes (PPSs) in the WRF model on the simulation of landfall tropical cyclones (TCs), we design 43 sensitivity experiments based on three types of PPSs, and select three disastrous TCs that landed on the east coast of China, namely Lekima (2019), Hagupit (2020) and In-Fa (2021). Qualitative analysis and quantitative evaluation are carried out from the aspects of model simulated TC track and intensity, as well as the landfall position, time and intensity. The 72h-average track errors of all sensitivity experiments are 105 km, 85 km and 38 km, by three TCs respectively. The temporal variations of simulated TC intensity in all sensitivity experiments are highly consistent with the observations, but the simulated TC intensities are inevitably weaker than the observations. The results of three groups of experiments show that the track and intensity of landfall TCs are most sensitive to cloud microphysical parameterization scheme (CMPS), but insensitive to planetary boundary layer parameterization scheme (PBLPS). All the simulated landfall positions are more southward than the observations, and the intensities at landfall moment are underestimated compared with the observations. The TC landfall position is the most sensitive to cumulus convection parameterization scheme (CCPS), followed by PBLPS and CMPS. However, the situation for the TC landfall intensity is the opposite. Finally, some optimal PPSs for simulating TC track, intensity and landfall position are given, so as to provide some references for the simulation of landfall TCs in regional prediction systems.

GOES-16 and GOES-17 are the first of NOAA’s Geostationary Operational Environmental Satellite (GOES)-R series of satellites. Each GOES-R satellite has a magnetometer mounted on the end (outboard) and one part-way down a long boom (inboard). This paper demonstrates the relative accuracy and stability of the measurements on a daily and long-term basis. The GOES-16 and GOES-17 magnetic field observations from 2017 to 2020 have been compared to simultaneous magnetic field observations from each other and from the previous GOES-NOP series satellites (GOES-13, GOES-14 and GOES-15). These comparisons provide assessments of relative accuracy and stability. We use a field model to facilitate the inter-satellite comparisons at different longitudes. GOES-16 inboard and outboard magnetometers data suffer daily variations which cannot be explained by natural phenomena. Long-term averaged GOES-16 outboard (OB) data has daily variations of ± 3 nT which are stable within ± 1.5 nT. Long-term averaged GOES-17OB magnetometer data have minimal daily variations (less than ± 1 nT). Daily average of the difference between the GOES-16 outboard or GOES-17 outboard measurements and the measurements made by another GOES satellite are computed. The long-term averaged results show the GOES-16OB and GOES-17OB measurements have long-term stability (± 2 nT or less) and match measurements from magnetometers on other GOES within limits stated herein. The GOES-17OB operational offset (zero field value) was refined using the GOES-17 satellite rotated 180° about the Earth pointing axis (known as a yaw flip).

Ground-based Global Navigation Satellite System (GNSS) receivers have become an ubiquitous tool for monitoring the ionosphere. Total Electron Content (TEC) data from globally distributed networks of ground-based GNSS receivers are increasingly being used to characterize the ionosphere and its variability. The deployment of these GNSS receivers is currently limited to landmasses. This means that 7/10 of Earth’s surface, which is covered by the oceans, is left unexplored for persistent ionospheric measurements. In this paper, we describe a new low-power dual-frequency Global Positioning System (GPS) receiver, called Remote Ionospheric Observatory (RIO), which is capable of operating from locations in the air, space, and the oceans as well as on land. Two RIO receivers were deployed and operated from the Tropical Atmosphere Ocean buoys in the Pacific Ocean, and the results are described in this paper. This is the first time that GPS receivers have been operated in open waters for an extended period of time. Data collected between September 1, 2018 and December 31, 2019 are shown. The observed TEC exhibits a clear seasonal dependence characterized by equinoctial maxima in the data at both locations. Both RIO receivers, deployed near the geomagnetic equator, show an 18-35% increase in TEC during moderately disturbed geomagnetic periods. Comparisons with the International Reference Ionosphere model show good agreement. The new capability presented in this paper addresses a critical gap in our ability to monitor the ionosphere from the seventy percent of the Earth’s surface that is covered by water.

Optical aurora can be classified into two broad categories, i.e., diffuse and discrete auroras. Recent studies based on optical observations obtained on the dayside reveal some important processes occurred in the dayside magnetosphere and are reviewed in this paper. Dayside diffuse auroras (DDAs) are classified into unstructured and structured DDAs. Unstructured DDAs predominantly occur in the morning but structured ones are mainly observed near magnetic local noon (MLN). Because structured diffuse auroras have been suggested to be associated with cold plasma structures in the magnetosphere, distribution and generation of cold plasma structures in the dayside outer magnetosphere are discussed based on the detailed observational properties of DDAs. A particular discrete auroral form, i.e., throat aurora, is defined during study on DDA. Detailed observational properties of throat aurora are presented, which suggest that throat auroras are ground signatures for localized magnetopause indentations that are most likely caused by localized high-speed jets impacting on the magnetopause. Studies on throat aurora reveal that the transient structures locally generated in the magnetosheath can frequently cause indentations on the subsolar magnetopause, trigger reconnection, result in a serial of responses in geospace, and thus will play important role on solar wind-magnetosphere coupling.

Abu Zarab locality is a part from Um Bogma area in southwestern Sinai, Egypt, where paleokarsts are widespread, especially in carbonate rocks. Abu Zarab area is covered by Carboniferous carbonate rocks containing several paleokarsts. One of these paleokarsts was selected to geochemical investigation. The paleokarst was dissected by three excavated trenches constructed by Nuclear Materials Authority team to reveal its geologic features. The paleokarst is filled with lateritic components represented mainly, by gibbsite, ferruginous siltstone and clay minerals. Twelve samples were collected from the walls of these trenches and chemically analyzed for this purpose in term of major oxides, traces and rare earth elements. The geochemical data of the major oxides display three important geochemical processes in the lateritic components of the paleokarst: (1) Enrichment of aluminum, iron and manganese; (2) depletion of calcium and magnesium (3) silicon experienced both depletion and enrichment. The geochemical data of trace and rare earth elements (REE) display enrichment of U, Cu, Pb, Zn, Ag, As and Cd with obvious enrichment of REE and conversely some elements were depleted such as V, Cr and Ga. It also, noticed that uranium has strong positive correlation with both iron and Aluminum. This paper attempts to establish the relation between uranium and other elements in the paleokarst conditions. It is more likely, according to geochemical features of radioactive elements, that the uranium enrichment process was postdating laterite formation and the iron played an important role in capturing and trapping uranium.

Data assimilation (DA) aims at forecasting the state of a dynamical system by combining a mathematical representation of the system with noisy observations taking into account their uncertainties. State of the art methods are based on the Gaussian error statistics and the linearization of the non-linear dynamics which may lead to sub-optimal methods. In this respect, there are still open questions how to improve these methods. In this paper, we propose a \textit{fully data driven deep learning architecture} generalizing recurrent Elman networks and data assimilation algorithms which approximate a sequence of prior and posterior densities conditioned on noisy observations. By construction our approach can be used for general nonlinear dynamics and non-Gaussian densities. On numerical experiments based on the well-known Lorenz-95 system and with Gaussian error statistics, our architecture achieves comparable performance to EnKF on both the analysis and the propagation of probability density functions of the system state at a given time without using any explicit regularization technique.

Plasma structures with enhanced dynamic pressure, density or speed are often observed in Earth’s magnetosheath. We present a statistical study of these structures, known as jets and fast plasmoids, in the magnetosheath, downstream of both the quasi-perpendicular and quasi-parallel bow shocks. Using measurements from the four Magnetospheric Multiscale (MMS) spacecraft and OMNI solar wind data from 2015–2017, we present observations of jets during different upstream conditions and in the wide range distances from the bow shock. Jets observed downstream of the quasi-parallel bow shock are seen to propagate deeper and faster into the magnetosheath and on towards the magnetopause. We estimate the shape of the structures by treating the leading edge as a shock surface, and the result is that the jets are elongated in the direction of propagation but also that they expand more quickly in the perpendicular direction as they propagate through the magnetosheath.

Although the core velocity of the Atlantic North Equatorial Undercurrent (NEUC) is low (0.1-0.3ms) it has been suggested to act as an important oxygen supply route towards the oxygen minimum zone in the eastern tropical North Atlantic. For the first time the intraseasonal to interannual NEUC variability and its impact on oxygen is investigated based on shipboard and moored velocity observations around 5°N, 23°W. In contrast to previous studies that were mainly based on models or hydrographic data, we find hardly any seasonal cycle of NEUC transports in the central Atlantic. The NEUC transport variability is instead dominated by sporadic intraseasonal events. Only some of these events are associated with high oxygen levels suggesting an occasional eastward oxygen supply by NEUC transport events. Nevertheless, they likely contribute to the local oxygen maximum in the mean shipboard section along 23°W at the NEUC core position.

At the equatorial latitude of a West African station (8.50N, 4.68E), we have examined the slab-thickness (τ) relative to peak electron density height (hmF2) at F2 layer, employing Digisonde Portable Sounder τ (DPS-τ) and Global Positioning System τ (GPS-τ) during the low solar activity year 2010. Our observation revealed maximum and minimum τ during the daytime and nighttime respectively, which may indicate maximum and minimum scale height in τ through daytime and nighttime, respectively. The discrepancies between the together reversed signatures of DPS-τ and GPS-τ around 0100 - 0600 LT in June could indicate the failure to incorporate a reflection of the composition changes in the topside-DPS model. We have reported the pre-sunrise and post-noon peaks in GPS-τ and hmF2, which are contributions of plasmaspheric TEC and pre-reversal enhancement (PRE) velocity, respectively. Around 1100 - 1700 LT, the stability in hmF2 show that the interaction of neutral wind and eastward electric field could be employed to predict the τ. We also reported that the pre-sunrise increase in GPS-τ is not an indication of PRE velocity as observed during the nighttime. The relationship between τ and hmF2 gives a high correlation coefficient (CC), but CC during the daytime is higher than the nighttime values which suggest the constant diffusion state of plasmasphere during the daytime whereas the nighttime is a function of the plasmaspheric flow of electron content and PRE velocity. We compared the experimental hmF2 with IRI-2016 and found that the IRI-2016 model is incapable of capturing the post-sunset and pre-sunrise increases.

The local redistribution of granular material by sublimation of the southern seasonal CO2 ice deposit is one of the most active surface shaping processes on Mars today. This unique geomorphic mechanism has been linked to the dendritic, branching, ‘spider’-like araneiform terrain and associated fans and spots - features which are native to Mars and have no Earth analogues. However, there is a paucity of empirical data to test the validity of this genetic hypothesis. Additionally, it is unclear whether the organised radial patterns of araneiforms require a singular or multiple seasonal events to form. Here we present the results of a suite of laboratory experiments undertaken to investigate if the interaction between a sublimating CO2 ice overburden with central vents and a porous, mobile regolith will mobilise grains from beneath the ice in the form of a plume to generate araneiform patterns. We investigate the physical constraints on the level of branching of these features and the area that they cover. We provide the first observations of plume activity via CO2 sublimation and consequent erosion of araneiform features. Based on calculations of the mass flux sublimation rate of CO2 ice blocks buried under sediment and consequent volume transport, we show that CO2 sublimation can be a highly efficient agent of sediment transport under Martian pressure.

The space-born geodetic temporal Mean Dynamic Topography (MDT) is obtained from the difference of altimetric Mean Sea Surface (MSS) $h$ and the geoid height $N$. With the geostrophic surface currents obtained from its gradient the MDT is an essential parameter when discribing the ocean dynamics. Spectral consistency of $h$ and $N$ is crucial to minimize MDT errors. Usually, $h$ is globalized to allows for a Spherical Harmonic (SH) analysis and small scales beyond maximum degree and order (d/o) resolved in the geoid are cut-off. However, the usual globalization causes ocean-land steps in $h-N$ and spectral inconsistencies of $N$ and $h$ over land. To overcome both issues a new methodology is proposed based on globalization of the MDT. A Laplacian smoother with the coastal MDT values as boundary condition is applied resulting in a flat surface over land and a continuous ocean-land transition. The new methodology strongly reduces Gibbs effects and the need to work with high resolution MDTs to minimize them. Reduction of resolution is tested to reduce MDT uncertainties caused by the commission error expected to increase whith decreasing scale. Applying drifter data and a high resolution hydrodynamic ocean model it is shown, that for the Gulf Stream and the Kuroshio geodetic MDTs applying recent combined geoid models contain physical information up to at least d/o 420 (48km spatial scale). Since for oceanic regions with strong gradients in $N$ still inconsistencies between the geoid and the MSS exist, it depends on application/region if a higher resolution MDT is needed.