A document by Eshrat Fatima. Click on the document to view its contents.

A document by Avelon Gerritsma. Click on the document to view its contents.

We characterize $117$ seismic events occurred in Chile and registered at the Wetzell Geodetic Observatory (BWLRAS) in Germany in terms of rotational seismic parameters. Using the Minimum Curvature Interpolation method, we create a $2$D map with the Vertical Rotation Rate (VRR) divided in three zones from the Chilean Coast: Northern, Central, and Southern area. In order to describe the behavior of VRR along time, we create a timeline and seismic moment model showing events in these areas with different values of VRR. The analyzed data includes four large earthquakes occurred in different zones with magnitudes greater than $M_w$7.5. We focus our analysis in the values of the rotational velocity for these earthquakes and show that the VRR does not have a clear relation with the seismic moment magnitude. Our results open a new way to describe and study seismic events. It can be useful to generate a deeper understanding of the dynamics in the underlying processes involved in the earthquake occurrence. As well, our results could serve to improve safety regulations in construction and mining, since important rotational movements may be present even within low moment magnitude events.

Dotson Ice Shelf has resisted acceleration and ice-front retreat despite high basal-melt rates and rapid disaggregation of the neighboring Crosson Ice Shelf. Because of this lack of acceleration, previous studies have assumed that Dotson is durable. Here we show clear evidence of Dotson's vulnerability as it decelerates, contrary to the common assumption that ice-flow deceleration is synonymous with increased ice-shelf buttressing. Ungrounding of a series of pinning points initiated acceleration in the Upper Dotson in the early 2000s, which subsequently plugged ice flow in the Lower Dotson. Discharge from the tributary Kohler Glacier into Crosson increased, but non-proportionally. Given current surface-lowering rates, we estimate that several remaining pinning points in the Upper Dotson could unground within one to three decades.

To reveal the spatial distribution of major active faults and structural discontinuities in the Himalayan-Tibetan orogen, this paper presents wavelet multiscale analysis of the Bouguer gravity field and solves the total horizontal derivatives of each wavelet detail. The results show that, in general, the crustal discontinuities on the Pamir Plateau and in the Himalayan tectonic zone are significant. On the northern margin of Tibet, active faults are mostly visible only in the deep crust. In eastern Tibet, crustal discontinuities decrease as depth increases. The Himalayan crust is undergoing E-W extension, and material discontinuities are significant along N-S-trending normal faults. The Sangri-Nacuo fault is the tectonic boundary between the Himalayan tectonic zone and the eastern Himalayan syntaxis and cuts off the entire lithosphere of Tibet. The spatial structural distributions of the western and eastern Himalayan syntaxes are very different. The former is relatively intact and extends deeper in the lithosphere, while the latter is more complex and shallower than the Mohorovicic discontinuity, and its overlying crust has deformed intensely from the collision between the Indian and Eurasian plates. Further, the structural distribution in the upper mantle reveals that the wedging Indian plate in the western Himalayan syntaxis almost reaches the SW margin of the Tarim basin and forms a closed structure in western Tibet, which could help to explain the eastward extrusion of the Tibetan Plateau.

The local scale of rotating convection, ℓ, is a fundamental parameter in many turbulent geophysical and astrophysical fluid systems, yet it is often poorly constrained. Here we conduct rotating convection laboratory experiments analogous to convecting flows in planetary cores and subsurface oceans to obtain measurements of the local scales of motion. Utilizing silicone oil as the working fluid, we employ shadowgraph imagery to visualize the flow, from which we extract values of the characteristic cross-axial scale of convective columns and plumes. These measurements are compared to the theoretical values of the critical onset length scale, ℓ_crit, and the turbulent length scale, ℓ_turb. Our experimentally-obtained length scale measurements simultaneously agree with both the onset and turbulent scale predictions across three orders of magnitude in convective supercriticality ($10^2\lesssim \widetilde{Ra}\lesssim10^5$), a correlation that is consistent with inferences made in prior studies. We further explore the nature of this correlation and its implications for geophysical and astrophysical systems.Abstract content goes here

Periglacial environments are characterized by highly dynamic landscapes. Freezing and thawing lead to ground movement, associated with cryoturbation and solifluction. These processes are sensitive to climate change and variably distributed depending on multiple environmental factors. In this study, we used multi-geometry Sentinel-1 Synthetic Aperture Radar Interferometry (InSAR) to investigate the spatial distribution of the mean annual ground velocity in a mountainous landscape in Northern Norway. Statistical modelling was employed to examine how periglacial ground velocity is related to environmental variables characterizing the diverse climatic, geomorphic, hydrological and ecological conditions within a 148 km2 study area. Two-dimensional (2D) InSAR results document mean annual ground velocity up to 15 mm/yr. Vertical and horizontal velocity components in the East–West plane show variable spatial distribution, which can be explained by the characteristics of cryoturbation and solifluction operating differently over flat and sloping terrain. Statistical modelling shows that slope angle and mean annual air temperature variables are the most important environmental factors explaining the distribution of the horizontal and vertical components, respectively. Vegetation and snow cover also have a local influence, interpreted as indicators of the ground material and moisture conditions. The results show contrasted model performance depending on the velocity component used as a response variable. In general, our study highlights the potential of integrating radar remote sensing and statistical modelling to investigate mountainous regions and better understand the relations between environmental factors, periglacial processes and ground dynamics.

Dried sea salt aerosol is commonly represented in aerosol-optics models by ideal cubical particles, while samples reveal that marine aerosol particles frequently display distorted cubical shapes, and they can have more or less rounded edges. In this study three types of non-ideal cuboidal model geometries are investigated, namely, convex polyhedra, Gaussian random cubes, and superellipsoids. Optical calculations were performed at a wavelength of 532 nm using the discrete dipole approximation and the T-matrix method. The main focus is on optical properties relevant to lidar remote sensing, namely, the linear depolarization ratio in the backscattering direction, and the extinction-to-backscatter or lidar ratio. Gaussian random distortions tend to increase the depolarization ratio in relation to that of perfect cubes, while superellipsoids mimicking cubes with rounded edges generally decrease the depolarization ratio. Convex polyhedra can describe randomly distorted cubes. Their computed depolarisation ratios display random fluctuations about those computed for ideal cubes. The results suggest that Gaussian random cubes and superellipsoids are most consistent with the observations if the geometries deviate only mildly from that of an ideal cube. Gaussian random cubes that strongly diverge from cubical shape pose a risk of overestimating both depolarization and extinction-to-backscatter ratio. Superellipsoids that approach octahedral shape yield unrealistically high depolarization ratios. Investigation of size-averaged optical properties of superellipsoids demonstrate that the presence of absorbing material in marine aerosols can have a dramatic effect on the lidar ratio, and its effect on the depolarization ratio can be of comparable magnitude as that caused by rounding of edges.

A 3D S-velocity model for the crust and upper-mantle beneath the South China Sea and Indonesia is presented in this paper, determined by means of Rayleigh-wave analysis, in the depth range from zero to 400 km. From this model, the most conspicuous features of the crust and upper mantle structure will be revealed for this study area, which are not so visible in other previous studies because of their low resolution. Also, this model will allow the confirmation of the principal structural features revealed in other previous studies. The results determined in the present study will allow to solve an open question largely time debated: if the northern continental margin of the South China Sea is volcanic or nonvolcanic. The final conclusion is that this continental margin is nonvolcanic.

In the ring current dynamics, various loss mechanisms contribute to the ring current decay, including the loss to the upper atmosphere through particle precipitation. This study implements the field-line curvature (FLC) scattering mechanism in a kinetic ring current model and investigates its role in precipitating ions into the ionosphere. The newly included process is solved via a diffusion equation in the model with associated pitch-angle dependent diffusion coefficients. The simulation results indicate that (1) the FLC scattering process exert mostly on energetic ions above 30 keV on the nightside where the magnetospheric configuration is more stretching. Such ion loss thereafter leads to a faster recovery of the ring current. (2) The FLC-associated ion precipitation mainly occurs in the outer region (L>5 for protons and L>4.5 for oxygen ions) on the nightside, and the oxygen ion precipitation takes places in a wider region than protons although its intensity is much lower. Comparisons with POES observations suggest that more precipitation is needed in the inner region, implying that other loss process is required in the model. (3) We further found that the precipitating energy flux of protons due to the FLC scattering can sometimes become comparable to the one from the electrons on the nightside, although electrons usually dominate the ionospheric energy deposit from the midnight eastward towards the dayside. (4) Finally, the FLC scattering process seems to be capable of explaining the formation of the isotropic boundary in the ionosphere.

Key questions remain about the atmospheric response to variability in the oceanic western boundary currents (WBCs). Here we exploit a unique high-resolution slab-ocean coupled climate model to investigate how ocean heat transport (OHT) anomalies in the major WBCs of both hemispheres affect the atmospheric circulation. In both hemispheres, prescribed OHT anomalies lead to robust changes in convective precipitation anomalies equatorward of the maximum surface warming. The response is deepest and most pronounced over the Northern Hemisphere (NH) WBCs, where it is associated with significant changes in upper tropospheric vertical motion, condensational heating and geopotential heights. The response is relatively shallow over the Southern Hemisphere (SH) WBCs. The findings reveal the robustness of the atmospheric response to OHT anomalies and highlight key hemispheric differences: in the NH, realistic OHT anomalies are balanced by deep atmospheric vertical motion; in the SH, they are balanced primarily by shallow horizontal temperature advection.

This study investigates the influence of the phase of quasi-biennial oscillation (QBO) and the 11-year solar cycle on the Arctic spring ozone, using satellite observations, reanalysis data, and outputs of a chemistry climate model (CCM) during the period of 1979–2011. For this duration, we found that the composite mean of the Northern Hemisphere high-latitude total ozone in the QBO-westerly (QBO-W)/solar minimum (S) phase indicates a large negative anomaly for the climatology in February–March. An analysis of the passive ozone tracer defined at the pressure levels between 220 hPa and 12 hPa in the CCM simulation indicates that this negative anomaly is primarily caused by transport. The negative anomaly is consistent with a weakening of the residual mean downward motion in the polar lower stratosphere. The contribution of chemical processes estimated using the total ozone difference between the chemically active ozone runs and the passive tracer simulations is less than 6% of the total anomaly in February and between 10–20% in March. The lower ozone levels in the Arctic spring during the QBO-W/Syears are associated with a stronger Arctic polar vortex from late winter to early spring, which is linked to the reduced occurrence of sudden stratospheric warming in the winter during the QBO-W/Syears.

A document by Pratik Shukla. Click on the document to view its contents.

Realistic representation of detailed rainfall characteristics on local scale by current state-of-the-art climate models remains a key challenge, especially on sub-daily timescales. In this research, the convection-permitting Weather Research and Forecasting (WRF) model configured with 1.5 km grid spacing is used to simulate precipitation on sub-daily timescales over the Yangtze River Delta Region of China for continuous 10 years (2005–2014). The simulations are compared to rain gauge observations, reanalysis data, and the simulations of a lower resolution WRF with 9 km grid spacing that has a parameterization of convection. The results show that precipitation over the region can be well captured by using the convection-permitting model (CPM). Furthermore, the intensity, duration and coverage of these precipitation events can be more accurately described by the CPM. On the convection timescales of 1–4 hours, especially for heavy rainfall events, the CPM is more accurate than the convection-parameterized model in capturing the short-duration events, which may be related to its better account of physical processes related with the convection on the convection-permitting scale. In addition, the extreme events which are more localized and with short-duration can be represented better by the CPM while the convection-parameterized model tends to produce widespread precipitation events covering more grid cells than observed. Biases of the simulation by the 9-km mesh convection-parameterized mode appear to be related to the deficiencies in the representation of convections.

Incoherent scatter radars (ISR) estimate the electron and ion temperatures in the ionosphere by fitting measured spectra of ion-acoustic waves to forward models. For radars looking at aspect angles within 5° of perpendicular to the Earth’s magnetic field, the magnetic field constrains electron movement and Coulomb collisions add an additional source of damping that narrows the spectra. Fitting the collisionally narrowed spectra to collisionless forward models leads to errors or underestimates of the plasma temperatures. This paper presents the first fully kinetic particle-in-cell simulations of ISR spectra with collisional damping by velocity dependent electron-electron and electron-ion collisions. For aspect angles between 0.5° and 2° off perpendicular, the damping effects of electron-ion and electron-electron collisions are the same and the resulting spectra are narrower than what current theories predict. For aspect angles larger than 3° away from perpendicular, the simulations with electron-ion collisions match collisionless ISR theory well, but spectra with electron-electron collisions are narrower than theory predicts at aspect angles as large as 5° away from perpendicular. At all aspect angles the particle-in-cell simulations produce narrower spectra than previous simulations using single particle displacement statistics. The narrowing of spectra by electron-electron collisions between 3° and 5° away from perpendicular is currently neglected when fitting measured spectra from the Jicamarca and Millstone Hill radars, leading to underestimates of electron temperatures by as much as 50% at these radars.

During the Asian Summer Monsoon Chemical and Climate Impact Project (ACCLIP), National Aeronautics and Space Administration (NASA) WB-57 high altitude research aircraft observed strong turbulence at an altitude of 15 to 18 km near the outflow of the Super Typhoon Hinnamnor in the Northwest Pacific. Our analyses based on the trial version of the “RRJ-ClimCORE” mesoscale reanalysis have revealed that a thin layer of strong vertical wind shear (VWS) extending just below the tropopause along the upper surface of the outflow from the typhoon eyewall provides favorable conditions for shear instability. Further analyses of the mesoscale background conditions based on RRJ-ClimCORE as well as the geostationary satellite Himawari-8 cloud imagery suggest that the convolution of such small-scale processes as convectively generated concentric gravity waves and shallow convection appearing as radially-banded cirrus clouds may have further increased the potential for turbulence generation. Absolute vorticity analysis suggests the occurrence of inertial instability to the north of the typhoon, which explains the development of radially-banded cirrus clouds as well as the layer of strong VWS around the flight altitudes. The present study thus demonstrates the advantages of the hourly output of RRJ-ClimCORE over 3-hourly output operational mesoscale analysis for investigating source mechanisms of turbulence in the upper-troposphere and lower-stratosphere.

Understanding the spatiotemporal characteristics of terrestrial water storage (TWS) variation is crucial for evaluating climate change and promoting sustainable water resource management. Numerical hydrological models and satellite data, particularly information obtained from gravity variations through the Gravity Recovery and Climate Experiment (GRACE) mission, are widely utilized for the analysis of TWS fluctuations. Even though GRACE holds excellent promise for large-scale exploration, these measurements are too coarse for localized quantification. Therefore, enhancing the resolution of GRACE measurements holds significant potential for application at the local to regional scale. The objective of this study is to produce higher-resolution images capable of depicting the local-scale TWS anomalies (TWSA) in the South America continent using a modified version of the Generative Adversarial Network (GAN). Our results demonstrate that the conditional WGAN-GP model can effectively replicate the structures of the TWSA signals with a reasonably close resemblance. This indicates that the model can successfully execute the downscaling task and harness high-resolution spatiotemporal structures within the low-resolution satellite observation for unseen temporal data.

Jupiter’s giant magnetosphere is a complex system seldom in a configuration approximating steady state, and a clear picture of its governing dynamics remains elusive. Crucial to understanding how the magnetosphere behaves on a large scale are disturbances to the system on length-scales comparable to the cavity, which are communicated by magnetohydrodynamic waves in the ultra-low-frequency band (≤ 1 mHz). In this study we used magnetometer data from multiple spacecraft to perform the first global heritage survey of these waves in the magnetosphere. To map the equatorial region, we relied on the large local-time coverage provided by the Galileo spacecraft. Flyby encounters performed by Voyager 1 and 2, Pioneer 10 and 11, and Ulysses provided local-time coverage of the dawn sector. We found several hundred events where significant wave power was present, with periods spanning ~5-60 min. The majority of events consisted of multiple superposed discrete periods. Periods at ~15, ~30 and ~40 min dominated the event-averaged spectrum, consistent with the spectra of quasi-periodic pulsations often reported in the literature. Most events were clustered in the outer magnetosphere close to the magnetopause at noon and dusk, suggesting that an external driving mechanism may dominate. The most energetic events occurred close to the planet, though more sporadically, indicating an accumulation of wave energy in the inner magnetosphere or infrequent impulsive drivers in the region. Our findings suggest that dynamics of the system at large scales is modulated by this diverse population of waves, which permeate the magnetosphere through several cavities and waveguides.