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Abstract

We developed an enhanced Kalman-based approach to quantify abrupt changes and significant non-linearity in vertical land motion (VLM) along the coast of Chile and the Antarctic Peninsula using a combination of multi-mission satellite altimetry (ALT), tide gauge (TG), and GPS data starting from the early 1990s. The data reveal the spatial variability of co-seismic and post-seismic subsidence at TGs along the Chilean subduction zone in response to the Mw8.8 Maule 2010, Mw8.1 Iquique 2014, and Mw8.3 Illapel 2015 earthquakes that are not retrievable from the interpolation of sparse GPS observations across space and time. In the Antarctic Peninsula, where continuous GPS data do not commence until ∼1998, the approach provides new insight into the ∼2002 change in VLM at the TGs of +5.3 ± 2.2 mm/yr (Palmer) and +3.5 ± 2.8 mm/yr (Vernadsky) due to the onset of ice-mass loss following the Larsen-B Ice Shelf breakup. We used these data to constrain viscoelastic Earth model parameters for the northern Antarctic Peninsula, obtaining a preferred lithosphere thickness of 115 km and upper mantle viscosity of 0.9 × 1018 Pa s. Our estimates of regionally-correlated ALT systematic errors are small, typically between ∼±0.5–2.5 mm/yr over single-mission time scales. These are consistent with competing orbit differences and the relative errors apparent in ALT crossovers. This study demonstrates that, with careful tuning, the ALT-TG technique can provide improved temporal and spatial sampling of VLM, yielding new constraints on geodynamic models and assisting sea-level change studies in otherwise data sparse regions and periods.

Quantum data assimilation: a new approach to solving data assimilation on quantum annealers
Shunji Kotsuki, Fumitoshi Kawasaki, and Masanao Ohashi
Nonlin. Processes Geophys., 31, 237–245, https://doi.org/10.5194/npg-31-237-2024, 2024
In Earth science, data assimilation plays an important role in integrating real-world observations with numerical simulations for improving subsequent predictions. To overcome the time-consuming computations of conventional data assimilation methods, this paper proposes using quantum annealing machines. Using the D-Wave quantum annealer, the proposed method found solutions with comparable accuracy to conventional approaches and significantly reduced computational time.

Abstract

In this paper, we study the ionization-recombination processes in the lower ionosphere during solar flares of various classes in June 2014 and September 2017. For the first time, ionization and recombination rates of the ionospheric D-region were estimated using the experimental data on variations in the amplitude and phase characteristics of very low frequencies (VLF) signals and two-channel data from the GOES satellite (0.05–0.4 nm and 0.1–0.8 nm). The empirical two-parameter Wait-Ferguson model was used to calculate temporal changes in the electron concentration Ne during solar flares of different classes. GOES satellite data and black body model were used to estimate the X-ray fluxes in the wavelength spectral range λ ≤ 0.3 nm. Joint analysis of the temporal evolution of the Ne vertical profile in the lower ionosphere and X-ray fluxes in different wavelength ranges was carried out. As a result, the values of the ionization and recombination rate coefficients were obtained, and the spectral ranges of radiation that have the greatest impact on Ne at given heights were determined. Calculated ionization and recombination rate coefficients and ranges were successfully verified using VLF data during different solar flares. The results obtained in this work can be used in future studies for a more accurate assessment of the response of lower ionosphere to solar flares of various classes.

Abstract

In this study, the Extreme Hourly Precipitation Areas (EHPAs) of three extreme levels (i.e., between the 95th and 99th percentiles, between the 99th and 99.9th percentiles, beyond the 99.9th percentile) in the Pearl River Delta over South China are identified; then the related events and associated Convective Cores (CCs) are tracked, and their macro-and-microphysical characteristics are analyzed using multi-year dual-polarization radar observations. Results show that >90% of EHPAs are smaller than 10 km2, and 65%–75% of EHPA events last only one hour. They tend to be more localized and persist longer with increasing hourly-precipitation extremity. The EHPAs overlap with the CCs during 50%–64% of the EHPAs' life span. Their occurrence frequencies are nearly quadrupled after the monsoon onset over South China Sea (SCS), with a major (secondary) peak at about 1400 LST (0600 LST) in the diurnal variations. The CCs are non-linear shaped with about 65% being meso-γ-scale and embedded within mostly meso-β or α-scale 20 dBZ regions. The CCs generally contain active warm-rain processes and about 70% possess moderate-to-intense mixed-phase microphysical processes. The ratios of ice water path to liquid water path are about 0.37, and coalescence dominates (about 68%) the liquid-phase processes. The average size of raindrop is slightly larger than the “maritime-like” regime and the average concentration is much higher than the “continental-like” regime. These CCs' characteristics roughly resemble those of the convection producing extreme instantaneous precipitation, except for a larger horizontal scale and less evident variations with the increasing hourly-precipitation extremity.

Abstract

The question of stratospheric aerosol type following the Raikoke eruption is revisited. Raman lidar measurements suggest the aerosols are predominately smoke, while Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) results indicate the aerosols are predominately sulfate aerosols. The suggested mechanism of smoke particles self-lofting into the stratosphere is inconsistent with observations in 2020, when more severe Siberian fires failed to invoke a response even vaguely similar to 2019. A side-by side comparison of the Sarychev and Raikoke eruptions invalidates model calculations that suggest sulfate aerosols should be at levels too low to explain the observed aerosol loading. Structure in infrared absorption spectra provides conclusive evidence of composition, a unique fingerprint for identifying aerosol type. Such information cannot be misinterpreted so long as there is sufficient resolution and spectral coverage. ACE-FTS infrared aerosol spectra often have an order of magnitude stronger absorption than that of background sulfate aerosols. These spectra can be accurately reproduced by laboratory measured sulfate aerosol spectroscopic information, providing unambiguous identification of the aerosols as sulfate. Visual inspection of thousands of infrared aerosol spectra from the period following the Raikoke eruption indicates the aerosols in the lower stratosphere are predominately sulfate, with no indication of smoke. The lidar study's identification of the aerosols as smoke was based primarily on observed lidar ratios that were more consistent with a material that absorbed significantly at the lidar wavelengths, inconsistent with expectations for sulfate aerosols. However, this could indicate the presence of a substance dissolved in the sulfate aerosols absorbing at those wavelengths rather than smoke particles.

Abstract

Based on satellite observations in the Arctic stratosphere at latitudes from 61° to 66°N in the second half of 2019, Boone et al. (2022, https://doi.org/10.1029/2022jd036600) provide the impression that the aerosol in the upper troposphere and lower stratosphere (UTLS) over the entire Arctic consisted of sulfate aerosol originating from the Raikoke volcanic eruption in the summer of 2019. Here, we show that this was most probably not the case and the aerosol layering conditions were much more complex. By combining the stratospheric aerosol typing results of Boone et al. (2022, https://doi.org/10.1029/2022jd036600) with lidar observations at 85°–86°N of Ohneiser et al. (2021, https://doi.org/10.5194/acp-21-15783-2021) of a dominating wildfire smoke layer in the UTLS height range, we demonstrate that the Arctic UTLS aerosol most likely consisted of Siberian wildfire smoke in the lower part and sulfate aerosol in the upper part of the aerosol layer which extended from 7 to 19 km height and was well observable until May 2020. The smoke- and sulfate-related aerosol optical thickness (AOT) fractions were about 0.7–0.8 and 0.2–0.3, respectively, according to our analysis. The sulfate AOT is in good agreement with model-based predictions of the Raikoke sulfate AOT.

Abstract

The South Atlantic Ocean hosts several well-studied volcanic ridges and seamount chains, but the origin of their associated mantle plumes is debated. Reduced seismicity on the southern Mid-Atlantic Ridge (MAR) suggests anomalously ductile thermomechanical conditions at 52°S and 47.5°S. These low seismicity patches extend 120–560 km along-axis, and correspond with axial high spreading ridge morphology, geochemical anomalies, and mantle wave speed patterns likely associated with the Shona and Discovery plumes. Bathymetric data show that the northern extent of the Shona swell is associated with increased volcanism, elevated axial bathymetry, and a series of northward-propagating rifts, with the overall swell geometry suggesting a buoyancy flux of 0.4–0.5 Mg s−1. The nearby Bouvet Island may be a product of a branch of the larger Shona plume swell, which has influenced crustal accretion on the southern MAR for the past 24 million years.

Science, Volume 384, Issue 6700, June 2024.

Science, Volume 384, Issue 6700, June 2024.

Science, Volume 384, Issue 6700, June 2024.

Science, Volume 384, Issue 6700, June 2024.

Science, Volume 384, Issue 6700, June 2024.

Abstract

Relativistic electron fluxes in the outer radiation belt exhibit significant variability during geomagnetic storms and substorms. This study investigates rapid relativistic electron enhancements (REE) in the outer radiation belt throughout the entire Van Allen Probes (RBSP) era from October 2012 to October 2019. Utilizing RBSP measurements, we identify 182 rapid REE events characterized by a factor of greater than two increase in relativistic electron fluxes within a half RBSP orbit (approximately 4.5 hr) at L = 4.5–5.5. Approximately 76% of rapid REE events occur during geomagnetic storms. Rapid REEs during storms are concentrated within the 12-hr period preceding and the 24-hr period following the end of the storm's main phase. Intense REE are more likely found in storm's main phase compared to moderate REE. Sub-relativistic and relativistic electron injections are commonly observed during rapid REE. Substorm activities (AL/AE, MPB index) and convection (AU index) are more intense before and during REE, in contrast to the intervals following REEs. The intensity of rapid REE correlates with the strength of substorms and convection. This comprehensive survey suggests that rapid REEs in the outer radiation belt are likely associated with, but not strictly tied to, geomagnetic storms. Enhanced convection and substorm appear to create favorable conditions for rapid REE. These substorms and enhanced convection are likely linked to favorable solar wind conditions for REEs, as documented in previous studies.

Abstract

The generation of medium-scale traveling ionospheric disturbances (MSTIDs) in the mid-latitude F region ionosphere, particularly in the presence of sporadic E (Es) layers or geomagnetically conjugate features, has been the focus of extensive investigation using both observational and numerical modeling approaches. Recent observations have revealed the occurrence of nighttime MSTIDs over the continental US during storm conditions even without invoking the Es instability. While this phenomenon is considered to be electrified and likely associated with the Perkins instability, the influences of storm-enhanced density (SED), electric fields, and winds on the excitation of nighttime MSTIDs remain a complicated issue and require further quantitative analysis. In this study, we develop a two-dimensional numerical model of the nighttime ionospheric electrodynamics at midlatitudes using the ionospheric ion continuity equation and the electric field Poisson equation to investigate the characteristics of MSTIDs in the SED base region during storm conditions. We demonstrate that the magnetic inclination effect can explain the lower latitude preference of the MSTIDs during magnetic storms, while the development of MSTIDs is primarily influenced by intense storm electric fields under the background ionospheric condition of large density gradients associated with SED. However, the impact of neutral winds on the MSTIDs growth varies, depending on their specific direction determined by the strongly dynamic spatiotemporal variation of the thermosphere and ionosphere during storms. Therefore, the MSTIDs stormtime scenario results from a combination of multiple important factors.

Abstract

The ionospheres of Jupiter's icy moons have been observed by in situ plasma measurements and radio science. However, their spatial structures have not yet been fully characterized. To address this, we developed a new ray tracing method for modeling the radio occultation of the ionospheres using Jovian auroral radio sources. Applying our method to Jovian auroral radio observations with the Galileo spacecraft, we derived the electron density of the ionosphere of Ganymede and Callisto. For Ganymede's ionosphere, we found that the maximum electron density on the surface was 76.5–288.5 cm−3 in the open magnetic field line regions and 5.0–20.5 cm−3 in the closed magnetic field line region during the Galileo Ganymede 01 flyby. The difference in the electron density distribution was correlated with the accessibility of Jovian magnetospheric plasma to the atmosphere and surface of the moons. These results indicated that electron-impact ionization of the Ganymede exosphere and sputtering of the surface water ice were effective for the producing Ganymede's ionosphere. For Callisto's ionosphere, we found that the densities were approximately 350 and 12.5 cm−3 on the night side hemisphere during Callisto 09 and 30 flybys, respectively. These results combined with previous observations indicated that atmospheric production through sublimation controlled the ionospheric density of Callisto. This method is also applicable to upcoming Jovian radio observation data from the Jupiter Icy Moon Explorer, JUICE.

Abstract

To ensure the robustness of both civilian and military infrastructure, it is important to protect electric power grids, smart grids, and other electrotechnologies from known and possibly as-of-yet unknown space weather hazards. Space weather can generate intense geoelectric fields at the surface of the Earth, as well as large voltage gradients across long distances of the Earth. These voltage gradients can lead to geomagnetically induced currents (GICs), which are known to produce hazards to electric power grids. The finite-difference time-domain (FDTD) method is a powerful and versatile method that has already been applied to the study of geoelectric fields. The advantages of FDTD over other methods are that it can account for more geometrical complexities and realistic time waveforms and that it directly solves for geoelectric fields. Snell's Law predicts that any electromagnetic waves incident on the ground should essentially propagate straight downwards into the low resistivity ground. For this reason, vertical FDTD grid resolutions of 1/3 of a skin depth were usually chosen, while the horizontal grid resolution was relaxed. We find, however, that there is another important consideration for choosing an FDTD grid resolution applied to real-world scenarios: localized field variations due to currents generated by ground features. It turns out the grid resolution requirements are much stricter when taking this physics into account.

Addressing class imbalance in soil movement predictions
Praveen Kumar, Priyanka Priyanka, Kala Venkata Uday, and Varun Dutt
Nat. Hazards Earth Syst. Sci., 24, 1913–1928, https://doi.org/10.5194/nhess-24-1913-2024, 2024
Our study focuses on predicting soil movement to mitigate landslide risks. We develop machine learning models with oversampling techniques to address the class imbalance in monitoring data. The dynamic ensemble model with K-means SMOTE (synthetic minority oversampling technique) achieves high precision, high recall, and a high F1 score. Our findings highlight the potential of these models with oversampling techniques to improve soil movement predictions in landslide-prone areas.

Regional modelling of extreme sea levels induced by hurricanes
Alisée A. Chaigneau, Melisa Menéndez, Marta Ramírez-Pérez, and Alexandra Toimil
Nat. Hazards Earth Syst. Sci. Discuss., https//doi.org/10.5194/nhess-2024-100,2024
Preprint under review for NHESS (discussion: open, 0 comments)
Tropical cyclones drive extreme sea levels, causing large storm surges due to low atmospheric pressure and strong winds. This study explores factors affecting the numerical modelling of storm surges induced by hurricanes in the tropical Atlantic. Two ocean models are compared and used for sensitivity experiments. ERA5 atmospheric reanalysis forcing generally improves storm surge estimates compared to parametric wind models. Including ocean circulations reduces errors in storm surge estimates.

Science, Volume 384, Issue 6700, June 2024.

Abstract

Stratified turbulence (ST) has been proposed as a model for the dynamics of the mesosphere-lower thermosphere (MLT) region. This theory postulates that for horizontal mesoscales (∼1–400 km), the kinetic energy of horizontal winds dissipates from large to small scales with an approximately mean constant rate. In this investigation, dissipation rates are quantified using meteor-radar observations conducted in Northern Norway. The observed seasonal variability of dissipation rates exhibits maxima during the summer and winter, and minima near the equinoxes, between 80 and 95 km altitude. The results are compared with model predictions and earlier medium frequency radar, rocket, lidar, and satellite observations of MLT turbulence. The findings suggest that multi-static meteor radar measurements of ST can provide a novel way to continuously monitor turbulent dissipation rates in the MLT region.