Nearly-Lagrangian observations from two EM-APEX velocity and density profiling floats on concentric trajectories determine profiles of ocean eddy vorticity and velocity, and the intrinsic frequency, energy, vertical wavenumber, vertical phase velocity, and vertical group velocity of a near-inertial-wave (NIW). For the first time, NIW 𝐶 and 𝐶 are computed from firs principles (by direct computation of 𝜔⁄𝑚 and 𝜕𝜔⁄𝜕𝑚 vs. depth without a dispersion relation). This novel experiment, moving with turbulent zone produced by a downgoing NIW packet observed stalling at 135-m depth. KE flux convergence initiates KE dissipation at 115 m. Below 135 m, shear production is hypothesized to support dissipation. These observations compare well with a theory of NIW interaction with the eddy, not in solid-body rotation. Theory and observations show that the observed turbulent zone arises from wave stalling and instability in a critical or caustic layer as the vertical group velocity of the wave goes toward zero.

In this study, we evaluated the variations of air quality in Lanzhou, a typical city in Northwestern China impacted by the COVID-19 lockdown. The mass concentration and chemical composition of non-refractory submicron particulate matter (NR-PM) were determined by a high-resolution aerosol mass spectrometry from January to March 2020. The concentration of NR-PM dropped by 40% from pre- to during control period. The five aerosol components (sulfate, nitrate, ammonium, chloride, and organic aerosol (OA)) were all decreased during control period with the largest from secondary inorganic species (70% of the total reduction), whereas the OA sources did not vary synchronously. OA from coal and biomass burning remained stably from pre- to during control period, while traffic and cooking related emissions were reduced by 30% and 50%, respectively. The production rates for secondary inorganic and organic aerosols were also evaluated and represented a decreased trend from pre- to during control periods.

Spectra of small-scale sprite structures, downward and upward propagating streamers, glow, and beads, were recorded with a slit-less spectrograph at 10,000 frames per second (fps) from aircraft missions in 2009 and 2013. The spectra are dominated by emissions from molecular nitrogen, the 1 positive band in the red, and in the blue the 2 positive band plus the 1 negative band of molecular nitrogen ions. The excitation threshold for the blue emissions is higher than for the red emissions so the blue/red ratio can, in principle, be used as a proxy for the electron energy leading to the emissions. We extracted for analysis time series of spectra from 11 sprites: 18 time series from downwards propagating streamers, 6 from upward propagating streamers, 14 from glow and 12 from beads. The total number of spectra in the 50 time series is 953. Blue emissions are almost exclusively associated with streamers indicating the more energetic nature of streamers compared with glow and beads. Both downward and upward propagating streamers start and end with low blue emissions indicating time variations in the associated processes. Because the red and blue nitrogen emissions are significantly affected by quenching, which is altitude dependent, and we do not have sufficiently accurate altitudes, the observed spectral blue/red ratios cannot be directly applied to sprite models.

The coupled operation of fracture, diffusion, and intracrystalline-plastic micromechanisms during semibrittle deformation of rock is directly relevant to understanding crustal processes such as earthquake rupture at the base of the seismogenic zone and failure of salt caverns for energy storage. Triaxial stress-cycling experiments are used to investigate elastic-plastic and viscoelastic behaviors in two synthetic salt-rocks deformed at room temperature and low confinement. During semibrittle flow at high differential stress, porous, granular, work-hardened samples deform predominantly by grain boundary sliding and opening accompanied by minor intragranular cracking and dislocation glide. In contrast, fully annealed, near-zero porosity samples deform at lower differential stress by dislocation glide, grain-boundary sliding and opening accompanied by minor intragranular cracking. During high-stress cycling and semibrittle flow, grain boundary sliding is predominantly frictional; but, associated dispersal of water previously trapped in fluid inclusions can activate fluid-assisted diffusional sliding along grain boundaries at low strain rates. Young’s modulus and Poisson’s ratio are largely controlled by the behavior of closed grain boundaries. Grain boundary sliding accommodated by fluid-assisted diffusion leads to nearly complete stress relaxation after semibrittle flow, and in subsequent low-stress cycling both viscoelasticity and pronounced hysteresis are observed. However, such time-dependent effects vanish with grain boundary healing over days-long holds at low differential stress. Experimental results suggest that within the semibrittle regime, high-stress events can lead to significant transient reduction in viscosity and related phenomena.

The Early Cretaceous Jehol Biota evolution has remarkable spatiotemporal correlation with the destruction of the North China craton though the coupling mechanism remains enigmatic. The craton destruction was accompanied by intense magmatic activity and the released volatiles and nutrients might have had climatic and environmental impacts on the biotic evolution. In this study, we investigated the mentioned hypothetical causal link by determining concentrations and total emissions of volatile elements (S, F, Cl) and bulk-rock P contents of volcanic rocks that were erupted during the pre-flourishing, flourishing and post-flourishing stages of the Jehol Biota. Our results show that the volcanism near the flourishing stage has lower S (1083-2370 ppm), Cl (1277-5608 ppm) and higher P2O5 contents (0.48-0.84 wt.%) than that in non-flourishing stages with S of 1991-3288 ppm, Cl of 7915-12315 ppm and P2O5 of 0.17-0.23 wt.%. Fluorine contents in the three stages vary from 893 to 3746 ppm. The total volatile emissions are minor in the flourishing stage (3.6-6.6 Gt S, 2.2-4.6 Gt Cl and 2.1-4.0 Gt F) but elevated in the non-flourishing stages (1-690 Gt S, 4-934 Gt Cl and 1-308 Gt F). Our data suggest that regional climatic and environmental impacts of volcanism in the non-flourishing stages probably hindered the species diversification. The high P flux released from lithospheric mantle-derived lavas during the peak time of craton destruction might enhance primary productivity and contribute to the flourishing of the Jehol Biota. Our study provides insights into the relationship between the biosphere and deep geodynamic processes driven by volcanism.

Over–the–Horizon (OTH) communication is strongly dependent on the state of the ionosphere, which is susceptible to solar flares. Trans–ionospheric high frequency (HF) signals experience a strong attenuation following a solar flare, commonly referred to as Short–Wave Fadeout (SWF). In this study, we examine the role of dispersion relation–collision frequency formulations on the estimation of flare–driven HF absorption seen in Riometer observation using a data assimilation framework. Specifically, the framework first uses modified solar irradiance models (such as EUVAC, FISM), which incorporate high–resolution solar flux data from GOES satellite X-ray sensors, to compute the enhanced ionization produced during the flare events. The framework then uses different dispersion relation–collision frequency formulations to estimate enhanced HF absorption. Finally, the modeled HF absorption is compared against the data to determine which combination of dispersion relation–collision frequency formulation best reproduces the Riometer observations. From the modeling work, we find that the Appleton–Hartree dispersion relation in combination with Schunk–Nagy collision frequency profile produces the best agreement with Riometer data.

Despite the importance of turbidity currents in environmental and resource geology, their flow conditions and mechanism are not well understood. To resolve this issue, a novel method for the inverse analysis of turbidity current using deep learning neural network (DNN) was proposed. This study aims to verify this method using artificial and flume experiment datasets. Development of inverse model by DNN involves two steps. First, artificial datasets of turbidites are produced using a forward model based on shallow water equation. To develop a inverse model, DNN then explores the functional relationship between initial flow conditions and characteristics of the turbidite deposit through the processing of artificial datasets. The developed inverse model was applied to 200 sets of artificial test data and four sets of experiment data. Results of inverse analysis of artificial test data indicated that the flow conditions can be precisely reconstructed from depositional characteristics of turbidites. For experimental turbidites, spatial distributions of grain size and thickness were accurately reconstructed. With regard to hydraulic conditions, reconstructed values of flow heights, sediment concentrations, and flow durations were close to the measured values. In contrast to the other values, there was a larger discrepancy between the measured and reconstructed values of flow velocity, which may be attributed to inaccuracies in sediment entrainment functions employed in the forward model.

The term “ionospheric sluggishness” is used to describe the time delay between maximum radio absorption in the ionosphere following the time of maximum irradiance during a solar flare. Sluggishness is one of the characteristic properties known to be maximized around D-region heights and can be used for studying lower ionospheric (D-region) and mesospheric chemistry. This article is our first attempt to estimate ionospheric sluggishness using high frequency (HF, 3 – 30 MHz) instruments. Specifically, we report on first estimates of sluggishness from riometer and SuperDARN observations following a solar flare and propose two new methods to estimate sluggishness. Sluggishness is shown to be anti-correlated with the peak solar X-ray flux and positively correlated with solar zenith angle and geographic latitude. The choice of instrument, method, and reference solar waveband effects the sluggishness estimation. A simulation study was performed to estimate the effective recombination coefficient, which was found to vary between 4-5 orders of magnitude. We suggest that the effective recombination coefficient is highly sensitive to D-region’s negative and positive ion chemistry.

Oceanic transform faults are intriguing in that they do not produce earthquakes as large as might be expected given their dimensions. We use 1-year of local seismicity recorded on an array of ocean bottom seismometers (OBS) and geophysical data to study the seismotectonic properties of the Chain transform, located in the equatorial Mid-Atlantic. We extend our analysis back in time by considering stronger earthquakes (MW ≥ 5.0) from global catalogs. We divide Chain into three areas (eastern, central, and western) based on multi-dimensional OBS seismicity cluster analysis. Seismic activity recorded by the OBS is the highest at the eastern area of Chain where there is a lozenge shaped topographic high, a negative rMBA gravity anomaly, and only a few historical MW ≥ 5.5 events. OBS seismicity rates are lower in the western and central areas. However, these areas accommodate the majority of seismic moment release, as inferred from both OBS and historical data. We find no evidence of remote dynamic triggering and only weak evidence of tidal and static stress triggering. Higher b-values are significantly correlated with lower rMBA and also with shallower bathymetry, potentially related to thickened crust. Our results suggest high lateral heterogeneity along Chain: Patches with moderate to low OBS seismicity rates that occasionally host MW ≥ 6.0 earthquakes are interrupted by segments with abundant OBS activity but few historical events with 5.5 ≤ MW < 6.0. This segmentation is possibly due to variable fluid circulation and alteration, which may also be variable in time.

Phenology and its interannual variability are altered through anthropogenic climate change. Feedbacks of plant phenology to the regional climate system affect fluxes of energy, water, CO2, biogenic volatile organic compounds as well as canopy conductance, surface roughness length, and are influencing the seasonality of albedo. We performed simulations with the regional climate model COSMO-CLM (CCLM) with 3km horizontal resolution over Germany covering the period 1999 to 2015 to study the sensitivity of grass phenology to different environmental conditions by implementing a new phenology module. We provide new evidence that the standard annually-recurring phenology of CCLM is improved by the new calculation of leaf area index (LAI) dependent upon surface temperature, day length, and water availability. Results with the new phenology implemented in the model showed a significantly higher correlation with observations than simulations with the standard phenology. The interannual variability of LAI, the representation of years with extremely warm spring or extremely dry summer, and the start of the growing season also improved with the new phenology module. The number of hot days with maximum temperature exceeding the 90th percentile and heavy precipitation events (> 20mm) with the new phenology are in very good agreement with the observations. We also show that lower LAI values in summer lead to a decrease of latent heat flux in the model due to less evapotranspiration. The CCLM simulation with improved representation of the phenology should be used in future applications with an extension on more plant functional types.

In a recent paper, Gerritsen et al. (2022) propose to modify the well-accepted sampling strategy in paleomagnetism by collecting more single-sample sites. They also argue that the paleomagnetic community commonly applies a loosely defined set of quantitative data filters and that there is no need for an expert-eye to analyze and interpret paleomagnetic data. Many paleomagnetists will disagree with these claims as paleomagnetic methods provide very robust results at the site level when the study is done with sufficient rigor. As stated in Gerritsen et al. (2022) they deliberately kept directions that an experienced paleomagnetist would likely immediately discard as unreliable. Can we really draw conclusions from such an approach to paleomagnetism? The strategy proposed by Gerritsen et al. (2022) has serious drawbacks well illustrated by the datasets from Turkey (van Hinsbergen et al., 2010), Mongolia (van Hinsbergen et al., 2008), Norway (Haldan et al., 2014), and Antarctica (Asefaw et al., 2021) used by Gerritsen et al. (2022). The main objective of this comment is to support standard methods (Butler, 1992; Tauxe et al., 2018) for a well-defined determination of the paleomagnetic direction per site based on the sampling of several samples per site.

The Braiding Index (BI), defined as the average count of intercepted channels per cross-section, is a widely used metric for characterizing multi-thread river systems. However, it does not account for the diversity of channels (e.g., in terms of discharge) within different cross-sections, omitting important information related to system complexity. Here we present a modification of BI (the Entropic Braiding Index, eBI) which augments the information content in BI by using Shannon Entropy to encode the diversity of channels in each cross section. eBI is interpreted as the number of “effective channels” per cross-section, allowing a direct comparison with the traditional BI. We demonstrate the superior capabilities of eBI via analysis of synthetic, numerical and field examples. In addition, we show that interrogating cross-sections via the ratio BI/eBI has the potential to quantify channel disparity, differentiate types of multi-thread systems, and inform about cross-section stability to forcing variability (e.g., seasonal flooding).

The polarity of first P-wave arrivals plays a significant role in the effective determination of focal mechanisms specially for smaller earthquakes. Manual estimation of polarities is not only time-consuming but also prone to human errors. This warrants a need for an automated algorithm for first motion polarity determination. We present a deep learning model - PolarCAP that uses an autoencoder architecture to identify first-motion polarities of earthquake waveforms. PolarCAP is trained in a supervised fashion using more than 130,000 labelled traces from the Italian seismic dataset (INSTANCE) and is cross-validated on $\sim$22,000 traces to choose the most optimal set of hyperparameters. We obtain an accuracy of 0.98 on a completely unseen test dataset of almost 33,000 traces. Furthermore, We check the model generalizability by testing it on the datasets provided by previous works and show that our model achieves a higher recall on both positive and negative polarities.

Apollo lunar missions remain the most ambitious manned spaceflights in history, five decades after their conclusion. Apollo free-return mission design atmospheric reentry speeds reached 11.1 km/s, or 98.66% of Earth escape kinetic energy. Heat shield testing at such conditions was a major challenge, requiring high-reliability science. The 1960s solution involved analytic equations with numeric simulation, both verified by hypervelocity plasma arc jet lab testing, a triple standard for reliable design. Researchers at NASA Ames used tektite specimens for the task. This mostly silicate cosmic impact ejecta melt had been blasted into space, vacuum quenched during an extended loft, and naturally ablated from a cold initial state during atmospheric entry. After carefully reproducing Australasian tektite glass, spherical samples were exposed to arc jet conditions simulating near-escape speeds and upper-atmospheric conditions. The NASA scientists were able to control ablative effects at those extreme speeds to exactly match condition-sensitive features found on the natural tektites, including anterior face ring waves and flange flattening in addition to overall mass loss. Reproducing morphologic features of naturally ablated tektite via hundreds of tests over several years allowed D. R. Chapman to tune coefficients of the heat transfer equation describing hypervelocity transit from the free molecular to the collisional regime of the upper atmospheric column. The NASA Ames team determined ablated tektite reentry speeds and vertical flight path angles, and the ‘Chapman equation’ is still used for modern spacecraft heat shield design, a win-win for NASA’s Apollo program. In an error of omission, the same team never accounted for longitude shift due to 3.5 to 11.5 hours of Australasian tektite loft at those reentry speeds in order to determine regions of possible terrestrial origin. Instead, they promoted lunar origin. Terrestrial origin of tektites became clear after lunar sample return, while lunar origin of tektites led to mistrust of Chapman’s tektite reentry conditions, a case of throwing away the baby with the ‘lunar origin’ bathwater. Today, dynamically correct assessment of the A-given-B suborbital problem reveals the Australasian tektite source as roughly coincident with the N. American Great Lakes.

• Brightness map of Ganymede’s ultraviolet auroral emission has been constructed based on a large set of HST observations • Auroral ovals are structured in upstream and downstream ‘crescents’ • Brightness on sub-Jovian and anti-Jovian side is strongly reduced by a factor of 3-4 compared to upstream and downstream side *

Enduring questions remain regarding the transition from relatively warm and stable pre- and early-Pleistocene climate to that of the high amplitude glacial-interglacial cycles later in the Quaternary. The main shift in glacial intensity and periodicity around 1 Ma is known as the Mid Pleistocene Transition (MPT). Here we analyze detrital strontium (Sr) and neodymium (Nd) isotopes in a Western Arctic sediment core P23 previously investigated using several litho/biostratigraphic proxies. Based on an improved age framework combining lithostratigraphic cyclicity and Sr isotope stratigraphy, the P23 record extends to ~3.3 Ma, thus providing a rare insight into the Quaternary Arctic climate change. The distinct pre-MPT P23 record is dominated by Pacific-sourced sediment inputs, with little to no intra-Arctic glacial inputs except for a sandy interval around ~2.5 Ma. A consistent decrease of Nd isotopic values towards North American glacigenic signature started in both the Arctic and Bering Sea at ~1.5 Ma and led to a major threshold shift in P23 proxies at ~0.9 Ma. We argue that this threshold is associated with the first prolonged closure of the Bering Strait for an entire obliquity cycle. This shift marks the expansion of the North American ice sheets to the Arctic margin, with dramatic impacts on depositional and hydrographic environments in the Arctic Ocean. These impacts strengthened in the subsequent glacial intervals indicating further ice-sheet growth, probably fed back by continuing prolonged Bering Strait closures. Potential implications of these Arctic changes for the evolution of North Atlantic circulation require further investigation.

The shallow 1971 Mw 6.6 San Fernando, California earthquake involved a complex rupture process on an immature thrust fault with a non-planar geometry, and is notable for having a higher component of left-lateral surface slip than expected from seismic models. We extract its 3-D coseismic surface displacement field from aerial stereo photographs and document the amount and width of the vertical and strike-parallel components of distributed deformation along strike. The results confirm the significant left-lateral surface offsets, suggesting a slip vector rotation at shallow depths. Comparing our offsets against field measurements of fault slip, we observe that most of the offset was accommodated in the damage zone, with off-fault deformation averaging 68% in both the strike-parallel and vertical components. However, the magnitude and width of off-fault deformation behave differently between the vertical and strike-parallel components, which, along with the rotation in rake near the surface, can be explained by dynamic rupture effects.

In recent years, various models have been developed to describe Arctic coastal erosion. Many models are process-based, simulating multiple physical processes and combining them interactively to resemble Arctic coastal erosion. One limitation of the current process-based models is the difficulties in including the hydrodynamic forces. The morphological changes by the hydrodynamics are either simplified or simulated by some empirical relation. The reason for excluding detailed hydrodynamic forcing is the absence of thermal energy conservation in the systems of equations inside the available software. Most hydrodynamic models are designed considering the warmer climate, where waves, tides and storm surges cause changes in morphology. The available models cannot be applied where permafrost is a significant environmental parameter. This paper explains a methodology that allows us to use the models designed for warmer climates to simulate Arctic coastal erosion. The open-source software XBeach is used to simulate the waves, sediment transport and morphological changes. We developed different submodules for the processes related to permafrost thawing-freezing, slumping, wave-cut niche, bluff failure, etc. The submodules are coupled with the XBeach following a workflow where ice concentration, storm surge and bluff collapse work as an on-off switch. The submodules communicate with each other at three-hour intervals. The input parameters of the model are calibrated with field measurements. The model is then validated by another set of mutually exclusive field measurements under different geological conditions. The model can simulate the short term (one year) and long term (a few years) with the same level of fidelity.