Sudden stratospheric warmings (SSWs) are impressive fluid dynamical events in which large and rapid temperature increases in the winter polar stratosphere (~0–50km) are associated with a complete reversal of the climatological wintertime westerly winds. SSWs are fundamentally caused by the breaking of planetary-scale waves that propagate upwards from the troposphere. During an SSW, the polar vortex breaks down, accompanied by rapid warming of the polar air column. This rapid warming and descent of the polar air column affects tropospheric weather, shifting jet streams, storm tracks, and the Northern Annular Mode (NAM), including increased frequency of cold air outbreaks over North America and Eurasia. SSWs affect the whole atmosphere above the stratosphere producing widespread effects on atmospheric chemistry, temperatures, winds, neutral (non-ionized) particle and electron densities, and electric fields. These effects span the surface to the thermosphere and across both hemispheres. Given their crucial role in the whole atmosphere, SSWs are also seen as a key process to analyze in climate change studies and subseasonal to seasonal predictions. This work reviews the current knowledge on the most important aspects related to SSWs from the historical background to involved dynamical processes, modelling, chemistry and impact on other atmospheric layers.

Subduction-induced deep hydration and water cycling may play significant roles in the modification and destruction of the overriding cratonic lithosphere. Two contrasting modes are generally proposed: (1) flat subduction (FS) regime with slab subducting sub-horizontally beneath the overriding lithosphere, and (2) big mantle wedge (BMW) regime with slab flattening in the mantle transition zone. Here, systematic petrological-thermomechanical models are conducted to investigate the fluid/melt activities in the contrasting subduction regimes as well as their effects on the modification of overriding lithosphere. The model results indicate that the dehydration process in the FS regime can significantly modify the overriding lithosphere for a region of about 600 km from the trench. During the progressive flat subduction, the partial melting and magmatism migrate towards the inner land of the overriding plate, which will be reversed and backward to the trench during the transition from flat to steep subduction. On the other hand, the deep hydration in the BMW regime is strongly dependent on the sub-crustal serpentinite layer in the subducting slab, whereas the oceanic crust cannot carry water to the transition zone. The modification of the overriding lithosphere in the BMW regime occurs in a larger region of >1000 km from trench, which is however generally slower and weaker. The modification and destruction of North China Craton is more likely to be controlled by the flat subduction of paleo-Pacific plate in the late Jurassic to early Cretaceous, which may be accompanied by the effects of deep water cycling in the BMW regime.

Prior to 2009, the Moon was believed to be anhydrous. However, observations by three spacecraft revealed a hydrated surface by reporting a 3 µm absorption band attributed to hydroxyl and possibly molecular water. The Moon Mineralogy Mapper (M) spectrometer, onboard the Chandrayaan-1 spacecraft is mainly used to study the lunar 3 µm band but its spectral range ends at 3 µm. The limited wavelength range of Mhas allowed observed variations in the 3 µm band to be called into question due to uncertainties in thermal corrections. To investigate the validity of variations in the lunar 3 µm band, we used the SpeX infrared spectrograph at the NASA InfraRed Telescope Facility at Maunakea Observatory in Hawaiʻi. With SpeX, we are able to obtain lunar data over a wavelength range of 1.67 to 4.2 µm at 1 – 2 km spatial resolution. The long wavelengths provide strong constraints on thermal emission corrections. We confirm that the 3 µm band varies with lunar time of day as well as with latitude and composition. Each observation reveals strong variations in abundances of hydroxyl and possibly molecular water. The data reveal a decrease in abundance with increasing lunar local time, an asymmetric trend about the equator that favors the southern latitudes, and higher concentrations in highland regions. The longer wavelengths provided by SpeX have allowed us to examine variations in the 3 µm band and provide definitive evidence that the variations are due to changes in hydration.

This paper describes laboratory experiments (using a high-speed wind-wave flume) of the effects of water waves on heat and momentum exchange in the near-water atmospheric boundary layer at high wind speeds. Different from previous experiments of this type, the parameters of waves were controlled by a net stretched along the entire channel to effectively decrease the fetch. This helped to achieve dependency of the transfer coefficients on two independent parameters, namely the wind speed and fetch. Another key to the experiment was using a stable temperature stratification of the air flow, with the temperature of the air entering the flume 15–25 degrees higher than the water. The experiments showed a sharp increase in the heat exchange coefficient at winds exceeding 33–35 m/s, similar to that observed earlier in the high-speed wind-wave flume of Kyoto University with conditions of unstable temperature stratification of the air flow. The joint analysis of the data obtained in the high-speed wind-wave flumes of IAP RAS and Kyoto University yields the universal dependency of the exchange coefficients and the temperature roughness on the peak wave number of surface wave spectra. This is independent of the type of temperature stratification of the atmospheric boundary layer, either stable or unstable. The sharp increase in the heat exchange coefficient is shown to be associated with increased whitecapping.

River deltas and enclosed lagoons represent a zone where fluvial and littoral processes interacts through a redistribution, erosion, and deposition of sediment, with a huge impact on coastal management and engineering. The focus of the study is to understand the correct balance between strategies to maintain the navigational efficiency of tidal inlets and the respect of the ecological and economical function in coastal lagoons. We applied an integrated modeling system which will link multiple hydrodynamic and morphodynamic models to understand how coastal processes and the associated sediment transport can influence the functioning of the southern inlet of the Barbamarco lagoon in the Po River Delta, Italy. Furthermore, our study provides engineering solutions aimed at the inlet functioning efficiency with a proposal for the monitoring plan. Our results highlight the importance of the seasonal effects of wave climate on the littoral sediment transport. Model outcomes show that the dredging volume is approximately 15,000 cubic meter/year for the southern inlet that might vary with wave climate. However, shaping a wider tidal channel seaward will reduce the dredging activities with a longer interval than the actual sediment removal. A design of a deeper and wider channel will deflect the along shore current seaward with a sediment bypass of the inlet. Therefore, the sediment will reach the erosional side of the inlet enhancing the redistribution of the sediment which might reduce the over-wash during storms and high-water levels. Our results display the ephemeral equilibrium of tidal inlets and coastal lagoons in deltaic systems impacted by large riverine sediment delivery. Shore management scenario and decision relies on hydro-morphodyanmic numerical model to predict the best practice for coastal sustainability.

Magmatic fluids within the crust may exist under supercritical conditions (e.g. >374°C and >22.1 MPa for pure water). Geothermal systems using such supercritical fluids have gained attention as unconventional geothermal resources because they can offer significantly more energy than conventional geothermal fluids with temperatures <350°C. Although an understanding of the spatial distribution and fluid fraction of supercritical geothermal reservoirs is necessary for their resource assessment, the spatial distribution and fluid fraction of supercritical geothermal reservoirs worldwide are poorly understood due to the limited number of geophysical observations. Here, the magnetotelluric (MT) method with electrical resistivity imaging was used in the Yuzawa geothermal field, northeastern Japan, to obtain information on the fluid fraction and spatial distribution of a supercritical geothermal reservoir. Our MT data revealed a potential supercritical geothermal reservoir (>400°C) with a horizontal dimension of 3 km (width) × 5 km (length) at a depth of 2.5–6 km. The estimated fluid fraction of the supercritical reservoir was 0.5–2% with a salinity of 5–10 wt%. The melt was imaged below a supercritical geothermal reservoir. Based on the resistivity model, we propose a mechanism for the evolution of a supercritical fluid reservoir, wherein upwelling supercritical fluids supplied from the melt are trapped under less permeable silica sealing. As a result, supercritical fluids accumulate under the silica sealing. This study is the first to present a detailed estimation of the spatial distribution and fluid fraction of a potential supercritical geothermal reservoir.

Whistler-mode waves have often been proposed as a plausible mechanism for pitch angle scattering and energization of electron populations in the solar wind. Recent studies reported observations of obliquely propagating and narrowband waves consistent with the whistler mode at 1 AU. Close to 0.3 AU, similar waves have also been observed in PSP data, where evidence of strong scattering of strahl electrons indicates that these waves regulate the electron heat flux. At both radial distances, the wave amplitude can be as high as 10% of the ambient magnetic field. The oblique propagation angle enables resonant interactions without requiring that the electrons counter-stream with the waves. Self-consistent PIC simulations by Roberg-Clark et al (2019) and Micera et al (2020) studied the strahl scattering and subsequent halo formation due to anomalous resonant interactions enabled by oblique whistlers generated from the heat flux fan instability. Observational studies of whistlers near the Sun have also concluded that they are connected to this instability. Cattell and Vo (2021) also demonstrated the same features of the scattering from a particle tracing simulation, one advantage of which is the ability to calculate kinetic quantities such as the diffusion coefficients. Also, the tracing code includes variational calculations to ensure energy conservation in the presence of highly chaotic dynamics. In this study, we investigate in more detail the resonant interactions of electrons with these high amplitude and oblique whistlers. We will show that these waves at 0.3 AU may exceed the stochasticity condition where resonance overlap occurs. Furthermore, the stochastic width around the primary islands might be large enough that diffusion is enabled even before they overlap. In simulations with 1 AU parameters, the particle motion is strongly stochastic where all harmonics significantly overlap, leading to an isotropic pitch angle diffusion which forms the halo population. Our calculations also indicate the presence of higher-order effects, allowing for sub- and super-harmonic resonant interactions.

Rock heights and three-dimensional shapes around the InSight lander in Homestead hollow, Mars, provide new constraints on modification of the degraded 27 m in diameter impact crater and are a tool for characterizing degradation on regolith-covered lava plains on Mars. Decreasing average rock height and increasing percentage of fragments where height comprises the short axis from outside to within the hollow supports significant ejecta deflation accompanied by infilling of the interior. Rock relief outside the hollow is compared with expectations of pristine ejecta thickness and indicates up to ~40 cm of near-rim early deflation (decreasing to a few cm out to one diameter) can account for the predicted eolian component of infilling and that other eolian infilling sources are not required. Scattered rocks in the hollow are ejecta from subsequent nearby impacts and their mostly buried expression is consistent with subsequent long-term degradation estimated to be 10-4 m/Myr. Basalt rock shapes at InSight are likely similar to basalt rock shapes on Earth, but appear more platy, bladed, and elongate in a triangular form factor plot and more discoidal and bladed in an axes ratio plot. Nevertheless, addition of 10 cm to near rim rock heights to account for continued partial embedding in ejecta would result in rock shapes quite similar to terrestrial rocks. Consistency between degradation estimates based on current rock relief and rock shape after accounting for partial embedding in ejecta indicates up to ~30-40 cm early (~0.1 Ga) near-rim deflation was followed by much lesser long-term degradation.

Wildfire emissions affect downwind air quality and human health. Predictions of these impacts using models are limited by uncertainties in emissions and chemical evolution of smoke plumes. Using high-time-resolution aircraft measurements, we illustrate spatial variations that can exist horizontally and vertically within a plume due to differences in the photochemical environment. Dilution-corrected mixing ratio gradients were observed for reactive compounds and their oxidation products, such as nitrous acid, catechol, and ozone, likely due to faster photochemistry in optically-thinner plume edges relative to darker plume cores. Mixing ratio gradients in midday plumes, driven by jHONO gradients, are often steepest in the freshest transects, and become flatter with chemical aging. Gradients in plumes emitted close to sunset are characterized by titration of O3 in the plume and little to no gradient formation. We show how gradients can lead to underestimated emission ratios for reactive compounds and overestimated emission ratios for oxidation products.

This study conducts an analysis of the polar numerical noise in the barotropic shallow-water version of the Grid-point Atmospheric Model of IAP LASG (GAMIL-SW) and provides a good solution to the problem. GAMIL-SW suffers from numerical noise in the polar region in some ideal test cases, which is likely to be detrimental to the full physical model. The noise is suspected to be related to the nonlinear advection term in the momentum equation. Thus, a new shallow-water model with a vector-invariant form of the momentum equation is developed on the latitude-longitude grid to analyze the polar noise. It is found that the version with meridional wind component staggered on the pole is free from noise, while the version with zonal wind component staggered on the pole is still contaminated. By redefining the polar relative vorticity, the polar noise is eliminated in the latter version. In addition, the test cases demonstrate that the new shallow-water model maintains the properties of the original GAMIL-SW with respect to numerical accuracy and computational stability. This study helps to identify appropriate governing equations to further develop the next generation of GAMIL dynamical core.

The global distribution and variations of the monthly mesopause temperature are presented during 2002-2019 covering the latitudes of 83°S-83°N based on Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) observations. To investigate the long-term trend and solar response of the mesopause temperature, a three-component harmonic fit is first applied to remove the seasonal variation from the monthly temperature data series. Then a multiple linear regression model is performed to residual temperatures versus constant, time series, solar activity, and geomagnetic activity terms. In this study, the mesopause temperature shows a cooling trend through all latitudes ranging from -0.002 to -0.113 K/year with a mean of -0.069 ± 0.036 K/year. The cooling trends in the southern hemisphere are observed to be relatively stronger than those in the northern hemisphere. For high latitudes (60°– 80°), significant negative trends can be detected during the non-summer time, while no significant trends are found for summertime. The mesopause temperature shows apparent positive responses to solar activity through all latitudes ranging from 2.74 to 4.76 K/100sfu with a mean of 3.94 ± 0.59 K/100sfu, which are more significant and stable in the northern hemisphere. There is a pronounced drop in solar response near the equator, which could be caused by tidal forcing at low latitudes. It is noteworthy that the length of the time interval for analysis is the main factor influencing the quality of the results. Our results, using an eighteen years interval, are expected to be a robust reference for the mesopause temperature variations.

Climate models contain atmospheric and oceanic components that are coupled together to simulate the thermodynamic and dynamic processes during air-sea interactions. Community Earth System Model (CESM, version 1.2.1) is a state-of-the-art coupled model that is widely used and participates in Coupled Model Intercomparison Projects. Community Atmospheric Model (CAM), the atmospheric component of CESM, is based on the finite-volume dynamic core, which utilizes staggered Arakawa-D grids. However, the dynamics-physics (D-P) coupling in CAM causes the prognostic winds of the dynamic core be interpolated onto non-staggered locations, which affects the wind structure for computing the air-sea interaction and dynamical coupling. In this study we propose a new scheme that eliminates the extra interpolation during D-P coupling for the atmosphere-ocean interaction. By numerical experiments and comparative study of the new scheme, we show that it improves the simulated climatology in key regions including eastern-boundary upwelling regions and Southern Oceans. In turn, existing problems of the model, such as warm SST biases, are reduced. The new scheme contain code changes in CAM and the coupler, and they are provided as open-source files. Similar approaches can also be adopted in coupled models that utilize the atmospheric components with on staggered dynamics and physics, such as spectral-element method based CAM.

Fractional crystallization is an essential process proposed to explain worldwide compositional abundances of igneous rocks. It requires crystals to precipitate from the melt and segregate from its residual melt, or crystal fractionation. The compositional abundances of volcanic systems show a bell-curve distribution suggesting that the process has variable efficiencies. We test crystal fractionation efficiency in convective flow in low to intermediate crystallinity regime. We simulate the physical segregation of crystals from their residual melt at the scale of individual crystals, using a direct numerical method. We find that at low particle Reynolds numbers, crystals sink in clusters. The relatively rapid motion of clusters strips away residual melt. Our results show cluster settling can imprint observational signatures at the crystalline scale. The collective crystal behavior results in a crystal convection that governs the efficiency of crystal fractionation, providing a possible explanation for the bell curve distribution in volcanic systems.

During an extended volcanic unrest starting in 2017, two main moderate stratospheric eruptions occurred at the Ambae volcano (15°S and 167°E), Vanuatu, in April and July 2018. Observations from a geostationary orbit show that the April and July eruptions injected a volcanic plume into the lower stratosphere. While aerosol enhancements from the April eruption have only had an impact on the Southern Hemisphere, the plume from the July eruption was distributed within the lower branch of the Brewer-Dobson circulation to both hemispheres. Satellite, ground-based and in situ observations show that the background aerosol is enhanced throughout the year after the July eruption on a global scale. A volcanic-induced perturbation of the global stratospheric aerosol optical depth up to 0.012 is found, in the ultraviolet/visible spectral range. This perturbation is comparable to that of recent moderate stratospheric eruptions like from Kasatochi, Sarychev and Nabro. Top of the atmosphere radiative forcing values are estimated between -0.45 and -0.6 W/m2 for this event, showing that the Ambae eruption had the strongest climatic impact of the year 2018. Thus, the Ambae eruption in 2018 has to be taken into account when studying the decadal lower stratospheric aerosol budget and in climate studies.

On any given day, some region of the globe is likely to be affected by significant negative temperature anomalies. Depending on the severity, extreme cold periods may be deemed cold air outbreaks (CAOs). These CAOs can be detrimental to the agricultural industry and human health, especially in less prepared regions. A systematic CAO classification was developed using a set of criteria concerning magnitude, duration, and spatial extent from two gridded reanalysis datasets from 1979 – 2018. Trends in CAOs were calculated for different regions across the globe and the results from each reanalysis dataset compared with one another to identify discrepancies. CAOs were found to have decreased in spatial extent, frequency, duration, and magnitude across much of the globe, particularly across Alaska, Canada, and the North Atlantic, while an increase in CAOs was observed in Eastern Europe, Central Eurasia, and the Southern Ocean.

Arctic sea-ice extent (SIE) has declined drastically in recent decades, yet its evolution prior to the satellite era is highly uncertain. Studies using SIE observations find little variability prior to the 1970s; however, these reconstructions are based on limited data, especially prior to the 1950s. We use ensemble Kalman filter data assimilation of surface air temperature observations with Last Millennium climate model simulations to create a fully gridded Arctic sea-ice concentration reconstruction from 1850–2018, and investigate the evolution of Arctic SIE during this period. We find a decline of ~1.25 x 106 km2 during the early 20th-century warming (1910-1940). The 25-year trends during this period are ~33-38% smaller than the satellite era (1979-2018) but almost twice as large as previous estimates. Additionally we find that variability of SIE on decadal timescales prior to satellite era is ~40% greater than previously estimated.

The Australian 2019/2020 bushfires were unprecedented in both their extent and intensity, causing a catastrophic loss of habitat and human and animal life across eastern-Australia. Between October 2019 and February 2020 hundreds of fires burned, peaking in size in December and January and releasing the equivalent of half of Australia’s annual carbon dioxide (CO2) emissions. We use a high-resolution atmospheric-chemistry transport model to assess the impact of the bushfires on particulate matter with a diameter less than 2.5 µm (PM2.5) concentrations across eastern Australia. The health burden from short-term population exposure to PM2.5 is then quantified using a concentration response function. We find that between October and February an additional ~1.9 million people in eastern-Australia were exposed to ‘Poor’, ‘Very Poor’ and ‘Hazardous’ air quality index levels due to the fires. The impact of the bushfires on AQ was concentrated in the cities of Sydney, Newcastle-Maitland and Canberra-Queanbeyan during November, December and, also in Melbourne, in January. The health burden of bushfire PM2.5 across eastern-Australia, regionally and at city level is also estimated. Our estimate indicates that between October and February 171 (95% CI: 66 – 291) deaths were brought forward. The health burden was largest in New South Wales (109 (95% CI: 41 – 176) deaths brought forward), Queensland (15 (95% CI: 5 – 24)) and Victoria (35 (95% CI: 13 – 56)). At a city level the health burden was concentrated in Sydney (65 (95% CI: 24 – 105)), Melbourne (23 (95% CI: 9 – 38)) and Canberra-Queanbeyan (9 (95% CI: 4 – 14)), where large populations were exposed to high PM2.5 concentrations due to the bushfires.

The processes leading to the depletion of oceanic mesoscale kinetic energy (KE) and the energization of near-inertial internal waves are investigated using a suite of realistically forced regional ocean simulations. By carefully modifying the forcing fields we show that solutions where internal waves are forced have ~25% less mesoscale KE compared with solutions where they are not. We apply a coarse-graining method to quantify the KE fluxes across time scales and demonstrate that the decrease in mesoscale KE is a result of an internal wave-induced reduction of the inverse energy cascade and an enhancement of the forward energy cascade from sub- to super-inertial frequencies. The integrated KE forward transfer rate in the upper ocean is equivalent to half and a quarter of the regionally averaged near-inertial wind work in winter and summer, respectively, with the strongest fluxes localized at surface submesoscale fronts and filaments.