Changes in vegetation in North America indicate Holocene shifts in the latitudinal temperature gradient along the western margin of the North Atlantic. The dynamics of tree taxa such as oak (Quercus) and hickory (Carya) showed opposing directions of change across different latitudes, consistent with changes in temperature gradients. Pollen-inferred temperatures from 34 sites quantify the changes and reconstruct a long-term southward shift of the sharpest temperature gradient in winter and a northward shift in summer. During the mid-Holocene, however, an oscillation in tree distributions interrupted the trends indicating that the steepest portion of the seasonal temperature gradients migrated rapidly northward at 5.8-3.2 ka. The shift produced an unusually late summer thermal maxima at 42-43.5°N where oak abundance peaked both in the early and mid-Holocene. The changes appear consistent with orbital and ice sheet forcing as well as millennial variability in the North Atlantic pressure field during the mid-Holocene.

Regions along the edges of the tropics host vast populations and ecosystems which are sensitive to climate change. Here we examine the extent of tropical climate land areas in the ERA5 and MERRA-2 reanalyses in high-emission scenarios of 45 models participating in phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5/6). Based on the definition of tropical climate land areas as regions where the diurnal temperature range exceeds the seasonal temperature range, we find a net reduction of tropical land area with global warming. This change is primarily due to an increased seasonal temperature range, driven by enhanced summer warming. The reduction in tropical land area is consistent with the expansion of the subtropical descending zones and with the expansion of drylands with global warming. However, the particular contributions of dynamic and thermodynamic processes are not clear.

Based on reanalysis datasets and sea-ice sensitivity experiments, this study has pointed out that the autumn sea ice loss in East Siberian-Chukchi-Beaufort (EsCB) Seas significantly increases the frequency of winter extreme low temperature over western-central China. Autumn sea ice loss warms the troposphere and generates anticyclonic anomaly over the Arctic region one month later. Under the effects of synoptic eddy-mean flow interaction and anomalous upward propagated planetary wave 2, the Arctic anticyclonic anomaly strengthens and develops toward Greenland-Northern Europe, accompanied by a weakened stratospheric polar vortex. In winter, following intra-seasonal downward propagation of stratospheric anomalies, the Northern European positive geopotential anomalies enhance and expand downstream within 7 days, favoring Arctic cold air east of Novaya Zemlya southward (hyperpolar path) accumulating in Siberia around Lake of Baikal. In the subsequent 2~3 days, these cold anomalies rapidly intrude western-central China and induce abrupt sharp cooling, thus more frequent extreme low temperature there.

How are particles being energized by turbulent electromagnetic fields is an outstanding question in plasma physics and astrophysics. This paper investigates the electron acceleration mechanism in strong turbulence (δB/B0 ~ 1) in the Earth’s magnetosheath based on the novel observations of the Magnetospheric Multiscale (MMS) mission. We find that electrons are magnetized in turbulent fields for the majority of the time. By directly calculating the electron acceleration rate from Fermi, betatron mechanism, and parallel electric field, it is found that electrons are primarily accelerated by the parallel electric field within coherent structures. Moreover, the acceleration rate by parallel electric fields increases as the spatial scale reduces, with the most intense acceleration occurring over about one ion inertial length. This study is an important step towards fully understanding the turbulent energy dissipation in weakly collisional plasmas.

Observed rapid Arctic warming and sea-ice loss are likely to continue in the future, unless and after greenhouse gas emissions are reduced to net-zero. Here, we examine the possible effects of future sea-ice loss at 2°C global warming above pre-industrial levels on winter temperature extremes across the Northern Hemisphere, using coordinated experiments from the Polar Amplification Model Intercomparison Project. 1-in-20-year cold extremes are simulated to become less severe at high- and mid-latitudes in response to Arctic sea-ice loss. 1-in-20-year winter warm extremes become warmer at northern high latitudes due to sea-ice loss, but warm by less than cold extremes. We compare the response to sea-ice loss to that from global SST change also at 2°C global warming. SST change causes less severe cold extremes and more severe warm extremes globally. Except northern high latitudes, the response to SST change is of larger magnitude than that to Arctic sea-ice loss.

Eyewall replacements occur in 70% of major tropical cyclones (TCs), and are associated with rapid changes in storm intensity and rapid broadening of strong winds. In this study, we present to use the radial gradient of absolute angular momentum with Holland’s wind profile as a simple diagnostic for eyewall replacement as internal variability of the storm. The diagnostic is solely dependent on the maximum wind speed, the radius of maximum wind, and the latitude and found to coincident with 70% of satellite observed concentric eyewalls for 1991-2020. The diagnostic can be expressed as a latitude-irrelevant Rossby Number of primary eyewall, varying with the peakedness of wind. It highlights the importance of pressure-wind relationship in eyewall replacement and provides a valuable tool to improve the understanding, modeling and risk assessment of storms with eyewall replacements.

Winter cold spells over North America have been correlated with European wind extremes, but the physical mechanisms behind such “pan-Atlantic” compound extremes have not been clarified yet. In this study, we propose that pan–Atlantic cold and windy extremes occur following two possible dynamical pathways. The first one involves the propagation of a Rossby wave train from the Pacific Ocean, associated with windstorms over north-western Europe in the 5-10 days after the cold spell peak. The second is associated with a high-latitude anticyclone over the North Atlantic and an equatorward-shifted jet, leading to windstorms over south-western Europe already in the days preceding the cold spell peak. European windstorms are thus consistently tied to North American cold spells according to the different flow configuration. The analysis underscores that seemingly similar surface extremes may be driven by different processes, and that overlooking these subtleties and conflating them together could lead to misleading conclusions.

Interactions between atmospheric aerosols and ozone have a significant impact on air pollution and the climate. However, the relative importance of the response of surface ozone to aerosol scattering and absorption has been poorly quantified from in situ observations. Results derived from a one-year in situ observational study conducted in a semi-arid region showed that the response of ozone to aerosol absorption was more sensitive than to scattering. Specifically, the change in surface ozone from low to high absorption coefficients was approximately five times that from low to high scattering coefficients. The mass scattering and absorption efficiencies, rather than the single-scattering albedo, which are commonly applied in numerical simulations, were able to clearly distinguish surface ozone. The positive correlation between aerosol and ozone in summer showed the promotion of secondary aerosols by ozone. This study provides robust observational evidence of the response of surface ozone to aerosol scattering and absorption.

Aeolian processes on Mars form a distinct class of meter-scale ripples, whose mechanisms of formation are debated. We present a global morphometric survey of bedforms on Mars, adding relevant observational constraints to the ongoing debate. We show that the bedforms located in the Tharsis region form a distinct group, not akin to the large dark-toned ripples which cover dune fields elsewhere on the planet. The relation between wavelength and atmospheric density derived from the new data is consistent with the predictions of a wind-drag mechanism, favoring the model that uses a saltation saturation length. Regardless of the mechanism that limits the size of bedforms, these results confirm the existence of a robust relationship between the wavelength of large ripples and atmospheric density (ripples spacings increases with decreasing atmospheric density). This provides further support to the interpretation of paleoatmospheric conditions on Mars through the analysis of its aeolian sedimentary record.

Entrainment of dry moat air with low equivalent potential temperature laterally into the eyewall and rainbands is a unique turbulent process in the inner-core region of a tropical cyclone (TC). By analyzing in-situ aircraft measurements collected by the reconnaissance flights that penetrated the eyewalls and rainbands of Hurricanes Rita (2005), Patricia (2015), Harvey (2017), and Michael (2018), as well as numerical simulations of Hurricanes Patricia (2015) and Michael (2018), we show that the moat air entrained into the eyewall and rainbands meets the instability criterion, and therefore, sinks unstably as a convective downdraft. The resultant positive buoyancy fluxes are an important source for the turbulent kinetic energy (TKE) in the eyewall and rainband clouds. This mechanism of TKE generation via lateral entrainment instability should be included in the TKE-type turbulent mixing schemes for a better representation of turbulent transport processes in numerical forecasts of TCs.

Impacts of small-scale surface irregularities, or surface roughness, of atmospheric ice crystals on lidar backscattering properties are quantified. Geometric ice crystal models with various degrees of surface roughness and state-of-the-science light-scattering computational capabilities are used to simulate single-scattering properties across the entire practical size parameter range. The simulated bulk lidar and depolarization ratios of polydisperse ice crystals at 532 nm are strongly sensitive to the degree of surface roughness. Comparisons of these quantities between the theoretical simulations and counterparts inferred from spaceborne lidar observations for cold cirrus clouds suggest a typical surface roughness range of 0.03--0.15, which is most consistent with direct measurements of scanning electron microscopic images. The degree of surface roughness needs to be accounted for to properly interpret lidar backscattering observations of ice clouds.

We report the first detection of unrest at Socompa, Northern Chile, a stratovolcano which has recorded no eruptions since ~7,200 years ago. We measure deformation at and around Socompa using Interferometric Synthetic Aperture Radar (InSAR) observations between Jan 2018 and Oct 2021. We find that, whilst initially inactive, Socompa shows a steady uplift (17.5 mm/yr) from Dec 2019, independently recorded by near-field continuous Global Positioning System (GPS) data. The data can be fit with pressure increase in an ellipsoidal source region stretching from 1.9 to 9.5 km, with a volume change rate of ~5.8×106 m3/yr. Our observations of the onset of uplift preclude the possibility that a nearby Mw 6.8 deep intraslab earthquake on 3rd June 2020 triggered the unrest. The deformation signal we detect indicates the initiation of unrest at Socompa, after at least two decades without measurable deformation, and many thousands of years without volcanic activity.

Climate change has altered the frequency, intensity, and timing of mean and extreme precipitation events. Extreme precipitation has caused tremendous socio-economic losses and displays strong regional variability. Although many previous studies have addressed daily extreme precipitation, hourly extreme rainfall still needs to be thoroughly investigated. In this study, we investigated the trends, spatio-temporal variability, and long-term variations in mean and extreme precipitation over South Korea using daily and hourly observational data. During the past 50 years (1973–2022), there has been a notable escalation in maximum hourly precipitation, although the boreal summer mean precipitation has increased only marginally. Regionally, an increase in mean and extreme rainfall occurred in the northern part of the central region. Moreover, increased intensity and frequency of extreme precipitation have contributed more to the total summer precipitation in recent years. Our findings provide scientific insights into the progression of extreme summer precipitation events in South Korea.

The ability of satellite instruments to accurately observe long-term changes in atmospheric temperature depends on many factors including the absolute accuracy of the measurement, the stability of the calibration of the instrument, the stability of the satellite orbit, and the stability of the numerical algorithm that produces the temperature data. We present an example of algorithm instability recently discovered in the temperature dataset from the SABER instrument on the NASA TIMED satellite. The instability resulted in derived temperatures that were substantially colder than anticipated from mid-December 2019 to mid-2022. This algorithm-induced change in temperature over one to two years corresponded to the expected change over several decades from increasing anthropogenic CO2. This paper highlights the importance of algorithm stability in developing Geospace Data Records (GDRs) for Earth’s mesosphere and lower thermosphere. A corrected version (Version 2.08) of the temperatures from SABER is described.

Volcanic seismicity provides essential insights into the behavior of an active volcano across multiple time scales. However, to understand how magma moves as an eruption evolves, better knowledge of the geometry and physical properties of the magma plumbing system is required. In this study, using full-wave ambient noise tomography, we image the 3-D crustal shear-wave velocity structure below GreatSitkin Volcano in the central Aleutian Arc. The new velocity model reveals two low-velocity anomalies, which correlate with the migration of volcanic seismicity. With a partial melt of up to about 30%, these low-velocity anomalies are characterized as mushy magma reservoirs. We propose a six-stage eruption cycle to explain the migration of seismicity and the alternating eruption of two reservoirs with different recharging histories. The findings in this study have broad implications for the dynamics of magma plumbing systems and the structural control of eruption behaviors.Published on GRL on 6/8/2023: https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2022GL102438

Previous studies on South China’s convective precipitation forecast focused on the effects of multi-scale dynamics and microphysics parameterizations. However, how the uncertainty in aerosol data might cause errors in quantitative precipitation forecast (QPF) has yet to be investigated. In this case study, we estimate the impact of aerosol uncertainties on the QPF for South China’s severe convection using convection-permitting simulations. The variability range of aerosol concentrations is estimated with past observation for the pre-summer months. Simulation results suggest that the rainfall pattern and intensity change notably when aerosol concentrations are varied. The simulation with low aerosol concentrations produces the most intense precipitation, approximately 50\% stronger than the high-concentration simulation. Decreasing aerosol hygroscopicity also increases precipitation intensity, especially in pristine clouds. The aerosol uncertainty changes alter the number of cloud condensation and ice nuclei, which modifies the altitude and amount of latent heating and thereby modulates convection.

We present the first evidence for a lower S-wave velocity (Vs ~3.3 to 3.5 km/s) at 8-17 km depth underlying a 4 km thick high-velocity zone with Vs >3.8 km/s beneath the west coast and the neighbouring parts of the Deccan Volcanic Province, India, coinciding with the last phase of volcanism. The velocity structure is derived from joint inversion of receiver function from 9 seismographs operated along ~106 km long W-E profile with the surface wave dispersion data. The low-velocity layer possibly represents the horizontally elongated frozen magma reservoir, the source for the magma eruption at ~65 million years produced due to the interaction of the Reunion hotspot with India. The shallow, high-velocity layer could be basaltic mafic intrusions responsible for the production of massive CO2 degassing. The Moho deepens beneath the west coast to ~45 km due to 10-15 km of underplating as a consequence of magma upwelling.

On Jan. 15, 2022, the Hunga Tonga-Hunga Ha’apai (HT) eruption injected SO2 and water into the middle stratosphere. Shortly after the eruption, the water vapor anomaly moved northward toward and across the equator. This northward movement appears to be due to a Rossby wave forced by the excessive IR water vapor cooling. Following the early eruption stage, persistent mid-stratospheric water vapor and aerosol layers were mostly confined to Southern Hemisphere (SH) tropics (Eq. to 30°S). However, during the spring of 2022, the westerly phase of the tropical quasi-biennial oscillation (QBO) descended through the tropics. The HT water vapor and aerosol anomalies were observed to again split across the equator coincident with the descent of the QBO shear zone. This split occurred because of the enhanced meridional transport circulation associated with the QBO. Neither transport event can be reproduced using MERRA2 assimilated winds.