GRL

Accurate precipitation simulations for various climate scenarios are critical for understanding and predicting the impacts of climate change. This study employs a Cycle-generative adversarial network (CycleGAN) to improve global 3-hr-average precipitation fields predicted by a coarse grid (200 km) atmospheric model across a range of climates, morphing them to match their statistical properties with those of reference fine-grid (25 km) simulations. We evaluate its performance on both the target climates and an independent ramped-SST simulation. The translated precipitation fields remove most of the biases simulated by the coarse-grid model in the mean precipitation climatology, the cumulative distribution function of 3-hourly precipitation, and the diurnal cycle of precipitation over land. These results highlight the potential of CycleGAN as a powerful tool for bias correction in climate change simulations, paving the way for more reliable predictions of precipitation patterns across a wide range of climates.

Extreme melt and rainfall events can induce temporary acceleration of Greenland Ice Sheet motion, leading to increased advection of ice to lower elevations where melt rates are higher. In a warmer climate, these events are likely to become more frequent. In September 2022, seasonally unprecedented air temperatures caused multiple melt events over the Greenland Ice Sheet, generating the highest melt rates of the year. The scale and timing of the largest event overwhelmed the subglacial drainage system, enhancing basal sliding and increasing ice velocities by up to ∼240% relative to pre-event velocities. However, ice motion returned rapidly to pre-event levels, and the speed-ups caused a regional increase in annual ice discharge of only ∼2% compared to when the effects of the speed-ups were excluded. Therefore, although late melt-season events are forecast to become more frequent and drive significant runoff, their impact on net mass loss via ice discharge is minimal.

While some previous studies examined the contribution of Eastern Pacific (EP) hurricanes toward precipitation in the arid Southwest US (SWUS), their potential to influence wildfires in that region has not been explored. Here we show, using observations and simulations from the Energy Exascale Earth System Model (E3SM), that recurving EP hurricanes modulate the wildfire environment in the SWUS by increasing precipitation and soil moisture, and reducing the vapor pressure deficit. This is especially the case during late season months of September–October when the likelihood of storms to recurve and make landfall increases. Further, analysis of burnt area observations reveals that for the months of September–October, recurving EP hurricanes may significantly reduce the prevalence of wildfires in the SWUS. Finally, E3SM simulations indicate that late season EP hurricanes have been on the decline, with important implications for wildfires in the SWUS.

This letter uses simultaneous observations from Magnetosphere Multiscale (MMS) and Time History of Events and Macroscale Interactions during Substorms (THEMIS) to address the dynamics of the magnetopause and magnetosheath boundary layers during the main phase of a storm during which the interplanetary magnetic field (IMF) reverses from south to north. Near the dawn terminator, MMS observes two boundary layers comprising open and closed field lines and containing energetic electrons and ring current oxygen. Some closed field line regions exhibit sunward convection, presenting an avenue to replenish dayside magnetic flux lost during the storm. Meanwhile, THEMIS observes two boundary layers in the pre-noon sector which strongly resemble those observed at the flank by MMS. Observations from the three THEMIS spacecraft indicate the boundary layers are still evolving several hours after the IMF has turned northward. These observations advance our knowledge of the dynamic magnetopause and magnetosheath boundary layers under the combined effects of an ongoing storm and changing IMF.

ENSO's atmospheric teleconnections drive anomalous North Pacific sea surface temperatures through changes in surface heat fluxes (“the atmospheric bridge”). Previous research focusing on the bridge as a seasonal phenomenon did not consider how ENSO-related changes in synoptic variability might also impact surface turbulent heat fluxes (STHF). In this study, we find that while well over half of ENSO's impact on STHF occurs on low-frequency (>8 days) time scales, up to 20% of its impact arises on high-frequency (<8 days) time scales, through changes in the covariance between surface wind speed and air-sea enthalpy difference that typically warms the ocean south of the storm track. During El Niño, the North Pacific storm track and its attendant sea surface warming shift southward, reducing warming of the central North Pacific ocean and thereby enhancing the bridge signal there. Additionally, changes in the bulk formula coefficients between ENSO phases drive STHF differences (5%–10%).

The close relationship between the Indian Ocean Basin mode (IOBM) and summer precipitation in Central Asia (CA) has been documented in several studies. Nonetheless, this relationship has weakened since the 1990s and varies with the Atlantic Multi-decadal Oscillation (AMO) phase transition. During the cold phase of the AMO (1970–1998), precipitation in CA was significantly positively correlated with the IOBM. Conversely, during the warm phase of the AMO (1999–2019), this correlation became insignificant. The decrease in the interannual variation in the IOBM resulted in the weakening of the atmospheric heat source variation over the North Indian continent and the south-north movement of the subtropical westerly jet (SWJ). Along with the southerly SWJ, the IOBM exhibited only a weak positive correlation with precipitation in southern CA after the 1990s. This remarkable contrast in the impact of IOBM during different phases of the AMO offers intriguing possibilities for improving climate prediction in CA.

Accurately representing the ocean carbon cycle in Earth System Models (ESMs) is essential to understanding the oceanic CO2 sink evolution under CO2 emissions and global warming. A key uncertainty arises from the ESM's inability to explicitly represent mesoscale eddies. To address this limitation, we conduct eddy-resolving experiments of CO2 uptake under global warming in an idealized mid-latitude ocean model. In comparison with similar experiments at coarser resolution, we show that the CO2 sink is 34% larger in the eddy-resolving experiments. 80% of the increase stems from a more efficient anthropogenic CO2 uptake due to a stronger Meridional Overturning circulation (MOC). The remainder results from a weaker reduction in CO2 uptake associated to a weaker MOC decline under global warming. Although being only a fraction of the overall response to climate change, these results emphasize the importance of an accurate representation of small-scale ocean processes to better constrain the CO2 sink.

Electromagnetic ion cyclotron (EMIC) waves are known to exhibit frequency chirping occasionally, contributing to the rapid acceleration and precipitation of energetic particles in the magnetosphere. However, the chirping mechanism of EMIC waves remains elusive. In this work, a phenomenological model of whistler mode chorus waves named the Trap-Release-Amplify (TaRA) model is applied to EMIC waves. Based on the proposed model, we explain how the chirping of EMIC waves occurs, and give predictions on their frequency chirping rates. For the first time, we relate the frequency chirping rate of EMIC waves to both the wave amplitude and the background magnetic field inhomogeneity. Direct observational evidence is provided to validate the model using previously published events of chirping EMIC waves. Our results not only provide a new model for EMIC wave frequency chirping, but more importantly, they indicate the potential wide applicability of the underlying principles of TaRA model.

Heterogeneous chemical cycles of pyrogenic nitrogen and halides influence tropospheric ozone and affect the stratosphere during extreme Pyrocumulonimbus (PyroCB) events. We report field-derived N2O5 uptake coefficients, γ(N2O5), and ClNO2 yields, φ(ClNO2), from two aircraft campaigns observing fresh smoke in the lower and mid troposphere and processed/aged smoke in the upper troposphere and lower stratosphere (UTLS). Derived φ(ClNO2) varied across the full 0–1 range but was typically <0.5 and smallest in a PyroCB (<0.05). Derived γ(N2O5) was low in agricultural smoke (0.2–3.6 × 10−3), extremely low in mid-tropospheric wildfire smoke (0.1 × 10−3), but larger in PyroCB processed smoke (0.7–5.0 × 10−3). Aged biomass burning aerosol in the UTLS had a higher γ(N2O5) of 17 × 10−3 that increased with sulfate and liquid water, but that was 1–2 orders of magnitude lower than values for aqueous sulfuric aerosol used in stratospheric models.

Enhanced continental phosphorus input into the ocean has been suggested as a potential trigger for the transient oxygenation events during the mid-Proterozoic; however, the response of phosphorus cycling to these marine oxygenations remains unclear. Here, we report the changes in phosphorus cycling associated with a ∼1.7 Ga transient oxygenation. Abundant authigenic aluminum phosphate–sulfate mineral svanbergite (SrAl3(PO4) (SO4) (OH)6; 8.02 ± 4.92 wt%) is identified within the ∼1.7 Ga Yunmengshan ironstones from the Xiong'er Basin, North China and other contemporaneous basins. This observation provides new evidence to support the suggestion that early diagenetic aluminum phosphate-sulfate minerals could have represented a critical sink of marine phosphorus during the Proterozoic. We suggest that atmospheric oxygenation and concomitant changes in porewater redox chemistry may have enhanced the formation of early diagenetic phosphates, leading to a negative feedback on the oceanic phosphorus reservoir and atmospheric oxygen levels.

Ocean ventilation translates atmospheric forcing into the ocean interior. The Southern Ocean is an important ventilation site for heat and carbon and is likely to influence the outcome of anthropogenic climate change. We conduct an extensive backwards-in-time trajectory experiment to identify spatial and temporal patterns of ventilation. Temporally, almost all ventilation occurs between August and November. Spatially, “hotspots” of ventilation account for 60% of open-ocean ventilation on a 30 years timescale; the remaining 40% ventilates in a circumpolar pattern. The densest waters ventilate on the Antarctic shelf, primarily near the Antarctic Peninsula (40%) and the west Ross sea (20%); the remaining 40% is distributed across East Antarctica. Shelf-ventilated waters experience significant densification outside of the mixed layer.

Airborne mineral dust is sensitive to climatic changes, but its response to orbital forcing is still not fully understood. Here, we present a reconstruction of dust input to the Subarctic Pacific Ocean covering the past 190 kyr. The dust composition record is indicative of source moisture conditions, which were dominated by precessional variations. In contrast, the dust flux record is dominated by obliquity variations and displays an out-of-phase relationship with a dust record from the mid-latitude North Pacific Ocean. Climate model simulations suggest precession likely drove changes in the aridity and extent of dust source regions. Additionally, the obliquity variations in dust flux can be explained by meridional shifts in the North Pacific westerly jet, driven by changes in the meridional atmospheric temperature gradient. Overall, our findings suggest that North Pacific dust input was primarily modulated by orbital-controlled source aridity and the strength and position of the westerly winds.

The eruption of the Hunga Tonga-Hunga Ha'apai volcano on 15 January 2022 was one of the most explosive eruptions of the last decades. The amount of water vapor injected into the stratosphere was unprecedented in the observational record, increasing the stratospheric water vapor burden by about 10%. Using model runs from the ATLAS chemistry and transport model and Microwave Limb Sounder (MLS) satellite observations, we show that while 20%–40% more water vapor than usual was entrained into the Antarctic polar vortex in 2023 as it formed, the direct chemical effect of the increased water vapor on Antarctic ozone depletion in June through October was minor (less than 4 DU). This is because low temperatures in the vortex, as occur every year in the Antarctic, limit water vapor to the saturation pressure and thus reset any anomalies through the process of dehydration before they can affect ozone loss.

Concurrent heat extremes (CHEs) are becoming increasingly common in the mid-high latitudes across the Northern Hemisphere (NH), underscoring the need to comprehend their spatiotemporal characteristics and underlying causes. Here we reveal a phase-locking behavior in Wave-4 pattern, particularly after mid-1990s, giving rise to a prominent CHE mode akin to heat extreme pattern observed in 2022, which swept most NH regions. Wave-4 pattern significantly amplifies the likelihood of CHEs in Eastern Europe (∼30%), Northeast Asia (∼25%), and northwestern coast of North America (∼15%), while reducing the likelihood in central North America and northern Central Asia. During 1979–2022, the identified pattern accounted for over 69.7% of the trends in heat extremes over the mid-high latitudes of the NH, directly exposing approximately 333.5 million people to heat extremes. Observations and simulations indicate that radiation anomalies over Eastern European Plain and West Siberian Plain play pivotal roles as primary forcing sources for Wave-4 pattern.

Taiwan offers a distinctive tectonic setting as a collisional orogen, ideal for studying tectonic tremors and the slow deformation process in the mountain-building process. Using continuous seismic data at many stations, which have become available recently, and employing the envelope correlation method, we detected ∼7,000 tremor events from 2012 to 2022, with waveform characteristics similar to tectonic tremors worldwide. Beyond the previously known tremor zone beneath the southern Central Range, where newly detected tremors align along a low-angle thrust plane, we identified several new tremor “hotspots” spanning 200 km along the mountain belt. These hotspots are situated at the termination of the subducting slabs and around the deep (25–50 km) extension of the Central Range fault, where repeating earthquakes occur at a depth of 10–25 km. Our findings suggest a strong linkage between the tremor generation mechanism and the mountain-building process, potentially influenced by underground fluid and temperature anomalies.

A key uncertainty in Aerosol-cloud interactions is the cloud liquid water path (LWP) response to increased aerosols (λ). LWP can either increase due to precipitation suppression or decrease due to entrainment-drying. Previous research suggests that precipitation suppression dominates in thick clouds, while entrainment-drying prevails in thin clouds. The time scales of the two competing effects are vastly different, requiring temporally resolved observations. We analyze 3-day Lagrangian trajectories of stratocumulus clouds over the southeast Pacific using 2019–2021 geostationary data. We find that clouds with a LWP exceeding 200 g m−2 exhibit a positive response, while clouds with lower LWP show a negative response. We observe a significant diurnal cycle in λ, indicating a more strongly negative daytime adjustment driven by entrainment-drying. In contrast, at night, precipitation suppression can occasionally fully counteract the entrainment-drying mechanism. Overall, λ appears weaker than previously suggested in studies that do not account for the diurnal cycle.

In order to understand the oceans role as a global carbon sink, we must accurately quantify the amount of carbon exchanged at the air-sea interface. A widely used machine learning neural network product, the SOM-FFN, uses observations to reconstruct a monthly, 1° × 1° global CO2 flux estimate. However, uncertainties in neural network and interpolation techniques can be large, especially in seldom-sampled regions. Here, we present a three-dimensional (latitude, longitude, time) gridded product for our SOM-FFN observational data set consisting of uncertainties (pCO2 mapping, transfer velocity, wind) and biases (pCO2 mapping). We find that polar regions are dominated by uncertainty from gas exchange transfer velocity, with an average 48.7% contribution. In contrast, for subtropical regions, wind product choice contributes an average 50.0%. Regions with fewer observations correlate with higher uncertainty and biases, illustrating the importance of maintaining and expanding existing measurements.

Shorelines face growing threats due to climate change and diminishing sand supply. Coastal headlands, common rocky features along coastlines, are crucial in shaping hydrodynamics and sediment transport. Yet, the influence of future climate conditions, including sea-level rise (SLR) and intensified storm energy on complex shorelines with headlands has remained relatively unexplored. In this study, we model changes in hydrodynamics and headland bypassing under different SLR and higher storm wave scenarios. Our findings reveal the formation of circulation cells on both sides of a headland, where wave energy converges around the headland zone. Future climate conditions result in larger storm waves on the beach. However, SLR enhances nearshore currents through a landward shifting of the circulation cells, while higher storm waves intensify offshore flow currents due to the seaward movement of the cells. This effect, in turn, increases the potential for headland sediment bypassing.

Planetary-scale mountain waves have been observed at the cloud top of Venus and throughout the cloud deck. As they propagate from the surface to the cloud layers, multiple observations and numerical simulations have shown that they grow in size and do not break. However, the fate of mountain waves in the transition region and thermosphere, above the super-rotating atmosphere, has only been addressed with two-dimensional models. We conduct for the first time a simulation of mountain waves with a state-of-the-art Venus climate model that includes the thermosphere. We find that mountain waves can propagate up to at least 150 km altitude, well above the transition region. They affect the circulation of the transition region, by reducing winds speeds, and the subsolar-to-antisolar circulation.

Internal tides (ITs) play a critical role in ocean mixing, and have strong signatures in ocean observations. Here, global IT sea surface height (SSH) in nadir altimetry is compared with an ocean forecast model that assimilates de-tided SSH from nadir altimetry. The forecast model removes IT SSH variance from nadir altimetry at skill levels comparable to those achieved with empirical analysis of nadir altimetry. Accurate removal of IT SSH is needed to fully reveal lower-frequency mesoscale eddies and currents in altimeter data. Analysis windows of order 30–120 days, made possible by the frequent (hourly) outputs of the forecast model, remove more IT SSH variance than longer windows. Forecast models offer a promising new approach for global internal tide mapping and altimetry correction. Because they provide information on the full water column, forecast models can also help to improve understanding of the underlying dynamics of ITs.