GRL

Marine heatwaves (MHWs) are prolonged extreme warm water events, threatening marine ecosystems. Understanding drivers of MHWs over the global ocean is essential for their forecast. Here, we use an eddy-resolving coupled global climate model with improved realism of MHWs to evaluate the drivers of MHWs at different spatial scales, that is, MHWs defined based on temperature anomalies at different spatial scales. The properties of MHWs are scale-dependent, being generally weaker, less frequent, and longer with increasing spatial scales. The primary driver of MHWs shifts from local oceanic intrinsic advection to atmospheric forcing as their spatial scale becomes larger. The transition spatial scale between the ocean and atmosphere-driven regimes varies geographically, being larger in eddy-rich regions but smaller in gyre interior. This study suggests the complicated dynamics of MHWs at different spatial scales and provides guidance on improving their forecast capacity.

The role of stishovite in transporting water in subducting slabs has been a subject of debate for several decades. Here we investigated stishovite's water solubility and its potential role in water transportation as a function of temperature from 1300 to 2100°C at 22 GPa. Under water-saturated conditions, high-quality, Al-free stishovite single crystals were synthesized with multi-anvil press, and their water contents were measured using infrared spectroscopy. The H2O solubility in stishovite increases from 128(20) to 521(47) wt. ppm with increasing temperature from 1300 to 1700°C and decreased to 145(26) wt. ppm at 2100°C. The maximum H2O content was about seven times larger than earlier high-temperature multi-anvil studies but significantly lower than recent laser-heated diamond anvil cell and low-temperature multi-anvil studies. We suggest that Al-free stishovite may not be a significant H2O carrier in subducting slabs, at least at the topmost lower mantle corresponding to our experimental conditions.

We use a version of the NOAA Climate Forecast System with enhanced (up to 1-m) ocean model vertical resolution to investigate the mean diurnal cycles of upper ocean temperature and currents. The model sea surface temperature diurnal cycle agrees well with a global observational analysis. The simulated time-depth profiles of temperature and current also match closely observations from densely instrumented moorings in the tropical Pacific. Our analyses provide new insights into subsurface ocean diurnal cycles. Significant temperature diurnal range occurs, with seasonal modulation, at depths greater than 10 m across broad areas of the subtropical and midlatitude oceans. Significant current diurnal cycles are evident below 30 m across parts of the tropics, including in areas where deep-cycle turbulence has been observed.

We examined rapid variations in the electron zebra stripe patterns, specifically at L = 1.5, over a three-month duration, using twin Van Allen Probes within Earth's inner magnetosphere. During geomagnetically quiet intervals, these stripes exhibit a peak-to-valley ratio (Δj) ∼1.25 in detrended electron fluxes. However, during geomagnetic storms, they became highly prominent, with Δj > 2.5. The correlation between Δj and net field-aligned currents (FACs) is observed to be high (0.70). Global magnetohydrodynamic (MHD) simulation results indicate that the westward electric field at midnight at low latitudes in the deep inner magnetosphere correlates well with net FACs. An increase in net FACs could amplify the dawn-to-dusk electric field in the deep inner magnetosphere, thereby causing the inward transport of electrons. Given that FACs are linked to the interaction between solar wind and the magnetosphere, our findings emphasize the importance of solar wind-magnetosphere coupling in the deeper regions of the inner magnetosphere.

Recent observations revealed the existence of ice slabs and aquifers on the Greenland ice sheet (GrIS). Both affect the ice sheet's hydrology: ice slabs facilitate runoff and aquifers modulate drainage to the bed. However, their climatic drivers and history remain unclear, as most observations cover only two decades. Here, we present a model simulation of the evolution of GrIS ice slabs and aquifers (1980–2020), evaluated using radar measurements. The results show that accumulation, melt and rain rates are good predictors for the spatial distribution of ice slabs and aquifers. Both features were already present in the late 1980s, and their extent remained relatively constant until the beginning of this century, after which increased melt led to their expansion. We show that almost any transect from the coast to the ice-sheet interior will cross either an ice slab region, or an aquifer, or both.

We present the first ground-based measurements of daytime stable auroral red (SAR) arc using OI 630.0 nm emissions. SAR arc is a direct consequence of heat conduction from the inner-magnetosphere to the ionospheric regions characterized by increased electron temperatures and low electron density in the region of mid-latitude trough. So far, SAR arc emissions have only been reported for nighttime conditions. For the present study, daytime optical measurements were enabled using a high-resolution imaging echelle spectrograph from Boston (42.36°N, 71.05°W, MLAT ≈ 53°). Simultaneous Millstone Hill Incoherent Scatter Radar and Defense Meteorological Satellite Program measurements of electron density and temperature confirm our findings. Forward modeling approach enabled estimation of daytime electron temperatures in 200–650 km altitude during this SAR arc event to be varying between 3,500 and 4,400 K. These observations open numerous possibilities of optical investigations of magnetospheric-ionospheric interactions during daytime, when the upper atmosphere is dynamic with large gradients in ionospheric conductivities, temperatures, and winds.

Due to global warming, precipitation extremes are becoming more frequent and more severe, further exacerbating the uneven distribution of daily precipitation. In this study, we explored how many days in a year it takes to get to a certain amount of the precipitation that falls annually. We analyzed daily precipitation from gridded observations across the European continent and found that it generally took 22 to 34 of the wettest days to contribute to 50% of yearly totals (WD50). We found various degrees of alignment between gridded observations and ground measurements. Building on this, we examined changes in WD50 and detected widespread shifts toward fewer days in WD50 between the periods of 1950–1985 and 1986–2021. In addition, about one quarter of the European land also exhibited significant, decreasing trends in WD50 over the last 7 decades. Overall, this work showed an intensification of annual precipitation regimes.

Accurate quantification of the absorption properties of brown carbon (BrC) aerosols is crucial to assess the Earth-atmosphere radiative impacts of BrC. However, the BrC absorption properties were often misestimated in field observations, due to neglecting the contribution of dust absorption. This study solved this problem by coupling a method for calculating the dust concentration into the traditional model for quantifying BrC absorption. The results show that dust absorption was up to 16.8% of the sum of BrC and dust absorption in northwestern China. The potential contribution of dust to the sum of BrC and dust absorption was significantly higher in the Asia-located studies (0.4%–16.8%) than in the Americas-located (<1.2%) and Europe-located (<2.3%) studies. This work underscores the necessity of eliminating the negative effect of dust in BrC quantitative model. It prompts us to revisit the BrC absorption properties resolved by previous studies, especially in dust-influenced areas such as Asia.

The Pacific–Japan (PJ) pattern traditionally refers to the meridional dipole mode of rainfall and the low-level circulation over the tropical western North Pacific and mid-latitude East Asia. However, recent studies have reported that the PJ pattern can also affect the Indian summer monsoon (ISM) via the anomalous circulation over the North Indian Ocean. We summarize the currently available PJ indices and re-examine the linkage between the PJ pattern and the ISM. We found that the only PJ indices that are significantly correlated with rainfall in southern India are the two indices containing signals of the Maritime Continent. The Maritime Continent rainfall can also stimulate circulation anomalies in the North Indian Ocean, thereby strengthening the PJ–ISM linkage. When the signals associated with the Maritime Continent are removed, the PJ–ISM linkage becomes weak and insignificant. The PJ indices should be chosen carefully when studying the climatic impacts of the PJ pattern.

In this study, we perform online sea ice bias correction within a Geophysical Fluid Dynamics Laboratory global ice-ocean model. For this, we use a convolutional neural network (CNN) which was developed in a previous study (Gregory et al., 2023, https://doi.org/10.1029/2023ms003757) for the purpose of predicting sea ice concentration (SIC) data assimilation (DA) increments. An initial implementation of the CNN shows systematic improvements in SIC biases relative to the free-running model, however large summertime errors remain. We show that these residual errors can be significantly improved with a novel sea ice data augmentation approach. This approach applies sequential CNN and DA corrections to a new simulation over the training period, which then provides a new training data set to refine the weights of the initial network. We propose that this machine-learned correction scheme could be utilized for generating improved initial conditions, and also for real-time sea ice bias correction within seasonal-to-subseasonal sea ice forecasts.

We used local P and S waves, and regional Lg waves to investigate the M w 4.9 Offshore Jeju Island earthquake, whose records show evidence of a complex rupture. This earthquake provides a rare window to understand the seismogenesis of moderate-sized earthquakes on the southern Korea–East China Sea continental shelf. We computed the relative source time functions (RSTFs) by aligning the signals on the origin time of the main and its empirical Green's function (EGF) events, allowing us to use them as differential times of the EGF pair. We determined subevent locations using direct-wave RSTFs, and captured the rupture variability of the two large subevents using waveform inversion of stacked Lg-wave RSTFs. The first subevent rupture started by two weak nucleation phases and propagated slowly and bilaterally. Then the second subevent ruptured westward. Our analysis demonstrates that the Lg-wave train observed at regional distances is useful in investigating detailed slip history.

Understanding the diurnal variation of horizontal wind in the atmospheric boundary layer is important for weather and climate research and wind energy applications. Here we analyze the hourly data from 91 wind profiler radar sites in China and observe that the power spectral density of horizontal wind in lower troposphere approximately follows the −5/3 power law in the mesoscale range over the ocean and coastal areas. However, in inland areas, the slopes of the power spectra are significantly greater than −5/3. We characterize the temporal and spatial variations of maximum wind speed and low level jets and find that the thermal wind effect may partially contribute to the high percentage of low-level jets observed in the southeastern coast of China and Hainan Island. While the ERA5 reanalysis reproduces wind spectrum well for time scales >1 day, its spectrum diverges significantly from that of profiler data at shorter time scales.

Tibetan Plateau (TP) snow cover is featured by sub-seasonal changes, affecting weather and climate in surrounding and downstream areas. Previous studies emphasize the effect of background atmospheric circulation on rapid changes of TP snow cover as a whole. However, spatial discrepant changes of snow cover over the TP with complex topography and uneven snowfall remain unaddressed. Our research indicates that snow cover fraction dominates the rapid changes of surface albedo across the TP, and snow depth also significantly influences surface albedo changes through modulating snow albedo in central and eastern TP with shallow snow. However, the excessive snow amount and empirical snow cover fraction schemes introduce spatially divergent biases of surface albedo changes in simulations. Our research highlights the instant response of TP surface albedo to both snow coverage and depth in snow season, and provides a promising perspective for improving TP snow and surface albedo simulations.

The high-resolution Whole Atmosphere Community Climate Model with thermosphere/ionosphere extension (WACCM-X) is used to study the impacts of gravity waves (GWs) on the thermospheric circulation and composition. The resolved GWs are found to propagate anisotropically with stronger eastward components at most altitudes. The dissipation of these waves in the thermosphere produces a net eastward forcing that reaches peak values between 200 and 250 km at mid-high latitudes in both hemispheres. Consequently, the mean circulation is weakened in the winter hemisphere and enhanced in the summer, which in turn impacts the thermospheric composition. Most notably, the column integrated O/N2 in both hemispheres is reduced and agrees better with observations. The mean thermospheric GW forcing in the meridional direction has comparable amplitude and acts to modify the gradient-wind relationship.

Subseasonal reversal of warm Arctic–cold Eurasia (SR-WACE) pattern has significant impacts on transitions of weather and climate extremes in Eurasia. This study explored the performances of climate models to simulate the main features of SR-WACE. For real-time predictions, most of the state-of-the-art climate models showed limited ability to accurately forecast SR-WACE in advance. Furthermore, most of the historical simulations from Phase 6 of the Coupled Model Intercomparison Project (CMIP6) had also difficulties in well simulating the SR-WACE. Further exploration showed that the simultaneous reversal of the Ural blocking high (UB) and Siberian high (SH) is the key atmospheric driver of the SR-WACE occurrences, which were verified by both of the real-time predictions and historical simulations. Our results implied that the simulation of SR-WACE was a huge challenge and the critical solutions included improving simulation of subseasonal reversals of UB and SH in the atmosphere.

No abstract is available for this article.