A document by Fucent Hsuan Wei Hsu. Click on the document to view its contents.

To discuss slip behaviors in shallow slow earthquake regions, we investigate source characteristics of shallow very low frequency earthquakes (VLFEs) southeast off the Kii Peninsula in the Nankai subduction zone. VLFEs are a kind of slow earthquakes and are clearly observed at frequencies below 0.1 Hz. A non-linear inversion technique for moment rate function estimation and the permanent ocean-bottom seismometer network provided us with precise locations and detailed kinematic source characteristics of shallow VLFEs. The high activity of shallow VLFEs around the western edge of the subducted Paleo-Zenisu ridge is similar to previous studies. A notable trend change in the along-dip dependency of shallow VLFE moment rates was found. Along the profile west side of the Paleo-Zenisu ridge, moment rates of shallow VLFEs increase with reaching the megathrust zone. Small-scale topographic fluctuations of the subducted oceanic plate exist along this profile, but large-scale seamount subduction has not been identified even from dense seismic surveys. Similar tendencies have been reported in tectonic tremors in the Nankai and Cascadia subduction zones. On the other hand, the opposite trend appeared along the profile with the Paleo-Zenisu ridge. Small shallow VLFEs were dominant near the summit of the Paleo-Zenisu ridge. Fracture networks or stress fields due to seamount subduction possibly impede large shallow VLFEs around the subducted seamount. Our results suggest that the large-scale heterogeneity of the upper surface of the subducted oceanic plate could control source characteristics of shallow slow earthquakes.

As extreme precipitation events become more frequent and intense, local-scale climate services are increasingly needed to help communities adapt. We here evaluate two fully-coupled convection-permitting Earth System Models for their ability to resolve mesoscale extreme weather events. Using the Integrated Forecasting System (IFS) and Icosahedral Nonhydrostatic Weather and Climate Model (ICON) within the Next Generation Earth Modelling Systems (nextGEMS) project, we evaluate their depiction of extreme precipitation with a focus on the Mediterranean region through a comparison with high resolution reanalysis, gridded observations, a regional climate model, and a large-ensemble lower-resolution climate model. The results are then compared at a coarser resolution globally with CESM2. For dry extremes, we find that the higher resolution and hybrid/explicit representation of convection of the nextGEMS models improve the representation of dry hour frequency and alleviates the drizzle bias observed in CMIP6 models. The explicit representation of convection in ICON helps create realistic dry spell lengths over land, but also generates overly intense convective precipitation. Generally, the nextGEMS models concentrate dry spells into limited frequency yet overly long periods. For wet extremes, the nextGEMS models properly high intensities of heavy precipitation, aside from overestimation in ICON over mountainous terrain. The models appear capable of resolving extreme weather systems like medicanes and tropical cyclones making them useful for extreme weather climatology studies. Overall, the depiction of wet and dry precipitation extremes in the Mediterranean region are representative of the nextGEMS’ models performance across the global mid-latitudes demonstrating the models’ value in simulating extreme weather systems.

This study unveils the ability of 200-m near to Large-Eddy Simulation (LES) to resolve smaller scales in urban areas of a coastal megacity Chennai in India, which are crucial for accurately modelling Urban Induced Turbulence (UIT) and Urban Heat Island (UHI) effects. Unlike physics-based ensemble (PBE) models in kilometre-scale simulations, LES captures fine-scale atmospheric dynamics, offering enhanced resolution to simulate localized turbulence and heat flux variations. With a resolution of 200 m, Weather Research Forecasting (WRF) LES simulation can convincingly resolve a higher urban heat flux, friction velocity, surface wind speeds, and moisture transport over urban areas. These factors are found to play a critical role in intensifying extreme weather events such as heavy rainfall, especially in the downwind regions of coastal megacities like Chennai. This phenomenon is driven by LES-resolved interaction between the urban heat island effect and the prevailing winds.

A document by Alice Puppin. Click on the document to view its contents.

Forest biomass changes influence the forest area required to meet the demand for timber and carbon storage, and thus land use and land cover change (LULCC). The worldwide impacts of global change (e.g., climate change, CO2 fertilization, nitrogen deposition) on forest biomass have been widely recognized and examined, yet are usually ignored by existing LULCC projections. This study explores the role of forest biomass change driven by global change in future global LULCC projections and investigates the underlying drivers. We incorporated the global change impacts on forest biomass from a land surface model driven by the projections from two Earth system models (ESMs) under three Shared Socioeconomic Pathways (SSP) scenarios (SSP126, SSP370, and SSP585) into an integrated assessment model, the Global Change Analysis Model. Considering forest biomass change decreases the projected expansion of managed forests and managed pastures, reduces the loss of unmanaged pastures and unmanaged forests, and provides more areas for cropland. The relative decrease in managed forest is-4.0%,-21.7% and-31.9%, respectively under SSP126, SSP370, and SSP585 in 2100 if forest biomass change is considered. CO2 fertilization is the dominant driver of increasing forest biomass and thus LULCC, compared to the change in climate and nitrogen deposition under SSP585. Using climate forcing data from two ESMs leads to similar impacts of forest biomass change on LULCC in terms of sign and trend but different magnitudes. This study highlights the large impact of forest biomass change on shaping future LULCC dynamics and the critical role of CO2 fertilization.

Topobathymetric scanning LiDAR deployed on unmanned aerial systems (UAS) is a powerful tool for high-resolution mapping of the dynamic interface between topography and bathymetry. However, standardized methods for empirical resolution validation have not been widely adopted across LiDAR applications. While theoretical models of idealized LiDAR sampling resolution can be used to describe topographical resolution, misrepresented or unknown behaviors in an instrument, platform, or environment can degrade expected performance or introduce georeferencing inaccuracies. Furthermore, bathymetric resolution is strongly dependent on water surface and column conditions. Thus, only empirical methods for evaluating resolution will provide reliable estimates for both topographic and bathymetric surveys. Presented is an extension of standard modulation transfer function (MTF) methods used by passive imaging systems applied to high-resolution scanning LiDAR. Compact retroreflectors characterized as point and line sources are employed to empirically assess effective LiDAR system resolution through MTF analysis in topographic and bathymetric scenes. These targets enable MTF analyses using range-height measurements without reliance on intensity data, promoting widespread applicability among LiDAR systems. Empirical MTFs calculated using these targets are compared against theory-derived counterparts as empirical measurements elucidate influences by elements that are unknown or difficult to model. Simulated point cloud data were incorporated into theoretical MTF descriptions to better represent empirically-derived topographic MTFs, revealing mirror pointing uncertainties in the across-track axis. Similarly, theoretical bathymetric MTFs augmented with simulated, subaqueous data enabled water surface slope estimation using empirical measurements of submerged retroreflector targets, where rough water surfaces strongly influenced beam steering and the corresponding point spread MTFs.

• We propose a strategy combining geodetic reference frame definition and time series analysis to extract slow slip events from GNSS data. • We detect and characterize a shallow, 10-km-long, three-week-long SSE along the central section of the North Anatolian Fault. • We show that persistent aseismic slip and SSEs are spatially complementary and interact at shallow depth.

not-yet-known not-yet-known not-yet-known unknown Ocean wave activity in polar seas is intensifying, so that modeling waves in ice-covered seas accurately is critical for navigational safety and forecasting the response of the declining sea ice.WAVEWATCH III® (WW3) has emerged as the leading spectral wave model for high-latitude regions in recent years, having incorporated an extensive suite of 14 ice-induced wave damping parameterizations. A set of WW3 hindcast simulations of the wave event observed during the 2017 PIPERS wave buoy deployment in the Ross Sea is conducted to assess the performance of all ice damping parameterizations and identify consistent biases. Collocated spectra obtained from each WW3 hindcast and buoy measurements are analyzed and compared in relation to wave and ice conditions. It is found that 9 of the 14 parameterizations are able to reproduce large wave events accurately for relatively low ice concentrations. WW3 consistently overestimates significant wave height and underestimates mean wave period at high ice concentrations. Our findings suggest WW3 does not sufficiently damp the mid-to-high frequency tail of the wave spectrum in ice-covered oceans.

Quasi-two-dimensional visualizations of microstructure in the thermocline are created by processing χpod signals in a non-standard way. As the moored instrument is pumped by surface waves, the fast thermistors at each end trace out vertically overlapping paths, from which we produce 2–3 m tall swaths. A swath capturing the unmistakable form of Kelvin–Helmholtz billows provides a proof of concept—albeit by relying on what is a rare event in our dataset. More commonly, swaths exhibit steppy temperature fields during weaker turbulence, an abundance of small overturns during stronger turbulence, or some combination thereof. To examine this continuum statistically, we take a 13-month dataset from an equatorial χpod at 120 m deep and divide it into 53 000 swaths, each 10 minutes long. Swaths are ordered based on their associated buoyancy Reynolds number (Reb) inferred from our standard χpod processing. Clear visual differences in swath characteristics arise when comparing across an order of magnitude or more (e.g., Reb < 10 vs Reb = 10–100 vs Reb > 100). With the help of a convolutional neural network to semi-objectively pick representative swaths, we present our best estimates of what microstructure looks like in two dimensions as a function of Reb.

The fire season of 2020 in Siberia set a precedent for extreme wildfires in the Arctic tundra. Large fires burned in the carbon-rich permafrost landscape, releasing vast amounts of carbon, and changing land surface processes by burning vegetation and organic soils. However, little is known about the mosaics of burned and unburned patches formed by tundra fires and the underlying processes that generate them. In this study, we investigated six fire scars in the northeastern Siberian tundra using high-resolution PlanetScope imagery (3 m) to map burned fraction within the scars. We then used Bayesian mixed models to identify which biotic and abiotic predictors influenced the burned fraction. We observed high spatial variation in burned fraction across all tundra landforms common to the region. Current medium-resolution fire products could not capture this heterogeneity, thereby underestimating the burned area of fire scars by a factor of 1.1 to 4.4. The heterogeneity of the burn mosaic indicates a mix of burned and unburned patches, with median unburned patch sizes being smaller than 180 to 324 m². Pre-fire land surface temperature, vegetation heterogeneity and topography predicted burn fraction in our analysis, matching factors previously shown to influence large-scale fire occurrence in the Arctic. Future studies need to consider the fine-scale heterogeneity within tundra landscapes to improve our understanding and predictions of fire spread, carbon emissions, post-fire recovery and ecosystem functioning.

Glacial lake outburst floods can transport large volumes of sediment. Where these floods reach the coastline, much of that particulate load is delivered directly to the marine environment. It has been suggested that offshore deposits, specifically in fjord settings, may provide a faithful record of the frequency and timing of past outburst flood events. However, a paucity of observations means that the mechanics and the timing of offshore transport of sediment following a glacial lake outburst event remain poorly constrained. Here, we document the changes in sea surface sediment dynamics following the 28th November 2020 Elliot Lake outburst flood in British Columbia, which transported ~4.3x106 m3 of sediment into an adjacent fjord (Bute Inlet) as a deep nepheloid layer directly following the event. However, analysis of sea surface turbidity using in situ measurements and satellite-derived estimates reveals that changes in fjord-head surface turbidity immediately following the major flood were surprisingly small. The highest measured sea surface turbidity instead occurred five months after the initial outburst flood. This delayed increase in seaward sediment flux was coincident with the onset of the spring freshet, when discharge of the rivers feeding Bute Inlet increase each year. We suggest that large quantities of sediment were temporarily stored within the river catchment, and only remobilised when river discharge exceeded a threshold level following seasonal snowmelt. Our results reveal a temporal disconnect, where onshore to offshore transfer of sediment is stepped following a glacial lake outburst flood, which could complicate the architecture of subsequent deposits.

A travelling ionospheric disturbance (TID) containing embedded plasma structures which generated Fresnel type asymmetric quasi-periodic scintillations (QPS: Maruyama, 1991) was tracked over a distance of >1200 km across Northern Europe using the LOw Frequency ARray (LOFAR: van Haarlem et al., 2013). Broadband ionospheric scintillation observations of these phenomena are rarely reported in the literature as is the ability to track asymmetric QPS generating plasma structures over such a distance. Asymmetric QPS are characterised by an initial broadband signal fade and enhancement which is then followed by ‘ringing pattern’ interference fringes. These results demonstrate that QPS generating plasma structures can retain their characteristics consistently for several hours, and over distances exceeding 1200 km. A propagation altitude of 110 km was estimated with observations of plasma density modulation in a sporadic-E region detected by the Juliusruh ionosonde, and direct measurements of a wavefront from the TID by co-located medium frequency radar, in which the front is clearly oriented NW-SE, and at an altitude of ~110 km. The TID propagated SW with a calculated velocity of 170 ms-1 and an azimuth of 255°. Periodicity analysis, using the calculated velocity, yielded a spacing between each QPS-generating plasma sub-structure of between 20-40 km. Co-temporal GNSS data were used to establish that these plasma density variations were very small, with a maximum amplitude of no more than +/- 0.05 TECu deviation from the background average.

The paleoenvironments and ecosystems of northern China during the Miocene are complex topics, especially concerning the impact of the uplift of the Tibetan Plateau on the surrounding areas and the ecological adaptations of mammals. Our analyses using stable carbon and oxygen isotope analysis, cenograms, and hypsodonty of herbivorous mammals reveal open, arid, savanna-like habitats in the Junggar Basin during the middle Miocene, which subsequently spread to northern China by the late Middle Miocene. Large herbivores, particularly proboscideans and rhinocerotids, exhibited strong adaptations to these open environments. However, smaller taxa maintained a preference for more closed, forested areas. Despite global climate events, faunal diets in the Junggar Basin remained consistent, although biodiversity declined, indicating increased ecological pressure. Our findings contribute to understanding middle Miocene paleoecology in northern China and the adaptive strategies of mammals in response to environmental changes.

Estimating the probability of rare or yet unobserved rainfall extremes is essential for hazard quantification, especially in the context of an intensifying water cycle and of short observational records, common even in countries with long hydro-meteorological monitoring tradition. Data limitations can be mitigated by using regionalization techniques, which augment observational information, and by employing effective statistical models , such as the Metastatistical Extreme Value Distribution (MEVD), which maximizes the use of available observations. In this work, we develop the MEVD Regionalized framework (MEVD-R) to reduce uncertainty in estimating the probability of rare events that are not present in the training sample. Extensive testing using a global dataset of 40,000 rain gauges across Europe, North America, and Australia demonstrates that MEVD-R yields negligible systematic error and greatly reduces uncertainty compared to traditional approaches. MEVD-R can even provide estimates when available data are too sparse for conventional methodologies to offer reliable results.

Seismic velocity inversion of upper crustal structures in deep sea is challenging, as the unique condition of thick water column often limits the applicability of conventional inversion techniques. For example, while dispersion curves of guided P waves are commonly utilized for estimating subsurface P-wave velocity in land and shallow water environments, these waves have remained in obscurity in deep-water environments due to interference from subseafloor reflections, making them difficult to observe and, until now, unobserved. In this work, we report the first observation of guided P waves in deep water from multichannel seismic data and successfully extract multimode dispersion curves. The dispersive modes of deep water guided P waves are controlled by layered medium beneath the seafloor. Analyzing the dispersive modes of deep water guided P waves provides a tool for subsurface structural inversion in deep water environments.

Ionospheric topside O+ diffusive flux is derived using Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation data, to investigate its global distribution and also its role in winter nighttime enhancement (WNE) of electron density. The flux of the winter hemisphere maintains downward throughout the night. It is much larger between 30o and 50o geomagnetic latitudes and keeps increasing until 22:00-00:00 LT. It peaks at 60oW and 60oE-120oE geographic longitudes during the December solstice, and at 180oE during the June solstice. These features are similar to those of WNE in NmF2. Furthermore, the derived flux is applied as the upper boundary condition to run the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM). The simulated spatial-temporal variations of WNE are consistent with the observations. The results indicate that downward plasma diffusion from the plasmasphere is the major mechanism of WNE, and the simulation quantifies its contribution.

This study presents an information content analysis of the retrieval of global carbon monoxide (CO) from the 2 nd generation of Hyperspectral Infrared Atmospheric Sounder on board Fengyun-3E (FY-3E/HIRAS-II), which is the world's first dawn-dusk orbiting meteorological satellite for civilian use with equatorial overpass times at about 5:30 am/pm. Using the distinctive absorption features of CO around 2145 cm-1 in the infrared band, a retrieval algorithm based on optimal estimation is first developed to retrieve the CO profiles from FY-3E/HIRAS-II. The thermal contrast, defined as the temperature difference between the surface and the lower atmosphere, is then examined for the FY-3E/HIRAS-II observations to investigate the potential sensitivity of the observations. Retrievals of CO columns on four representative days over four seasons reveal strong enhancements from global wildfire emissions. Furthermore, the information content from the spectra, quantified by the degree of freedom for signal (DOFS), is assessed using the retrievals. The retrievals are compared with model simulations, which show good agreement. Finally, synthetic experiments are performed to investigate the impacts of thermal contrast and the vertical structure of wildfire-induced CO enhancement on the observational sensitivity. The result highlights the effectiveness of observing wildfire-induced CO enhancement during the dawn and dusk hours, even thermal contrast conditions are not favorable. This study demonstrates the capability of FY-3E/HIRAS-II to monitor global CO, which sheds light on the potential benefits of adding dawn-dusk orbit observations to the current global air quality observations from mid-morning and early-afternoon orbit constellations.