A document by Eshrat Fatima. Click on the document to view its contents.

A document by Mason Perry. Click on the document to view its contents.

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.

Mars, characterized as a “desert” planet with little water vapor, primarily relies on dry deposition processes for dust removal. Although dry deposition processes include gravitational sedimentation, turbulent transfer, Brownian diffusion, impaction, and interception, gravitational sedimentation is considered the only way for dust removal in most current models. To have a more comprehensive understanding of the effects of Martian dust removal processes, a physics-based scheme of dry deposition processes (e.g., turbulent transfer, Brownian diffusion, impaction, and interception) with resolved dust particle sizes representing the lifting dust size distribution is implemented in the MarsWRF general circulation model in this study. The model results reveal that the dry deposition velocity increases significantly with the decrease in dust size, especially for small dust particles. This enhancement in the removal efficiency of small particles leads to an increase in the effective particle radius of airborne dust and a decrease in dust opacity, particularly in the high latitudes of the northern hemisphere during the period of high dust loading. In these latitudes, the atmospheric temperature rises from the surface up to an altitude of 55 km, with a peak temperature difference of about 3.8 K, driven by dynamical warming from the strengthened descending branch of the upper meridional circulation. In addition, the sublimation of CO2 surface ice in the high latitudes of the northern hemisphere is increased, and the condensation of the gas phase is decreased.

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.

It is well known that the Kepler constant R^3/T^2 is a constant of celestial mechanics. It is shown here that the ratio of the cube of the distance to the square of time is a constant for many physical objects and is of a universal nature. The cosmological equation GMUTU 2 =RU 3 is obtained, which includes the constant RU^3/TU^2 as a ratio of the parameters of the Universe. The cosmological equation combines 4 parameters of the Universe: mass MU, radius RU, time TU and the Newtonian constant of gravitation G. In the cosmological equation, the constant RU^3/TU^2 is a constant of the Universe. The electrodynamic equation e 2 t0 2 =mere 3 4πε0 is obtained, which includes the constant re^3/t0^2 as a ratio of the parameters of the electron. The equation combines 4 parameters of the electron: mass me, classical radius of the electron re, characteristic time t0, electric charge e. In the equation containing the electron parameters, the constant re^3/t0^2 is a constant of electromagnetism. These equations show that the limits of applicability of Kepler's ratio R^3/T^2 go far beyond planetary mechanics. Ratio R^3/T^2 is a constant not only of celestial mechanics, but also a constant of the Universe and even a constant of the electron.

The Salish Sea is a semi-enclosed estuary whose largest basin (Strait of Georgia) is connected to the north-eastern Pacific Ocean through regions with tight constructions and sills that cause intense tidal mixing. The estuarine circulation is complicated through the tidally mixed region around the San Juan and Gulf Islands (SJGI), which consists of three different straits: Haro Strait, Rosario Strait, and San Juan Channel. Haro Strait, as the largest and deepest of the channels, is the dominant pathway; however, we determine that Rosario Strait also has an important influence in this region. To examine the differences in water transport through the different channels, Lagrangian particle tracking simulations were performed for a 4-year hindcast (from 2018-2022) using the 3-dimensional numerical model SalishSeaCast. While Haro Strait has southward surface flow and northward deep flow, there is primarily southward flow at all depths through Rosario Strait and San Juan Channel. The proportion of the total southward flow through these two channels is higher from May – October and this increase is attributed to the influence of both the Fraser River and the river discharge from Puget Sound. Rosario Strait is the dominant pathway of southward exchange from the Strait of Georgia to Puget Sound, while the majority of deep northward flow to the Strait of Georgia is through Haro Strait.

Three significant changes have occurred in the winter climate in Europe recently: increased UK flooding; Iberian drought; and warmer temperatures north of the Alps. The literature links all three to a persistent, significant increase in sea level pressure over Southern Europe, the Mediterranean, Iberia and the Eastern Atlantic (SEMIEA) which changes the atmospheric circulation system: forcing cold fronts to the north away from Iberia; and creating a south westerly flow around the northern perimeter of the high-pressure region bringing warmer, moist air from the subtropical Atlantic to the UK and Europe which increases precipitation in the UK and raises the temperature in Europe. I use CMIP6, the Last Millennium Ensemble, MERRA-2 and Terra-NCEP-ERA5 data to demonstrate that the extreme, anthropogenic, West African aerosol Plume (WAP) which exists from December to April perturbs the northern, regional Hadley Circulation creating the high pressure in SEMIEA. I also show that the anthropogenic WAP has only existed in its extreme form in recent decades as the two major sources of the WAP: biomass burning; and gas flaring have both increased significantly since 1950 due to: a four-fold increase in population; and gas flaring rising from zero to 7.4 billion m3/annum and note that this time span coincides with the changes in Europe’s winter climate. I also suggest that it may be possible to eliminate the WAP and return the winter climate of Europe to its natural state after the crucial step of recognising the cause of the changes is taken.

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.

Coupled land-atmosphere models exchange grid cell mean values of states and fluxes even as they separately simulate subgrid variability. The characteristics of atmospheric heterogeneity driven by land surface heterogeneity are examined in large eddy simulations. The degree of spatial variance in the atmosphere is highly correlated with the spatial variance of land surface fluxes, but the impacts are entirely at scales larger than 10-30 km. Between 1-10 km throughout most of the day there is no difference in power spectra over heterogeneous and homogeneous surfaces, as synoptic situations and internal dynamics associated with atmospheric turbulent transfer is insensitive to surface heterogeneity. To improve forecasts, the ability of land surface heterogeneity to organize mesoscale circulations affecting boundary layer evolution and convective development should be represented in non-cloud-resolving models, as modern convective parameterizations can account for such subgrid processes. This will require the exchange of subgrid information between land and atmosphere models.

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.

Understanding the fate of microplastics (MPs) in soil is one of the most urgent environmental tasks we face. It is also a very challenging one, as there are numerous properties of both MPs and the soil, as well as hydrological and geochemical conditions, that interplay to affect MPs transport. In this study, we conduct laboratory experiments in which two of the most commonly used MPs types in agriculture (polyethylene terephthalate (PET) and polypropylene (PP)) are leached into an idealized soil analog (glass beads). We find that MPs inhibit water flow, delaying its passage through the sample and making it more tortuous, forcing the flow to occur through preferential pathways (fingers). These effects are more pronounced for PP, which is more hydrophobic, than for PET. The transport of PP is inhibited relative to that of PET, which is attributed to its both its impeding effect on water flow (the driving force), as well as its surface charge which increases its tendency to adsorb onto soil particles, and lower density which curbs downward transport.

During periods of northward interplanetary magnetic field (IMF), the magnetospheric structure and dynamics are dramatically different compared to the southward IMF case. Previous studies using both observations and simulations have shown that the magnetotail becomes dominated by closed magnetic flux and associated trapped particle populations. In this study, we analyse three intervals of plasma observed in the high latitude magnetotail during a period of prolonged northward IMF, coinciding with observations of cusp-aligned arcs in the polar region. We observe that the plasma is typically continuous with some substructure observed on length scales of 0.5 - 1.5 R$_E$ which may be linked to the substructure observed in cusp-aligned arcs. The plasma characteristics in each of the three intervals studied are similar. The ion and electron densities are on the order of 0.2 - 1 cm$^{-3}$. The electron energies typically vary between 10$^2$ - 10$^3$ eV. The ion energies are higher compared to the electron energies and range between 10$^2$ - 10$^4$ eV. The ion temperatures are on the order of 5 - 18 MK. The speed of the plasma crossing the Cluster spacecraft is between 4 - 21 km/s which is on the order of magnitude of convection speeds in the magnetotail plasma sheet. We tentatively suggest that this may provide supporting evidence for dual lobe reconnection acting to trap plasma within the magneotsphere and resulting cusp-aligned arc formation.

The radiation exposure on the lunar surface from galactic cosmic rays and solar energtic particles was predicted with model calculations. The effectiveness of regolith shielding against cosmic radiation was investigated.

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.

Many iron meteorites sample the metallic cores of planetesimals, providing a unique opportunity to study early Solar System planetary processes. Modeling the chemical evolution during crystallization of these iron meteorite groups provides evidence that both S and P were present as light elements in planetesimal cores. As fractional crystallization of these cores proceeded, the concentrations of both S and P in the residual metallic liquid in the core increased, and eventually, liquid immiscibility in the Fe-Ni-S-P system would be expected to be encountered in many cases. For example, the IIAB and IIG irons may be related in this way. Considerable previous experimental work has determined element partitioning behaviors between solid metal and liquid metal as a function of the S and P concentrations of the metallic liquid, but few experimental studies have examined trace element partitioning behavior after the onset of liquid immiscibility. In this work, we present new experimental results that determine element partitioning behavior between two coexisting immiscible metallic liquids in the Fe-Ni-S-P system, as may be experienced during the later stages of the evolution of planetesimal cores.

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.

The frictional velocity dependence and healing behavior of subduction fault zones play key roles in the nucleation of stick-slip instabilities at convergent margins. Diagenetic to low-grade metamorphic processes such as pressure solution are proposed to be responsible for the change in frictional properties of fault materials along plate interfaces; pressure solution also likely contributes to the acceleration of healing according to previous studies. Here, we report velocity-step experiments using rocks collected from ancient subduction fault zones, the Lower Mugi and Makimine mélanges of the Cretaceous Shimanto belt. The two mélanges preserve paleotemperature records corresponding to the updip and downdip limits of the seismogenic zone and deformation recording a lower versus higher degree of pressure solution. Our data show that the Lower Mugi mélange sample exhibits velocity-weakening to velocity-neutral behavior under low normal stress, and the Makimine mélange sample shows velocity-strengthening behavior under high normal stress. This is consistent with the slip behavior observed at the depths they have been subducted to along the plate interface. We also perform a series of slide-hold-slide experiments under different hydrothermal conditions using the Lower Mugi mélange sample to evaluate the role of pressure solution in fault healing and its dependency on temperature. The results show that healing rates increase in tests operated at higher temperatures. The microstructures related to pressure solution found in the postexperimental gouges support the idea that the elevated healing rate can be related to pressure solution.