Carbon (C) emissions from headwater streams are derived from both terrestrial inputs and in-stream metabolism of organic C (OC), but the role of metabolism in boreal stream C fluxes remains uncertain. Determining the factors that regulate OC metabolism will help predict how the C balance of boreal streams will respond to future environmental change. In this study, we addressed the question: what controls OC metabolism in boreal headwater streams draining catchments with discontinuous permafrost? We hypothesized that metabolism is collectively regulated by OC reactivity, phosphorus availability, and temperature, with discharge modulating each of these conditions. We tested these hypotheses using a combination of laboratory experiments and whole-stream ecosystem metabolism measurements throughout the Caribou-Poker Creeks Research Watershed (CPCRW) in Interior Alaska, USA. In the laboratory experiments, respiration and dissolved organic carbon (DOC) removal were both co-limited by the supply of reactive C and phosphorus, but temperature and residence time acted as stronger controls of DOC removal. Ecosystem respiration (ER) was largely predicted by discharge and site, with some variance explained by gross primary production (GPP) and temperature. Both ER and GPP varied inversely with watershed permafrost extent, with an inverse relationship between temperature and permafrost extent providing the most plausible explanation. Our results provide some of the first evidence of a functional response to permafrost thaw in stream ecosystems and suggest that the contribution of metabolism to stream C emissions may increase as climate change progresses.

Interseismic deformation and strain rates derived from Global Navigation Satellite Systems (GNSS) or Interferometric Synthetic Aperture Radar (InSAR) data are often used to assess earthquake potential. InSAR measurements require GNSS data to put results into a geodetic reference frame, posing an issue in regions with limited GNSS data. Deformation rates are assumed to be indicative of long-term strain accumulation, and the evolution of strain rate throughout the interseismic period is poorly studied. We observe the interseismic period prior to the 2021 Mw 7.4 Maduo Earthquake. Using InSAR, we derive eastward velocities and maximum shear strain rate for three independent time windows to observe the temporal evolution of strain rate over time, whilst minimising the influence of near-field GNSS data. We find that strain rate peaks several years before the earthquake, contrary to recent studies showing acceleration of strain rate before large earthquakes, which has implications for earthquake hazard models globally.

A document by Roshan Jha. Click on the document to view its contents.

A key aspect in interaction between upwelling mantle plumes and spreading mid-ocean ridges is the along-axis dispersion of the plume, reflecting how far the plume flows along the spreading ridge axis. Observational studies measure the dispersion distance based on the width of geophysical or geochemical anomalies, while theoretical models often define it as the distance reached by plume flow through material advection or thermal diffusion. However, variability in these measurements and the underlying causes remain unresolved. To fill this gap, we explore the dynamics of plume-ridge interactions using three-dimensional non-Newtonian geodynamic models that simulate both material and thermal flow. Unlike previous studies that suggest a steady and uniform ascent, our results show a two-stage plume upwelling process: an initially accelerated ascent from the deep mantle to the mantle dehydration zone, followed by deceleration with lateral dispersion across and along the ridge axis. During the dispersion stage, plume flux and plume-ridge separation distance significantly influence both along-axis dispersion distance and thermal topography of the plume, while ridge spreading rate primarily affects the former. Observations and models consistently show that plume thermal diffusion extends farther along the ridge axis than material advection, with the thermal dispersion distance being approximately 1.55 times greater. We further propose two practical geodynamic indicators—a 0.7 plume material isoconcentration and an isotherm at 0.1 times the excess plume temperature—that can serve as references for estimating plume properties during along-axis dispersion in future studies of more complex plume-ridge systems.

The current research was carried out to investigate conventional heat transfer enhancement inside the tube by using twisted stainless-steel angle insert. Main objectives were to find the percentage of increment of heat transfer enhancement using twisted stainless-steel insert and to find the relation between Reynolds number and Nusselt number. A 940mm long copper tube of 26.6 mm internal diameter and 30 mm outer diameter, of which length of 762 mm has been used as the test section. A constant heat flux condition has been maintained by wrapping Nichrome wire around the test section and fiber glass insulation over the wire. K-type thermocouples and rotameter were used to measure temperature and rate of flow. With insert, heat transfer rate has been increased up to 140 percent. This technique does not rely on external power or activation. This experiment has shown simultaneous effects on Reynolds number and Nusselt number too.

Magnetic field-line curvature scattering (FLCS) of energetic particles in the equatorial magnetotail results in isotropization of pitch-angle distributions, loss-cone filling, and precipitation above a minimum energy at a given latitude. At a fixed energy, the lowest latitude of isotropization is the isotropy boundary (IB) for that energy. Nominally, the IB (latitude) exhibits a characteristic energy dependence due to the monotonic variation of the equatorial magnetic field intensity Beq with radial distance. Deviations from this nominal IB dispersion can occur if the radial Beq variation (spatial or temporal) is non-mononotic and/or if other precipitation mechanisms prevail. With its sensitive and detailed measurements of electron spectra up to relativistic energies, ELFIN’s recent observations reveal a variety of electron IBe patterns near magnetic midnight which are repeatable enough to warrant classification. This study aims to categorize the various IBe patterns observed by ELFIN’s high-fidelity but short lived dataset (a few months), compare them with simultaneous nearby POES observations, which are made with a limited energy coverage and resolution but last for decades, and discuss their possible interpretation. The general agreement between ELFIN and POES IB observations indicate a relatively large-scale nature of IBe patterns. Surprisingly, there exists a large number (up to 2/3 of all events) of non-monotonic-or steep/multiple-IB patterns. This suggest an abundance of non-trivial tail current sheet structures or a mixed contribution of two mechanisms in the vicinity of IBe in these cases.

Extreme climate events (ECEs) like heavy rainfall and heatwaves significantly impact society, and climate change is altering their frequency. Generalised Extreme Value (GEV) distributions help quantify these ECEs and guide human system design (e.g., return value of extreme wind gust sets construction codes at specific locations). We train a machine learning (ML) model using GEV distributions to determine the sample size required to estimate return values with specific uncertainties. For ECEs like heatwaves (with negative GEV shape parameters), fewer samples are needed to estimate the return value with specific uncertainty than rainfall extremes (positive shape parameters). For the heatwave example, a sample size of more than 20 times the annual recurrence interval is typically required to estimate the return value to ±10% uncertainty. A 1-in-20-year heatwave requires 400 samples, equating to 20 different 20-year simulations. Achieving such quantities will require extensive climate downscaling efforts, potentially aided by ML-based downscaling methods.

Palaeointenisty measurements are vital for understanding the deep Earth and the evolution of the geomagnetic field, however, they suffer from non-ideal behaviour that compromises the fidelity of the results. In an attempt to screen for the non-ideal behaviour that plagues palaeointensity experiments, selection criteria are used. One such non-ideal behaviour is partial thermoremanent magnetisation (pTRM) tails, which in the IZZI protocol result in a zig-zagging pattern in the Arai plot. While pTRM tail checks can be carried out, these are not routinely used in IZZI experiments. We set out a new framework with which to create, develop and re-assess selection criteria before applying it to our proposed new selection statistic, Ziggie, which is specific to detecting zig-zagging behaviour. Ziggie meets all the requirements set out; that is, it is able to objectively and robustly identify the target behaviour, consistently provide a quantifiable assessment of the target behaviour, and is predominately sensitive to the target behaviour while being free of undue influences. Other pre-existing statistics for zig-zagging in Arai plots, Z*, IZZI_MD, β and SCAT, are also tested, but fail to meet all requirements. We find that Ziggie should be adopted in selection criteria sets for the IZZI protocol with a criterion of Ziggie ≤ 0.1.

Accurate modeling of dependencies between variables of interest is imperative for understanding biophysical processes and mechanisms relevant to Earth Science research. This study presents a methodology to model the temporal or spatial distributions of variables using copula-based cosimulation (CopCoSim). This technique models and simulates the joint distribution of multiple variables by capturing their dependencies and correlations. We compared CopCoSim with the traditional Sequential Gaussian CoSimulation (SGCoSim) technique through two applications relevant to Earth Science representing one (i.e., time) and two dimensions (i.e., space). We present an application for soil CO2 efflux, which is a major flux in the global carbon budget, using two case studies: (1) temporal distribution of soil CO2 efflux and temperature, and (2) spatial distribution of soil CO2 efflux and temperature across the conterminous United States (CONUS). The methodology involves three steps: data input, application of stochastic simulation methods, and comparison of simulation outputs. The results indicate that CopCoSim provides a better model with higher precision and accuracy for representing variables of interest. CopCoSim better reproduces the univariate probability distribution, temporal or spatial autocorrelation, and dependency relationship between the predictor and response variables. We propose that CopCoSim is useful for research in Earth Science, where variables of interest (e.g., soil CO2 efflux and temperature) are often interdependent and exhibit complex temporal or spatial patterns.

New particle formation (NPF) is a complex atmospheric phenomenon defined by the gas-to-particle conversion that leads to the sudden burst and growth in aerosol particles. Extensive prior ambient, laboratory and chamber studies have demonstrated chemical mechanisms within the atmosphere that allow for aerosol nucleation and subsequent growth. A deeper understanding of the physical mechanisms within the atmosphere enhancing NPF are beginning to emerge with recent studies. For example, processes within the atmospheric boundary layer (ABL), such as turbulent mixing, can lead to the decoupling and recoupling of different atmospheric reservoirs to create favorable conditions that help initiate NPF. Using observations from the 2022 CFACT (Cold Fog Amongst Complex Terrain) field study conducted in the Heber Valley of northern Utah, this study demonstrates an interconnection between turbulence and the occurrence of NPF. The CFACT field study incorporated spatially distributed boundary layer instrumentation on a scale not typically seen in previous literature. Three case studies are presented that depict unique boundary layer conditions that modulate the development of NPF, characterized by sustained turbulence and weak intermittent turbulence. This analysis presents in situ measurements and derived variables to quantify the relationship between specific boundary layer processes and NPF.

Oxygen Deficient Zones (ODZs) are the largest pelagic sink of N containing nutrients in the ocean. The offshore Eastern Tropical North Pacific ODZ has been shown to be organic matter limited. We propose zooplankton/forage fish as a key source of organic matter for N2 production that has previously been ignored. We examined datasets from four cruises (April 2012, Jan 2017, April 2018, Oct 2019) at a station in the central ETNP. Backscattering data was used to determine zooplankton vertical migration depths (250-450 m, maximum at 270-280 m). Metazoan DNA concentrations, as measured by quantitative PCR, had a reproducible maximum at 270-280 m, confirming that these signals indicate the presence of zooplankton/forage fish. Additionally, a large maximum in sinking pteropod shells was found at 270 m, indicating that pteropods were part of the migrating community. While crustacean zooplankton have been shown to reduce respiration and excretion of ammonium under anoxia, we found intermittently measurable ammonium concentrations at 270 m. Here we show signatures consistent with organic matter of zooplankton/forage fish origin in the C:N and \(\delta\)13C of suspended and sinking organic matter at the vertical migration depth that suggest transportation to these depths by migrating zooplankton/forage fish. Also coincident with the migration maximum was a reproducible-between-years maximum in the biological N2 gas, and a tertiary nitrite maximum, which suggest that the migrating zooplankton are linked to N loss. Thus zooplankton/forage fish appear to be one source of organic matter which can fuel biological N2 production in ODZs.

The present study investigated the shear strain energy changes in a shear zone associated with interseismic plastic deformation and strike-slip earthquakes. A model of a very long strike-slip fault system was developed in which deep plastic flow is represented by an inelastic strain distribution. We derived analytical solutions for displacement and stress to estimate the changes in the shear strain energy. Applying this model to the San-in shear zone, Japan, we reproduced the observed surface velocity distribution by assuming a deep plastic flow with a horizontal thickness of T = 30 km, vertical thickness of 17 km, and strain rate of where 9 mm/year. We also found that the deep plastic flow roughly obeys a simple flow law. By using the stress changes induced by the deep plastic flow and the background stress estimated by a stress tensor inversion, we evaluated the changes in shear strain energy density in the shear zone. The energy at the seismogenic zone increases by J/m3/year when we assumed a differential stress of 100 MPa. We also evaluated the energy drop after two large earthquakes (MW 7.0 and 6.6). The estimated energy drop corresponded to an energy accumulation period of ~700 to ~1000 years, which is shorter than the period expected from geological observations.

In the upper ocean, the surface mixed layer is rich in submesoscale flows characterized by large vertical velocities and significant vertical transport. In addition, the vertical flux is also modulated by a variety of smaller-scale features, with dynamics approaching three-dimensional turbulence. Surface gravity waves significantly influence the submesoscale regime, particularly through the formation of Langmuir circulations, which are a direct outcome of wave-current interactions. However, current models often parameterize these effects, leaving their precise impact on vertical transport unclear. This study addresses this gap by investigating the roles of wave-modulated submesoscale structures, parameterized turbulent mixing, and Langmuir circulations on Lagrangian particle movement, utilizing high-resolution ($\Delta x \lessapprox$ $100$ m) realistic ocean simulations able to resolve this smaller-scale dynamics. Our high resolution ($\Delta x = 30$ m) simulations reveal that Langmuir circulations dominate the vertical transport with their strong vertical velocities. This wave-induced vertical fluxes significantly affect Lagrangian particle movement, increasing their vertical displacement and Lagrangian relative horizontal diffusivity. These effects occur alongside downwelling from submesoscale features, suggesting that Langmuir circulations are integral in transporting biological and ecological materials vertically and horizontally in the ocean, while Stokes drift, another product of the wave-current interactions, have a lesser role in the particle stirring in this open-ocean simulation. This study also suggests that sub-grid-scale parameterization via diffusion may be limited when trying to reproduce the effects of ephemeral and heterogeneous small scale flows included in high-resolution Eulerian flows.

During the winter season, stratification in the central Labrador Sea is eroded by surface heat fluxes causing convective overturning exceeding depths of 2km. This is one of the few locations globally in which deep convection occurs, making it an important feature of the climate system and ocean ventilation. Large-scale atmospheric circulation patterns modulate the air-sea interaction that drives the loss of ocean buoyancy. Here we investigate the process by which weather patterns driven by the North Atlantic Oscillation (NAO), and its northern centre of action, the Icelandic Low, modulate convective depths. A one-dimensional ocean model is used to quantify the mixed layer depth’s response to various atmospheric forcing conditions. We find that while net heat flux is the strongest modulating factor of mixed layer depth’s seasonal maximum, it is also strongly affected by the NAO. The Icelandic Low, despite its proximity to the Labrador Sea, does not affect mixed layer deepening as strongly. From geospatial correlation fields with heat flux, NAO, and Icelandic Low time series, it is evident that the NAO more efficiently regulates strong, cold, westerly winds from over the North American continent, which are more effective at cooling the ocean surface boundary layer. These correlations are supported by a compositing approach with a peak-over-threshold technique.

Kelvin-Helmholtz Instabilities (KHI) are known to be significant drivers of atmospheric turbulence. Recent observations show KHI forming with misaligned or angled billow segments that develop connecting vortex tubes and knots (T&K); these features promote distinctive, event-defining instability and mixing characteristics that were not accounted for in prior idealized studies. Though T&K have been shown to increase mixing in KHI events with low Richardson numbers (Ri), their influence in weakly KH-unstable, less-idealized environments is unknown. Here we present modeling results of KHI in the stratosphere to assess the impact of T&K dynamics in weakly KH-unstable environments. Radiosonde wind and temperature profiles from 22 February, 2006 near Lamont, Oklahoma measured vertically offset shear and stability peaks near 16.15 km with a minimum Ri = 0.11. Direct numerical simulations (DNS) of this event reveal decreasing shear and increasing stratification, where Ri increases to 0.2 as the shear and stratification peaks move to a common altitude. The resulting KHI exhibit T&K features forming adjacent to, and in superposition with, secondary convective instabilities (CI) rather than superseding them as in prior T&K studies with Ri = 0.05. Newly-discovered “crankshaft” instabilities distort the billows and give rise to secondary KHI with delayed, elevated dissipation. KHI that exhibit T&K dynamics are found to accumulate ~60% greater mixing than axially-uniform KHI with equal or lower mixing efficiency. The substantial increase in mixing suggests significant contributions of T&K dynamics to KHI events throughout the atmosphere that remain unaddressed in general circulation models’ turbulence parameterizations.

We investigate changes in the Madden-Julian Oscillation (MJO) modulation of cool-season North Pacific atmospheric rivers (ARs) and associated AR-landfall North American precipitation during La Niña (LN) years. Overall, AR frequency is reduced over the northeastern Pacific and western North America in phases 2-5 of the MJO. However, under LN, increased AR activity appears over those regions in phases 4-5 and across the central North Pacific in phase 3. Distinct effects of LN on the basic state and MJO contribute to the persistence of AR anomalous patterns in phases 3-5. For instance, MJO intensifies in phase 3 under LN, favoring the coupling between anomalous northeastward integrated water vapor transport (IVT) and the MJO convection over the eastern Indian Ocean. Also, suppressed MJO convection in phase 4 strengthens and shifts eastwards in LN, affecting the MJO teleconnection associated with North Pacific ARs. The northern Pacific subtropical jet extends northeastwards in LN, supporting an extratropical cyclonic flow over the Gulf of Alaska. The MJO propagates eastward more slowly over the Maritime Continent in LN, favoring a second coupling between eastward IVT and the MJO convection in phase 5. Decreased AR precipitation and frequency of AR rainfall extremes in phases 2-5 over western North America fade in LN years. Furthermore, increased AR precipitation and frequency of AR extremes over the Pacific Northwest and British Columbia intensify and shift from phases 3-4 to 4-5. Therefore, LN has nonlinear effects on the North Pacific MJO-AR connections and their AR landfalling impacts on western North American precipitation.

This paper investigates the behavior of photon orbits around black holes using the Eikonal equation and models of effective refractive index using the Schwarzschild metric, inspired by Lagrangian optics and the foundational work of David Nolte. Conducted as an educational exercise for advanced high school and undergraduate students, this research aims to help students combine multiple topics in physics to explore analogical relationships between different concepts such as the calculus of variations, optics, and general relativity. By employing numerical simulations to recalibrate photon trajectories, we highlight how the curvature of spacetime influences photon paths, particularly focusing on the stability of circular orbits. These results reveal significant deviations from classical predictions, emphasizing the critical role of gravitational lensing and the formation of black hole shadows. This paper is expected to provide consolidated information to understand and reproduce simulations of orbiting photons for interested high school or undergraduate students.

The implementation of dual-polarization weather radars has improved the accuracy of precipitation estimates. However, identifying hydrometeor types and evaluating related algorithms remains challenging. This study introduces a novel method to evaluate hydrometeor classification (HMC) schemes using Doppler spectra from a mm-wave dual-frequency Doppler-polarimetric slanted profiler. The output of the HMC scheme is used to calculate mixing ratios that are then combined with the ARTS Microwave Single Scattering Properties Database to simulate Doppler spectra of polarimetric variables that would be measured by the profiler. Comparing these with actual profiler measurements provides valuable validation information. We have tested this method on the wradlib HMC scheme using C-band weather radar data from the Netherlands (2021–2022) and a Ka- and W-band Doppler-polarimetric profiler operating at an elevation angle of 45°. The method works well in stratiform cases, but convective cases reveal the influence of turbulence and wind variability, highlighting the need for improved approaches. Uncertainty arises from selecting specific parameterizations for the particle size distribution (PSD) and for the relationship between hydrometeor size and terminal fall velocity, as well as from the derived mixing ratios. Additionally, observing at a 45° angle complicates separating horizontal wind from hydrometeor fall velocities, though the Mie notch in the dual-wavelength ratio can be effectively used to remove the radial wind component. Our results highlight both the potential and limitations of using this profiler configuration to evaluate HMC schemes.