Ultraviolet images of Earth’s polar regions obtained by high altitude spacecraft have proved to be immensely useful for documenting numerous features of the aurora and understanding the coupling between Earth’s magnetosphere and ionosphere. In this study we have examined images obtained by the Far Ultraviolet (FUV) Spectrographic Imager (SI) camera on the IMAGE satellite during the first three years of its mission (2000-2002) for comparison with observations of large geomagnetic disturbances (GMDs) by ground-based magnetometers in eastern Arctic Canada. Such GMDs are the physical drivers of geomagnetically induced currents (GICs) in susceptible technological infrastructure such as long-distance power lines and pipelines, but to our knowledge this is the first study to investigate the use of high-altitude imager data to identify the global context of GMDs. We found that rapid auroral motions or localized intensifications visible in these images coincide with regions of large dB/dt as well as localized and closely spaced up/down vertical currents and increased equivalent ionospheric currents. These magnetic perturbations and currents can appear or disappear in a few tens of seconds, thus highlighting the importance of images with a high cadence.

The recent European Space Agency Aeolus mission provided global coverage of horizontal line-of-sight (HLOS) wind profiles. Using observing system experiments with HLOS winds in the ECMWF data assimilation system, we quantify the effects of HLOS winds on wave circulation and the mean zonal state in the tropical upper troposphere and lower stratosphere (UTLS) in relation to the background shear. Despite large observation errors, the assimilation of HLOS winds produced substantial effects on Kelvin and n=1 Rossby wave zonal winds, and, through 4D-Var, on mixed Rossby-gravity waves. The effects are asymmetric in easterlies and westerlies, consistent with the background shear. The largest analysis increments due to HLOS winds occurred during the 2019/2020 disruption of the quasi-biennial oscillation. The results highlight the importance of observing shear zones within the UTLS for reducing tropical analysis uncertainties.

This study aimed to evaluate the potential dam breach scenario of the proposed Naumure Dam using the HEC-RAS model. Hydrological and meteorological data from the study area were used to calculate the probable maximum flood, serving as a hydrological input for the model. Geometric data such as reservoir area, inline structure, streamline, riverbank, and flow path were modeled using the HEC-RAS RAS-Mapper tool. Various parametric equations were employed to calculate the breach parameters, which were then input into the HEC-RAS 5.0.7 simulation model along with the input hydrograph. Subsequently, an unsteady flow analysis was conducted to direct the flood through each cross section of the river. The model yielded a maximum flow rate of 141,423.48 m3/s at the dam axis 3.8 hours after the onset of dam failure. The study area, which extended 31.6 km downstream, was analyzed and hydrographs at different cross sections were examined. The results were mapped onto topographic GIS maps to identify affected areas. Approximately 30 km downstream, the settlement area in Bhalubang was inundated with a peak discharge of 48,579.29 m3/s at this location. The research will help relevant authorities devise an emergency response strategy and implement flood mitigation measures.

Highly productive summer phytoplankton blooms in the central North Pacific Subtropical Gyre (NPSG) are a near annual occurrence that lead to the export of significant amounts of surface particulate carbon being exported to depth. The cause for the formation of these blooms remains unresolved, but the availability iron (Fe) may be a potentially important factor controlling productivity in the central NPSG. From July to October 2022, a large persistent phytoplankton bloom formed around 23.3{degree sign}N, 154.6{degree sign}W that was observable through satellite imagery. We measured elevated Fe concentrations within the bloom that might have stimulated nitrogen (N2) fixation. We estimate that waters that hosted the diazotroph-fueled bloom received up to 20 percent more soluble and total Fe through aerosol deposition than in nearby waters that passed through locations outside the bloom. Even though this moderate increase does not represent incontrovertible evidence that the bloom was stimulated by aerosol Fe deposition, we note evidence of a particularly intense pulse of Fe deposition which occurred roughly 1 month before the bloom. Thus, we suggest a possible role for a lagged Fe stimulation of N2 fixation and blooms and encourage studies which further explore whether Fe deposition might elicit a biological response after approximately 1 month.

Biological activity in the surface ocean leads to emissions of methanethiol (MeSH) and dimethyl sulfide (DMS). Measurements of MeSH in the marine atmosphere are sparse and the impact of NOx pollution on MeSH oxidation remains unexplored. We present measurements of MeSH and DMS at a coastal site with NOx concentrations up to 24.3 ppb in the United Kingdom during May and June. Winds coming from the seaward (northerly) direction showed a median (25th quantiles) MeSH mole fraction of 15.7 (7.9-26.9) ppt. Mole fractions were generally higher in winds coming from the sea over those from land. The measurements reveal significantly lower MeSH during daytime. Using an atmospheric box model, we suggest substantial night-time oxidation of MeSH by NO3 and that NOx pollution has the potential to reduce the SO2 yield from MeSH. This work confirms the prevalence of MeSH and illustrates the impact of NOx pollution on MeSH oxidation.

A key component of the ocean’s global overturning circulation is the return of deep water from the Indian and Pacific Oceans to the Southern Ocean, transporting heat, carbon and nutrients poleward and towards the ocean surface. Indian Deep Water (IDW) and Pacific Deep Water (PDW) traverse the South Australian basin as they bring high carbon, low oxygen water to upwell in the Southern Ocean. Historically, limited sampling of this basin has made characterizing this circulation difficult. Here, we use data from the Biogeochemical and Core Argo arrays to identify the upper portion of the deep water in this basin. We map potential vorticity, oxygen, temperature, and salinity. We combine profiles with trajectory data to calculate mean geostrophic velocities on isopycnals. From these property and velocity maps, we identify three branches of flow within the σ1=32.2 to 32.3 kg/m3 isopycnal layer, which captures the deep water within the Argo range: a deep eastern boundary current (DEBC) carrying warm salty IDW along the continental slope, a central southeast pathway carrying IDW through the center of the basin, and a westward pathway carrying fresher, cooler PDW into the basin. We measure these pathways with a transport of 0.29 ± 0.28 Sv, 3.6±2.3 Sv, and 3.4±0.93 Sv respectively in the neutral density layer γN = 27.77 kg/m3 -27.87 kg/m3; we estimate the full transport of the DEBC as 2.2±2.1 Sv, the southeast IDW as 27±17 Sv, and the westward PDW as 18±5.8 Sv. These three pathways characterize the properties across the South Australian Basin.

Giant sequoia trees (sequoiadendron giganteum) are the world's largest single-stemmed tree and an iconic species in the Sierra Nevada mountains. Giant sequoias require large volumes of groundwater for transpiration, but little is known about subsurface critical zone structure beneath giant sequoias, hindering our understanding of the resilience of these giants to environmental change. We determined the quasi-3D seismic P-wave velocity structure beneath a grove of four giant sequoia trees in the Mariposa Grove, Yosemite National Park, CA, using seismic refraction tomography. A key feature of this study is the implementation of an interactive, semi-automatic picker based on the dynamic time warping algorithm to precisely identify seismic first arrivals. This advanced picking method enhances the precision of seismic first arrivals and significantly reduces data processing time. The resulting detailed seismic velocity structure provides valuable insights into the subsurface characteristics beneath these ancient trees. High seismic velocities are observed directly beneath standing sequoia stems, but not under a recently fallen sequoia, suggesting that enhanced pressure from the mass of the tree changes soil structure beneath the trees. The velocity structure also reveals important details about root zone structure and the extent of weathering in the critical zone beneath the giant sequoias, giving us a better understanding of the subsurface environment that supports the giant sequoias.

Using three-dimensional MHD simulations, we explore the stability of magnetotail configurations that include a local enhancement of $B_z$ (a “$B_z$ hump”). We focus on configurations that were previously found to be unstable in 2-D, neglecting cross-tail ($y$) variations as well as a cross-tail magnetic field component $B_y$.\, but approached final 2-D stable states. Not surprisingly, the 2-D unstable configurations were also found unstable in 3-D, developing 3-D structure after an initial rise as in 2-D. This is consistent with the fact that the selected $B_z$ hump configurations are characterized also by a local tailward decrease of field line entropy, which has been found to govern ballooning/interchange (B/I) instability \cite{schi04}. The evolution of the maximum electric field of the unstable 3-D modes showed an early exponential growth, which was only modestly faster than the 2-D mode. This might suggest that the unstable ballooning regime extends from $k_y \to \infty$ (proper ballooning modes) over finite $k_y$ even to $k_y \to 0$, at least for some equilibria. When the 3-D modes had evolved they grew significantly faster than the 2-D modes. This was associated with an evolution into several narrow beams. The 3-D modes did not approach stable final configurations. The final 2-D stable configurations approached from the unstable ones were found to be unstable in 3-D. These findings are again consistent with the fact that the 2-D evolution, governed by ideal MHD, did not alter the characteristics of the entropy function.

A document by NAGNON BERNARD YEO. Click on the document to view its contents.

Mesoscale numerical weather prediction models currently operate at kilometre-scale and even sub-kilometre-scale resolutions. Although shallow cumulus convection is partly resolved at these resolutions, it is still common to use a shallow cumulus parameterisation (SCP). Within the context of the EUREC4A model intercomparison project, we evaluate how the modelled mesoscale cloud field in the trades responds to parameterised or explicit shallow convection in the mesoscale model HARMONIE-AROME. We simulate a region of 3200 x 2025 km2 east of Barbados using a grid spacing of 2.5 km for a two month period (1 January to 29 February, 2020). We compare three configurations of HARMONIE-AROME: 1) one with an active SCP (control), 2) one without parameterised momentum transport by shallow convection, and 3) one with an inactive SCP. The experiments produce different responses in the cloud field that are not incremental. With the SCP inactive, the model produces a warmer lower troposphere with many smaller but deeper clouds that precipitate more. Along with stronger resolved eddy kinetic energy, wider and stronger shallow meridional overturning circulations develop. In the configuration without parameterised momentum transport by shallow convection, the eddy-diffusivity scheme effectively takes over the missing transport in the sub-cloud layer up to ~800 m. Above that level, horizontal wind variance increases as the total momentum flux decreases, enhancing eddy kinetic energy at scales of 2.5 km and larger. In contrast to the configuration with an inactive SCP, cloud top heights hardly deepen, but stratiform cloudiness below the inversion and mean cloud size increase.

Thermally-driven upvalley wind in the upper East River Valley in the Colorado Rocky Mountains often unexpectedly stops in mid-morning and reverses back to downvalley wind. We use a comprehensive observational data set for a nearly two-year long period to analyze the wind system and boundary layer evolution in this high-altitude valley and determine the reason for this early wind reversal. Days with short upvalley wind predominantly occur during the warm season when the valley floor is free of snow and the convective boundary layer grows well above the height of the surrounding ridges. Upvalley wind persists throughout the day only on a few days during the warm season. We link differences in valley wind evolution to wind direction at upper levels at and above ridge height and propose forced channeling mechanisms to describe coupling between valley and upper-level wind when the convective boundary layer grows above ridge height. The frequency distribution of upper-level wind direction is such that channeling in the downvalley direction is favored, which explains the predominance of days with short upvalley wind. The deep convective boundary layer is supported by the presence of a deep weakly stably stratified residual layer with high aerosol content, which is regularly present over the mountain range during the warm season. On days when the convective boundary layer does not grow above ridge height, for example when the valley floor is covered by snow, thermally-driven upvalley wind is able to persist throughout the day independent of upper-level wind direction.

The 2002 drought in South Asia was during a strong El Niño that are known to be strongly coupled. However, contemporary operational models—both dynamical and statistical— that are capable of simulating the effects of El Niño-drought coupling failed to predict the monsoon rainfall deficit that year. This failure highlights a critical gap in understanding the processes involved in predicting extreme droughts. Observations indicate that the 2002 drought was also marked by extremely high interannual mineral dust aerosol loading. This study investigates the complex role aerosols could have played on the drought. We utilized observational datasets, reanalysis products, satellite observations, outputs from the Aerosols and Chemistry Model Intercomparison Project (AerChemMIP-CMIP6), and conducted coupled simulations from the IITM Earth System Model to investigate the physical mechanisms influenced by varying sea surface temperatures and aerosol loading. Results indicate mix of dust and anthropogenic aerosols could indeed be an important factor in reducing rains over the Indian monsoon region. The mechanism for this reduced rains is the dynamical weakening of the land-atmosphere coupling under high aerosol conditions.

The Community Earth System Model version 2 (CESM2) has a higher equilibrium climate sensitivity (ECS) than previous versions of CESM and many other Coupled Model Intercomparison Project (CMIP) models. Relatedly, CESM2 simulates too-cold ice-age and too-hot warm paleoclimates. An inappropriate ice number limiter in the CESM2 microphysics scheme was discovered, and some simulations indicate that the high ECS may be partially attributable to this inappropriate limiter. In light of those findings, we seek to provide users of CESM2 guidance on the fitness of CESM2 for a variety of applications. We find that despite concerns about its climate sensitivity and simulations of past climates, the transient climate response (TCR) in CESM2 is moderate relative to the CMIP6 ensemble and robust across different versions of CESM. The changes made between CESM1 and CESM2 and the fixes to the microphysical issues of CESM2 have little impact on its simulated 20th and 21st century climates under SSP3-7.0. As a result, the simulated 20th and 21st century climates of CESM2 fall well within the range of the CMIP6 ensemble and agree well with observations over the historical record. However, hotter and colder paleoclimates simulated by CESM2 are inconsistent with paleoclimate evidence. A modified version of CESM2, PaleoCalibr CESM2, may be suitable for paleoclimate studies. Simulations past the end of the 21st century with default CESM2 and studies of microphysical processes in all GCMs should be analyzed with care.

This chapter experimentally investigated the impacts of rough-impermeable/permeable beds on turbulent kinetic energy (TKE), turbulence intermittency, and anisotropy of gravity currents. Results reveal that the larger bed roughness or porosity leads to smaller upper TKE peaks. The lower TKE peaks are inversely proportional to the bed roughness, while proportional to the bed porosity. Rough surfaces intensify the asymmetry around maximum streamwise velocity resulting in a transfer barrier of turbulent momentum. Inside the gravity current, the turbulent momentum fluxes transfer downstream and downward, which favors the sweep events. Inside the ambient water, they transfer upstream and upward, contributing to the formation of ejection events. At the current-ambient water interface, they do not tend to transfer in particular directions resulting in almost equal quantities of sweep and ejection events. From the bed to the free surface, the anisotropy invariant maps appear as the two-component plain strain limit, three-dimensional isotropy, axisymmetric contraction limit and two-dimensional isotropy. Along the streamwise direction, the rough-permeable boundary causes alternations between the anisotropic and isotropic turbulence, but the arranged patterns of bed emelents determine the period of these alternations.

Diamonds are primary records of carbon transport in the deep mantle. Their growth is mediated by carbon-bearing fluids, but this process is challenging to study, due both to the rarity of fluid inclusions and limitations in imaging crystal growth structures and trace element abundances. We overcome some of these limitations in two ways: 1) by careful sample selection of twinned diamonds, which tend to incorporate remnants of their growth fluids in the regions next to the twinning plane; and 2) by using a custom 3D fluorescence-lifetime imaging system to map the concentration of A-center N aggregates in the diamonds using the quenching of N3 lifetime. The mapping reveals the 3D internal growth structure in high resolution, offering a marked advantage over current popular techniques such as cathodoluminescence imaging that can only image 2D diamond surfaces.The 3D analysis shows growth initially from a central nucleation site, and then subsequently in concentric layers. The layers are periodic in their A-center concentrations but are crosscut by sinuous linear features with elevated A-center concentrations oriented roughly perpendicular to the (111) twin plane. These features have a triangular cross section aligned with the (111) face’s triangular morphology, interpreted as growth spirals centered on screw dislocations, which act as nucleation sites during periods of crystal growth. Initial crystal growth is often rapid due to supersaturation of reactants in the fluid. Rapid growth tends to incorporate more incompatible elements which may explain the relatively high N (as A-centers) concentrations along these linear features. The periodic banding suggests a pulsed fluid supply and either a change in growth rate (growth starts fast, then slows and stops at the end of each pulse); or a change in fluid composition over the course of a pulse (fluid reacts, diamond precipitates, and fluid matures).Twinned diamonds often entrap clusters of micro fluid-inclusions at the twin plane during growth. Raman mapping of these inclusions reveals the presence of hydrous-silicic fluids, N-bearing phases, hydrocarbons, as well as olivine and enstatite. These inclusions clusters are likely remnants of the primary growth fluid and will help connect our observations of growth with fluid compositions over time.Plain-Language SummaryWe studied the growth of diamonds because they are one of the primary records of carbon transport deep in earth’s mantle. This study demonstrates that diamonds grow due to periodic pulses of carbon rich-fluid moving through, and then reacting with the solid rock of the mantle. We show that a new imaging method, 3D fluorescence-lifetime mapping, is a powerful tool to add to the suite of methods available for studying the growth of diamonds. By imaging diamond growth bands, we learn about trends in the episodic nature of crystallization. It helps distinguish changes in diamond composition over time and provides context for growth around inclusions. We looked at a specific type of sample that contains remnants of the diamond forming fluid, trapped in clusters of very small inclusions. The 3D fluorescence-lifetime mapping helps us determine that the inclusions were trapped early in diamond growth. Using another method, Raman spectroscopy mapping, we identify that individual micro-inclusions within the clusters have different compositions. We find fluid inclusions rich in hydrated-silica, in nitrogen and others in hydrocarbons. This work helps us to determine more about the composition and transport of the carbon-rich diamond forming fluids deep in the earth.

We present a statistical study of large magnetic field vector residuals between Swarm observations and the 13th generation International Geomagnetic Reference Field (IGRF-13) model under quiet to weakly disturbed geomagnetic conditions. Since the vast majority of data are taken during relatively quiet geomagnetic conditions, statistics of these large residuals are important for estimating potential errors for satellite operation when using IGRF-13 as reference, as well as for magnetosphere-ionosphere-thermosphere (MIT) studies. Residuals with magnitude of vector differences between Swarm observations and IGRF-13 estimations larger than 300 nT under Dst >-50 nT are studied from 2014 to 2020. All large residuals appear in the high-latitude auroral zone region peaking around 70° (-70°) magnetic latitude (MLAT) in the northern hemisphere (southern hemisphere) but there is also a secondary occurrence peak just below 80° (-80°) MLAT. However, the two hemispheres show clear asymmetries in the magnetic longitude (MLON) distribution where both hemispheres show high concentration of large residuals around the geographic poles. Since the two geographic poles are located at different geomagnetic locations and polar satellite’s orbits give rise to highly biased number of observations around the geographic poles, it results in high occurrence of large residuals around the geographic poles but a decrease in occurrence rate with respect to the total number of measurements. Identifying the interhemispheric asymmetries resulting from the asymmetry of the geographic poles with respect to the magnetic poles under relatively quiet geomagnetic conditions is helpful for a better understanding of interhemispheric asymmetry for the MIT system.

A document by Tianning Su. Click on the document to view its contents.

We refine the newly developed seismicity catalog of the Apollo 17 Lunar Seismic Profiling Experiment using quality control algorithms, and speculate on the source mechanisms of thousands of catalogued events using cross-correlation and calculation of event and waveform properties. We first sort these events into two types – “repeating’ or “isolated’ – based on whether or not the event shares similar waveforms with at least one other event. Repeating events are characterized by minimal time between signal onset and maximum, a prevalence during early sunrise, a periodicity consistent with the diurnal cycle, and a preferential direction due east, coincident with the Lunar Module. Isolated events, on the other hand, are distributed throughout the lunar day, originate from a wide variety of directions, and are characterized by a more gradual increase in amplitude. Many repeating events are likely caused by thermal expansion of the Lunar Module or its trapped volatiles, while most isolated events may be caused by thermal fracturing of rock or sliding of regolith along crater slopes. Across both the repeating and isolated events, we pinpoint 43 moonquakes whose time-of-day and waveform characteristics are consistent with thermally-induced fracture of several boulders at the Apollo 17 site. Future lunar missions, particularly those sensitive to ground motion, should be aware of thermally-induced, repeating seismic signals caused by nearby boulders and structures.