A document by Zhongzheng Wang. Click on the document to view its contents.

The directional derivative approach (DDA) has the potential to rapidly and accurately quantify emission distributions based on the directional derivative of satellite-observed column amounts with respect to the horizontal wind. From the first principles, this paper derives the DDA emission estimators with a range of complexity by vertically integrating the 3D continuity equation and simplifying the results under several assumptions and approximations. The connection and difference between the DDA and a widely used divergence method for emission estimation are highlighted. A key difference is that the DDA integrates from the surface to an intermediate altitude instead of to the top of the observed column. This leads to the inherent background removal of the DDA, in contrast to the explicit background removal necessitated by the divergence method theory. Linear fittings are used to account for the effects of topography, chemical reactions, and retrieval biases. Realistic estimators of NOx emissions using satellite-observed NO2 column amounts are proposed, leveraging external climatology of the NOx:NO2 ratio and its directional derivative. These estimators are evaluated within a WRF-CMAQ simulation of NOx by comparisons with the model NOx emissions. The DDA estimators consistently outperform the divergence method estimator, and the DDA estimator that considers both topography and chemistry features the lowest root mean square error (RMSE). Lessons learned from this study using synthetic model data can be readily applied to the usage of actual satellite observations for emission estimation.

The recovery of the thermosphere after a strong geomagnetic storm on 12 May 2021 is investigated using lower and middle thermospheric temperature (Tdisk), ratio of atomic oxygen and molecular nitrogen column densities (O/N2), cooling due to Nitric Oxide (NO), and model simulations. The peak influence of the geomagnetic storm lasted about five hours and generated latitudinal gradients in Tdisk and O/N2. Following the storm, the latitudinal gradient in temperature recovered faster compared to that of O/N2. Measured NO-cooling rate and simulated NO-densities are enhanced on the storm day compared to a quiet-day, consistent with a rapid recovery in temperatures. Based on this, we conclude that the faster recovery of the Tdisk latitudinal gradient is driven by the combined effect of NO cooling and strong thermal conductivity. Furthermore, the slower recovery of the O/N2 latitudinal gradients can be attributed to the lack of poleward advection after the storm.

In this study, we show that non-thermal collisions can play a significant role in shaping Europa's exospheric structure. Collisions between radiolytically produced O2 and the O produced via electron impact dissociation of O2 play a significant role in affecting the exospheric structure and escape rates. Specifically, O+O2 collisions lead to the production of a non-thermal O2 population, and increase the O2 escape while decreasing the O escape. These collisions are dependent on three specific physical parameters: (1) the density of O2 , (2) the electron impact dissociation rate of O2 , and (3) the O+O2 collision cross section. We demonstrate here that O+O2 collisions affect Europa's atmosphere even in the lowest limits considered. Thus, to more accurately determine the influence O+O2 collisions have on Europa's atmosphere in preparation for the forthcoming spacecraft missions, Europa Clipper and the JUpiter ICy moons Explorer (JUICE), these physical parameters need to be better constrained.

Both composition and temperature play a crucial role in determining the NO radiative cooling in lower thermosphere as observed by TIMED/SABER. In this work, we present a detailed investigation of seasonal variation in thermospheric NO radiative cooling. We have carried forward the investigation of [1] regarding the variations in local nighttime peak NO radiative cooling and its altitude during solar maximum and solar minimum conditions. By analyzing latitudinal changes over quiet times for each month in year 2018, it is evident that both the investigative parameters exhibit summer-winter variability. The qualitative contribution of different species (i.e., NO, and O), and temperatures in determining the vertical profile of NO radiative cooling for different latitudes is investigated by utilizing the NRLMSISE-00 estimated parameters, and SNOE observed NO density. The temperature, NO density, meridional wind, and associated compositional variations due to asymmetrical solar heating in both the hemispheres during solar minimum conditions seem to be the dominating factor in controlling the NO radiative cooling during different seasons. The altitudes at which maximum cooling by NO occurs exhibits an inverse correlation with the amount of radiative cooling. The region of enhanced NO densities (polar and summer hemispheric low-mid latitude regions) have larger NO radiative cooling with lower peak altitudes in comparison to other regions (equatorial to winter hemispheric low-mid latitude regions), where NO radiative cooling is low with higher peak altitude values.

A series of processes involving sediment delivery from channels, its dispersal onto the floodplain, and storage at their channel margins, often generates natural levees. When levees breach, they release water and sediment onto the floodplain, leading to crevasse splays or avulsions. Despite their importance in constructing floodplains and influencing channel mobility, levee growth is poorly understood. Presently, no model fully explains dynamic channel-levee evolution. A common assumption is that levee and channel bed aggradation rates are coupled. If they coevolve, levees should progressively accumulate along any aggrading channel belt, yet observations indicate otherwise. Using a one-dimensional numerical model, we investigate levee growth decoupled from channel bed aggradation across two flood scenarios wherein the flooded level: 1) exceeds the levee crest height (i.e., front loading); 2) is lower than the levee crest causing partial inundation of distal levee deposits (i.e., back loading). Initially, rapid levee aggradation confines the channel and increases bankfull depth, which mitigates flooding. As confinement slows levee growth, channel bed aggrades until bankfull depth is sufficiently reduced to trigger overflows. This releasing process increases flood likelihood and enhances overbank accumulation, promoting front loading and re-confining the channel. Our findings suggest aggradational channels may experience confined-release phases, characterized by episodic levee growth and fluctuations in bankfull depth. Rapid in-channel aggradation increases flood frequency and variability with more confined-release cycles. These results imply that river avulsions and associated floods might preferentially occur when the channel bed aggrades faster than adjacent levees, whereby the channel becomes shallower and destabilized.

The benthic biolayer is a reaction hotspot that contributes disproportionately to whole-stream reactions, including aerobic respiration and contaminant transformation. Quantifying the relative contribution of the biolayer to whole-stream mass transformation remains challenging because it requires that hyporheic zone solute transport and reaction heterogeneity are explicitly captured within a single upscaled modeling framework. Here, we use field experiments and modeling to quantify mass transformation in the biolayer relative to other stream compartments. We co-injected and monitored several fluorescent tracers, including the reactive tracer resazurin, into a controlled experimental stream whose 8.5 cm hyporheic zone is isolated from groundwater. We characterized reactive transport in the water column and at multiple hyporheic zone depths by simultaneously fitting concentration time series measured at these locations to a new mobile-immobile model, using resazurin-to-resorufin transformation as an indicator of aerobic bioreactivity. Results show that the biolayer transformed 2× more resazurin to resorufin than all other stream compartments combined, and over half of all reactions occurred within 2 advective travel times through the reach. This hotspot and hot moment behavior is attributed to the biolayer’s propensity to rapidly acquire, transiently retain, and rapidly degrade stream-borne solutes. Model analysis shows that mass transformation is highest in the biolayer across a wide range of biolayer structural properties, including scenarios when the biolayer is less reactive than deeper regions of the hyporheic zone. Together, our results point to the biolayer as a common feature of streams and rivers that should be considered in network-scale models of river corridor biogeochemistry.

The Southern Ocean (SO) south of 35°S represents a small source of natural inorganic carbon for the atmosphere but a major sink of anthropogenic carbon. The magnitude of the total (natural plus anthropogenic) carbon sink strongly depends on the rate at which carbon is subducted below the mixed layer. We use a global ocean model at eddying resolution under preindustrial and historical conditions to provide a detailed view of total and anthropogenic dissolved inorganic carbon (DIC) pathways across and within the time-varying mixed layer of five physically consistent regions. Within each region, subduction fluxes at the mixed layer base are decomposed into advective and diffusive contributions to determine which process dominates. Total DIC is found to be obducted south of the Antarctic Circumpolar Current (ACC), transferred northward within the mixed layer and subducted north of the ACC. This results in a net obduction of 11.2 PgC/year, with advective processes dominating the total transfer (67%). Anthropogenic carbon is taken up in all regions but anthropogenic DIC is mainly subducted north of the ACC, the carbon taken up in the south being advected northward within the mixed layer before being subducted. This subduction (1.05 PgC/year) is achieved mainly through advection and diffusion, which dominate respectively north and south of the Subantarctic Front. Advective subduction fluxes show strong zonal variations and are increased near major topographic features and boundary currents. Our results suggest that we need to untangle advective and diffusive pathways regionally in order to understand how carbon subduction will evolve.

Training data: 1.6 million 2x8x8 patches of SAR data randomly sampled from 105 bursts of OPERA RTC-S1; 30m resolution, with two channels: VV (Vertical transmit and Vertical receive) and VH (Vertical transmit and Horizontal receive). Validation Sites: On May 24, 2024, a large landslide in Papua New Guinea buried a village and killed between 650 and 2,000 people. In February 2024, a series of wildfires broke out in the Valparaiso region of Chile. At least 137 people were killed and over 23,000 hectares were burned.

Convective dust events are common in the greater Phoenix area over the summer. These short-duration dust events degrade the air quality and pose a potential health threat to millions. In this study, 85 convective dust events that occurred in July and August 2015 to 2021 were examined to determine their impact on air quality. Seven PM10 sensors were used to evaluate the changes in PM10 concentrations over different time intervals (10 minutes, hourly, and daily). Each dust event had to have at least one sensor with hourly PM10 concentrations >100 µg m-3. Out of these 85 dust events, only 16.5% had a daily average above the EPA PM10 daily threshold, however, daily concentrations were 11 and 14 times lower compared to hourly and 10-minute (respectively) concentrations at the peak of the dust. 10-minute PM10 concentrations were >2.3 times higher than the hourly concentrations. The findings of this study demonstrated that the traditional methods of daily or hourly average underestimate the atmospheric PM10 concentrations and therefore lower the estimated exposure. There is a need to consider shorter time intervals to capture the PM concentrations accurately and highlight the importance of real-time monitoring and accurate characterization of short-duration events to assess their impacts on air quality and human health.

Sorghum elemental content response to altered nitrogen input timing and drought stressBenjamin D. Duval1, Jamie Martin1, Bonnie Frey2, Mark A. Marsalis31Biology Department, New Mexico Institute of Mining and Technology, Socorro, New Mexico 878012New Mexico Bureau of Geology and Mineral Resources, Socorro, New Mexico, 878013Los Lunas Agricultural Science Center, New Mexico State University, Los Lunas, New Mexico 87031*corresponding author: [email protected] contributionsBDD: conceived of study, field sampling, data analysis/interpretation, manuscript preparationJM: field sampling, laboratory analysis, manuscript editingBF: laboratory oversight (ICP-MS/OES), laboratory analysis, manuscript editingMAM: farm infrastructure, field experiment monitoring/management, sample collection, manuscript editing

While the theory of random isotropic scalar fields on the sphere is well established, it has not been fully extended to the case of vector fields yet. In this contribution, several theoretical results are thus generalized to random isotropic vector fields on the sphere, including an equivalent of the Wiener-Khinchin theorem, which relates the distance-dependent covariance of the field's components in a particular rotationally invariant basis with the covariance of the vector spherical harmonic coefficients of the field, i.e., its angular power spectrum. A parametric model, based on a stochastic partial differential equation, is proposed to represent the spatial covariance and angular power spectrum of such fields. Such a model is adjusted, with minor modifications, to empirical spatial correlations of the white noise and flicker noise components of 3D displacement time series of ground Global Navigation Satellite Systems (GNSS) tracking stations. The obtained spatial correlation model may find several applications such as enhanced detection of offsets in GNSS station position time series, enhanced estimation of long-term ground deformation (i.e., station velocities), enhanced isolation of station-specific displacements (i.e., spatial filtering), and more realistic assessment of uncertainties in all GNSS-network-based applications (e.g., estimation of crustal strain rates, of glacial isostatic adjustment models, or of tectonic plate motion models).

A document by Kyle Duncan. Click on the document to view its contents.

On January 18, 2021, a blind mid-crustal Mw ~6.4 earthquake occured near San Juán, Argentina. The observation of associated ground deformation with InSAR is hidden by strong tropospheric signals. We properly correct the data and reconstruct the deformation field through InSAR timeseries approach. We show it is possible to retrieve such signal with sufficient quality to invert the fault parameters. The ground deformation can be explained by uniform slip of a single NW dipping fault plane at a depth of 19km, and the geometry of such fault supports the reactivation of inherited structures on top of the Cuyania Terrane, insinuating a direct connection and strain transfer to the active east-vergent Precordillera front.

Previous work has pointed to the physical mechanisms behind the nocturnal offshore propagation of convection south-west of Sumatra. Low-level moisture flux convergence due to the land breeze front controls the progression of a squall line away from the coast overnight. However, the diurnal convection over the mountains occurs on only 57% of days in December-February (DJF) and propagates offshore on only 49% of those days. We investigate day-to-day variability in dynamical and thermodynamical conditions to explain the variability in diurnal convection and offshore propagation, using a convection-permitting simulation run for 900 DJF days. A convolutional neural network is used to identify regimes of diurnal cycle and offshore propagation behaviour. The diurnal cycle and offshore propagation are most likely to occur ahead of an active Madden-Julian Oscillation, or during El Niño or positive Indian Ocean Dipole; however, any regime can occur in any phase of these large-scale drivers, since the major control arises from the local scale. When the diurnal cycle of convection occurs, low-level wind is generally onshore, providing convergence over the mountains; and low-level humidity over the mountains is high enough to make the air column unstable for moist convection. When this convection propagates offshore, mid-level offshore winds provide a steering flow, combined with stronger convergence offshore due to the land breeze or convection-triggered cold pools. Low-level moisture around the coast also means that, as the convection propagates, the storm-relative inflow of air into the system adds greater instability than would be the case on other days.

Precursory spurious arrivals, commonly observed in ambient noise correlations, are generated by near-field noise sources. We have developed an inversion method to evaluate the noise source distribution based on the precursory waves. This method is applied to the BASIN experiment in Los Angeles, revealing that the noise sources show coherent patterns with features like faults and structure boundaries. Our spectral analysis indicates that the energy of the noise source in generating the precursory signal is predominant at higher frequencies, suggesting a shallow source(¡200m). We conclude that near-field noise is primarily produced by scattering from geological structures with significant velocity contrasts, such as faults at shallow depths. This method offers a new way to map faults using ambient noise correlations.

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.

Recent evidence has revealed that strong coupling between the lower atmosphere and the thermosphere ($>$100 km) occurs on intra-seasonal (IS) timescales (~30-90 days). The Madden-Julian Oscillation (MJO), a key source of IS variability in tropical convection and circulation, influences the generation and propagation of atmospheric tides and is believed to be a significant driver of thermospheric IS oscillations (ISOs). However, limited satellite observations in the ‘thermospheric gap’ (100-300 km) and challenges faced by numerical models in characterizing this region have hindered a comprehensive understanding of this connection. This study utilizes an ICON-adapted version of the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM), incorporating lower boundary tides from Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) observations, to quantify the impact of the upward-propagating tidal spectrum on thermospheric ISOs and elucidate connections to the MJO. Thermospheric zonal and diurnal mean zonal winds exhibit prominent (~20 m/s) tidally-driven ISOs throughout 2020-2021, largest at low latitudes ($\pm$30$^\circ$) near 110-150 km altitude. Correlation analyses (r>0.6) confirm a robust connection between thermospheric ISOs, tides, and the MJO. Additionally, Hovmoller diagrams show eastward tidal propagation consistent with MJO and concurrent Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) observations. This study demonstrates that vertically propagating tides play a crucial role in linking IS variability from the lower atmosphere to the thermosphere, with the MJO identified as a primary driver of this whole-atmosphere teleconnection. Understanding these connections is vital for advancing our knowledge in space physics, particularly regarding the dynamics of the upper atmosphere and ionosphere.