The land-sea connection of nutrients via rivers is an essential component in the global nutrient biogeochemistry. Rivers alone transport approximately 80% of the dissolved nutrients from land to ocean and play a vital role in nourishing riverine, coastal and oceanic ecosystems. During the past decades, global scale investigations have estimated the riverine nutrient flux to the oceans along with the significant drivers. However, most of the previous estimations are based on nutrient discharge by a few major rivers. Despite being large in number and high yields, the tropical coastal/mountainous rivers have received less attention. To fill the gap, we have investigated 70 west-flowing coastal rivers, draining the Western Ghats (WG), for their Dissolved Inorganic Nutrient (DIN) transport characteristics and influencing factors. Previous studies in the selected estuaries along the WG coast are combined to update the land-sea fluxes estimation to understand the spatial pattern of DIN over the WG rivers-the Arabian sea coast continuum. Altogether, the DIN fluxes from entire WG (including non-sampled rivers) region to the estuaries are 664, 241 and 6277 Tg yr-1 for Nitrate (N), Phosphate (P) and Silicate (DSi) respectively. The natural factors, such as discharge, cropland, and forest cover each explain 30–85% of the spatial variation in DIN levels at the basin scales. DIN concentrations of rivers reduces to ~ 90% after reaching the respective estuaries. Based on Redfield ratio of C:N:P (106:16:1), annual export of 66.4 Tg of dissolved inorganic N from the WG rivers would support 439.9 Tg of new carbon production in the Arabian Sea coast. The humid tropical climate and high population density (> 300 people per km2 among the bio-diversity hotspots) of the WG region favour the high DIN export, thus, making the Arabian sea coast highly productive among the global coastal regions. Keywords: Dissolved Inorganic Nutrients; Rivers-Coast Continuum; Influencing Factors; Small Mountainous Rivers; Western Ghats.

A document by Paul, Obiakara Amaechi. Click on the document to view its contents.

A document by Damian Winston Walwer. Click on the document to view its contents.

Transpolar arcs (TPAs) are auroral features that occur polewards of the main auroral oval suggesting that the magnetosphere has acquired a complicated magnetic topology. They are primarily a northward interplanetary magnetic field (IMF) auroral phenomenon, and their formation and evolution have no single explanation that is unanimously agreed upon. An automated detection algorithm has been developed to detect the occurrence of TPAs in UV images captured from the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) instrument onboard the Defense Meteorological Satellite Program (DMSP) spacecraft, in order to further study their occurrence. Via this detection algorithm TPAs are identified as a peak in the average radiance intensity poleward of 12.5 degrees colatitude, in two or more of the wavelengths/bands sensed by SSUSI. Orbital biases in the data have been investigated and these differ from spacecraft to spacecraft. For the spacecraft of interest (F16, F17 and F18) this leads to a preferential observation of the northern hemisphere with the detection algorithm missing TPAs in the southern hemisphere between approximately 01 - 06 UT. No seasonal bias has been found for these spacecraft. Using the detection algorithm on observations from the years 2010 to 2016, over 5000 images containing TPAs are identified. The occurrence of these TPA images shows a seasonal dependence, with more arcs being visible in the winter hemisphere. We discuss the ramifications of these findings in terms of proposed TPA generation mechanisms.

In recent years, India has been increasingly experiencing widespread flooding induced by large-scale extreme rainfall events (LEREs). These events are mainly associated with the monsoon low-pressure systems (LPSs) and occur mostly in their southwestern sector. The forecast of these high-flood-potential events, however, has remained challenging. In this study, we compare the LPSs of the Indian summer monsoon that lead to LEREs (LPS-Lg) and the strong LPSs that did not result in LEREs (LPS-noLg) over central India for the period 1979-2012. We show that having a strong LPS is not a sufficient condition to produce LEREs. Rather, an observed consistent feature is that the LPS-Lgs are accompanied by Secondary Cyclonic Vortices (SCVs). SCVs enhance dynamic lifting, static instability, and moisture transport from the Arabian Sea that precondition the atmosphere for deep convection. The simultaneous existence of an LPS and an SCV creates a giant mid-tropospheric vortex that helps in organizing the deep convection. SCVs also slow down the propagation of LPSs. We show that the interaction of multiple synoptic-scale systems can lead to LERE even if individual systems are not strong enough.

In this study, the super droplet-method (SDM) is used in large-eddy simulations of an isolated cumulus congestus observed during the 1995 Small Cumulus Microphysics Study field project in order to investigate the intra-cloud variability associated with entrainment and mixing. The SDM is a Lagrangian particle-based method for cloud microphysics that provides droplet size distributions (DSD) coupled to the simulated cloud-scale dynamics. The authors show that sensitivity to the spatial resolution and the initial number of particles is larger, and sensitivity to the initial conditions is smaller, when the order of the DSD moment is smaller. Through the use of simulations with reliable statistics, microphysical variability is investigated at scales of ∼ 100 m that can be considered well resolved in both the numerical simulations and in-situ aircraft observations. Large spatial variability in cloudy volumes is shown to be strongly affected by entrainment. Mean values of the adiabatic fraction (AF), cloud droplet number concentration, and the cubed ratio of the mean volume radius and the effective radius (k) agree well with observations in the middle and upper cloud layers. Moreover, the AF and k values are found to be positively correlated, and the reduction of the mean volume radius scaled by its adiabatic value with the decrease of the mean droplet concentration scaled by its adiabatic value is found to be smaller than the theoretical prediction of homogeneous mixing. The latter supports the notion of inhomogeneous mixing due to entrainment.

Subsurface imaging is key to understanding the origin of intraplate volcanos. The Changbaishan volcano, located about 2000 km away from the western Pacific subduction zone, has several debated origins. To investigate this, we compared regional seismic tomography with the electrical resistivity results and performed high-resolution 1D and quasi-2D velocity-depth profiles. We show that the upper mantle is characterized by two anomalies exhibiting distinct features which cannot be explained by the same mechanism. We document a localized low-velocity anomaly atop the 410-km discontinuity, where the P-wave velocity is reduced more than that of the S-wave (i.e., low Vp/Vs). We propose that this anomaly is caused by the reduction of the effective moduli during the phase transformation of olivine. The other anomaly, located between 300 km and 370 km depth, reveals a significant reduction of the S-wave velocity (i.e., high Vp/Vs), associated with a reduction of the electrical resistivity, altogether consistent with partial melting.

Mixed siliciclastic and carbonate active orogens are common on Earth’s surface, yet most studies have focused on physical erosion and chemical weathering in silicate-rich landscapes. Relative to purely siliciclastic landscapes, the response of erosion and weathering to uplift may differ in mixed-lithology regions. However, our knowledge of weathering and erosion in mixed carbonate-silicate lithologies is limited and thus our understanding of the mechanistic coupling between uplift, chemical weathering, and the carbon cycle. Here, we partition the denudation fluxes into erosion and weathering fluxes of carbonates and silicates in the Northern Apennine Mountains of Italy—a mixed siliciclastic-carbonate active orogen—using dissolved solutes, the fraction of carbonate sand in sediments, and existing 10Be denudation rates. Erosion fluxes are generally an order of magnitude higher than weathering fluxes and dominate total denudation. The contribution of carbonate and silicate minerals to erosion varies between lithologic units, but weathering fluxes are systematically dominated by carbonates. Silicate weathering may be limited by reaction rates, whereas carbonate weathering may be limited by acidity of the rivers that drain the orogen. Precipitation of secondary calcite from super-saturated streams leads to the loss of up to 90% of dissolved Ca2+ from carbonate-rich catchments. Thus, in the weathering zone, [Ca2+] is exceptionally high, likely driven by high soil pCO2; however, re-equilibration with atmospheric pCO2 in rivers converts solutes back into solid grains that become part of the physical denudation flux. Limits on weathering in this landscape therefore differ between the subsurface weathering zone and what is exported by rivers.

Optimization of spatially consistent parameter fields is believed to increase the robustness of parameter estimation and its transferability to ungauged basins. The current paper extends previous multi-objective and transferability studies by exploring the value of both multi-basin and spatial pattern calibration of distributed hydrologic models as compared to single-basin and single-objective model calibrations, with respect to tradeoffs, performance and transferability. The mesoscale Hydrological Model (mHM) is used across six large central European basins. Model simulations are evaluated against daily streamflow observations at the basin outlets and remotely sensed evapotranspiration patterns obtained with a two-source energy balance approach. Several model validation experiments are performed through combinations of single- (discharge) and multi-objective (discharge and spatial evapotranspiration patterns) calibrations with holdout experiments saving alternating basins for model evaluation. The study shows that there are very minimal tradeoffs between spatial and temporal performance objectives and that a joint calibration of multiple basins using multiple objective functions provides the most robust estimations of parameter fields that perform better when transferred to ungauged basins. The study indicates that particularly the multi-basin calibration approach is key for robust parametrizations, and that the addition of an objective function tailored for matching spatial patterns of ET fields alters the spatial parameter fields while significantly improving the spatial pattern performance without any tradeoffs with discharge performance. In light of model equifinality, the minimal tradeoff between spatial and temporal performance shows that adding spatial pattern evaluation to the traditional temporal evaluation of hydrological models can assist in identifying optimal parameter sets.

Changes in the heavy ion composition in the terrestrial ionosphere and magnetosphere can have significant impact on particle dynamics in the Earth’s magnetosphere-ionosphere system. Most instruments flying in space, such as MMS and Van Allen Probes, lack the possibility to distinguish N+ from O+ due to their close masses. However, observations of N+ both in the ionosphere and magnetosphere indicate that N+ is a constant companion of O+ , especially during the storm time. Because N+ originates from the Earth’s ionosphere, we further develop the Polar Wind Outflow Model (PWOM) to investigate the behavior and acceleration mechanisms of heavy ions in Earth’s ionosphere. The PWOM solves the particle dynamics of O+, H+ and He+ in the ionospheric outflow and the modified PWOM can further simulate the behavior of N+ and N2+ in Earth’s polar wind. The escape of heavy ions from the Earth atmosphere is consequences of energization and transport mechanisms, including photo ionization, electron precipitation, ion-electron-neutral chemistry and collisions. The modified PWOM is coupled with a two-stream model of superthermal electrons (GLobal airglow, or GLOW) to deal with attenuated radiation, electron beam energy dissipation, and secondary electron impact. In this study, we show that during various solar conditions, the ion-electron-neutral densities in the ionospheric outflow show significant difference when we consider N+ ions in the polar wind. Furthermore, we will compare the simulation results of the modified PWOM with observation data for validation.

Vegetation is a natural component of river systems and plays important hydrological, ecological and geomorphic roles. However, vegetation cover and dynamics are controlled by numerous factors operating at multiple scales, making it challenging to determine the drivers of changes over time. The Beas and Sutlej Rivers are two of the ‘water towers’ of the Himalayas that supply water and power for large populations. Previous research has shown that significant geomorphic change has occurred over that last 150 years in both rivers, with differences in the type and magnitude of change in the last few decades. The aim of this study was to quantify the spatial distribution and dynamics of riparian and in-channel vegetation in two Himalayan rivers and evaluate the local and global drivers, such as climate change, alteration of river flows, and river geomorphic adjustment. Annual changes in vegetation cover and channel width were quantified using Normalized Difference Vegetation Index (NDVI), modified Normalized Difference Water Index (mNDWI), and a multispectral supervised classification over a 30-year period, for pre- and post-monsoon seasons, using Landsat data. The results show statistically significant upward trends in NDVI across both catchments, indicating large-scale drivers of change. Relatively greater increases in NDVI in the valley bottom and the active channel zones suggest more localized processes such as recruitment and succession of vegetation and conversion to agriculture following channel narrowing. Spatial variations in vegetation dynamics helps us to better understand vegetation-geomorphology interactions in these large systems and the impacts of human activity and climate change.

We present ~1.5 Mars Years (MY) of ozone vertical profiles, covering Ls = 163deg; in MY34 to Ls = 320deg; in MY35, a period which includes the 2018 global dust storm. Since April 2018, the Ultraviolet and Visible Spectrometer (UVIS) channel of the Nadir and Occultation for Mars Discovery (NOMAD) spectrometer aboard the ExoMars Trace Gas Orbiter has observed the vertical, latitudinal and seasonal distributions of ozone. Around perihelion, the relative abundance of ozone (and water from coincident NOMAD measurements) increases strongly together below ~40 km. Around aphelion, decreases in ozone abundance exist between 25-35 km coincident with the location of modelled peak water abundances. We report high latitude (above 55deg;), high altitude (40-55 km) equinoctial ozone enhancements in both hemispheres. The northern equinoctial high altitude enhancement is previously unobserved and forms prior to vernal equinox lasting for almost 100 sols (Ls ~350‑40deg), whereas the southern enhancement persists for over twice as long (Ls = ~5-140deg;). Both layers reform at autumnal equinox, with the northern layer at a lower abundance. These layers likely form through a combination of anti-correlation with water and the equinoctial meridional transport of O and H atoms to high-latitude regions. The descending branch of the main Hadley cell shapes the ozone distribution at Ls = 40-60deg;, with the possible signature of a northern hemisphere thermally indirect cell identifiable from Ls = 40-80deg;. The ozone retrievals presented here provide the most complete global description of Mars ozone vertical distributions as a function of season and latitude.

River deltas and enclosed lagoons represent a zone where fluvial and littoral processes interacts through a redistribution, erosion, and deposition of sediment, with a huge impact on coastal management and engineering. The focus of the study is to understand the correct balance between strategies to maintain the navigational efficiency of tidal inlets and the respect of the ecological and economical function in coastal lagoons. We applied an integrated modeling system which will link multiple hydrodynamic and morphodynamic models to understand how coastal processes and the associated sediment transport can influence the functioning of the southern inlet of the Barbamarco lagoon in the Po River Delta, Italy. Furthermore, our study provides engineering solutions aimed at the inlet functioning efficiency with a proposal for the monitoring plan. Our results highlight the importance of the seasonal effects of wave climate on the littoral sediment transport. Model outcomes show that the dredging volume is approximately 15,000 cubic meter/year for the southern inlet that might vary with wave climate. However, shaping a wider tidal channel seaward will reduce the dredging activities with a longer interval than the actual sediment removal. A design of a deeper and wider channel will deflect the along shore current seaward with a sediment bypass of the inlet. Therefore, the sediment will reach the erosional side of the inlet enhancing the redistribution of the sediment which might reduce the over-wash during storms and high-water levels. Our results display the ephemeral equilibrium of tidal inlets and coastal lagoons in deltaic systems impacted by large riverine sediment delivery. Shore management scenario and decision relies on hydro-morphodyanmic numerical model to predict the best practice for coastal sustainability.

A key step in model development is selection of an appropriate representational system, including both the representation of what is observed (the data), and the formal mathematical structure used to construct the input-state-output mapping. These choices are critical, because they completely determine the questions we can ask, the nature of the analyses and inferences we can perform, and the answers that we can obtain. Accordingly, a representation that is suitable for one kind of investigation might be limited in its ability to support some other kind. Arguably, how different representational approaches affect what we can learn from data is poorly understood. This paper explores three complementary representational strategies as vehicles for understanding how catchment-scale hydrological processes vary across hydro-geo-climatologically diverse Chile. Specifically, we test a lumped water-balance model (GR4J), a data-based dynamical systems model (LSTM), and a data-based regression-tree model (Random Forest). Insights were obtained regarding system memory encoded in data, spatial transferability by use of surrogate attributes, and informational deficiencies of the dataset that limit our ability to learn an adequate input-output relationship. As expected, each approach exhibits specific strengths, with LSTM providing the best characterization of dynamics, GR4J being the most robust under informationally deficient conditions, and RF being most supportive of interpretation. Overall, the complementary nature of the three approaches suggests the value of adopting a multi-representational framework in order to more fully extract information from the data. Our results show that a multi-representational approach better supports the goals of prediction, understanding, and scientific discovery in Hydrology.

A document by Yechul Shin. Click on the document to view its contents.

Over half of the global population experiences water scarcity for at least one month during the year. Such situations of household water insecurity (HWI), where household water provisioning is reduced in such a way that affordability, adequacy, reliability, or safety is compromised to threaten human well-being, can be the result of complex interactions between humans and the water systems in which they live. To advance understanding regarding the cause-and-effect relationships between variable hydrological conditions and how humans experience domestic water provisioning, we conduct a systematic literature review to synthesize existing research and identify knowledge gaps of seasonal climate and hydrological influence on HWI. We incorporate a socio-ecological framework of drinking water services as well as process-based hydrological information to interpret results. Following the PRISMA 2020 systematic review guidelines, we retained 67 studies for final analysis. Examining studies by country as well as Major Freshwater Habitat, we find most study sites have been in sub-Saharan Africa (n=61, 89.7%) and in areas characterized by Tropical and Subtropical Coastal Rivers (n=37, 54.4%). Discussion of seasonality has centered on bimodal rainy/dry seasons; pre-monsoon, monsoon, and post-monsoon seasons; seasonal droughts and floods; winter snow and ice conditions; and seasonal migration. Water infrastructure, household characteristics, institutional factors, and water sharing practices mediate seasonal influences, either ameliorating or exacerbating its effects. To date, there have been few HWI seasonality studies in East Asia and the Pacific, Middle East and North Africa, North America, and Europe and Central Asia, and no studies in areas of Temperate Floodplain Rivers and Wetlands and Temperate Upland Rivers. Additionally, despite efforts to incorporate seasonality, most studies are cross-sectional, demonstrating an urgent need for more longitudinal studies to better characterize HWI within and between years. With climate change expected to disproportionately affect the portion of the global population that relies on seasonally varying environmental resources, it is critical to address these research gaps to ensure availability and sustainable management of water for all.

A document by Luke A Parsons. Click on the document to view its contents.

Notwithstanding the large number of studies on bedforms such as dunes and antidunes, performing quantitative predictions of bedform type and geometry remains an open problem. Here we present the results of laboratory experiments specifically designed to study how sediment supply and caliber may impact equilibrium bedform type and geometry in the upper regime. Experiments were performed in a sediment feed flume with flow rates varying between 5 l/s and 30 l/s, sand supply rates varying between 0.6 kg/min and 20 kg/min, uniform and non-uniform sediment grain sizes with geometric mean diameter varying between 0.22 mm and 0.87 mm. The experimental data and the comparison with datasets available in the literature revealed that the ratio of the volume transport of sediment to the volume transport of water Qs/Qw plays a prime control on the equilibrium bed configuration. The equilibrium bed configuration transitions from washed out dunes (lower regime), to downstream migrating antidunes (upper regime) for Qs/Qw between 0.0003 and 0.0007. For values of Qs/Qw greater than those typical of downstream migrating antidunes, the bedform wavelength increases with Qs/Qw. At these high values of Qs/Qw equilibrium bed configurations with fine sand are characterized by upstream migrating antidunes or cyclic steps, and significant suspended load. In experiments with coarse sand, equilibrium is characterized by plane bed with bedload transport in sheet flow mode. Standing waves form at the transition between downstream migrating antidunes and bed configurations with upstream migrating bedforms.