Storm Season Research Articles

Relationship between Concentration and Discharge on Storm Events: Case Study at Cakardipa Catchment, Cisukabirus Subwatershed, Upper Ciliwung Watershed, Bogor, West Java

River nutrient loadings rates are frequently determined from discharge and hydrochemistry relationships using regression techniques. Unfortunately such methods as a conventional technique are inadequate for dealing with the problem such as differences in shape and direction of loop forming in individual and seasonal storms. Besides the relationships are nonlinear and time-dependent, they also varies from site to site. There is a currently method to study hysteresis between discharge and concentration of hydrochemistry. The relationship between discharge and solute concentration was investigated at Cakardipa catchment, Upper Ciliwung watershed, between the years of 2009-2010. The characteristics of the hysteresis loops were used to evaluate the temporal variation of the relative contribution to stream flow of source waters at Cakardipa Catchment including groundwater (CG), soil water (CSO), and rain water (CR). Chemical water analysis was carried out on 497 water samples on storm event. The chemical analysis of storm event of Februari 14, 2010 was carried out for the concentrations of K+, Ca2+, Mg2+, Na+, SiO2, SO42-NO3-, Cl-, and HCO3-. Results of the experiment showed that concentrations displayed circular hysteresis loops during the events, highlighting the complex relation among solutes and discharge during storm hydrographs. The solutes of K, Na, and Ca produced concave curvature, anti-clockwise hysteresis loops, and positive trend, so that classified as A2 loops with components ranking were CR> CG> CSO. .The solutes of Mg, SO4, NO3 assumed to come from groundwater produced convex curvature, clockwise hysteresis loops, and positive trend, indicating a concentration component ranking of CG > CR > CSO (C2 model). While Si and Cl produced clockwise hysteresis loops, indicating a concentration component ranking of CG> CSO> CR which was C1 model.

Differences in the Effects of Storms on Dissolved Organic Carbon (DOC) in Boreal Lakes during an Early Summer Storm and an Autumn Storm

In boreal lakes, increased precipitation events have been linked to increased concentrations of dissolved organic carbon (DOC), however the effects of seasonal differences on DOC and how this may impact storm response remain unclear. We evaluated DOC concentration and a set of DOC quality metrics during an early summer storm and an autumn storm on a suite of six lakes in Acadia National Park in Maine, USA. to better understand differences in seasonal storm responses. Our results revealed differences in the response of DOC quality metrics to an early summer versus an autumn storm, with changes in DOC quality metrics varying by storm and lake features. During the early summer storm, we observed greater changes in various DOC quality metrics in deep lakes with longer residence times, whereas during the autumn storm, lakes with large watershed area to lake area ratios experienced the greatest changes. Land cover was highly correlated with changing DOC quality metrics in the early summer storm but did not play a significant role in the autumn storm response. Our research provides evidence of seasonal differences in the effects of storms on boreal lakes, which are ultimately mediated by a combination of lake and watershed characteristics as well as seasonal differences in climate such as solar radiation and antecedent weather conditions.

Ancient rip current records and their implications: an example from the Cretaceous Ukra Member, Kutch, India

Poorly-sorted conglomerate patches rich in granules or sturdy fossils or both, and reddish mud matrix within the interstices stand out amidst fine-grained siliciclastic shelf sediments of the trangressive systems tract (TST) of the Lower Cretaceous Ukra Member, Kutch Basin, India. The siliciclastic shelf sediments contrast the conglomerates with their remarkable lateral extension. The fossils belong to a low-diversity group of sedentary bivalves that can be traced into the shoreface facies assemblage. The shelf sandstones are almost always sculpted by wave structures, especially hummocky cross-stratification while textures in the conglomerates suggest that the sediment settling was generally from suspensions. Textural variations in conglomerates reflect an immediate variation in flow viscosity prior to the downloading. The current structures obtained from the conglomerates record offshoreward palaeocurrent, in contrast to the shore-parallel palaeocurrent in the TST. The hummocky cross-stratified (HCS) beds are interpreted as seasonal storm deposits, while the conglomerate patches are taken as rip current deposits induced by waves of much longer periods. The glauconite-rich shale that alternates with conglomerates is probable fair-weather products. The conglomerates could not be recognized either in the coarse-grained shoreface deposits occupying the lower part of the overall fining-upward TST or in the coarsening-upward and glauconite-depleted highstand systems tract (HST). In contrast to the TST, the HST is dominantly tide-imprinted, having shore-normal palaeocurrent direction. It appears that intensification of waves and weakening of tides during transgression favored strong rip currents generation, which had presumably caused severe damage to the sea coast and to the shell banks growing preferably at the necks of the rip current channels. Rapid lateral facies transitions in the shoreface deposits at the basal part of the TST suggest enhanced irregularity in the coastline, possibly because of the mega cusps indented upon it. Frequency and intensity of storms enhanced during periods of global warming caused the transgression of the Early Cretaceous Ukra Sea.

Feasibility/Design Study for a Cloud Seeding Program in the Yadkin River Basin, North Carolina

North American Weather Consultants (NAWC) was contracted by Cube Hydro Partners, LLC with headquarters in Bethesda, Maryland, to conduct a cloud seeding feasibility/design study for the Yadkin River Basin located in North Carolina. This study was prepared in conformance with American Society of Civil Engineer’s Guidelines and Standards. The goal of the program would be to augment precipitation over the Yadkin River Basin to increase streamflow into a series of Cube Hydro reservoirs along the Yadkin River. This increased streamflow would then be used to generate additional hydropower (clean energy) from facilities installed on project dams. NAWC compiled a site-specific climatology for this Basin. Both ground-based and airborne seeding was considered, but only airborne seeding was recommended due to the lack of significant topographic features in the Basin and the rather high average height of the -5° C level in potentially “seedable” storms (630 mb), as well as other meteorological factors. Regression equations relating precipitation to streamflow suggest that seeding only during the cool season produces streamflow increases not only during the cool season, but would also have a residual effect that increases streamflow throughout the remainder of the year. Overall, cool-season seeding is likely to have about 1.4 times as much impact on total streamflow as warm-season seeding (assuming the same increase percentage-wise in precipitation), with the cool season increase more evenly distributed throughout the year in terms of the resultant streamflow. Therefore, only a cool season program was recommended. Detailed examination of a 3-year cool season storm climatology in the Yadkin Basin suggest that aircraft-based cloud seeding during the cool season could enhance precipitation by 4.1%, resulting in an estimated 5.2% increase in annual streamflow (109,200 acre-feet). Cost estimates were prepared for a seasonal program. Once the estimated costs were established, NAWC was able to develop benefit/cost ratio estimates. Using information provided by Cube Hydro, NAWC calculated a potential benefit/cost ratio of 5/1. NAWC concluded that the proposed program was feasible based upon both technical and economic considerations as recommended in the “Guidelines for Cloud Seeding to Augment Precipitation”, Third Edition by the American Society of Civil Engineers (ASCE,2016).

Effects of lake water level fluctuation due to drought and extreme winter precipitation on mixing and water quality of an alpine lake, Case Study: Lake Arrowhead, California

Lake Arrowhead, an oligotrophic alpine lake in southern California, experienced a drought period from summer 2012 to winter 2018 followed by a season of intense storms in winter 2019 resulting in lake flooding. This study investigates the effects of seasonal variations combined with 3.5 m water level fluctuation from May 2018 to April 2019, on water quality and hydrodynamics of Lake Arrowhead. In-situ measured meteorological data and water quality profiles in five different bays were used to develop and calibrate a three-dimensional lake hydrodynamic model. The mean relative errors between simulated and measured temperature and salinity profiles were 6.1% and 4.2%, respectively. Root mean square errors between the measured and simulated water temperatures were slightly larger during the stratified period. However, no specific pattern was observed in error analysis of salinity simulations.Strong thermal stratification during summer and early-fall resulted in hypoxic hypolimnetic waters with dissolved oxygen (DO) concentrations of <1 mg L−1. Turbulent kinetic energy (TKE) generated by convective motions in the water column due to surface heat loss was typically more than two times greater than the wind-induced mixing energy during the stratification period. The lake experienced an energetic turbulent mixing regime with TKE fluxes >1.5 m−3 s−3, and Lake numbers <0.1 during the winter cooling period, resulting in a complete water column turnover and resuspension of bottom sediments. Entrainment of the hypoxic hypolimnion layers and sediment resuspension resulted in decreased DO and pH in the water column from December 2018 through mid-January 2019. Comparisons of Wedderburn and Lake numbers during different stratification conditions indicated the same trends in the strong stratification period (square of buoyancy frequency >10−4 s−2). However, in other conditions, the Lake number, considering the lake bathymetry and density profile, could better reflect vertical mixing conditions.

Spatiotemporal Patterns of Microbial Composition and Diversity in Precipitation

We characterized trends of bacteria and fungi assemblages from 72 precipitation events in three US states over four seasons. We determined that (1) bacterial assemblages were associated with season and high-altitude characteristics of storms, whereas fungal assemblages were correlated with particular spatial locations; and (2) bacterial assemblages had higher contributions to total β-diversity from nestedness, due to taxa losses during dispersal, particularly among potentially ice-nucleating bacteria, whereas fungal assemblages had higher contributions to total β-diversity from taxa turnover. Our findings advance the understanding of aerosolized microbial deposition and the development of theory concerning potential assembly rules for bioaerosol assemblages. These photographs illustrate the article “Spatiotemporal patterns of microbial composition and diversity in precipitation” by K. Aho, C. F. Weber, B. C. Christner, B. A. Vinatzer, C. E. Morris, R. Joyce, K. Failor, J. T. Werth, A. L. H. Bayless-Edwards, and D. G. Schmale III, published in Ecological Monographs. https​://doi.org/10.1002/ecm.1394

Using social media to measure impacts of named storm events in the United Kingdom and Ireland

AbstractDespite increasing use of impact‐based weather warnings, the social impacts of extreme weather events lie beyond the reach of conventional meteorological observations and remain difficult to quantify. This presents a challenge for validation of warnings and weather impact models. This study considers the application of social sensing, the systematic analysis of unsolicited social media data to observe real‐world events, to determine the impacts of named storms in the United Kingdom and Ireland during the winter storm season 2017–2018. User posts on Twitter are analysed to show that social sensing can robustly detect and locate storm events. Comprehensive filtering of tweets containing weather keywords reveals that ~3% of tweets are relevant to severe weather events and, for those, locations could be derived for about 75%. Impacts of storms on Twitter users are explored using the text content of storm‐related tweets to assess changes in sentiment and topics of discussion over the period before, during and after each storm event. Sentiment shows a consistent response to storms, with an increase in expressed negative emotion. Topics of discussion move from warnings as the storm approaches, to local observations and reportage during the storm, to accounts of damage/disruption and sharing of news reports following the event. There is a high level of humour expressed throughout. This study demonstrates a novel methodology for identifying tweets which can be used to assess the impacts of storms and other extreme weather events. Further development could lead to improved understanding of social impacts of storms and impact model validation.

Seasonal fine fuel and coarse woody debris dynamics in north Australian savannas

Several studies have separately explored accumulation of the dominant fuels (grass, fine litter (&amp;lt;6mm diameter) and coarse woody debris (CWD, 6–50mm diameter)) in north Australian savannas. We report an analysis of two longitudinal datasets describing how these three fuel components covary in abundance throughout the year in eucalypt-dominated savanna over a rainfall gradient of 700–1700mm mean annual rainfall (MAR). Our observations concur generally with previous observations that litter accumulation results in a late dry season (LDS) peak in biomass, whereas cured grassy fuels typically are seasonally invariant, and CWD inputs are associated with stochastic severe wet season storms and dry season fires. The distinct LDS litter peak contributes significantly to the potential for LDS fires to be of higher intensity, burn more fuel per unit area and produce greater emissions relative to early dry season (EDS) fires. However, Australia’s current (2018) formal savanna burning emissions avoidance methodology erroneously deems greater EDS fine fuel (grass and fine litter) biomass in four of nine designated vegetation fuel types. The study highlights the need to develop seasonally dynamic modelling approaches that better account for significant seasonal variation in fine fuel inputs and decomposition.

Proton Aurora on Mars: A Dayside Phenomenon Pervasive in Southern Summer

AbstractWe present observations of proton aurora at Mars made using the Imaging UltraViolet Spectrograph (IUVS) onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. Martian proton aurora display a prominent intensity enhancement in the hydrogen Lyman‐alpha (121.6 nm) emission between ~110 and 150 km altitude. Using altitude‐intensity profiles from periapsis limb scan data spanning nearly two Martian years, we create a comprehensive database of proton aurora and characterize their phenomenology. Due to Mars' lack of a global dipole magnetic field, Martian proton aurora are expected to form on the dayside via electron stripping and charge exchange between solar wind protons and the neutral corona. We observe proton aurora in ~14% of dayside periapsis profiles (with notable seasonal variability), making proton aurora the most commonly observed type of aurora at Mars. We determine that the primary factors influencing proton aurora occurrence rates are solar zenith angle and season. The highest proton aurora occurrence rates are at low solar zenith angles on the Mars dayside, consistent with known formation processes. Proton aurora have highest emission enhancements, peak intensities, peak altitudes, and occurrence rates (nearing 100%) around southern summer solstice. This time period corresponds with the seasonal inflation of the neutral lower atmosphere, the onset of Martian dust storm season, seasonally increased coronal hydrogen column densities, and higher atmospheric temperature and solar wind flux following perihelion. The results of our study provide a new understanding of the primary factors influencing proton aurora, and the long‐term variability of these phenomena as observed over multiple Mars years.

USING SPATIAL ANALYSIS TO OPTIMIZE DISASTER PREPAREDNESS FOR FRAIL OLDER ADULTS

The Florida Department of Elder Affairs (DOEA) provides programs and services for over 65,300 older people and adults with disabilities. These individuals are uniquely vulnerable and may be disrupted, displaced, and disoriented during the natural disasters common to Florida. DOEA clients are homebound or dependent upon community-based services to provide supervision or direct assistance to perform basic self-care. Often, clients are unable to complete personal care independently, which makes sheltering in place a unique challenge, yet they can only evacuate with special transportation and support arrangements in the shelter. It is critical to DOEA to accurately predict clients likely to be seriously affected by storms, plan for relocation before an event, and arrange for the provision of extended care after. DOEA responded by utilizing ArcGIS mapping software to join client residence locations to evacuation zone polygons and developed a methodology to prioritize clients with personal and functional barriers to evacuation. Proven during Hurricane Michael (2018), local emergency managers were able to use this tool to complete wellness checks on survivors before outside aid arrived. This initiative is evolving with the challenges posed by each storm season. Hurricane Dorian (2019) required the addition of latitude and longitude of client locations for when traditional street navigation became unavailable. Importing and overlaying primary data on secondary emergency management resources is a strategy that could be replicated by other organizations that have similar needs to reconcile individual locations in context of local threats, making this methodology transferrable to other disaster and flood-prone communities.

Performance of MAR model for stormwater management in Barind Tract, Bangladesh

Bangladesh is a riverine country, but its north-western part, popularly known as Barind Tract, is mostly drought-prone and faces scarcity of water. Because of very limited surface water resource, groundwater is the main source of water for drinking and irrigation purposes. The increasing demand and withdrawal of groundwater result permanent depletion of groundwater level (GWL). Due to low infiltration capacity the monsoon rainwater cannot percolate through thick surface clay layer (Barind Clay of Pleistocene age). So an attempt is made in the present study for artificial recharge of aquifer by adopting Managed Aquifer Recharge (MAR) model through recharge well (RW) and recharge shaft (RS) installed in Khari (canal) bed for infiltrating flowing rainy season storm water. The study also compares performance and effectiveness of application of conventional MAR model with the modified engineering model as viable adaptive menu to restore the depleting GWL. The conventional MAR model has functioned well initially, but recharge rate (RR) has gradually reduced (1.5–2.5 L/min) from the initial stage (28.64–48.0 L/min) due to clogging of the recharge units with clay (Barind Clay). To improve the recharge capacity, modification of the engineering design in MAR model has been adopted and their performance have been assessed. In modified MAR model, it is possible to replace clogged sand layer any time even during storm water surge in the Khari. Performance was more effective with increased amount of recharge than that of conventional one in the long run. Moreover, the groundwater quality has improved due to dilution process, and found suitable for drinking purpose within acceptable and allowable limits of BDWS (2005) and WHO (2008). Finally, in-depth research activities and regular monitoring and maintenance are necessary for fruitful operation of MAR model to elevate the water scarcity for drinking and irrigation purposes in the area.

Oceanic conditions associated with Euro-Atlantic high pressure and UK drought

Persistent atmospheric high pressures can lead to long-lasting droughts and heatwaves with severe societal and environmental impacts, as evident in summer 2018 in Europe. It is known that oceanic and atmospheric features connected with the tropical Pacific influence the atmospheric circulation regimes over the North Atlantic/European sector leading to blocking high pressures in the cold season. Here we show that in the warm season, different combinations of sea surface temperatures in the North Pacific and the North Atlantic are associated with distinctly different atmospheric circulation patterns over northwest Europe some three months later. While most studies are restricted to atmospheric variables, for the UK we also investigate the hydrological impact and find that the effect of the preferred seasonal storm tracks is more clearly seen in regional streamflow observations than in precipitation, presumably because streamflows integrate the influences of precipitation and evapotranspiration. These relationships open up the possibility of skilful statistical forecasts for much of spring to autumn, which will usefully complement the currently available skilful winter forecasts based on general circulation models. Our results deliver new understanding of the truly global driving processes of UK droughts and highlight the potential for improved early warning for the wider European domain.

Summer Seasonal Sea-level Rise and Associated Potential Storm Surge Vulnerability of the West Coast of Korea

Kim, H.-J. and Suh, S.-W., 2019. Summer seasonal sea-level rise and associated potential storm surge vulnerability of the West Coast of Korea. In: Lee, J.L.; Yoon, J.-S.; Cho, W.C.; Muin, M., and Lee, J. (eds.), The 3rd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 91, pp. 21-25. Coconut Creek (Florida), ISSN 0749-0208.Typhoon-induced storm surge usually occurs during the summer season. Thus, it is important to account for seasonal sea-level (SL) rise in coastal hazard mitigation. In this study, we analyzed one hour intervals of tidal records for Incheon (INC), Kunsan (KUN), and Mokpo (MOK) stations, located on the West Coast of Korea (WCK), as well as atmospheric pressure, to determine the correlation of SL fluctuations as they relate to the inverse barometer effect. Results exhibited annual (summer) sea-level rise (SLR) of 0.35 (0.32), 0.39 (0.39), and 0.55 (0.53) cm/year at the three stations, respectively. However, the mean SL (MSL) during the summer season was approximately 20 cm higher than the annual MSL. It was found that seasonal atmospheric pressure highly affected SL, with 1.58–1.73 cm per hPa owing to the inverse barometer effect; however, there were phase lags in the summer of one month or more. Although the nodal factor accounted for ± 3.7% of the M2 tidal amplitude over 18.6-year return period, the resulting M2 amplitude was maximized in 2090 at 2.87 m, 2.14 m, and 1.62 m at the three reference stations, owing to the macro-tidal environment of the WCK than in 2100. Thus, the target year associated with global warming and SLR, which is normally 2100, should be shifted one decade prior to ensure effective coastal storm surge vulnerability hazards analyses.

Seasonal predictability of high sea level frequency using ENSO patterns along the U.S. West Coast

High sea levels can be conducive to coastal flooding, coastal erosion and inland salt-water intrusion, and thus pose a significant threat to coastal communities, ecosystems and coastal assets. Increases in high water levels have been attributed largely to rising mean sea levels associated with intra-seasonal to interannual climate modes of variability such as the El Niño-Southern Oscillation (ENSO). Here, we examine the predictability of the seasonal frequency of high sea levels using the Niño3.4 index. Different high sea level quantities are considered at 23 tide gauges along the U.S. West Coast, including storm surge and nuisance (minor) floods. At each site, we develop a statistical probabilistic forecasting model for seasonal high sea level frequency during the cold period of October-March. As predictors, we compare the use of (1) seasonal Niño3.4 index observations over the warm antecedent period of July-September and (2) seasonal Niño3.4 index forecasts from the North American Multi-Model Ensemble (NMME) over the cold concurrent period of October-March. Results indicate that the Niño3.4 observations are a good predictor of seasonal high sea level frequency, especially for predicting the storm surge frequency. Correlation coefficients between the observed and modelled seasonal storm surge frequency range from 0.6 to 0.95 at most of the 23 tide gauges. In the predictive model, when using NMME Niño3.4 index, correlation coefficients range between approximately 0.4 and 0.7 at the southern gauges for Niño3.4 index forecasts initialized from October to June (the skill decreases with lead time). Our results provide insights into the seasonal predictability of high sea levels using ENSO patterns which is important for planning and coastal management.

Numerical Simulations of Seasonal Variations of Rainfall over the Island of Hawaii

AbstractThe seasonal variations of rainfall over the island of Hawaii are studied using the archives of the daily model run from the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) from June 2004 to February 2010. Local effects mainly drive the rainfall on the Kona coast in the early morning and the lower slopes in the afternoon. During the summer, the incoming trade winds are more persistent and moister than in winter. The moisture content in the wake zone is higher than open-ocean values because of the convergent airflow associated with dual counterrotating vortices. As the westerly reversed flow moves toward the Kona coast, it decelerates with increasing moisture and a moisture maximum over the coastal area, especially in the afternoon hours in summer months. The higher afternoon rainfall on the Kona lower slopes in summer than in winter is caused by a moister (&gt;6 mm) westerly reversed flow bringing moisture inland and merging with a stronger upslope flow resulting from solar heating. Higher nocturnal rainfall off the Kona coast in summer than in winter is caused by the low-level convergence between a moister westerly reversed flow and offshore flow. On the windward slopes, the simulated rainfall accumulation in winter is higher because of frequently occurring synoptic disturbances during the winter storm season. Nevertheless, early morning rainfall along the windward coast and afternoon rainfall over the windward slopes of the Kohala Mountains is lower in winter because the incoming trades are drier.

Using Radar-Derived Parameters to Develop Probabilistic Guidance for Lightning Cessation within Isolated Convection near Cape Canaveral, Florida

Abstract Thunderstorms in central Florida frequently halt outdoor activities, requiring that one wait some prescribed time after an assumed last flash before safely resuming activities. The goal of this research is to develop a high-skill probabilistic method that can be used in high pressure real-world operations to terminate lightning warnings more quickly while maintaining safety. Probabilistic guidance tools are created for isolated warm season storms in central Florida using dual-polarized radar data at 1-min intervals. The parameters examined are maximum reflectivity and graupel presence at the 0°, −5°, −10°, −15°, and −20°C levels as well as composite reflectivity. Random samples of the radar data are used to train a generalized linear model (GLM) to make a probabilistic prediction whether a given flash is the storm’s last flash. The most statistically significant predictors for lightning cessation are found to be the storm’s maximum reflectivity in the composite and the 0°C levels, along with graupel presence or absence at the −5°, −10°, −15°, and −20°C levels. Statistical verification is used to analyze the performance of the two GLMs at different probability thresholds (95.0%, 97.5%, and 99.0%). When applying the cessation guidance as though storms are occurring in real time, results showed ~99% of the storms produced no additional lightning after the GLM suggested cessation had already occurred. Although these results are encouraging, the procedure must be tested on much larger datasets having different convective modes and different areal coverages to prove its value compared to operational forecasters.

Spatial Variability of Coastal Foredune Evolution, Part A: Timescales of Months to Years

Coastal foredunes are topographically high features that can reduce vulnerability to storm-related flooding hazards. While the dominant aeolian, hydrodynamic, and ecological processes leading to dune growth and erosion are fairly well-understood, predictive capabilities of spatial variations in dune evolution on management and engineering timescales (days to years) remain relatively poor. In this work, monthly high-resolution terrestrial lidar scans were used to quantify topographic and vegetation changes over a 2.5 year period along a micro-tidal intermediate beach and dune. Three-dimensional topographic changes to the coastal landscape were used to investigate the relative importance of environmental, ecological, and morphological factors in controlling spatial and temporal variability in foredune growth patterns at two 50 m alongshore stretches of coast. Despite being separated by only 700 m in the alongshore, the two sites evolved differently over the study period. The northern dune retreated landward and lost volume, whereas the southern dune prograded and vertically accreted. At the start of and throughout the study, the erosive site had steeper foredune faces with less overall vegetation coverage, and dune growth varied spatially and temporally within the site. Deposition occurred mainly at or behind the vegetated dune crest and primarily during periods with strong, oblique winds (&gt;∼45 ∘ from shore normal). Minimal deposition was observed on the mostly bare-sand dune face, except where patchy vegetation was present. In contrast, the response of the accretive site was more spatially uniform, with growth focused on the heavily vegetated foredune face. The largest differences in dune response between the two sections of dunes occurred during the fall storm season, when each of the systems’ geomorphic and ecological properties modulated dune growth patterns. These findings highlight the complex eco-morphodynamic feedback controlling dune dynamics across a range of spatial scales.

The state of Western Australia’s coral reefs

Western Australia’s coral reefs have largely escaped the chronic pressures affecting other reefs around the world, but are regularly affected by seasonal storms and cyclones, and increasingly by heat stress and coral bleaching. Reef systems north of 18°S have been impacted by heat stress and coral bleaching during strong El Nino phases and those further south during strong La Nina phases. Cumulative heat stress and the extent of bleaching throughout the northern reefs in 2016 were higher than at any other time on record. To assess the changing regime of disturbance to reef systems across Western Australia (WA), we linked their site-specific exposure to damaging waves and heat stress since 1990 with mean changes in coral cover. Since 2010, there has been a noticeable increase in heat stress and coral bleaching across WA. Over half the reef systems have been severely impacted by coral bleaching since 2010, which was further compounded by cyclones at some reefs. For most (75%) reef systems with long-term data (5–26 yrs), mean coral cover is currently at (or near) the lowest on record and a full recovery is unlikely if disturbances continue to intensify with climate change. However, some reefs have not yet experienced severe bleaching and their coral cover has remained relatively stable or increased in recent years. Additionally, within all reef systems the condition of communities and their exposure to disturbances varied spatially. Identifying the communities least susceptible to future disturbances and linking them through networks of protected areas, based on patterns of larval connectivity, are important research and management priorities in coming years while the causes of climate change are addressed.

Enhanced Ionization in Magnetic Anomaly Regions of the Martian Lower Ionosphere Associated With Dust Storms

AbstractThe Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument aboard the Mars Express spacecraft observes vertical echoes from the normal ionosphere and oblique echoes from ionization bulges. The peak frequencies of these two kinds of echoes are, in general, nearly equal. In the present study, we report the detection of oblique echoes whose peak frequencies are much larger than those of the vertical echoes. These echoes were observed on 15 June, 21 June, 28 June, and 10 July 2007, respectively. All these oblique echoes were observed from a region of strong crustal magnetic fields. After correcting for dispersion effects, the maximum electron density in the first case is found to be 3.75 × 105 cm−3 and is observed at an altitude of ~88 km. In subsequent cases, a gradual decrease in peak electron density and an increase in altitude are observed. The causative mechanism of these oblique echoes is examined by considering various forces from top and bottom. During the times of the observations, there were no solar flares or meteor in fall. The presence of solar energetic particles also could not be firmly established. We found that these strong oblique echoes were observed at the initial phase and during the progression of a planet‐encircling dust storm in Martian Year 28. A similar, but weaker features were observed in other dust storm seasons as well. Mechanisms causing such oblique echoes in regions of strong magnetic fields are discussed.

High resolution, extreme isotopic variability of precipitation nitrate

Deposition of atmospheric nitrate (NO3−) in precipitation can be an important source of reactive nitrogen (N) to ecosystems, particularly in regions with high nitrogen oxide (NOx = nitric oxide (NO)+nitrogen dioxide (NO2)) emissions. However, high resolution deposition data are lacking for most systems. We conducted hourly precipitation sampling across six growing season storms in a forested area historically subjected to some of the highest levels of chronic N deposition in the United States. To characterize the influence of electricity generating unit (EGU), vehicle, and biogenic NOx emissions on NO3− deposition, we calculated the total NOx emitted from these sources within a 100 km radius of air mass back trajectories determined for Fernow Experimental Forest (West Virginia, USA). We combined these emissions estimates with established 15N isotope values for NOx sources in a three end-member mixing model to predict source-based δ15N values of deposition reaching the study site on an hourly basis. To evaluate the effect of NOx oxidation pathways on measured δ15N-NO3- values, we compared observed hourly isotope values to a coupled δ15N and Δ17O array representing N isotope exchange between atmospheric oxidized N molecules. Within individual events, δ15N, δ18O, and Δ17O values ranged by as much as 19.5‰, 28.9‰, and 13.8‰, respectively. This extreme short-term isotopic variability suggests a dynamic mix of NOx sources, oxidation pathways, and fractionation processes contributing to HNO3 formation. During every storm, precipitation δ15N-NO3- values were lower than those expected to result from predominant HNO3 formation pathways or oxidation of estimated NOx emissions along back trajectories, suggesting a systematic underestimation of NOx contributions to atmospheric HNO3 formation from isotopically depleted soil emissions. Together, these analyses represent the most comprehensive assessment to date relating high temporal resolution δ15N-NO3- observations to NOx emission sources, oxidation chemistry, and isotopic fractionation effects. We present the first observations of extreme intra-storm δ15N, δ18O, and Δ17O variability, emphasizing the need for improved constraints on soil NOx emissions, forest canopy effects, and their role in atmospheric NO3− deposition and isotope dynamics in forests.