Main Plume Research Articles

Dust Transport from North Africa to the Middle East: Synoptic Patterns and Numerical Forecast

Every year, large quantities of dust are transported from North Africa to the Americas, Europe, and West Asia. The purpose of this study is to analyze four intense and pervasive dust storms that entered the Middle East from Northern Africa. Satellite products, ground-based remote sensing measurements, reanalysis data, and the outputs of the Aire Limitée Adaptation dynamique Développement InterNational-Dust (ALADIN-Dust) and the ICOsahedral Nonhydrostatic weather and climate model with Aerosols and Reactive Trace gases (ICON-ART) forecasting models were synergized. The dust storms originated from different source regions located in the north, northeastern, and central parts of the Sahara Desert. The transport height of the main dust plumes was about 3–5 km, triggered by the westerly zonal winds. The presence of a closed low over the Eastern Mediterranean and the penetration of a deep trough into North Africa at 500 hPa were the main synoptic circulation patterns favoring long-range dust transport during the four dust events. A comparison of aerosol optical depth (AOD) outputs from the two models with satellite data revealed that although both models forecasted dust transport from Africa to the Middle East, they considerably underestimated the AOD values, especially near the dust sources. The ICON-ART model performed slightly better than ALADIN in forecasting these dust storms, and for longer forecasting leading time, although the performance of both models decreased, the superiority of the ICON-ART model became more apparent.

Late summer northwestward Amazon plume pathway under the action of the North Brazil Current rings

The North Brazil Current (NBC) flows offshore of the mouth of the Amazon River and seasonally sheds anticyclonic rings (NBC rings) that propagate northwestward and interact with the Amazon River plume (ARP). Mesoscale features have a high temporal variability that is hard to monitor from current weekly and monthly sea surface salinity (SSS) satellite fields. Novel SSS fields with a higher temporal resolution analyzed together with satellite geostrophic currents, chlorophyll-a, and wind speed and in-situ data from the “Microbiomes cruise” on the SV Tara in August–September 2021 revealed a late summer freshwater pathway, which was not well documented in earlier studies. By combining these datasets, we improved the characterization of summer ARP pathways. In 2021, the ARP was a succession of freshwater patches cut off from the main plume by the NBC rings. A patch of about 200.000 km2 with salinity <33.5 pss was observed in September 2021, bringing 0.5 Sv of Amazon water northwestward in a period where the mean ocean currents lead to eastward transport. This patch was shallow, very stratified, and it created a surface steric-height anomaly that was identified as an anticyclonic feature in altimetric sea level products. Once separated from the NBC retroflection, it was mainly driven by Ekman currents. Other similar patches were observed during the 2021 summer, leading to a strong intermittency of the ARP transport. They strongly contributed to make 2021 the year with the largest northwestward freshwater transport in late summer within the 2010–2021 time-period investigated. This freshwater transport pathway is important for all plume-related phenomena, and show the ability of combined SMOS and SMAP data to accurately represent the day-to-day SSS variability.

OIB-type mafic–ultramafic rocks in South Guangxi, South China: A record of interaction between Paleo-Tethys subduction and Emeishan large Igneous Province

Late Permian ultramafic–mafic igneous rocks in the Pingxiang area, Guangxi, South China include wehrlite, gabbro, diabase, and amygdaloidal basalt. Geochemical characteristics document interaction between the Emeishan Large Igneous Province (ELIP) and the mantle wedge related to subduction of the Paleo–Tethys. Gabbro and basalt show chondrite–normalized rare earth elements (REEs) and primitive mantle–normalized trace element patterns that parallel ocean island basalts (OIB) and mafic intrusions from the ELIP. Melts in equilibrium with clinopyroxenes, in both wehrlite and gabbro, have REEs and trace element compositions similar to OIB and high–Ti mafic rock of the ELIP. The clinopyroxenes also show a rift–related compositional trend and cover those from the ELIP rocks. These compositional features, along with their moderate initial 87Sr/86Sr and εNd(t) values (−0.8 to +3), are consistent with derivation from an enriched mantle plume source. This is the first time that ultramafic–mafic rocks are reported beyond the established extent of the ELIP and could represent an offshoot from the main mantle plume or indicate that the ELIP plume was considerably bigger than current proposals but has been significantly denuded by subsequent erosion. In addition, the Pingxiang rock units display slightly enriched εNd(t) values and slight negative Nb, Ta, and Zr relative to OIB rocks, indicating an enriched component in the mantle source. Formation of the ELIP spatially and temporally overlapped with subduction of the Paleo–Tethys ocean and interaction between the plume and mantle wedge accounts for the compositional diversity of the ELIP. Such interaction is probably common along the southwestern–southern margin of the Yangtze Block.

Dyke swarm history in Belet-ili and Gaia (Gaya) Coronae Region (13°–26°E, 0°–10°N), Central Eistla Regio, Venus

Eistla Regio, Venus, is a locus of major plume-generated magmatism and tectonics. We focus on the central portion, termed Central Eistla Regio. More than 19,000 extensional lineaments (grabens, fissures and fractures) were mapped in the area 13°-26°E, 0°-10°N, at 1:500,000 scale using full resolution Magellan SAR (radar) images. These structures are interpreted to represent the surface expression of underlying mafic dykes and have been grouped, on the basis of trend, into radiating, circumferential and linear dyke swarms. Thirty-two swarms are identified and linked to 20 magmatic centres, most of which are located within or near two coronae, Belet-ili and Gaia (Gaya) coronae, while others are linked to magmatic centres outside the study area. These magmatic centres are interpreted to be linked to underlying mantle plumes, and the sizes of the underlying flattened plume heads are estimated from the interpreted dyke swarms: for radiating swarms, the radius of the transition from proximal radiating to more distal linear pattern, and for circumferential dykes, the radial distance to the outer boundary of the circumferential pattern. Plume heads for the largest centres, Belet-ili and Gaia coronae are estimated at about 230 km and 275 km in radius, respectively. These sizes are less than the 1200 km radii predicted for a plume arriving from the deep mantle, and would suggest an origin at a shallower level (likely a mid-mantle boundary, i.e. between upper and lower mantle). The NW alignment of Belet-ili and Gaia corona and other magmatic centres in our study area potentially represents structural control by a rift zone, which can be traced further north to Anala Mons (one of two main plume centres of Central Eistla Regio).

Research and management challenges following soil and landscape decontamination at the onset of the reopening of the Difficult-to-Return Zone, Fukushima (Japan)

Abstract. Twelve years after the nuclear accident that occurred at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) in March 2011, radiocesium contamination (with a large dominance of 137Cs, with a 30-year half-life) remains a major concern in various municipalities of north-eastern Japan. The Japanese authorities completed an unprecedented soil decontamination programme in residential and cultivated areas affected by the main radioactive plume (8953 km2). They implemented a complex remediation programme scheme to remediate soils that are fundamental to life on Earth, relying on different decision rules depending on the waste type, its contamination level and its region of origin, after delineating different zones exposed to contrasted radiation rates. The central objective was not to expose local inhabitants to radioactive doses exceeding 1 mSv yr−1 in addition to the natural levels. At the onset of the full reopening of the Difficult-to-Return Zone (DTRZ) in spring 2023, the current review provides an update of a previous synthesis published in 2019 (Evrard et al., 2019). Although this ambitious soil remediation and reconstruction programme has almost been completed in the 12 municipalities of Fukushima Prefecture in which an evacuation order was imposed in at least one neighbourhood in 2011, from the 147 443 inhabitants who lived there before the accident, only 29.9 % of them had returned by 2020. Waste generated by decontamination and tsunami cleaning/demolition work is planned to have been fully transported to (interim) storage facilities by the end of 2023. The cost of the operations conducted between 2011 and 2020 for the so-called “nuclear recovery” operations (including decontamination) was estimated by the Board of Audit of Japan in 2023 as JPY 6122.3 billion (∼ EUR 44 billion). Decontamination of cropland was shown to have impacted soil fertility, and potassium fertilisation is recommended to limit the transfer of residual radiocesium to new crops. In forests that cover 71 % of the surface area of Fukushima Prefecture and that were not targeted by remediation, radiocesium is now found in the upper mineral layer of the soil in a quasi-equilibrium state. Nevertheless, 137Cs concentrations in forest products (including wood for heating and construction, wild plants, wildlife game, mushrooms) often keep exceeding the threshold values authorised in Japan, which prohibits their exploitation in the area affected by the main plume. Radionuclides from forests were shown to be exported in dissolved and particle-bound forms to downstream river systems and floodplains, although multiple monitoring records showed the continuous decrease in radiocesium concentrations in both river water and sediment across the main plume between 2011 and 2021. Fish contamination is now generally found to be below the threshold limits although reputational damage remains a major concern for local fishing communities. The remobilisation of radiocesium from sediment accumulated in reservoirs of the region is also of potential concern as it may lead to secondary contamination of fish or irrigation waters supplied to decontaminated fields. Overall, this synthesis demonstrates the need to continue monitoring post-accidental radiocesium transfer in these environments and to keep sharing data in order to refine our predictive understanding of radiocesium mobility and consolidate the tools available to model contaminant transfer in ecosystems. In forests in particular, novel countermeasures and wood uses remain to be developed and tested. Furthermore, the hydrologic connectivity between soils under different ecosystems greatly influences long-term radiocesium transport. The consequences of extreme phenomena (e.g. typhoons, forest fires) that may become more frequent in the future as a result of global change in these contaminated environments should be further anticipated.

Evolution of aerosol plumes from 2019 Raikoke volcanic eruption observed with polarization lidar over central China

The Raikoke volcano erupted on 21–22 June 2019 and emitted large amounts of volcanic ash into the upper troposphere, and later might impose long-term effects on the global and regional radiation budget after the long-range transport of volcanic aerosol plumes. Height-resolved ground-based lidar observations are beneficial to trace and cross-check the 3-D evolution of complicated aerosol plumes, which are, however, scarce at mid-latitude regions. Here, we present a rare ground-based lidar observation of Raikoke aerosol plumes in the mid-latitudes of the Northern Hemisphere (site: Wuhan; location: 30.5°N, 114.4°E) from 25 July to 30 September 2019. The main aerosol plume first arrived at Wuhan on 25 July and was intermittently observed during the following 2 months at altitudes of 15.0–20.5 km. From 22 August to 23 September, this aerosol plume underwent two quasi-elliptical transport pathways in East Asia driven by an Asian monsoon anticyclone. The particle depolarization ratio of volcanic aerosols is < 0.05. The layer-integrated AODs (aerosol optical depths) of 0.001–0.017 are smaller than those observed from other high-altitude sites previously owing to the dispersal of particles. Interestingly, another separated dense aerosol cloud was observed twice, closely followed by a thin and horizontally extended aerosol plume (named ‘trail’). This study provides valuable information for studying the evolution of the vertical distribution and optical properties of Raikoke volcanic aerosols, which is anticipated to be a crucial supplement/reference for dispersion model simulation, data assimilation, and forecasting refinement.

Dust impacts on Mongolian cyclone and cold front in East Asia: a case study during 18–22 March 2010

The Gobi Desert in East Asia experiences dust outbreaks during the spring, which are often caused by high winds associated with Mongolian cyclones. The radiative forcing that arises from dust aerosols could affect the intensity and movement of Mongolian cyclones and cold fronts. A case study on a Mongolian cyclone that occurred during 18–22 March 2010 in East Asia examines these factors using an atmosphere-dust coupled model. Our numerical results show that dust’s impact on the intensity of the cyclone and its cold front varies between day and night and depends on the relative position of the weather systems of interest to the dust plume, i.e., the edge or the main dust plume region. When the dust plume approaches the cold front, most of the dust is trapped behind the cold front at low levels, but a small amount of dust extends to the middle levels, thereby reaching the warm side of the middle-level front. As a result, dust weakens the intensity of the low-level front and intensifies the middle-level front during the daytime, modifying the cold front oppositely at night. On the other hand, dust influences the cyclone in two phases. During the first phase, the dust plume edge arrives at the center of the cyclone in the daytime and warms the region, slightly intensifying the cyclone. During the second phase, the major dust plume feeds into the cyclone center in the early morning. The net dust effect is negative, which cools the cyclone center and decreases or stops the intensification. Subsequently, the cyclone is taken over by a nearby cyclonic circulation downstream. The dust plume approaches the new cyclone center, which repeats a similar pattern of intensity change: intensifying and then leveling off. Our results show that dust has no apparent influence on the movement of the cyclone and its cold front for this case study.

Plume characterization of a waveguide ECR thruster

A circular waveguide electron cyclotron resonance plasma thruster prototype driven by microwaves at 5.8 GHz (80–300 W) is characterized. The magnetic field is generated by a combination of Sm-CoYXG32 magnets and an electromagnet, which enables the tuning of the resonance position and magnetic nozzle shape. The main plasma plume properties are analyzed by using electrostatic probes when the mass flow rate (Xenon), microwave power, electromagnet current, and propellant injector design are varied. An estimation of the propulsive performance of the device is also presented. Results show that a single radial injector hole is not sufficient for a symmetric ion current profile and that magnetic nozzle shape and strength tuning can significantly affect the divergence angle and thruster floating potential. A utilization efficiency of up to 70% and electron temperatures of up to 16 eV have been measured.

Cluster and multivariate analysis to study the diffuse contamination of emerging per- and polyfluoroalkyl substances (PFAS) in the Veneto Region plain (North-eastern Italy)

In recent years, per- and polyfluoroalkyl substances (PFAS) have emerged as major pollutants of concern. This study considered a real case of superficial and groundwater contamination caused by a set of 15 persistent, carcinogenic, and bioaccumulative compounds. The study area is the Veneto Region floodplain in Italy, where a huge contamination mainly caused by a persistent spill-over from a former chemical factory was discovered in 2013. The contamination path studied in 2013 followed mainly two directions: the first towards east, to the city of Vicenza, and the second following the course of Chiampo and Agno streams, southwards.To identify the major patterns of contamination, a Factor Analysis (PCA) in conjunction with a Cluster Analysis (CA) was performed. The reviewed dataset is composed by PFAS concentration values collected from 2013 to 2021 in groundwater, superficial waters, in natural sources, and in proximity to three industrial discharges, throughout a 3600 km2 area. The CA results were cross-referenced with the water table interpolation, yielding a match between the groundwater flow directions and the observed patterns of the two main plumes. The persistence of pollutants was finally investigated by analyzing distances between the former chemical factory, an industrial wastewater collector which lies along Chiampo and Agno valleys that host residential and industrial areas, and the other sampling points collected in the dataset. The findings confirmed the importance of assessing anthropic background levels of contamination and highlighted the necessity to include the PFAS issue in a national health-based drinking water quality guideline.

Why did so few refugees return to the Fukushima fallout-impacted region after remediation? An interdisciplinary case study from Iitate village, Japan

Large volumes of radionuclides were deposited on the soils in North-eastern Japan after the accident at the Fukushima Dai-ichi nuclear Power Plant (FDNPP) in March 2011. The village of Iitate, with a population of 6544 inhabitants in early 2011, was located in the main radioactive plume. Its population was evacuated between 2011 and 2017, when the town reopened after decontamination was completed in some cultivated and residential areas. This situation is unprecedented in history. Even around Chernobyl, access to the most contaminated area has remained forbidden until today. This manuscript compiles measurements of radiation dose rates and sediment radioactive contamination, socio-economic statistics, and reports the results of interviews conducted among refugees since 2011. Despite this reopening, which was presented as desirable by the authorities, less than ten percent of the original population - almost all of them over 70 years old – had returned to live in the village by January 2022. An analysis of the evolution of the population shows that it is now declining again. When the village was evacuated in 2011, most of the families that used to live with three generations under the same roof were often separated. The majority of the inhabitants took refuge in neighbouring municipalities, and many lived in temporary housing sites with a strong feeling of promiscuity. This study shows the difficulty for the majority of villagers who had never heard of Becquerels before the accident in 2011 to return to a very different environment with forests remaining contaminated and major landscape transformations having occurred after several years of abandonment and through the remediation process itself. Before 2011, forests and cropland were the main land uses in the village, and the local authorities promoted a model of eco-village. While decontamination has been effective in limiting the dispersion of radionuclides across the landscape, it did not affect the large stock of radionuclides stored in forests that cover ∼80% of the surface area. Moreover, the lack of facilities and public services remains problematic for an elderly population that has a limited mobility to travel to nearby towns to find the necessities of everyday life. This study provides a benchmark for comparison with the evolution of the seven other municipalities located nearby FDNPP that are being reopened to settlement. This research, which shows the situation after a remediation tentative, will provide a unique reference in post-accident management.

Improved Darcian streambed measurements to quantify flux and mass discharge of volatile organic compounds from a contaminated aquifer to an urban stream

Quantifying VOC transport from contaminated groundwater to streams is challenging and important for understanding off-site migration of VOCs, cross-media contamination (groundwater to surface water and eventually air), and potential impacts on downstream ecosystems and human populations. A streambed point sampling approach was used to quantify fluxes of water and 14 VOCs from groundwater to an urban stream in North Carolina, USA, during summer (June 2015) and winter (January 2016). The approach is unique in coupling measurements of vertical hydraulic conductivity, vertical hydraulic head gradient, and groundwater VOC concentration at each individual sampling point, reducing or eliminating some potential concerns with other Darcian methods for quantifying VOC inputs to streams.Most results were consistent with discharge of two main VOC plumes on opposite sides of the stream. Plume 1 from the west side was dominated by cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC) at mean concentrations of 19 and 11 μg L−1, respectively. Plume 2 from the east side was dominated by benzene (mean concentration 56 μg L−1). Plume 2 was not previously known, and the improved sampling approach allowed VOC discharge from both plumes to be quantified simultaneously.For 13 of the 14 detected VOCs, the mean VOC flux from groundwater to the stream (fVOC) was higher in January 2016 than in June 2015, mainly because groundwater flux was higher in January. The only exception was cDCE, the most abundant VOC in Plume 1, which had mean fVOC values of 9.8 and 9.5 mg m−2 d−1 in June 2015 and January 2016, respectively. Benzene was the most abundant VOC in Plume 2 and had mean fVOC values of 11 and 37 mg m−2 d−1 in June 2015 and January 2016, respectively. High groundwater flux drove almost all the occurrences of high VOC flux. For a given VOC, the flow-weighted mean concentration (with each VOC concentration weighted by the upward groundwater flux at the VOC sampling point) was generally larger than the unweighted mean concentration. Thus, flow-weighting of concentrations gave a more accurate indication of the average VOC concentration in net groundwater discharge to the stream.An estimate of total VOC mass discharge from groundwater to the study reach of the stream, 3.6 kg of VOC per year, was based on the fVOC results and streambed area in the reach. The bulk of this discharge was due to benzene, cDCE, and VC, with individual mass discharges of 2.1, 0.83, and 0.40 kg yr−1, respectively. Estimates of maximum potential VOC degradation in the streambed suggest that the 3.6 kg yr−1 estimate of mass discharge was not sensitive to potential degradation of VOCs in the streambed sediments above the groundwater sampling depth.

Development of a numerical model for sector-average plume gamma dose and its validation with dose rate measurements at Kalpakkam NPP site, India

A Gaussian Plume based simple numerical model, named DIFFUSE is developed to simulate the long-term sector-average plume gamma dose due to radioactive plume released during normal operation of nuclear facilities. DIFFUSE calculates site specific joint frequency distributions of wind speed, wind direction and atmospheric stability using micrometeorological observations. It performs the finite sector-average dose integration for any stack height and gamma energy using Simpson's 1/3rd method with sufficient computational efficiency within the site boundary up to 2 km. Plume dose contribution to the main plume sector from nearest and next nearest side plume sectors is also calculated. DIFFUSE is validated with a 3-month long, starting from February 2021 to April 2021, dose rate observation data during operational releases from 100 m stack of Madras Atomic Power Station, Kalpakkam, India. Meteorological data from onsite 50 m tower and continuous dose rate observation from two sets of Autonomous Gamma Dose Logger (AGDL) detectors, namely n-AGDLs and r-AGDLs, placed in two different configurations along the geometric arcs of wind sectors around the stack are used. Simulated doses are compared with look-up table based dose estimates by Hukkoo et al. (1988). Linear spatial averaging of cumulative AGDL doses on a sector arc is used as measured sector-average dose for model validation. Simulations performed for both n-AGDL and r-AGDL configurations show DIFFUSE estimated doses are ∼37% lower and Hukkoo estimated doses are at least ∼50% lower than the measured doses. Statistical analysis of DIFFUSE simulated doses shows a statistical correlation of R2∼98.3%, slope of the fit ∼1.36 for n-AGDL setup and R2∼75.3%, slope of the fit ∼1.57 for r-AGDL setup. Overall, DIFFUSE produces conservative doses compared to look-up table based doses as required by regulatory bodies.

Chronostratigraphic Studies of the Ootun Area Revealing the Late Holocene Plume Volcanism of the Oldoinyo Lengai, Ngorongoro, Tanzania

Oldoinyo Lengai has been a subject of international attention for geoscientists because of its uniqueness. The mountain is the world’s only active natrocarbonatite volcano whose recent activities are well documented. However, little is known about its eruptive history during the Holocene. One way of uncovering past volcanic activities is through chronostratigraphic studies. A rare stratigraphic sequence in the Ootun area containing buried tephra beds and paleosols is presented in this article. The beds suggest that the nearby active Oldoinyo Lengai volcano experienced the main plume volcanism during the late Holocene. This work presents the lithology of the area, estimated deposition period, and elemental and mineralogical compositions of strata, and establishing similarities between ash properties and information from previously reported chemistry and eruptions of the Oldoinyo Lengai volcano. Energy dispersive X-ray fluorescence, X-ray diffractometry, and accelerated mass spectrometry techniques were used for elemental, mineralogical, and radiocarbon dating analyses. A 1.3-m vertical soil profile revealed three major strata: topsoil, tephra bed, and paleosols. The paleosols are presumed to have been topsoil of the Ootun area during the Holocene. Subsurface tephra layers were found to contain similar properties to the volcanic material of the Oldoinyo Lengai. Based on the experimental findings and literature data, the study reports the occurrence of two major plume eruption events from the Oldoinyo Lengai, which happened around the minimum (oldest) age of490±10 BCand 771 AD. This work is essentially important in demonstrating the relevance of the region’s tephra chronostratigraphic studies by revealing the prospect of collecting additional scientific data on past geological processes and paleoenvironmental conditions of northern Tanzania.

Analysis of the 2020 Taal Volcano tephra fall deposits from crowdsourced information and field data

After 43 years of dormancy, Taal Volcano violently erupted in January 2020 forming a towering eruption plume. The fall deposits covered an area of 8605 km2, which includes Metro Manila of the National Capital Region of the Philippines. The tephra fall caused damage to crops, traffic congestion, roof collapse, and changes in air quality in the affected areas. In a tropical region where heavy rains are frequent, immediate collection of data is crucial in order to preserve the tephra fall deposit record, which is readily washed away by surface water runoff and prevailing winds. Crowdsourcing, field surveys, and laboratory analysis of the tephra fall deposits were conducted to document and characterize the tephra fall deposits of the 2020 Taal Volcano eruption and their impacts. Results show that the tephra fall deposit thins downwind exponentially with a thickness half distance of about 1.40 km and 9.49 km for the proximal and distal exponential segments, respectively. The total calculated volume of erupted fallout deposit is 0.057 km3, 0.042 km3, or 0.090 km3 using the exponential, power-law, and Weibull models, respectively, and all translate to a VEI of 3. However, using a probabilistic approach (Weibull method) with 90% confidence interval, the volume estimate is as high as 0.097 km3. With the addition of the base surge deposits amounting to 0.019 km3, the volume translates to a VEI of 4, consistent with the classification for the observed height and umbrella radius of the 2020 main eruption plume. VEI 4 is also consistent with the calculated median eruption plume height of 17.8 km and sub-plinian classification based on combined analysis of isopleth and isopach data. Phreatomagmatic activity originated from a vent located in Taal Volcano’s Main Crater Lake (MCL), which contained 42 million m3 of water. This eruptive style is further supported by the characteristics of the ash grain components of the distal 12 January 2020 tephra fall deposits, consisting dominantly of andesitic vitric fragments (83–90%). Other components of the fall deposits are lithic (7–11%) and crystal (less than 6%) grains. Further textural and geochemical analysis of these tephra fall deposits contributes to better understand the volcanic processes that occurred at Taal Volcano, one of the 16 Decade Volcanoes identified by the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) because of its destructive nature and proximity to densely populated areas. The crowdsourcing initiative provided a significant portion of the data used for this study while at the same time educating and empowering the community to build resilience.

Hybrid Continuum/Rarefied Flow Simulations of Plume Interaction with Full-Sized Spacecraft

The present study performs hybrid Navier–Stokes (N-S) and direct simulation Monte Carlo (DSMC) simulations to predict surface pressures and heat fluxes imposed by plumes impinging on spacecraft in actual length scale. The first application was the impingement of H-II Transfer Vehicle main engine plumes on the International Space Station. It was found that the profiles of the surface pressure and heat flux imposed by the plume interactions strongly depend on the high-density regions generated by the interactions among multiple plumes and between plumes and upstream structures. The plume of a lunar lander was another application. A plume impinging on the lunar surface generated a strong shock wave near ground level, and some of the hot gases imposed larger pressures and heat fluxes as the altitude decreased. The third application was a cold-gas plume vented from rocket tanks. Although the nozzles were small, plumes expanded rapidly and subjected some rocket assemblies to various forces and cooling effects. Last, the last application to a thruster plume impinging on debris showed that the plume can impart enough torque to detumble the rotation of a debris. This study adequately demonstrated that the usefulness of the hybrid N-S/DSMC technique for assessing risks or exploring new ideas regarding plume impingement in actual spacecraft length scale, including the plume–plume and plume–surface interactions.

Influence of emission inventory resolution on the modeled spatio-temporal distribution of air pollutants in Buenos Aires, Argentina, using WRF-Chem

The temporal and spatial resolution of the emission inventory included into an air quality model plays a key role in the appropriate representation of air pollution events and background atmospheric chemistry. Here, we use the Weather Research and Forecasting coupled with Chemistry (WRF-Chem v4.0) model to perform high-resolution air quality simulations over the city of Buenos Aires, Argentina, with two different anthropogenic emissions datasets: the High-resolution Emissions Inventory of Argentina (GEAA-AEI) and the Emissions Database for Global Atmospheric Research - Hemispheric Transport of Air Pollution (EDGAR-HTAP). A local optimized configuration considering 3 nested domains with a horizontal grid size of 20 × 20 km, 4 × 4 km, and 1.3 × 1.3 km and the MOZART chemical scheme was used. The model performance for NO2, PM10, PM2.5, and O3 concentrations was validated against measurements from the existing air quality monitoring stations in the Buenos Aires Metropolitan Area (AMBA) during austral fall 2018. Our results show that the daytime concentrations of air pollutants are influenced by the shape and shift of the hourly emissions profile, especially for NO2 where the reduction in nighttime emissions decreased the mean model bias by ∼50%. PM10 and PM2.5 generally satisfied the model performance criteria, but underestimation tended to occur in the GEAA-AEI simulations and overestimation for the EDGAR-HTAP case. Comparison with TROPOMI-derived tropospheric NO2 columns showed a high positive correlation (r > 0.75) and a positive bias. We found large discrepancies between the spatial distribution patterns of the simulations within the innermost high-resolution domain centered on AMBA, mostly in suburban areas where no observations are available. We propose additional monitoring sites to address such differences and determine the size and shape of the main pollutant plume. We conclude that high-resolution air quality modeling is important within underdeveloped or developing South American cities that lack continuous air quality measurements, as it represents a powerful tool in supporting the design of governmental monitoring networks and air pollution mitigation policies.

Lower Thermospheric Material Transport via Lagrangian Coherent Structures.

We show that inter‐model variation due to under‐constraint by observations impacts the ability to predict material transport in the lower thermosphere. Lagrangian coherent structures (LCSs), indicating regions of maximal separation (or convergence) in a time‐varying flow, are derived in the lower thermosphere from models for several space shuttle water vapor plume events. We find that inter‐model differences in thermospheric transport manifest in LCSs in a way that is more stringent than mean wind analyses. LCSs defined using horizontal flow fields from the Specified Dynamics version of the Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (SD‐WACCMX) at 109 km altitude are compared to Global Ultraviolet Imager (GUVI) observations of the space shuttle main engine plume. In one case, SD‐WACCMX predicts an LCS ridge to produce spreading not found in the observations. LCSs and tracer transport from SD‐WACCMX and from data assimilative WACCMX (WACCMX + DART) are compared to each other and to GUVI observations. Differences in the modeled LCSs and tracer positions appear between SD‐WACCMX and WACCMX + DART despite the similarity of mean winds. WACCMX + DART produces better tracer transport results for a July 2006 event, but it is unclear which model performs better in terms of LCS ridges. For a February 2010 event, when mean winds differ by up to 50 m/s between the models, differences in LCSs and tracer trajectories are even more severe. Low‐pass filtering the winds up to zonal wavenumber 6 reduces but does not eliminate inter‐model LCS differences. Inter‐model alignment of LCSs improves at a lower 60 km altitude.

Radionuclide contamination in flood sediment deposits in the coastal rivers draining the main radioactive pollution plume of Fukushima Prefecture, Japan (2011–2020)

Abstract. Artificial radionuclides including radiocesium (134Cs and 137Cs) and radiosilver (110mAg) were released into the environment following the Fukushima Dai-ichi nuclear power plant accident in March 2011. These particle-bound substances deposited on soils of north-eastern Japan, located predominantly within a ∼3000 km2 radioactive fallout plume and drained by several coastal rivers to the Pacific Ocean. The current dataset (Evrard et al., 2021), which can be accessed at https://doi.org/10.1594/PANGAEA.928594, compiles gamma-emitting artificial radionuclide activities measured in 782 sediment samples collected from 27 to 71 locations across catchments draining ∼6450 km2 during 16 fieldwork campaigns. These campaigns were conducted in Japan between November 2011 and November 2020 in river catchments draining the main radioactive plume. This database may be useful to evaluate and anticipate the post-accidental redistribution of radionuclides in the environment and for the spatial validation of models simulating the transfer of radiocesium across continental landscapes.

Evolution of Mid‐latitude Density Irregularities and Scintillation in North America During the 7–8 September 2017 Storm

AbstractUsing the University Navstar Consortium (UNAVCO) Global Positioning System (GPS) receiver network in North America, we present 2‐D distributions of GPS radio signal scintillation in the mid‐latitude ionosphere during the 7–8 September 2017 storm. The mid‐latitude ionosphere showed a variety of density structures such as the storm enhanced density (SED) base and plume, main trough, secondary plume, and secondary trough during the storm main and early recovery phases. Enhanced phase and amplitude scintillation indices were observed at the density gradients of those structures. SuperDARN radar echoes were also enhanced at the density gradients. The collocation of the scintillation and HF radar echoes indicates that density irregularities developed across a wide range of wavelengths (tens of meters to tens of kilometers) in the mid‐latitude density structures. The density gradients and irregularities were also detected by Swarm and DMSP as in‐situ density structures that disturbed the GPS signals. The irregularities were a substantial fraction (∼10%–50%) of the background density. The density irregularity had a power law spectrum with slope of ∼ −1.8, suggesting that gradient drift instability (GDI) contributed to turbulence formation. Both high‐latitude and low‐latitude processes likely contributed to forming the mid‐latitude density structures, and the mid‐latitude scintillation occurred at the interface of high‐latitude and low‐latitude forcing.

Formation of a low‐level barrier jet and its modulation by dust radiative forcing over the Hexi Corridor in Central China on March 17, 2010

AbstractA low‐level barrier jet (LLBJ) formed along the northeast slope of the Tibetan Plateau on March 17, 2010. The LLBJ was accompanied by a major dust event. Numerical simulations conducted with the Weather Research and Forecasting dust (WRF‐dust) model show that the formation of the LLBJ was primarily due to mid‐level, southeastward descent of high momentum air, which impinged on the north slope of the Tibetan Plateau, resulting in ageostrophic flow acceleration under geostrophic adjustment. The LLBJ was reinforced by the Bernoulli effect, where the physical barrier associated with the Tibetan Plateau to the southwest and the virtual barrier associated with sloped, packed isentropic surfaces to the northeast combined to constrict the air flow, thus augmenting the acceleration of the air as it entered the Hexi Corridor. The simulations show that the LLBJ, which stayed close to the western entrance of the Hexi Corridor, gradually descended during the daytime until early evening. During this period, the core of the LLBJ stayed directly above the 302‐K isentropic surface. The LLBJ, which was located to the south of the main dust plume, was modulated by dust radiative heating and cooling. Over the main dust plume, as well as in the LLBJ region, radiative heating of the dust warmed the upper part of the boundary layer and cooled it below, which stabilized the boundary layer, decreased the boundary layer depth, and reduced the vertical mixing, causing the surface winds to weaken. As a consequence of the feedback between the circulation and the dust radiative forcing, the total dust emission was reduced by ∼9.7–11% and peaked 1–2 hr earlier than without dust radiative effects, while the LLBJ's intensity, which was 1–2 m·s−1 stronger, was better maintained within the boundary layer during the daytime until early evening.