Hybrid Single-Particle Lagrangian Integrated Trajectory Research Articles

A multi-site passive approach to studying the emissions and evolution of smoke from prescribed fires

Abstract. We conducted a 2-year study utilizing a network of fixed sites with sampling throughout an extended prescribed burning period to characterize the emissions and evolution of smoke from silvicultural prescribed burning at a military base in the southeastern USA. The measurement approach and an assessment of the instrument performance are described. Smoke sources, including those within and off the base, are identified, and plume ages are determined to quantify emissions and study the evolution of smoke PM2.5 (particulate matter with aerodynamic diameters 2.5 µm or smaller) mass, black carbon (BC), and brown carbon (BrC). Over the 2021 and 2022 prescribed burning seasons (nominally January to May), we identified 64 smoke events based on high levels of PM2.5 mass, BC, BrC, and carbon monoxide (CO), of which 61 were linked to a specific burning area. Smoke transport times were estimated in two ways: using the mean wind speed and the distance between the fire and the measurement site, and from Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) back-trajectories. PM2.5 emission ratios based on ΔPM2.5 mass / ΔCO for fresh smoke (age ≤ 1 h) ranged between 0.04 and 0.18 µg m−3 ppb−1 with a mean of 0.117 µg m−3 ppb−1 (median of 0.121 µg m−3 ppb−1). Both the mean emission ratio and the variability were similar to findings from other prescribed fire studies but were lower than those from wildfires. The mean emission ratios of BC and BrC were 0.014 µg m−3 ppb−1 and 0.442 Mm−1 ppb−1, respectively. Ozone enhancements (ΔO3) were always observed in plumes detected in the afternoon. ΔPM2.5 mass / ΔCO was observed to increase with plume age in all of the ozone-enhanced plumes, suggesting photochemical secondary aerosol formation. In contrast, ΔBrC/ΔCO was not found to vary with plume ages less than 8 h during photochemically active periods.

A Novel Approach for Predicting the Mid–Long-Term Radiation Dose in the Case of a Hypothetical STSBO Nuclear Accident for an Operating Nuclear Power Plant

Four severe nuclear accident scenarios have been identified for operating nuclear power plants (ONPPs). However, there is a research gap in predicting the mid–long-term radiation doses for these scenarios. This study aims to address this gap by proposing a novel approach for predicting the mid–long-term radiation dose in the case of a hypothetical short-term station blackout (STSBO) scenario, one of the aforementioned scenarios. Firstly, the Weather Research and Forecasting (WRF) model was coupled with the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) (WRF-HYSPLIT) model to establish an atmospheric transport and diffusion model for airborne radionuclides, and the regularity of the atmospheric transport and diffusion for the airborne radionuclides was determined. Subsequently, the Residual Radioactive Material Guidelines (RESRAD) OFFSITE (RESRAD-OFFSITE) code was utilized to establish a radiation dose model for predicting the mid–long-term radiation dose resulting from the airborne radionuclides, and the evolution of the mid–long-term radiation dose was analyzed. Finally, the proposed approach was applied to an ONPP, and the results were used to predict the mid–long-term public radiation dose. The results indicated that the total radiation dose would be lower than the dose limit recommended by the International Commission on Radiological Protection (1 mSv/yr) from the second month to the 100th year after the hypothetical STSBO nuclear accident, and the total radiation dose would decrease slowly over time. Recommendations are made for offsite emergency response measures. These research findings can assist ONPPs in analyzing their environmental impacts in the event of an STSBO scenario.

Characteristics of Water Vapor Transport during the “7·20” Extraordinary Heavy Rain Process in Zhengzhou City Simulated by the HYSPLIT Model

Water vapor transport is an important foundation and prerequisite for the occurrence of rainstorms. Consequently, the understanding of water vapor transport as well as the sources of water vapor during rainstorm processes should be considered as essential to study the formation mechanism of rainstorms. In this study, the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model is adopted for backward tracking of water vapor transport trajectories and sources during the “7·20” extraordinary heavy rain process in Zhengzhou City of China that occurred on 20 July 2021. On this basis, the trajectory clustering method is applied to quantitatively analyze the contributions of water vapor sources, aiming to provide a basis for exploring the maintenance mechanism of this extreme rainstorm event. The spatio-temporal characteristics of this rainstorm event show that there are 4 consecutive days with the precipitation reaching or exceeding the rainstorm level across the whole Zhengzhou City, with the daily rainfall amounts at eight national meteorological stations all breaking their respective historical extreme values. The regional-averaged rainfall amount in Zhengzhou City is 527.4 mm, while the maximum accumulated rainfall amount reaches 985.2 mm at Xinmi station and the maximum hourly rainfall amount at Zhengzhou national meteorological station reaches 201.9 mm h−1. The water vapor sources for this rainfall process, ranked in descending order of contribution, are the Western Pacific, inland areas of Northwest China and South China, and South China Sea. The water vapor at lower levels is mainly transported from the Western Pacific and the South China Sea, while those from the inland areas of Northwest China and South China provide a supply of water vapor at upper levels to a certain extent. The water vapor at 950 hPa is mainly sourced from the Western Pacific and South China Sea, accounting for 56% and 44%, respectively. The water vapor at 850 hPa mainly derives from the Western Pacific and the inland areas of South China, contributing 58% and 34% of the total, respectively. The water vapor at 700 hPa mainly comes from the inland areas of Northwest China and South China Sea. Specifically, the water vapor from inland Northwest China contributes 44% of the total, acting as the primary source. The water vapor at 500 hPa is mainly transported from the inland areas of South China and Northwest China, with that from the inland South China (56%) being more prominent. The water vapor at all levels is mainly transported to the rainstorm region through the eastern and southern regions of China from the source areas. Additionally, there are some differences in the water vapor trajectories at a 6 h interval.

How Local Pollution and Transboundary Air Pollution Impact Air Quality in Jakarta?

Jakarta’s rapid population growth and industrialization have severely impacted air quality, with limited monitoring stations and increasingly complex pollutant sources influenced by meteorological factors. Source apportionment studies are critical for addressing urban air quality issues because knowing the source of pollution is an important step in overcoming urban air quality problems. This study uses the Geographically Weighted Regression (GWR) and Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) models to analyze the distribution and sources of NO2, SO2, and CO in Jakarta and surrounding areas. Data includes spatial information from road networks, industries, and the energy sector during the wet (December) and dry (June) months of 2023. GWR results show that network density significantly contributes to pollutant concentrations, particularly during the dry month, while industrial and energy sectors display seasonal variations. The HYSPLIT model indicates that in December, air masses carrying pollutants mainly originate from the northwest and north, and in June, from the southeast and southwest. These patterns underscore the regional influence of transboundary air pollution from industrial and energy plants. The combined GWR and HYSPLIT findings provide a comprehensive understanding of air pollution dynamics and the critical role of meteorological factors in pollutant distribution.

Unravelling the impacts of stratospheric intrusions on near-surface ozone during the springtime ozone pollution episodes in Lhasa, China

While air pollution due to fine particulate matter (PM2.5) has been effectively controlled in China; the photochemical pollution characterized by elevated ozone (O3) has emerged as a major concern for air quality improvement. Except for ozone, Lhasa is one of the cleanest cities in China with the lowest annual PM2.5 concentration in 2017. The levels of major air pollutants in Lhasa are much lower than those of other cities in the eastern region of China, especially in May, when the O3 concentration peaks. This study was based on multi-source observations in combination with the Goddard Earth Observing System coupled with chemistry (GEOS-Chem) and the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) models to explore the causes of O3 pollution in Lhasa in May 2023. The results indicated that during the high O3 episodes, the concentrations of O3 precursors were low in Lhasa. Surrounding cities in other parts of the Tibetan Plateau also experienced high ozone concentrations despite being in different airsheds, suggesting that the O3 pollution in Lhasa was caused by regional transport rather than purely local emissions. Stratospheric intrusion events modulated by the westerly jet led to elevated ozone in the troposphere above Lhasa City. The results of the GEOS-Chem model indicated that horizontal advection, turbulence, diffusion, and other effects led to high concentrations of ozone in the near-surface above Lhasa. Vertical transport was the dominant factor leading to ozone concentration increases during high ozone days, with a contribution of 6.33 Gg/day. In addition, high-altitude air masses with a maximum altitude of over 8000 m, were observed arriving in Lhasa during the high ozone days. This study revealed that stratospheric intrusions have a greater contribution to the high O3 concentration in Lhasa in spring and provided a scientific basis for mitigating O3 pollution in the plateau cities.

Evaluation of WRF-Chem air quality forecasts during the AEROMMA and STAQS 2023 field campaigns

ABSTRACT A real-time air quality forecasting system was developed using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) to provide support for flight planning activities during the NOAA Atmospheric Emissions and Reactions Observed from Megacities to Marine Areas (AEROMMA) and NASA Synergistic TEMPO Air Quality Science (STAQS) 2023 field campaigns. The forecasting system operated on two separate domains centered on Chicago, IL, and New York City, NY, and provided 72-hour predictions of atmospheric composition, aerosols, and clouds. This study evaluates the Chicago-centered forecasting system’s 1-, 2-, and 3-day ozone (O3) forecast skill for Chiwaukee Prairie, WI, a rural area downwind of Chicago that often experiences high levels of O3 pollution. Comparisons to vertical O3 profiles collected by a Tropospheric Ozone Lidar Network (TOLNet) instrument revealed that forecast skill decreases as forecast lead time increases. When compared to surface measurements, the forecasting system tended to underestimate O3 concentrations on high O3 days and overestimate on low O3 days at Chiwaukee Prairie regardless of forecast lead time. Using July 25, 2023, as a case study, analyses show that the forecasts underestimated peak O3 levels at Chiwaukee Prairie during this regionwide bad air quality day. Wind speed and direction data indicates that this underestimation can partially be attributed to lake breeze simulation errors. Surface fine particulate matter (PM2.5) measurements, Geostationary Operational Environmental Satellite-16 (GOES-16) aerosol optical depth (AOD) data, and back trajectories from the NOAA Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model show that transported Canadian wildfire smoke impacted the Lake Michigan region on this day. Errors in the forecasted chemical composition and transport of the smoke plumes also contributed to underpredictions of O3 levels at Chiwaukee Prairie on July 25, 2023. The results of this work help identify improvements that can be made for future iterations of the WRF-Chem forecasting system. Implications: Air quality forecasting is an important tool that can be used to inform the public about upcoming high pollution days so that individuals may plan accordingly to limit their exposure to health-damaging air pollutants. Forecasting also helps scientists make decisions about where to make observations during air quality field campaigns. A variety of observational datasets were used to evaluate the accuracy of an air quality forecasting system that was developed for NOAA and NASA field campaigns that occurred in the summer of 2023. These evaluations inform areas of improvement for future development of this air quality forecasting system.

Atmospheric pollutants in Rosario, Argentina analysed through remote sensing: Wildfires and COVID-19 lockdown effects

Spatial-temporal dynamics of atmospheric pollutants can be analysed by space-based observations, contributing to environmental management and public health interventions. The influence of wildfires and anthropogenic activities on air quality is studied for the city of Rosario and its surroundings, including both urban and non-urban areas. Utilizing advanced satellite-based observations, we assess Aerosol Optical Depth (AOD) and Nitrogen Dioxide (NO2). The study employs Multi-Angle Implementation of Atmospheric Correction (MAIAC) and Moderate Resolution Imaging Spectroradiometer (MODIS) onboard NASA's Terra and Aqua satellites for AOD analysis. NO2 measurements were derived from the Ozone Monitoring Instrument (OMI) on the Aura satellite. Backward trajectory analysis using Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) shows the connection between fire pixels and air masses reaching Rosario. During the COVID-19 lockdown, a period with no significant fire events in the studied region was selected. This provided, for the first time, a baseline on the AOD median value of 0.05 for Rosario city and its surroundings, while NO2 total column median values were close to 3.00 x 1015 molecules/cm2. In a business-as-usual scenario, AOD increased by approximately 52.8% (March 2022) up to 111.3% (March 2019). NO2 median values remain almost the same (March 2019) or reached a median value of 3.38 x 1015 molecules/cm2 (March 2022). During wildfire events, such as March 2023, AOD surged by around 50.9%–108.6% compared to the business-as-usual scenario (March 2019 and March 2022, respectively). NO2 median values ranged from 3.52 x 1015 molecules/cm2 (March 2023) to 3.66 x 1015 molecules/cm (March 01, 2020 to March 19, 2020). NO2 levels correlated with intense fire periods. The analysis provides valuable insights into the complex interplay between natural events, human activities, and air quality dynamics in the region.

Spatial source, simulating improvement, and short-term health effect of high PM2.5 exposure during mutation event in the key urban agglomeration regions in China

Air quality in China has significantly improved owing to the effective implementation of pollution control measures. However, mutation events caused by short-term spikes in PM2.5 in urban agglomeration regions continue to occur frequently. Identifying the spatial sources and influencing factors, as well as improving the prediction accuracy of high PM2.5 during mutation events, are crucial for public health. In this study, we firstly introduced discrete wavelet transform (DWT) to identify the mutation events with high PM2.5 concentration in the four key urban agglomerations, and evaluated the spatial sources for the polluted scenario using Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. Additionally, DWT was combined with a widely used artificial neural network (ANN) to improve the prediction accuracy of PM2.5 concentration seven days in advance (seven-day forecast). Results indicated that mutation events commonly occurred in the northern regions during winter time, which were under the control of both short-range transportation of dirty airmass as well as negative meteorology conditions. Compared with the ANN model alone, the average band errors decreased by 9% when using DWT-ANN model. The average correlation coefficient (R) and root mean square error (RMSE) obtained using the DWT-ANN improved by 10% and 12% compared to those obtained using the ANN, indicating the efficiency and accuracy of simulating PM2.5, by combining the DWT and ANN. The short-term mortality during mutation events was then calculated, with the total averted all-cause, cardiovascular, and respiratory deaths in the four regions, being 4751, 2554, and 582 persons, respectively. A declining trend in prevented deaths from 2018 to 2020 demonstrated that the pollution intensity during mutation events gradually decreased owing to the implementation of the Three-Year Action Plan to Win the Blue Sky Defense War. The method proposed in this study can be used by policymakers to take preventive measures in response to a sudden increase in PM2.5, thereby ensuring public health.

Tiny rain makers: How aerosols shape extreme rainfall simulation accuracy

Given the rapid spatiotemporal variability of aerosols and their complex impacts on the Earth system, investigating the role of aerosols in modelling extreme weather events, particularly various extreme rainfalls, remains limited. This study explored extreme rainfall simulation sensitivity to aerosol properties, transport and seasonality over the UK and Ireland during four seasons in 2020 by the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) model. Two sets of high-resolution simulations, one including aerosol direct and indirect effects and the other one without any aerosol effects, were conducted to investigate the improvements due to aerosol inputs. Meteorological results were verified using ground and satellite observations to examine the reliability of simulations. The 12 extreme rainfall events during the study months were classified by their backward trajectories from the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, and their simulation accuracies were quantified through six spatiotemporal metrics and one overall score. By comprehensive analyses of the simulation performances under different conditions, it is found that the model performs better in simulating rainfall events driven by sea salt aerosols (SSA) compared to those promoted by anthropogenic aerosols. Air masses transported from the Arctic and North Atlantic Ocean also help achieve higher rainfall simulation accuracy than European air masses. Rainfall simulations for winter and autumn events outperform those for spring and summer events. When considering aerosol effects in simulations, almost half of the events showed improved performance, while an equal number experienced a decrease and a small proportion remained unchanged. The most remarkable improvements are observed in rainfall simulations with higher concentrations of SSA and the participation of anthropogenic aerosols, while simulations promoted only by anthropogenic aerosols all experience performance reductions. The aerosol effects also led to significant increases in monthly rainfalls, accompanied by great reductions of Cl in larger particle size aerosols and NO3 in smaller particle size aerosols.

Analysis of a Rainstorm Process in Nanjing Based on Multi-Source Observational Data and Lagrangian Method

Using multi-source observation data including automatic stations, radar, satellite, new detection equipment, and the Fifth Generation European Centre for Medium-Range Weather Forecasts Reanalysis (ERA-5) data, along with the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) platform, an analysis was conducted on a rainstorm process that occurred in Nanjing on 15 June 2020, with the aim of providing reference for future urban flood control planning and heavy rainfall forecasting and early warning. The results showed that this rainstorm process was generated under the background of an eastward-moving northeast cold vortex and a southward retreat of the Western Pacific Subtropical High. Intense precipitation occurred near the region of large top brightness temperature (TBB) gradient values or the center of low TBB values on the northern side of the convective cloud cluster. During the heavy precipitation period, the differential propagation phase shift rate (KDP), differential reflectivity factor (ZDR), and zero-lag correlation coefficient (ρHV) detected by the S-band dual-polarization radar all increased significantly. The vertical structure of the wind field detected by the wind profile radar provided a good indication of changes in precipitation intensity, showing a strong correspondence between the timing of maximum precipitation and the intrusion of upper-level cold air. The abrupt increase in the integrated liquid water content observed by the microwave radiometer can serve as an important indicator of the onset of stronger precipitation. During the Meiyu season in Nanjing, convective precipitation was mainly composed of small to medium raindrops with diameters less than 3 mm, with falling velocities of raindrops mainly clustering between 2 and 6 m·s−1. The rainstorm process featured four water vapor transport channels: the mid-latitude westerly channel, the Indian Ocean channel, the South China Sea channel, and the Pacific Ocean channel. During heavy rainfall, the Pacific Ocean water vapor channel was the main channel at the middle and lower levels, while the South China Sea water vapor channel was the main channel at the upper level, both accounting for a trajectory proportion of 34.2%.

Drivers of High Concentration and Dispersal of PM10 and PM2.5 in the Eastern Part of Chhota Nagpur Plateau, India, Investigated Through HYSPLIT Model and Improvement of Environmental Health Quality

ABSTRACTThe ambient air quality is continuously declining especially in emerging countries because of rapid rate of urbanization, industrialization, and allied activities. Thus, the principal objective of this research is to inspect the spatiotemporal variation of particulate matters and to identify the drivers of pollutant dispersal. The month‐wise PM10 and PM2.5 data of 2022 and 2023 were obtained from the West Bengal Pollution Control Board. Meteorological datasets such as wind speed (m/s) and wind direction (degree) were collected from the NASA power access website. The HYSPLIT (Hybrid Single‐Particle Lagrangian Integrated Trajectory) model was applied to identify the pollutant's trajectories. Results showed that Purulia station stood highest in case of absolute AQI 715 (23‐1‐2022 at 7 a.m.), PM2.5 483.47 µg/m3 (23‐1‐2022 at 8 a.m.), and PM10 682.28 µg/m3 (23‐1‐2022 at 7 a.m.), respectively. During winter, the vertical expansion of particles was within the 100‐m boundary layer while during summer, it dispersed vertically and crossed 2000 m above the ground surface due to the combined effect of atmospheric conditions such as wind speed, wind direction, air pressure, and temperature. Moreover, the industrial outputs of Jharkhand and West Bengal play a significant role in elevating the pollution level. Plantation of suitable pollution‐resistant plants including Banyan (Ficus bengalensis), Mango (Mangifera indica), Peepul (Ficus religiosa), Guava (Psidium guajava), Kadam (Neolamarkia cadamba), Neem (Azadirachta indica) is a suitable management technique against pollution in this region.

Measurement report: Combined use of MAX-DOAS and AERONET ground-based measurements in Montevideo, Uruguay, for the detection of distant biomass burning

Abstract. Biomass burning releases large amounts of aerosols and chemical species into the atmosphere, representing a major source of air pollutants. Emissions and by-products can be transported over long distances, presenting challenges in quantification. This is mainly done using satellites, which offer global coverage and data acquisition for places that are difficult to access. In this study, ground-based observations are used to assess the abundance of trace gases and aerosols. On 24 November 2020, a significant increase in formaldehyde was observed with a Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) instrument located in Montevideo (Uruguay), and its vertical column densities reached values of 2.4×1016 molec. cm−2, more than twice the values observed during the previous days. This was accompanied by an increase in the aerosol levels measured by an AErosol RObotic NETwork (AERONET) photometer located at the same site. The aerosol optical depth (AOD) at 440 nm reached values close to 1, an order of magnitude larger than typical values in Montevideo. Our findings indicate that the increase was associated with the passage of a plume originating from distant biomass burning. This conclusion is supported by TROPOspheric Monitoring Instrument (TROPOMI) satellite observations as well as HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) simulations. The profiles of the gases and aerosols retrieved from the MAX-DOAS observations are consistent with the HYSPLIT analysis, showing the passage of a plume over Montevideo on 24 November located at a height of ∼ 1.5 km. This corroborates the finding that biomass burning events occurring about 800 km north of Montevideo can affect the local atmosphere through long-distance emissions transport. This study underscores the potential of ground-based atmospheric monitoring as a tool for detection of such events. Furthermore, it demonstrates greater sensitivity compared to satellite when it comes to detection of relatively small amounts of carbonyls like glyoxal and formaldehyde.

Characterization of aerosol composition: Insights from SEM-EDX analysis and CALIPSO overpasses

The effect of atmospheric aerosols on the earth’s radiation budget is primarily through their direct effects. Understanding aerosols’ morphology and elemental composition is crucial in this context. For two years, from January 2017 to December 2018, aerosol samples (PM10) were collected on quartz filter papers using a high-volume sampler (PM10) in Chennai, a semi-urban coastal environment located at 12.81°N, 80.03°E. These filter papers were stored under ambient laboratory conditions and were subsequently subjected to ultrasonication using ethanol as the solvent to separate the aerosols from the filters. The extracted samples were then analyzed using scanning electron microscopy (SEM) for the morphology and energy dispersive X-ray analysis (EDX) for elemental composition. The EDX analysis of the samples revealed the presence of various elements such as carbon (C), oxygen (O), aluminum (Al), silicon (Si), sulfur (S), potassium (K), iron (Fe), magnesium (Mg), calcium (Ca), vanadium (V), bismuth (Bi), sodium (Na), chlorine (Cl), phosphorus (P), and technetium (Tc). High concentrations of carbon, oxygen, and aluminum–silicate particles indicated the presence of carbonaceous aerosols and wind-blown dust particles. Concentration-weighted trajectory (CWT) analysis was carried out to assess the transport pathways of aerosols in the region. CALIPSO overpasses during the study period were selected, and the Vertical Feature Mask (VFM) identifiers for different aerosol types were compared with the local experimental results. The findings show that CALIPSO possess a reasonably effective capability in detecting and characterizing the local aerosol types. CALIPSO detected Dusty marine, Clean marine, Elevated smoke and Polluted dust in the study area across all four seasons. These findings closely match the characteristics of such aerosol types obtained from SEM/EDX analysis, HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory) modeling, and the Angstrom exponent derived from sunphotometer readings.

Isotopic composition of convective rainfall in the inland tropics of Brazil

Abstract. Strong convective systems characterize the tropical central-southern region of Brazil. These systems provide abundant water supply for agroindustrial activities and pose flood risks to large cities. Here, we present high-frequency (2–10 min; inter- and intra-event) rainfall isotopic compositions (n = 90 samples) to reveal regional and local atmospheric processes controlling the isotopic variability of convective systems between 2019–2021. Inter-event rainfall weighted-average (δwgd) values were low (δ18Owgd ≤ −10.0 ‰) due to the higher rainfall along the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model trajectories from the Amazon forest during the summer. In contrast, during autumn and spring seasons HYSPLIT model trajectories from the Atlantic Ocean and southern Brazil exhibited lower rainfall amounts, resulting in high δ18Owgd ≥ −4.2 ‰. This strong regional δwgd pattern often masks intra-event isotopic variability. Therefore, we analyzed the vertical structure of local rainfall using reflectivity (Z) from microradar data. Variations in Z indicate that microphysical processes as raindrops fall led to changes in δ18O and deuterium excess (d-excess). Our findings establish a novel framework for evaluating the meteorological controls on the isotopic variability of convective precipitation in tropical South America, fill the gap in high-frequency studies in this region, and generate an isotopic dataset for convective model evaluations.

Classifying moisture sources associated with snowfall in the mountains of Lesotho

An average of eight snowfall events occur each year in the eastern Lesotho Highlands. These snowfall events are typically associated with cut-off low (CoLs) systems and mid-latitude cyclones. However, the moisture sources of the snowfall are unclassified and unclear. The Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, an air mass back trajectory model, has been used to evaluate moisture source waters locally in southern Africa and internationally in China and Europe. This study uses HYSPLIT to determine the source moisture of snow in Lesotho. A list of all 82 snowfall events in Lesotho spanning 2017 to 2022 was compiled using the Snow Report SA Instagram page, including the date and location of snowfall. A 72-hour back trajectory for each snowfall event was initiated for both Afriski and the whole of Lesotho. This amounts to models of moisture source trajectories for 28 and 82 snowfall days, respectively. These air mass pathways are classified according to their frequency per snowfall event, per month in the snow season, per year and for the full period. From this, associated moisture source regions and dominant air mass trajectories were identified. This study reports that the air mass trajectories associated with Afriski and Lesotho as a whole are very similar. The most common pathway of air mass trajectories transporting snow-bearing moisture to Lesotho was an inland trajectory from the northern regions of southern Africa. This pathway makes up 16.6% of all trajectories reported and is associated with the Angola Low, the Congo Air Boundary and the St. Helena High Pressure.

Interaction of black carbon surface mass with meteorological variables and spatial pattern across the 36 states of tropical Nigeria

Black carbon (BC) has been linked to cardio-pulmonary diseases and lung cancer. It is also the second largest contributor to climate change, after carbon dioxide (CO2), Effective mitigation of BC is of much benefits, but it requires detailed knowledge of its spatial distribution, as well as the influence of local meteorology on the spread of the pollutant. Many countries in sub-Sahara Africa including Nigeria, lack data on BC level. There is also limited information on meteorological impact on BC spatial distribution. This study therefore assessed the spatial and temporal distribution of BC across the 36 states of Nigeria and the influence of meteorology on the pollutant spread. Data on BC surface mass (BCMASS) and seven meteorological variables (air temperature, relative humidity, rainfall, wind speed, planetary boundary layer height (PBLH), atmospheric pressure and wind direction) were obtained from Modern Era Retrospective analysis for Research (MERRA-2). Spatial distribution of BCSMASS across 36 states of Nigeria, and interaction with meteorology was studied using correlation analyses, Bayesian ridge regression with marginal maximum likelihood estimation, and a Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. There was significant (p < 0.05) variation in BCSMASS across the states. The meteorological variables, except wind direction, significantly influenced BCSMASS and they accounted for 63% of the variation. Five-day backward trajectory modelled for each month of the year revealed that northern Nigeria is majorly under the influence of the dry and dusty tropical continental wind, and this could partially account for the lower BCSMASS concentration in the region, compared to southern Nigeria. Based on population-weighted exposure, states in southern Nigeria, especially the south-eastern part, should be prioritized in planning mitigation, for effective climate action.

Lagrangian and Eulerian approach to predict the movement of radionuclides in selected potential sites in Malaysia during the monsoon period

In computing the movement of particles through the fluid, three types of dispersion models are used which are Gaussian plume models, Lagrangian puff models, and small-scale numerical models. Lagrangian particle dispersion models are increasingly used for nuclear applications. In this study, the usage of the Lagrangian model is implemented in a Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) which combines with the Eulerian model to predict the movement of radionuclides from the simulated nuclear power plant accident in selected locations in Malaysia. These include nuclear risk studies in these areas, emergency response systems, and source term analyses. This study aims to compare the risk from the dispersion of 137Cs from a simulated Nuclear Power Plant (NPP) at Mukah and Tasik Kenyir during the Northeast monsoon (8th October 2022) and Southeast monsoon (16th May 2022). The HYSPLIT model was set up based on the meteorological data during both monsoon periods and was simulated for 5 days. The outcomes revealed that the concentration of 137Cs is higher at Tasik Kenyir compared to Mukah for both during the Northeast monsoon period (3.5 x 107 Bq/m2) while for Southwest monsoon, the result is vice versa where the concentration of 137Cs at Mukah is (2.2 x 107Bq/m2). The activity concentration is then converted into rate effective dose measurement and compared with the limit suggested by ICRP which is 1 Sv per year. It is concluded that Tasik Kenyir is a more suitable location to build NPP compared to Mukah as the movement of radionuclides was dispersed to the location that contained less population.

Determination of Transport Pathways and Mutual Exchanges of Atmospheric Moisture between Source Regions of Yangtze and Yellow River Basins

Knowledge of the quantitative importance of the moisture transport pathways and mutual moisture exchange of the source regions of the Yangtze (SYZR) and Yellow (SYR) rivers’ basins, the adjacent origins of China’s two longest rivers, can provide insights into the regional atmospheric branch of the hydrological cycle over the source regions. The method with the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model and a Lagrangian moisture source diagnostic to identify the major moisture transport pathways quantifies their importance to two types of daily precipitation events—daily precipitation more than 10 mm (PM) events and daily precipitation less than 10 mm (PL) events—for the two rivers’ regions during the summer (June–August, 1986–2015) and finds the characteristics of mutual moisture exchange. The results indicated that both the Bay of Bengal group pathway and the northwest China group pathway play significant roles in PM and PL events over the SYZR, contributing 41.87% and 39.12% to PM events and 41.33% and 33.16% to PL events, respectively. The SYR has five main moisture path groups; the Bay of Bengal group pathway, the northwest China group pathway, and the southeast China group pathway play significant roles in PM and PL events over the SYR, contributing 32.34%, 23.28%, and 34.36% to PM events and 34.84%, 36.18%, and 19.83% to PL events, respectively. The volume of moisture passing from the SYZR to the SYR is approximately 60 times that of the reverse, constituting about 6.9% of the total moisture released in SYR precipitation. It is worth noting that the moisture release was concentrated in the nearer west group pathway, and the main moisture uptake locations were beyond the source region of the two rivers (remote sources) in the PM events. The aggregate moisture release high-frequency moisture transport path groups are found in the southeastern parts of Zhiduo County and the southeast of Zaduo County.

Temporal variability of the isotope compositions of plum rain in Nanjing from event to interannual time scales

Precipitation in the plum rain period accounts for 40%-50% of annual precipitation in the monsoon region. To clarify the temporal variability of the isotopic composition of precipitation during the plum rain period from event to interannual time scale and identify the influencing factors, we analyzed the isotopic composition of precipitation and its influencing factors in Nanjing from 2015 to 2022. By using the Hybrid Single-particle Lagran-gian Integrated Trajectory (HYSPLIT) model with specific humidity analysis, we investigated the water vapor source and influencing factors. The results showed that 1) the isotopic abundance of atmospheric precipitation was depleted in the summer and enriched in winter. dx was lower in summer and higher in winter. The isotopic abundance of precipitation from the plum rain was depleted compared to mean value of the whole-year. 2) There was no significant correlation between δ2H and δ18O of the plum rain (precipitation) with local meteorological factors. However, dx was lower in light rain, reflecting the effect of sub-cloud evaporation. The average dx was higher during plum rain period in years with more total plum rain precipitation. 3) The low-latitude South China Sea and the western Pacific Ocean source area provided water vapor for the plum rain. The shift of moisture source region led to abrupt changes in precipitation isotopes. Our results could provide data support for studies on precipitation isotopes in the monsoon region, as well as a reference point for further understanding the precipitation mechanism of the plum rain and stu-dying the seasonal variability of atmospheric circulation in the East Asian monsoon region.

Effect of oasis and irrigation on mountain precipitation in the northern slope of Tianshan Mountains based on stable isotopes

Water is one of the scarcest resources in arid regions, and irrigation is an important means to improve crop yield and ensure food security. The Xinjiang features an integrated irrigation agriculture and oasis economy paradigm. However, the understanding of the impact mechanism and quantitative analysis of irrigation on precipitation is inadequate now. With the aim of clarifying the response relationship between mountain precipitation and irrigation in oasis, we clarify and quantify the moisture sources of precipitation using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model and multisource data (including field-collected isotopes data, C-Isoscape, ERA5, and GDAS). The results obtained show: (1) Isotope analysis provides valuable insights into the climate background and precipitation recycling. The Local Meteoric Water Line's lower slope and intercept than Global Meteoric Water Line suggest a severe arid climate and strong sub-cloud evaporation. The intercept (13.44) of Local Meteoric Water Line in Mountain Areas exceeds the global average, indicating significant moisture recycling in mountain areas (MA). The d-excess in MA is prominent year-round, highlighting the influence of recycled moisture. (2) The oasis and irrigation influence the local precipitation through offset, remote, combination, and delayed effects. The offset effect hinders precipitation formation in irrigation areas (IA) due to the counteracting irrigation-induced humidification and cooling effect. Through the interaction of westerly circulation and local mountain-oasis hydrological cycle, irrigation-induced moisture is transported to MA and uplifted, which is remote effect. The combination effect synergistically enhances precipitation intensity, especially in intricate MA, through the combined influence of terrain's forced uplift and convective cells. Furthermore, the mountainous precipitation influenced by the mountain-oasis hydrological cycle often exhibits a delayed effect. (3) Based on HYSPLIT model tracking results, the contribution ratio of oasis and irrigation induced evapotranspiration to summer precipitation in MA is approximately 19.60%, ranging from 13.68% to 28.49%. The findings provide insights into the mechanisms of irrigation and water resource management in the northern slope of Tianshan Mountains.