Atmospheric Observations Research Articles

Increases in Global and East Asian Nitrogen Trifluoride (NF3) Emissions Inferred from Atmospheric Observations.

Nitrogen trifluoride (NF3) is a potent and long-lived greenhouse gas that is widely used in the manufacture of semiconductors, photovoltaic cells, and flat panel displays. Using atmospheric observations from eight monitoring stations from the Advanced Global Atmospheric Gases Experiment (AGAGE) and inverse modeling with a global 3-D atmospheric chemical transport model (GEOS-Chem), we quantify global and regional NF3 emission from 2015 to 2021. We find that global emissions have grown from 1.93 ± 0.58 Gg yr-1 (± one standard deviation) in 2015 to 3.38 ± 0.61 Gg yr-1 in 2021, with an average annual increase of 10% yr-1. The available observations allow us to attribute significant emissions to China (0.93 ± 0.15 Gg yr-1 in 2015 and 1.53 ± 0.20 Gg yr-1 in 2021) and South Korea (0.38 ± 0.07 Gg yr-1 to 0.65 ± 0.10 Gg yr-1). East Asia contributes around 73% of the global NF3 emission increase from 2015 to 2021: approximately 41% of the increase is from emissions from China (with Taiwan included), 19% from South Korea, and 13% from Japan. For Japan, which is the only one of these three countries to submit annual NF3 emissions to UNFCCC, our bottom-up and top-down estimates are higher than reported. With increasing demand for electronics, especially flat panel displays, emissions are expected to further increase in the future.

Substantial increase in perfluorocarbons CF4 (PFC-14) and C2F6 (PFC-116) emissions in China

The perfluorocarbons tetrafluoromethane (CF4, PFC-14) and hexafluoroethane (C2F6, PFC-116) are potent greenhouse gases with near-permanent atmospheric lifetimes relative to human timescales and global warming potentials thousands of times that of CO2. Using long-term atmospheric observations from a Chinese network and an inverse modeling approach (top-down method), we determined that CF4 emissions in China increased from 4.7 (4.2-5.0, 68% uncertainty interval) Gg y-1 in 2012 to 8.3 (7.7-8.9) Gg y-1 in 2021, and C2F6 emissions in China increased from 0.74 (0.66-0.80) Gg y-1 in 2011 to 1.32 (1.24-1.40) Gg y-1 in 2021, both increasing by approximately 78%. Combined emissions of CF4 and C2F6 in China reached 78 Mt CO2-eq in 2021. The absolute increase in emissions of each substance in China between 2011-2012 and 2017-2020 was similar to (for CF4), or greater than (for C2F6), the respective absolute increase in global emissions over the same period. Substantial CF4 and C2F6 emissions were identified in the less-populated western regions of China, probably due to emissions from the expanding aluminum industry in these resource-intensive regions. It is likely that the aluminum industry dominates CF4 emissions in China, while the aluminum and semiconductor industries both contribute to C2F6 emissions. Based on atmospheric observations, this study validates the emission magnitudes reported in national bottom-up inventories and provides insights into detailed spatial distributions and emission sources beyond what is reported in national bottom-up inventories.

Retrieval and analysis of the composition of an aerosol mixture through Mie–Raman–fluorescence lidar observations

Abstract. In the atmosphere, aerosols can originate from numerous sources, leading to the mixing of different particle types. This paper introduces an approach to the partitioning of aerosol mixtures in terms of backscattering coefficients. The method utilizes data collected from the Mie–Raman–fluorescence lidar, with the primary input information being the aerosol backscattering coefficient (β), particle depolarization ratio (δ), and fluorescence capacity (GF). The fluorescence capacity is defined as the ratio of the fluorescence backscattering coefficient to the particle backscattering coefficient at the laser wavelength. By solving a system of equations that model these three properties (β, δ and GF), it is possible to characterize a three-component aerosol mixture. Specifically, the paper assesses the contributions of smoke, urban, and dust aerosols to the overall backscattering coefficient at 532 nm. It is important to note that aerosol properties (δ and GF) may exhibit variations even within a specified aerosol type. To estimate the associated uncertainty, we employ the Monte Carlo technique, which assumes that GF and δ are random values uniformly distributed within predefined intervals. In each Monte Carlo run, a solution is obtained. Rather than relying on a singular solution, an average is computed across the whole set of solutions, and their dispersion serves as a metric for method uncertainty. This methodology was tested using observations conducted at the ATOLL (ATmospheric Observation at liLLe) observatory, Laboratoire d'Optique Atmosphérique, University of Lille, France.

Evaluation of the Coupled Arctic Forecast System’s representation of the Arctic atmospheric boundary layer vertical structure during MOSAiC

Observations from the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) were used to evaluate the Coupled Arctic Forecast System (CAFS) model’s ability to simulate the atmospheric boundary layer (ABL) structure in the central Arctic. MOSAiC observations of the lower atmosphere from radiosondes, downwelling longwave radiation (LWD) from a pyranometer, and near-surface wind conditions from a meteorological tower were compared to 6-hourly CAFS output. A self-organizing map (SOM) analysis reveals that CAFS reproduces the range of stability structures identified by the SOM trained with MOSAiC observations of virtual potential temperature (θv) profiles, but not necessarily with the correct frequency or at the correct time. Additionally, the wind speed profiles corresponding to a particular θv profile are not consistent between CAFS and the observations. When categorizing profiles by static stability, it was revealed that CAFS simulates all observed stability regimes, but overrepresents the frequency of near-surface strong stability, and underrepresents the frequency of strong stability between the top of the ABL and 1 km. The 10 m wind speeds corresponding to each stability regime consistently have larger values in CAFS versus observed, and this offset increases with decreasing stability. Whether LWD is over or underestimated in CAFS is dependent on stability regime. Both variables are most greatly overestimated in spring, leading to the largest near-surface θv bias, and the greatest underrepresentation of strong stability in spring. The results of this article serve to highlight the positive aspects of CAFS for representing the ABL and reveal impacts of misrepresentations of physical processes dictating energy, moisture, and momentum transfer in the lower troposphere on the simulation of central Arctic ABL structure and stability. This highlights potential areas for improvement in CAFS and other numerical weather prediction models. The SOM-based analysis especially provides a unique opportunity for process-based model evaluation.

Constraints on quantum spacetime-induced decoherence from neutrino oscillations

We investigate the implications of decoherence induced by quantum spacetime properties on neutrino oscillation phenomena. We develop a general formalism where the evolution of neutrinos is governed by a Lindblad-type equation and we compute the oscillation damping factor for various models that have been proposed in the literature. Furthermore, we discuss the sensitivity to these effects of different types of neutrino oscillation experiments, encompassing astrophysical, atmospheric, solar, and reactor neutrino experiments. By using neutrino oscillation data from long-baseline reactors and atmospheric neutrino observations, we establish stringent constraints on the energy scale governing the strength of the decoherence induced by stochastic metric fluctuations, amounting to, respectively, EQG≥2.6×1034 GeV and EQG≥2.5×1055 GeV. Published by the American Physical Society 2024

Evaluating the impact of control measures on sulfate-nitrate-ammonium aerosol variations and their formation mechanism in northern China during 2022 Winter Olympic Games

Sulfate, nitrate, and ammonium (SNA) significantly contribute to fine particulate matter (PM2.5). To ensure good air quality during 2022 Winter Olympic Games (WOG), stringent control measures were implemented in northern China. In this study, comprehensive atmospheric observations were conducted from 2022 January to March in four representative cities to investigate the changes in SNA and their formation mechanism in response to these control measures. The SNA concentrations obviously decreased (29.45%–42.83%) during the control periods in the four cities, but their proportion of PM2.5 remained relatively stable (>50%). SNA was the key factor driving the decrease and increase in the PM2.5 concentration during WOG, with nitrate making the most prominent contribution. The formation of SNA was largely dominated by aqueous heterogeneous chemistry instead of gas-phase oxidation. However, the aerosol liquid water content (ALWC) decreased while odd oxygen (OX) increased during the control periods. Such a variation influenced the role of aqueous heterogeneous and gas-phase reactions in SNA formation, with the former's dominant role being replaced by the latter. After the control periods, the aqueous heterogeneous reactions were enhanced again due to the increased ALWC. Among the cities in the study region, SNA formation became more intense from north to south with increased air temperature and relative humidity (RH). Moreover, ISORROPIA-II thermodynamic modelling revealed notable impacts of sulfate, ammonium, and nonvolatile cations (NVCs) on variations in particle acidity throughout WOG. These results provide a more comprehensive understanding of SNA responses to pollution control on a regional scale and insight into future conventional control.

Negative Anomalies in the Atmospheric Electric Field near the Earth's Surface in Seismically Active Regions

The paper examines poorly-studied negative bay-like anomalies in the near-earth atmospheric electric field in seismically active regions at fair weather suitable for atmospheric electric observations. Observation data analysis revealed characteristic features of anomalies formation that allow us to conclude that the anomalies are associated with the deformation of near-surface rocks at tectonoseismic process. On the basis of the concept of atmospheric electricity, the source of anomalies in the electric field is a local negative space charge of small ions in the near-earth air emerged at a negative vertical gradient of electrical conductivity. It was revealed that the charge and produced negative anomalies in the electric field have deformation and emanation processes in their origin. We propose a scheme of anomalies formation and consider the role of radon and thoron in their emergence. It was found that thoron plays a more important role in some cases.

Atmospheric Escape From Earth and Mars: Response to Solar and Solar Wind Drivers of Oxygen Escape

AbstractHabitability at the surface of a planet depends on having an atmosphere long enough for life to develop. The loss of atmosphere to space is an important component in assessing planetary surface habitability. Current models of atmospheric escape from exoplanets are not well constrained by observations. Atmospheric escape observations from the terrestrial planets are available in public data archives. We recast oxygen escape rates from Earth derived from an instrument on Dynamics Explorer‐1 as function of solar wind and compare them to similar data from Mars. Analysis demonstrates that oxygen escape rates from Mars are not as sensitive to variations in solar power components as those from Earth. Available data from Venus can confirm or refute the assertion that oxygen escape from magnetized planets is more sensitive than that from unmagnetized planets.

Continuous ion beam-induced luminescence (IBIL) spectroscopy of air-borne particulate matter hourly collected from the atmosphere

We investigated the applicability of Ion Beam Induced Luminescence (IBIL) analysis for identifying biological components in sequentially collected airborne particulate matter (PM) samples obtained using the automated sampler. A series of micro-IBIL spectroscopies were performed on a PTFE (polytetrafluoroethylene) membrane tape filter from the Atmospheric Environmental Regional Observation System (AEROS) during a highly concentrated air pollution event on 26–27 March 2020, collected at Ota, Japan (36.290°n, 139.381°e) using an external 3 MeV proton microprobe. IBIL at typical wavelengths associated with organic compounds such as NADH and riboflavin were identified through the series of IBIL analyses, which is a key factor for identifying existence of organic pollutions, or bioaerosols. The decay times of the IBIL indicate that the peak measured is due to organic compounds rather than inorganic particles or ambient substances. These results suggest that micro-IBIL spectroscopy can be used to identify bioaerosols in hourly collected AEROS PTFE membrane tape filters taken from the atmosphere.

Revealing the significant acceleration of hydrofluorocarbon (HFC) emissions in eastern Asia through long-term atmospheric observations

Abstract. Hydrofluorocarbons (HFCs) are powerful anthropogenic greenhouse gases (GHGs) with high global-warming potentials (GWPs). They have been widely used as refrigerants, insulation foam-blowing agents, aerosol propellants, and fire suppression agents. Since the mid-1990s, emissions of HFCs have been increasing rapidly as they are used in many applications to replace ozone-depleting chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) whose consumption and production have been phased out under the Montreal Protocol (MP). Due to the high GWP of HFCs, the Kigali Amendment to the MP requires the phasedown of production and consumption of HFCs to gradually achieve an 80 %–85 % reduction by 2047, starting in 2019 for non-Article 5 (developed) countries with a 10 % reduction against each defined baseline and later schedules for Article 5 (developing) countries. In this study, we have examined long-term high-precision measurements of atmospheric abundances of five major HFCs (HFC-134a, HFC-143a, HFC-32, HFC-125, and HFC-152a) at Gosan station, Jeju Island, South Korea, from 2008 to 2020. Background abundances of HFCs gradually increased, and the inflow of polluted air masses with elevated abundances from surrounding source regions were detected over the entire period. From these pollution events, we inferred regional and country-specific HFC emission estimates using two independent Lagrangian particle dispersion models and Bayesian inversion frameworks (FLEXPART-FLEXINVERT+ and NAME-InTEM). The spatial distribution of the derived “top-down” (measurement based) emissions for all HFCs shows large fluxes from megacities and industrial areas in the region. Our most important finding is that HFC emissions in eastern China and Japan have sharply increased from 2016 to 2018. The contribution of East Asian HFC emissions to the global total increased from 9 % (2008–2014) to 13 % (2016–2020). In particular, HFC emissions in Japan (Annex I country) rose rapidly from 2016 onward, with accumulated total inferred HFC emissions being ∼ 114 Gg yr−1, which is ∼ 76 Gg yr−1 higher for 2016–2020 than the “bottom-up” (i.e., based on activity data and emission factors) emissions of ∼ 38 Gg yr−1 reported to the United Nations Framework Convention on Climate Change (UNFCCC). This is likely related to the increase in domestic demand in Japan for refrigerants and air-conditioning-system-related products and incomplete accounting. A downward trend of HFC emissions that started in 2019 reflects the effectiveness of the F-gas policy in Japan. Eastern China and South Korea, though not obligated to report to the UNFCCC, voluntarily reported emissions, which also show differences between top-down and bottom-up emission estimates, demonstrating the need for atmospheric measurements, comprehensive data analysis, and accurate reporting for precise emission management. Further, the proportional contribution of each country's CO2-equivalent HFC emissions has changed over time, with HFC-134a decreasing and HFC-125 increasing. This demonstrates the transition in the predominant HFC substances contributing to global warming in each country.

Inversion of Critical Atmospheric 137Cs Emissions Following the Fukushima Accident by Resolving Temporal Formation from Total Deposition Data.

Understanding the transport of 137Cs emitted during the Fukushima accident is challenging because the critical emissions that produced the high-deposition area are not adequately resolved in existing source terms. This paper presents an objective inverse reconstruction of these emissions by fusing atmospheric concentrations with a-priori emissions extracted from total depositions. This extraction, previously considered impossible for complex real-world accidents, is achieved by identifying the critical temporal formation process of depositions in the high-deposition area and estimating the corresponding emissions by using an atmospheric transport model. The reconstructed source term reveals two emission peaks from 10:00-11:00 and 14:00-15:00 on March 15, which agree with the in situ pressure measurements and accident analysis, suggesting that they came from pressure drops in the primary containment vessels of Units 3 and 2, respectively. This finding explains the environmental observations of spherical 137Cs particles. The source term also objectively and independently confirms the widely used reverse estimate. The corresponding 137Cs transport simulations better match the various observations than those produced by other source terms, proving that the two-peak emission creates a high-deposition area. The proposed method outperforms the direct fusion of deposition and atmospheric concentration observations, providing a robust tool for multiobservation fusion.

Evidence of Surface-Tension Lowering of Atmospheric Aerosols by Organics from Field Observations in an Urban Atmosphere: Relation to Particle Size and Chemical Composition.

Surface-active organics lower the aerosol surface tension (σs/a), leading to enhanced cloud condensation nuclei (CCN) activity and potentially exerting impacts on the climate. Quantification of σs/a is mainly limited to laboratory or modeling work for particles with selected sizes and known chemical compositions. Inferred values from ambient aerosol populations are deficient. In this study, we propose a new method to derive σs/a by combining field measurements made at an urban site in northern China with the κ-Köhler theory. The results present new evidence that organics remarkably lower the surface tension of aerosols in a polluted atmosphere. Particles sized around 40 nm have an averaged σs/a of 53.8 mN m-1, while particles sized up to 100 nm show σs/a values approaching that of pure water. The dependence curve of σs/a with the organic mass resembles the behavior of dicarboxylic acids, suggesting their critical role in reducing the surface tension. The study further reveals that neglecting the σs/a lowering effect would result in lowered ultrafine CCN (diameter <100 nm) concentrations by 6.8-42.1% at a typical range of supersaturations in clouds, demonstrating the significant impact of surface tension on the CCN concentrations of urban aerosols.

CFC‐12 Emissions in China Inferred From Observation and Inverse Modeling

AbstractDichlorodifluoromethane (CFC‐12) is an ozone‐depleting substance and potent greenhouse gas, which was required to be phased out after 2010 under the Montreal Protocol. CFC‐12 emissions need to be quantitatively traced. However, estimates of CFC‐12 emissions in China based on atmospheric inversions are unavailable after 2010. Here, using atmospheric observations at nine sites across China and inversion techniques, we quantify CFC‐12 emissions in China during 2011–2020 (on average 11.0 ± 0.6 Gg yr−1). The emissions derived from observations are 8.5 times larger than the previously reported inventories. Apart from emissions from eastern China revealed in previous studies, this study reveals that 71% of national total emissions were from other parts of China. Moreover, this study reconciled the global CFC‐12 emissions during 2011–2020: 28% were traced to China by this study, 9% of emissions were traced in previous studies, while 63% remain untraced, indicating the need for more regional emission inversion studies.

Disk Evolution Study Through Imaging of Nearby Young Stars (DESTINYS): PDS 111, an old T Tauri star with a young-looking disk

The interplay between T\,Tauri stars and their circumstellar disks, and how this impacts the onset of planet formation has yet to be established. In the last years, major progress has been made using instrumentation that probes the dust structure in the mid-plane and at the surface of protoplanetary disks. Observations show a great variety of disk shapes and substructures that are crucial for understanding planet formation. We studied a seemingly old T\,Tauri star, PDS\,111, and its disk. We combined complementary observations of the stellar atmosphere, the circumstellar hot gas, the surface of the disk, and the mid-plane structure. We analyzed optical, infrared, and sub-millimeter observations obtained with VLT/X-shooter, Mercator/HERMES, TESS, VLT/SPHERE, and ALMA, providing a new view on PDS\,111 and its protoplanetary disk. The multi-epoch spectroscopy yields photospheric lines to classify the star and to update its stellar parameters, and emission lines to study variability in the hot inner disk and to determine the mass-accretion rate. The SPHERE and ALMA observations are used to characterize the dust distribution of the small and large grains, respectively. PDS\,111 is a weak-line T\,Tauri star with spectral type G2, exhibits strong Halpha variability and with a low mass-accretion rate of $1-5 odot $. We measured an age of the system of 15.9$^ $\,Myr using pre-main sequence tracks. The SPHERE observations show a strongly flaring disk with an asymmetric substructure. The ALMA observations reveal a 30\,au cavity in the dust continuum emission with a low contrast asymmetry in the South-West of the disk and a dust disk mass of 45.8\,$M_ or $ Jup $. The 12CO observations do not show a cavity and the 12CO radial extension is at least three times larger than that of the dust emission. Although the measured age is younger than often suggested in literature, PDS\,111 seems relatively old; this provides insight into disk properties at an advanced stage of pre-main sequence evolution. The characteristics of this disk are very similar to its younger counterparts: strongly flaring, an average disk mass, a typical radial extent of the disk gas and dust, and the presence of common substructures. This suggests that disk evolution has not significantly changed the disk properties. These results show similarities with the "Peter Pan disks" around M-dwarfs, that "refuse to evolve".

On the importance of middle-atmosphere observations on ionospheric dynamics using WACCM-X and SAMI3

Abstract. Recent advances in atmospheric observations and modeling have enabled the investigation of thermosphere–ionosphere interactions as a whole-atmosphere problem. This study examines how dynamical variability in the middle atmosphere (MA) affects intra-day changes in the thermosphere and ionosphere. Specifically, this study investigates ionosphere–thermosphere interactions during different time periods of January 2013 using the Specified Dynamics Whole Atmosphere Community Climate Model, eXtended version (SD-WACCM-X), coupled to the Naval Research Laboratory (NRL) ionosphere of the Sami3 is Another Model of the Ionosphere (SAMI3) model. To represent the weather of the day, the coupled thermosphere–ionosphere system is nudged below 90 km toward the atmospheric specifications provided by the Navy Global Environmental Model for High-Altitude (NAVGEM-HA). Hindcast simulations during January 2013 are carried out with the full dataset of observations normally assimilated by NAVGEM-HA and with a degraded dataset where observations above 40 km are not assimilated. Ionospheric regions with statistically significant changes are identified using key ionospheric properties, including the electron density, peak electron density, and height of the peak electron density. Ionospheric changes show a spatial structure that illustrates the impact of two different types of coupling between the thermosphere and the ionosphere: variability induced by wind-dynamo coupling through electric conductivity and ion-neutral interactions in the upper thermosphere. The two simulations presented in this study show that changing the state of the MA affects ionosphere–thermosphere coupling through changes in the behavior and amplitude of non-migrating tides, resulting in improved key ionospheric specifications.

Intercomparison of methods for atmospheric reactive mercury observations: Evidences to interpret what we are actually measuring

Accurate measurements of atmospheric reactive mercury (RM or HgII) including gaseous oxidized mercury (GOM) and particulate-bound mercury (PBM) are crucial to improving understanding of mercury (Hg) behavior in the ambient air and evaluating the effectiveness of the Minamata Convention. As part of the Speciation and Transformation of Atmospheric Mercury in a Polluted region (STAMP) campaign in eastern China, comparison of Tekran, the reactive mercury active system (RMAS) and the micro-orifice uniform deposit impactors (MOUDI) system for RM measurements was conducted in this study. The ratio of GOMTekran/GOMRMAS was found to be positively correlated with the ratio of PBM/GOM and the proportion of [-Br/Cl] in RM based on deconvolution of the RMAS thermal desorption profiles. HgII reduction by the aqueous HO2 radicals was found to be the most likely cause of GOM underestimation by denuder-based methods. PBM acting as a substitute for GOM in HgII reduction could limit the underestimation. High particulate matter (PM) environment could cause PBM breakthrough in RMAS sampling, resulting in PBM underestimation and GOM overestimation. The chemical compound characteristics of RM and HgII distribution on particles by size provide evidences for the sources of the discrepancies in PBM measurements by different methods. Particle-size-resolved compound profiles are useful approaches for accurate RM quantification.

Rovibrational analysis of AlCO3, OAlO2, and HOAlO2 for possible atmospheric detection.

The lack of observational data for the AlO molecule in the mesosphere/lower thermosphere may be due to ablated aluminum reacting quickly to form other species. Previously proposed reaction pathways show that aluminum could be ablated in the atmosphere from meteoritic activity, but there currently exist very limited spectroscopic data on the intermediates in these reactions, limiting the possible detection of said molecules. As such, rovibrational spectroscopic data are computed herein using quartic force field methodology at four different levels of theory for the neutral intermediates AlCO3, OAlO2, and HOAlO2. Each molecule exhibits multiple vibrational modes with large vibrational transition intensities. For instance, the C-O stretch (ν1) in AlCO3 has a harmonic intensity of 536 km mol-1, the Al-O stretch (ν2) in OAlO2 has an intensity of 678 km mol-1, and the out-of-plane torsion (ν9) in HOAlO2 has an intensity of 158 km mol-1. All three molecules have exceptionally large dipole moments of 6.27, 4.21, and 5.04D, respectively. These properties indicate that all three molecules are good candidates for potential atmospheric observation utilizing vibrational and/or rotational spectroscopic techniques.

Examining the Impact of Assimilating Surface, PBL, and Free Atmosphere Observations from TORUS on Analyses and Forecasts of Two Supercells on 8 June 2019

Abstract This study describes data-denial experiments conducted to examine the impact of assimilating subsets of data from the TORUS project on storm-scale ensemble forecasts of two supercells on 8 June 2019. Assimilated data from TORUS includes mobile mesonet, UAS, and radiosonde observations. The TORUS data are divided into three spatial subsets to evaluate the importance of observing different parts of the atmosphere on forecasts of this case: the SFC subset consisting of just the near-surface mobile mesonet observations, the PBL subset consisting of UAS observations and radiosonde profiles below 762 m, and the FREE subset consisting of radiosonde profiles above 762 m. Data denial experiments are then conducted by comparing analyses and free forecasts generated using a cycled EnKF data assimilation system assimilating conventional observations, radar observations, and all of the TORUS observations at once with experiments where one of the three subsets is removed in turn as well as a control experiment assimilating only conventional and radar observations. Our results show that assimilating all of the TORUS observations at once in the ALL experiment improves the storm-scale ensemble forecasts much more often than it degrades them, and that no one subset of the TORUS data was consistently most important for improving the analyses or forecasts.

Path-Following Formation of Fixed-Wing UAVs under Communication Delay: A Vector Field Approach

In many applications, such as atmospheric observation or disaster monitoring, cooperative control of a fleet of UAVs is crucial because it is effective in repeated tasks. In this work, we provide a workable and useful cooperative guiding algorithm for several fixed-wing UAVs to construct a path-following formation with communication delays. The two primary components of our concept are path-following (lateral guidance) and path formation (longitudinal guidance). The former is in charge of ensuring that, in the presence of wind disturbance, the lateral distance between the UAV and its targeted path converges using a well-known vector field technique. In the event of a communication delay, the latter ensures that several fixed-wing UAVs will create a predetermined formation shape. Furthermore, we provide a maximum delay bound that is dependent on the topology and a controller’s gain. Lastly, in order to confirm the viability and advantages of our suggested approach, we construct an effective platform for a hardware-in-the-loop (HIL) test.

On the retrieval of cloud optical thickness from spectral radiances - A sensitivity study with high albedo surfaces

Measurements of spectral zenith radiance in the 320–950 nm wavelength range have been carried out since 2021 at the Thule High Arctic Atmospheric Observatory (THAAO, https://www.thuleatmos-it.it/, 76.5° N, 68.8° W, 225 m a.s.l) located in Pituffik, northern Greenland. This study evaluates whether such observations could provide, in principle, scientifically meaningful cloud optical depth (τ) estimates, what would be the limitations, which are the necessary auxiliary measurements, and which radiance wavelengths would be better suited for the goal. Although clouds play a critical role in the Arctic, a climatology of τ in high albedo conditions is particularly difficult to obtain. THAAO might have the instrument capabilities to provide such a long-term dataset. We use a radiative transfer package to simulate visible spectra with different cloud and surface conditions, assuming homogeneous overcast sky and liquid water clouds of fixed geometrical thickness. Simulations are run to reproduce typical conditions encountered at THAAO when measurements are carried out. We find that the assumption of a broadband albedo instead of a spectrally-resolved one is the source of the largest uncertainties. Tests on size and phase of cloud particles showed that a 50% uncertainty in reff leads to a ∼10% error in τ, and that a 10% contamination of ice crystals in a low-level liquid water cloud leads to an error in τ estimates of less than 5%. All the tests showed that the most critical τ range is between the thin and thick cloud regimes (τ ∼ 7–15), where the retrievals can be less reliable. Otherwise, tests suggest that in the environmental conditions that characterize late spring and summer at THAAO, and given the observatory measurements capabilities, estimates of τ for low-level clouds could be accurately retrieved both in high and low surface albedo conditions by means of zenith radiance measurements in the UV-Vis-NIR range.