Altitude Band Research Articles

Intensified response of extreme precipitation to rising temperature over the Tibetan Plateau from CMIP6 multi-model ensembles

This study conducted bias correction of the high-performing general circulation model (GCM) data in combination with observed data based on the latest GCM data released by the Coupled Model Intercomparison Project Phase 6 (CMIP6). The ability of GCMs to simulate the characteristics of extreme precipitation over the Tibetan Plateau (TP) was systematically assessed, and the CMIP6 multi-model ensemble was used to accurately project extreme precipitation. Furthermore, the response of extreme precipitation over the TP to global warming was explored. The results demonstrated that daily translation efficiently addressed the issue of apparent overestimation in the model’s raw output, and CMIP6 multi-model ensemble mean exhibited better simulation performance for all extreme precipitation indices over the TP. Additionally, the simulation performance of each index exhibited a divergence across various elevation bands as altitude increased, with the best and worst performance observed at the altitude bands of 1500–2000 m and above 5000 m, respectively. For future changes in extreme precipitation, the indices representing the amount and intensity of extreme precipitation increase significantly, whereas the indices representing the duration of precipitation decrease. Moreover, the plateau will show a spatial pattern of “wet regions becoming dry and dry regions becoming wet”. The relationship between extreme precipitation and temperature follows a positive and peak pattern over most areas of the plateau, while the response of extreme precipitation to temperature will increase by 0.6 %–52.6 % with rising temperature. The present results have important implications for investigating the impacts of climate change on the water cycle in alpine regions.

Evaluation of the effectiveness of the 5-year rule — impact on the orbital environment at each altitude by reducing the post-mission disposal lifetime

This paper examines the effect of shortening the post-mission disposal (PMD) orbit lifetime (remaining orbit lifetime after PMD) from 25 years to 5 or 1 year. Using NEODEEM, the debris evolutionary model developed by Kyushu University and JAXA, the change in the orbital environment at various altitude bands for long-term stability and short-term safety are discussed. It was confirmed that the PMD compliance rate is more important than shortening the orbit lifetime for improving the long-term stability of the orbital environment. In the short term, the 5- or 1-year rule reduced the collision rate and collision avoidance frequency at an altitude below 700 km, more than the 25-year rule, thus shortening the PMD orbit lifetime improves short-term safety, especially at low altitudes. The paper also evaluates the effect of large constellations (LCs) and it was shown that shortening the PMD orbit lifetime of LCs improves short-term safety, but the long-term impact is dominated by the number of LCs that remain at high operational altitudes due to PMD failure. It shows that the post-mission disposal lifetime and required compliance rate should be set according to the number and size of objects expected to be launched in the future.

Crosses on peaks in Protected Areas: a functional mapping from the Apennines to the Italian Alps by altitude bands

Crosses on peaks in Protected Areas: a functional mapping from the Apennines to the Italian Alps by altitude bands

MODERN ASPECTS OF THE IMPLEMENTATION OF THE COURSE "METEOROLOGY AND CLIMATOLOGY" IN THE EDUCATIONAL PROCESS OF STUDENTS IN THE DIRECTION OF PREPARATION 101 ECOLOGY

Modern meteorology is a very practical science necessary for social life. Most meteorologists model weather and climate forecasts, while others work for government and military organizations as well as private companies, providing forecasts for aviation, navigation, agriculture, construction, and radio and television broadcasting. In many countries, meteorology is often called "atmospheric physics", and ordinary meteorologists deal more with complex mathematical formulas and calculations that model physical and physico-chemical processes in the Earth's atmosphere. However, since the latter is closely related to all other envelopes, the work of meteorologists also has a distinct geographic element, since only geography needs to be taken into account for weather forecasting and modeling of atmospheric processes. In addition, the conditions of the atmosphere and the processes that take place in it differ in different parts of the globe due to geographic patterns (regions, altitude bands, etc.). Long-term weather conditions in a certain area are called climate. So, climatology is a science that studies such issues as climate formation, description and classification of the global climate, and the impact of human activity on the climate. By its nature, it is more closely related to other geographical disciplines.
 Modern research in the field of meteorology and climatology is at the center of mass media reports, as it sheds light on the future of our planet and life on it in light of actual and potential climate change. This is their mission today. they can only answer questions posed as elements of the system of geographic science.
 The article contains basic provisions on the environment, aspects of life in various regions, especially natural areas and objects subject to special protection. The work on environmental impact assessment is characterized. The article covers some issues of human bioclimatology, synrheological effects of individual meteorological variables and atmospheric factors and methods of assessing the complex impact of weather on the human body. The influence of climate warming on the health of the population and adaptation to climate change in Ukraine are mentioned.

Formulation of the cosmic ray–driven electron-induced reaction mechanism for quantitative understanding of global ozone depletion

This paper formulates the cosmic ray-driven electron-induced reaction as a universal mechanism to provide a quantitative understanding of global ozone depletion. Based on a proposed electrostatic bonding mechanism for charge-induced adsorption of molecules on surfaces and on the measured dissociative electron transfer (DET) cross sections of ozone-depleting substances (ODSs) adsorbed on ice, an analytical equation is derived to give atmospheric chlorine atom concentration: [Formula: see text] where Φe is the prehydrated electron (epre-) flux produced by cosmic ray ionization on atmospheric particle surfaces, [Formula: see text] is the surface coverage of an ODS, and ki is the ODS's effective DET coefficient that is the product of the DET cross section, the lifetimes of surface-trapped epre- and Cl-, and the particle surface area density. With concentrations of ODSs as the sole variable, our calculated results of time-series ozone depletion rates in global regions in the 1960s, 1980s, and 2000s show generally good agreement with observations, particularly with ground-based ozonesonde data and satellite-measured data over Antarctica and with satellite data in a narrow altitude band at 13 to 20 km of the tropics. Good agreements with satellite data in the Arctic and midlatitudes are also found. A previously unreported effect of denitrification on ozone loss is found and expressed quantitatively. But this equation overestimates tropospheric ozone loss at northern midlatitudes and the Arctic, likely due to increased ozone production by the halogen chemistry in polluted regions. The results render confidence in applying the equation to achieve a quantitative understanding of global ozone depletion.

Modeling E‐Region Artificial Periodic Inhomogeneity

AbstractArtificial periodic inhomogeneity or API experiments were conducted at the HAARP facility in Gakona, Alaska, in October 2022. The experiments concentrated on measuring ionospheric irregularities induced in the E‐region. The irregularities exhibited characteristics regarding their occurrence altitudes, rise and fall times, and Doppler shifts comparable to results from experiments conducted previously at HAARP and elsewhere. The irregularities also occurred in discrete altitude bands. Seeking to quantify these results, we constructed a simple, one‐dimensional fluid model which includes the effects of HF wave heating (direct and indirect) together with electron and ion cooling and thermal conduction, ion production, loss, and diffusion. Critically, the model includes a potential solver and can represent the ambipolar electric field. The model produced API irregularities in three distinct altitude bands which decayed according to the ambipolar diffusion rate.

CCN Spectral Modality Compared to Droplet Spectra and Drizzle in RICO Cumuli

AbstractRain in Cumulus over the Ocean (RICO) warm cloud microphysics and drizzle comparisons with cloud condensation nuclei (CCN) spectra displayed similarities with earlier analyses of low‐altitude Ice in Clouds Experiment‐Tropical (ICE‐T) warm maritime cumuli. These comparisons of high‐resolution CCN spectra measured at 100 m altitude with cloud and drizzle measurements were consistent within three altitude bands between 600 and 3,700 m. For both projects, clouds associated with bimodal CCN (accumulation mode dominant) displayed more drizzle than clouds associated with unimodal CCN (Aitken mode dominant). Higher concentrations in clouds associated with bimodal CCN than clouds associated with unimodal CCN extended throughout the ranges of 3 drizzle drop probes (260X, 2DC, and 2DP) between 60 and 5,200 μm diameter. Ratios of drizzle drop concentrations in clouds associated with bimodal CCN to those in clouds associated with unimodal CCN were as much as an order of magnitude. Confirmation of a relationship between CCN modality and cloud droplet spectra found in ICE‐T was often obscured in RICO by drizzle effects on droplet spectra. There was also an association between cloudiness and CCN bimodality that is consistent with clouds as a source of accumulation mode particles. These consistent results now found in two warm maritime small low‐altitude cumulus cloud experiments show that CCN bimodality could inhibit the indirect aerosol effect (IAE), especially second IAE (cloud lifetime) in warm maritime cumuli. These RICO and ICE‐T observations in maritime cumuli are opposite of the results in the Marine Stratus/Stratocumulus Experiment, which indicated that CCN bimodality could enhance both IAE.

Spatiotemporal heterogeneity and attributions of streamflow and baseflow changes across the headstreams of the Tarim River Basin, Northwest China

Understanding spatiotemporal heterogeneity of streamflow and baseflow and revealing their changes contributed by climatic factors and human activities in the alpine region of inland river basin are critical for regional water management. However, the hydrology heterogeneity in the alpine region has remained unclear, which limits the scientific understanding of the interaction mechanism between the hydrological cycle and terrain, and further constrains the effective utilization of regional water resources in the water-shortage areas. In this study, the hydrological process and regimes for headstreams of Tarim River Basin (HTRB) during 1985–2011 were simulated by the Soil and Water Assessment Tool. We systematically characterized the spatial and temporal patterns of streamflow and baseflow through geostatistical and trend analyses, and subsequently investigated their heterogeneity responses to climate change and human activities at different sub-basins and elevation zones. Results show that the spatial distributions of streamflow and baseflow are highly related to terrain and river direction. Increased trends in precipitation enhanced with altitude, whereas decreased trends in potential evapotranspiration (PET) weakened with altitude, meanwhile, increased trends in streamflow and baseflow of HTRB are most pronounced in mid-altitude areas during 1985–2011. The climate elasticities of streamflow and baseflow are highly reliant on the altitudinal gradient. Increases in streamflow and baseflow in high-lying areas are more sensitive to precipitation variation, while they are more sensitive to PET change in low-lying areas. The magnitude and change rate with altitude bands of the precipitation has greater effects on streamflow and baseflow variations than those of PET. Furthermore, the percentage of sub-basins where climate changes dominate streamflow variation in each elevation band increases with height but decreases abruptly at elevations above 5000 m. The percentage of sub-basins where climate changes dominate baseflow variations gradually decreases in elevation bands above 3000 m. Our results indicate that climate change rather than human activities dominants the variation in streamflow and baseflow in most sub-basins and elevation bands.

Considerations on the lists of the top 50 debris removal targets

Remediation measures, such as Active Debris Removal (ADR) has been studied in order to preserve the space environment. Large derelict objects in crowded orbits are considered ADR targets because they are the source of numerous small debris in case of fragmentation. The target for removal must be chosen carefully because cost is the major issue in realizing ADR, and it is necessary to remediate the orbital environment as efficiently as possible. Last year, Dr. McKnight et al. presented the top 50 debris removal targets by combining each of the top 50 lists compiled by eleven international teams. This paper discusses the considerations involved in selecting debris removal targets. This study first considered the top 50 objects, to be removed according to each index, and then evaluated the consequences of the removal using Near-Earth Orbit Debris Environment Evolutionary Model (NEODEEM), a debris evolutionary model developed by Kyushu University and JAXA. Differences in debris removal targets were studied for long-term stability or short-term safety. This paper discusses why some indices are effective in the short or long term in terms of the orbital distribution of selected targets and the effects of removal in each altitude band. It also discusses the differences between removing 50 objects and removing one object each year, and the effects of removal timing and so on. It found that integrating different indices is effective, and that the removal target must be determined according to the situation. It is more important to remove as much debris as possible as early as possible rather than focusing on an object's ranking in a list.

Assessing the Contribution of Glacier Melt to Discharge in the Tropics: The Case of Study of the Antisana Glacier 12 in Ecuador

Tropical glaciers are excellent indicators of climate variability due to their fast response to temperature and precipitation variations. At same time, they supply freshwater to downstream populations. In this study, a hydro-glaciological model was adapted to analyze the influence of meteorological forcing on melting and discharge variations at Glacier 12 of Antisana volcano (4,735–5,720 m above sea level (a.s.l.), 1.68 km2, 0°29′S; 78°9′W). Energy fluxes and melting were calculated using a distributed surface energy balance model using 20 altitude bands from glacier snout to the summit at 30-min resolution for 684 days between 2011 and 2013. The discharge was computed using linear reservoirs for snow, firn, ice, and moraine zones. Meteorological variables were recorded at 4,750 m.a.s.l. in the ablation area and distributed through the altitudinal range using geometrical corrections, and measured lapse rate. The annual specific mass balance (−0.61 m of water equivalent -m w.e. y−1-) and the ablation gradient (22.76 kg m−2 m−1) agree with the values estimated from direct measurements. Sequential validations allowed the simulated discharge to reproduce hourly and daily discharge variability at the outlet of the catchment. The latter confirmed discharge simulated (0.187 m3 s−1) overestimates the streamflow measured. Hence it did not reflect the net meltwater production due to possible losses through the complex geology of the site. The lack of seasonality in cloud cover and incident short-wave radiation force the reflected short-wave radiation via albedo to drive melting energy from January to June and October to December. Whereas the wind speed was the most influencing variable during the July-September season. Results provide new insights on the behaviour of glaciers in the inner tropics since cloudiness and precipitation occur throughout the year yielding a constant short-wave attenuation and continuous variation of snow layer thickness.

Development and Evaluation of Global Korean Aviation Turbulence Forecast Systems Based on an Operational Numerical Weather Prediction Model and In Situ Flight Turbulence Observation Data

Abstract A global Korean deterministic aviation turbulence guidance (G-KTG) system and a global Korean probabilistic turbulence forecast (G-KPT) system are developed using outputs from the operational Global Data Assimilation and Prediction System of the Korea Meteorological Administration, and the performance skill of the systems are evaluated against in situ flight eddy dissipation rates (EDRs) recorded for one year (September 2018–August 2019). G-KTG and G-KPT consider clear-air turbulence (CAT) and mountain wave turbulence diagnostics, while G-KTG additionally considers near-cloud turbulence (NCT) diagnostics. In the G-KTG system, the various combinations of deterministic EDR forecasts are tested by different ensemble means of individual turbulence diagnostics. In the G-KPT system, the probabilistic forecast is established by counting the number of diagnostics that exceed a certain threshold for strong intensity turbulence on the given model grid. The evaluation results of the G-KTG system based on the area under the relative operating characteristic curve (AUC) reveal that G-KTG, which consists of CAT and NCT diagnostics, shows the highest AUC value among the various G-KTG combinations; in addition, the summertime performance is significantly improved when NCT diagnostics are included. In the evaluation results of the G-KTG system over the globe, U.S., and East Asia regions, the recent graphical turbulence guidance system–based G-KTG shows better performance than the regional KTG–based G-KTG for all three regions. For all altitude bands, the G-KPTs with 40% probability as the minimal threshold for alerting forecasters of strong turbulence show higher values of true skill statistic than the G-KTGs.

Evidence of phenotypic plasticity along an altitudinal gradient in the dung beetle Onthophagus proteus.

BackgroundHigh altitude insects are an ecologically specialized group and possess a suite of adaptions which allow persistence in the inhospitable conditions often associated with mountain tops. Changes in body coloration and reductions or increases in body size are thought to be examples of such adaptions. Melanic individuals, or individuals containing high levels of eumelanin, possess several traits which increase resistance to ultraviolet radiation and desiccation, while aiding thermoregulation. Trait variation is often observed in dung beetles and is associated with dimorphism and sexual selection. In this study, we identified trait changes which occur across an altitudinal gradient by measuring morphological color and body size traits in a montane insect.MethodsUsing standard digital photography and Image J, we examined individuals of Afromontane dung beetle Onthophagus proteus. Individuals were classified according to sex and color morph to identify intrasexual variance. Nine morphometric traits were measured per beetle to identify patterns of morphology across discrete 500 m altitude segments.ResultsThe results of this study provide one of the first descriptions of trait changes associated with elevation in an African dung beetle. We suggest that color polymorphism in Onthophagus proteus might be at least partly driven by environmental factors as there is significantly increased melanism with increasing elevation and significant differences in color hues between altitude bands. We also suggest changes in horn length are density dependent, as we observed an increase in cephalic horn length at high elevations where O. proteus is the most abundant species.

Short-term space safety analysis of LEO constellations and clusters

The large satellite constellations currently planned and deployed in Low Earth Orbit (LEO) bear some similarities with the clusters of derelict objects abandoned in different altitude bands in LEO. Given these similarities, an analysis of the collision risk associated with these orbital systems is performed with different analytical and numerical techniques.Different tools developed at IFAC-CNR for short to long-term constellation impact analysis are applied to ascertain the immediate (i.e., 1–20 years) effects related to the constellation deployment and execution and to evaluate the risk associated to the accumulation of massive derelict objects in a restricted region of space (i.e., clusters). The intra-group collision probability caused by the repeated orbital crossing between the members of two selected constellations and of some of the clusters of objects in LEO are computed, cumulated over the time span of the analysis (20 years) and compared. While the collision probability obtained in the case of the constellation could be efficiently mitigated by proper management and operations (i.e., debris mitigation practices and collision avoidance), the high level of risk associated with the clusters of derelict uncontrolled objects cannot be avoided, unless pro-active actions are undertaken to remove the large targets from the space. From all the analysis performed, the cluster located around 975 km of altitude stands up as particularly dangerous population in the already critical LEO region.

Material Flux From the Rings of Saturn Into Its Atmosphere

AbstractDuring Cassini's final, spectacular months, in situ instruments made the first direct measurements of nanoparticles, finding an exceptionally large flow from the rings into Saturn's atmosphere. Cassini's Ion and Neutral Mass Spectrometer measured material in three altitude bands and found a global‐integrated flux of 2–20 × 104 kg/s that is dominated by hydrocarbon material <104u. Ranging from clusters of a few molecules to radii of several nanometers, nanoparticles are ubiquitous throughout Saturn's rings but embedded in the regolith of larger particles and not detectable as independent particles using remote observations. The smallest nanoparticles are susceptible to atmosphere drag by Saturn's tenuous exosphere that reaches the inner edge of the D ring. The unsustainable large flux suggests a recent disturbance of Saturn's inner ring material, possibly associated with the clumping that appeared in the D68 ringlet in 2015.

The Drifting Phase of SARAL: Securing Stable Ocean Mesoscale Sampling with an Unmaintained Decaying Altitude

The French/Indian altimeter project Satellite with ARGOS and AltiKa (SARAL) completed its nominal 3-year mission on the historical European Remote-sensing Satellite (ERS) orbit in Spring 2016. In order to extend the lifetime of the satellite as much as possible, the agencies in charge of SARAL decided to initiate a so-called drifting phase where the satellite altitude is no longer maintained. In this paper we describe how the ocean mesoscale sampling capability of SARAL has been preserved during the drifting phase by initiating it at a specific altitude: the optimal starting point was approximately 1 km above the historical ERS/ENVIronment SATellite (ENVISAT) orbit. This strategy secured the ocean mesoscale sampling capability of SARAL drifting phase (DP) for 6 years or more. We also generalize these findings: any altimeter could follow SARAL’s drifting phase strategy if their maneuvering capability is limited. Lastly, we explain how an altimetry mission or an entire altimeter constellation could be operated without any form of altitude control: some specific altitude bands (e.g., near 1230 km) guarantee a high-quality mesoscale sampling for years or decades even if the altitude is not maintained.

Field validation of radar systems for monitoring bird migration

Abstract Advances in information technology are increasing the use of radar as a tool to investigate and monitor bird migration movements. We set up a field campaign to compare and validate outputs from different radar systems. Here we compare the pattern of nocturnal bird migration movements recorded by four different radar systems at a site in southern Sweden. Within the range of the weather radar (WR) Ängelholm, we operated a “BirdScan” (BS) dedicated bird radar, a standard marine radar (MR), and a tracking radar (TR). The measures of nightly migration intensities, provided by three of the radars (WR, BS, MR), corresponded well with respect to the relative seasonal course of migration, while absolute migration intensity agreed reasonably only between WR and BS. Flight directions derived from WR, BS and TR corresponded very well, despite very different sample sizes. Estimated mean ground speeds differed among all four systems. The correspondence among systems was highest under clear sky conditions and at high altitudes. Synthesis and applications. While different radar systems can provide useful information on nocturnal bird migration, they have distinct strengths and weaknesses, and all require supporting data to allow for species level inference. Weather radars continuously detect avian biomass flows across a wide altitude band, making them a useful tool for monitoring and predictive applications at regional to continental scales that do not rely on resolving individuals. BirdScan and marine radar’s strengths are in local and low altitude applications, such as collision risks with man‐made structures and airport safety, although marine radars should not be trusted for absolute intensities of movement. In quantifying flight behaviour of individuals, tracking radars are the most informative.

Three-Dimensional UAV Routing With Deconfliction

The work presented in this paper relates to the conceptual definition, simulation, and performance analysis of a novel, 3-D graph theory-based routing algorithm. The proposed router is designed to provide path planning with deconfliction, i.e., collision avoidance with other moving objects, for unmanned aerial vehicles (UAV) applications in general and autonomous UAV missions in particular. Thus, novel ways for “sampling” 3-D operating spaces containing hazard areas and other moving objects are presented. The router operates in a way that conforms to the commonly observed behavior of aircraft flying over relatively long periods of time at constant speed and barometric height. Thus, flying is restricted to a number of possible altitude bands, where changes in altitude and/or direction are restricted to values that ensure excessive airframe stress is avoided. The paper attaches considerable emphasis on algorithmic complexity reduction and develops a novel, adaptive, graph search scheme. The proposed router can also be used to support manned aircraft operation, both for pre-flight planning and during the mission as a pilot aid. Computer simulation results are indicative of a routing system which generates realistic flyable routes while algorithmic complexity is suppressed.

Gravity Wave‐Induced Ionospheric Irregularities in the Postsunset Equatorial Valley Region

AbstractPlasma irregularities in the postsunset equatorial valley region ionosphere are investigated experimentally and through numerical simulation. Coherent radar backscatter observed at the Jicamarca Radio Observatory shows two classes of irregularities in different altitude bands—one mainly below about 125 km and the other mainly above. Irregularities in both bands are organized into wavefronts with wavelengths of a few kilometers. However, only the irregularities in the high‐altitude band exhibit consistent propagation speeds and directions. Some previous observations of irregularities in the nighttime electrojet suggest that gravity waves may sometimes influence their morphology. The possibility that the valley region irregularities are also related to gravity waves (GWs) is therefore investigated numerically. A model of a GW packet propagating through a tidal wind field is used to drive another model which predicts the resulting ionospheric electrodynamics. The combined simulation shows that GWs can induce field‐aligned currents and excite resistive drift waves which could be responsible for the valley region irregularities in the high‐altitude band. The GWs also induce irregularities in the upper E region directly through simple dynamo action which subsequently deform under the influence of shear flow. This may explain the irregularities in the low‐altitude band.

Enhanced daytime occurrence of clouds in the tropical upper troposphere over land and ocean

Day-night changes in the altitudinal distribution of tropical clouds are examined using multi-year analyses of CloudSat and CALIPSO data. The combined occurrence of all cloud types maximizes in the nighttime throughout the middle and upper troposphere. In contrast to the nighttime maxima in the appearance of optically thick tropical clouds in the ~5–12km altitude band, the occurrence of such clouds exhibit a pronounced daytime enhancement in the upper troposphere (>12km). This arises from the more frequent occurrence of thick cirrus and deeper penetration of daytime convective clouds to the upper troposphere, as evidenced from more frequent daytime occurrence of clouds with thickness >9km. Apart from the afternoon convection over land and remnant cirrus from nighttime convection over ocean, the daytime cloud enhancement observed above 12km altitude might be also driven by the larger tropospheric net cloud radiative heating and its vertical gradient during the daytime.

Particulate sulfur in the upper troposphere and lowermost stratosphere – sources and climate forcing

Abstract. This study is based on fine-mode aerosol samples collected in the upper troposphere (UT) and the lowermost stratosphere (LMS) of the Northern Hemisphere extratropics during monthly intercontinental flights at 8.8–12 km altitude of the IAGOS-CARIBIC platform in the time period 1999–2014. The samples were analyzed for a large number of chemical elements using the accelerator-based methods PIXE (particle-induced X-ray emission) and PESA (particle elastic scattering analysis). Here the particulate sulfur concentrations, obtained by PIXE analysis, are investigated. In addition, the satellite-borne lidar aboard CALIPSO is used to study the stratospheric aerosol load. A steep gradient in particulate sulfur concentration extends several kilometers into the LMS, as a result of increasing dilution towards the tropopause of stratospheric, particulate sulfur-rich air. The stratospheric air is diluted with tropospheric air, forming the extratropical transition layer (ExTL). Observed concentrations are related to the distance to the dynamical tropopause. A linear regression methodology handled seasonal variation and impact from volcanism. This was used to convert each data point into stand-alone estimates of a concentration profile and column concentration of particulate sulfur in a 3 km altitude band above the tropopause. We find distinct responses to volcanic eruptions, and that this layer in the LMS has a significant contribution to the stratospheric aerosol optical depth and thus to its radiative forcing. Further, the origin of UT particulate sulfur shows strong seasonal variation. We find that tropospheric sources dominate during the fall as a result of downward transport of the Asian tropopause aerosol layer (ATAL) formed in the Asian monsoon, whereas transport down from the Junge layer is the main source of UT particulate sulfur in the first half of the year. In this latter part of the year, the stratosphere is the clearly dominating source of particulate sulfur in the UT during times of volcanic influence and under background conditions.