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Simulations of Antarctic chlorine and ozone chemistry in previous work show that in the core of the Antarctic vortex (16–18 km, 85–55 hPa, 390–430 K) HCl null cycles (initiated by reactions of Cl with CH4 and CH2O) are effective. These HCl null cycles cause both HCl molar mixing ratios to remain very low throughout Antarctic winter and spring. They cause ozone-destroying chlorine (ClOx) to remain enhanced so that rapid ozone depletion proceeds. Here we investigate the impact of the observed dehydration in Antarctica, which strongly reduces ice formation and the uptake of HNO3 from the gas phase; however the efficacy of HCl null cycles is not affected. Moreover, also when using the observed very low HCl molar mixing ratios in Antarctic winter as an initial value, HCl null cycles are efficient in maintaining low HCl (and high ClOx) throughout winter and spring. Further, the reaction CH3O2+ClO is important for the efficacy of the HCl null cycle initiated by the reaction CH4+Cl. Using the current kinetic recommendations instead of earlier ones has very little impact on the simulations. All simulations presented here for the core of the Antarctic vortex show extremely low minimum ozone values (below 50 ppb) in late September to early October in agreement with observations. [ABSTRACT FROM AUTHOR]

The Asian summer monsoon has a strong convectional component with which aerosols are able to be lifted up into the lower stratosphere. Due to usually long lifetimes and long-range transport aerosols remain there much longer than in the troposphere and are also able to be advected around the globe. Our aim of this study is a synergy between simulations by Chemical Lagrangian Model of the Stratosphere (CLaMS) and KARL (Koldewey Aerosol Raman Lidar) at AWIPEV, Ny-Ålesund in the Arctic, by comparing CLaMS results with exemplary days of lidar measurements as well as analyzing the stratospheric aerosol background. We use global three-dimensional Lagrangian transport simulations including surface origin tracers as well as back trajectories to identify source regions of the aerosol particles measured over Ny-Ålesund. We analyzed lidar data for the year 2021 and found the stratosphere generally clear, without obvious aerosol layers from volcanic eruptions or biomass burnings. Still an obvious annual cycle of the backscatter coefficient with higher values in late summer to autumn and lower values in late winter has been found. Results from CLaMS model simulations indicate that from late summer to early autumn filaments with high fractions of air which originate in South Asia – one of the most polluted regions in the world – reach the Arctic at altitudes between 360 and 380 K potential temperature. We found a coinciding measurement between the overpass of such a filament and lidar observations, and we estimated that backscatter and depolarization increased by roughly 15 % during this event compared to the background aerosol concentration. Hence we demonstrate that the Asian summer monsoon is a weak but measurable source for Arctic stratospheric aerosol in late summer to early autumn. [ABSTRACT FROM AUTHOR]

The Asian tropopause aerosol layer (ATAL) is present during the Asian summer monsoon season affecting the radiative balance of the atmosphere. However, the source regions and transport pathways of ATAL particles are still uncertain. Here, we investigate transport pathways from different regions at the model boundary layer (MBL) to the ATAL by combining two Lagrangian transport models (CLaMS, Chemical Lagrangian Model of the Stratosphere; MPTRAC, Massive-Parallel Trajectory Calculations) with balloon-borne measurements of the ATAL performed by the Compact Optical Backscatter Aerosol Detector (COBALD) above Nainital (India) in August 2016. Trajectories are initialised at the measured location of the ATAL and calculated 90 d backwards in time to investigate the relation between the measured, daily averaged, aerosol backscatter ratio and source regions at the MBL. Different simulation scenarios are performed to find differences and robust patterns when the reanalysis data (ERA5 or ERA-Interim), the trajectory model, the vertical coordinate (kinematic and diabatic approach) or the convective parameterisation are varied. The robust finding among all scenarios is that the largest continental air mass contributions originate from the Tibetan Plateau and the Indian subcontinent (mostly the Indo-Gangetic Plain), and the largest maritime air mass contributions in Asia come from the western Pacific (e.g. related to tropical cyclones). Additionally, all simulation scenarios indicate that the transport of maritime air from the tropical western Pacific to the region of the ATAL lowers the backscatter ratio (BSR) of the ATAL, while most scenarios indicate that the transport of polluted air from the Indo-Gangetic Plain increases the BSR. While the results corroborate key findings from previous ERA-Interim-based studies, they also highlight the variability in the contributions of different MBL regions to the ATAL depending on different simulation scenarios. [ABSTRACT FROM AUTHOR]

During the Asian monsoon season, greenhouse gases and pollution emitted near the ground are rapidly uplifted by convection up to an altitude of ∼ 13 km, with slower ascent and mixing with the stratospheric background above. Here, we address the robustness of the representation of these transport processes in different reanalysis data sets using ERA5, ERA-Interim and ERA5 1∘×1∘. This transport assessment includes the mean age of air from global three-dimensional simulations by the Lagrangian transport model CLaMS (Chemical Lagrangian Model of the Stratosphere), as well as different trajectory-based transport times and associated ascent rates compared with observation-based age of air and ascent rates of long-lived trace gases from airborne measurements during the Asian summer monsoon 2017 in Nepal. Our findings confirm that the ERA5 reanalysis yields a better representation of convection than ERA-Interim, resulting in different transport times and air mass origins at the Earth's surface. In the Asian monsoon region above 430 K, the mean age of air driven by ERA-Interim is too young, whereas the mean age of air from ERA5 1∘×1∘ is too old but somewhat closer to the observations. The mean effective ascent rates derived from ERA5 and ERA5 1∘×1∘ back trajectories are in good agreement with the observation-based mean ascent rates, unlike ERA-Interim, which is much faster above 430 K. Although a reliable CO2 reconstruction is a challenge for model simulations, we show that, up to 410 K, the CO2 reconstruction using ERA5 agrees best with high-resolution in situ aircraft CO2 measurements, indicating a better representation of Asian monsoon transport in the newest ECMWF reanalysis product, ERA5. [ABSTRACT FROM AUTHOR]

Diabatic transport schemes with hybrid zeta coordinates, which follow isentropes in the stratosphere, are known to greatly improve Lagrangian transport calculations compared to the kinematic approach. However, some Lagrangian transport calculations with a diabatic approach, such as the Chemical Lagrangian Transport Model of the Atmosphere (CLaMS), show low computational performance on modern high-performance computing (HPC) architectures. Here, we implemented and evaluated a new diabatic transport scheme in the Massive-Parallel Trajectory Calculations (MPTRAC) model. While MPTRAC effectively exploits modern HPC architectures, it was previously limited to kinematic trajectories on pressure coordinates. The extended modelling approach now enables the use of either kinematic or diabatic vertical velocities and the coupling of different MPTRAC modules based on pressure or hybrid zeta coordinates. The evaluation of the new transport scheme in MPTRAC shows that after 90-day forward calculations distributions of air parcels in the upper troposphere and lower stratosphere (UTLS) are almost identical for MPTRAC and CLaMS. No significant bias between the two Lagrangian models was found. Furthermore, after one day, internal uncertainties (e.g., due to interpolation or the numerical integration method) in the Lagrangian transport calculations are at least one order of magnitude smaller than external uncertainties (e.g., from reanalysis selection or downsampling of ERA5). Differences between trajectories using either CLaMS or MPTRAC are on the order of the combined internal uncertainties within MPTRAC. Since the largest systematic differences are caused by the reanalysis and the vertical velocity (diabatic vs. kinematic) the results support the development efforts for trajectory codes that can access the full resolution of ERA5 in combination with diabatic vertical velocities. This work is part of a larger effort to adapt Lagrangian transport in state-of-the-art models such as CLaMS and MPTRAC to current and future HPC architectures and exascale applications. [ABSTRACT FROM AUTHOR]

Aerosol particles with diameters larger than 40 nm were collected during the flight campaign StratoClim2017 within the Asian Tropopause Aerosol Layer (ATAL) of the 2017 Monsoon Anticyclone above the Indian subcontinent. A multiimpactor system was installed on board of the aircraft M-55 Geophysica, which was operated from Kathmandu, Nepal. The size and chemical composition of more than 5000 refractory particles/inclusions of 17 selected particle samples from 7 different flights were analyzed by use of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) combined with energy dispersive X-ray microanalysis (EDX). Based on chemical composition and morphology, the refractory particles were assigned to the particle groups: extraterrestrial, silicates, Fe-rich, Al-rich, Hg-rich, other metals, C-rich, soot, Cl-rich, and Ca-rich. Most abundant particle groups within the refractory particles are silicates and C-rich (nonvolatile organics). In samples taken above the tropopause extraterrestrial particles are becoming increasingly important with rising altitude. The most frequent particle sources for the small (maximum in size distribution DP-max = 120 nm) refractory particles carried into the ATAL are combustion processes at ground (burning of fossil fuels / biomass burning) and the agitation of soil material. The refractory particles in the ATAL represent only a very small fraction (< 2 % by number for particles > 40 nm) of the total aerosol particles which are dominated by species like ammonium, sulfate, nitrate, and volatile organics. During one flight additionally a large number of very small (DP-max = 25 nm) cinnabar particles (HgS) were detected. These particles are most likely generated directly on ground by coal combustion in Northeastern India or Southern China. [ABSTRACT FROM AUTHOR]

Atmospheric concentrations of many greenhouse gases especially CO2 are increasing globally. In particular the rapid increase of anthropogenic CO2 emissions in Asia contributes strongly to the acceleration of the CO2 growth rate in the atmosphere. During the Asian monsoon season, greenhouse gases as well as pollution emitted near the ground rapidly propagate up to an altitude of 13 km (~360 K potential temperature) with slower ascent and mixing with the stratospheric background above. However, CO2 sources in South Asia are poorly quantified. Here, differences in transport of air in the regions of the Asian summer monsoon 2017 were inferred using the Chemical Lagrangian Model of the Stratosphere (CLaMS) driven by three data sets, namely two ECMWF reanalyses in different resolutions (ERA-Interim, ERA5 and ERA5 1° x 1°). These model results are assessed using unique airborne measurements up to altitudes of ~20 km (~475 K) during the Asian summer monsoon 2017 conducted with the Geophysica aircraft during the StratoClim campaign in Nepal. Trajectory-based transport times, air mass source regions at the Earth's surface, mean effective ascent rates and age spectra as well as mean age of air from 3-dimensional CLaMS simulations are compared using the three data sets and evaluated by observation-based ascent rates. Our findings confirm that because of a better spatial and temporal resolution, ERA5 reanalysis yields a better representation of convection than ERA-Interim. Further, our findings show that transport times from the surface to the Asian monsoon anticyclone as well as the origin of air at the Earth's surface are both very sensitive to the used reanalysis. Above 430 K, the mean effective ascent rates derived from ERA5 back-trajectories and ERA5 1° x 1° (~0.2–0.3 K/day) are in good agreement with the observation-based mean ascent rates inferred from long-lived trace gases such as C2F6 and HFC-125 derived from air samples collected by the whole air sampler aboard Geophysica. Mean effective ascent rates derived from ERA-Interim back-trajectories are much faster ~0.5 K/day at these altitudes. In the Asian monsoon region at 470 K, mean age of air is larger than 3 years for ERA5 1° x 1° and about 2 years for ERA-Interim, whereas an observation-based age of air is up to 2.5 years. A reliable reconstruction (simulation) of vertical CO2 profiles during the Asian monsoon is a challenge for model simulations because the seasonal variability of CO2 at the ground, mixing with aged stratospheric air and the vertical velocities (including convection as well as vertical ascent caused by diabatic heating in the UTLS) have to be represented accurately in the simulations. Up to 410 K, the presented CO2 reconstruction agrees best with high-resolution in situ aircraft CO2 measurements using ERA5 compared to ERA5 1° x 1° and ERA-Interim, indicating a better representation of Asian monsoon transport for the newer ECMWF reanalysis product ERA5. Above 410 K the uncertainties of the CO2 reconstruction are increasing because of mixing with aged air. [ABSTRACT FROM AUTHOR]

Ozonesonde measurements from Hong Kong and Naha are combined with satellite observations to investigate the vertical structure of ozone and water vapor around the tropopause during typhoon Soudelor over the northwestern Pacific in 2015. The results show that the tropopause height is decreased compared to the mean tropopause during 2000–2017 in the western Pacific mode of the Asian summer monsoon anticyclone (ASMA). The vertical transport associated with Soudelor decreases the ozone concentration by 60% in the upper troposphere. Further the equatorward transport from high latitudes around the western Pacific mode of the ASMA increases ozone concentration by 40% in the lower stratosphere. Cross‐tropopause transport of water is observed above typhoon Soudelor, and water vapor to be enhanced at 80–100 hPa compared to nontyphoon regions. Dehydration is observed below the tropopause around the eye of Soudelor. [ABSTRACT FROM AUTHOR]