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The age of stratospheric air is a concept commonly used to evaluate transport timescales in atmospheric models. The mean age can be derived from observations of a single long-lived trace gas species with a known tropospheric trend. Commonly, deriving mean age is based on the assumption that all air enters the stratosphere through the tropical (TR) tropopause. However, in the lowermost stratosphere (LMS) close to the extra-tropical (exTR) tropopause, cross-tropopause transport needs to be taken into account. We introduce the new exTR–TR method, which considers exTR input into the stratosphere in addition to TR input. We apply the exTR–TR method to in situ SF6 measurements from three aircraft campaigns (PGS, WISE and SouthTRAC) and compare results to those from the conventional TR-only method. Using the TR-only method, negative mean age values are derived in the LMS close to the tropopause during the WISE campaign in Northern Hemispheric (NH) fall 2017. Using the new exTR–TR method instead, the number and extent of negative mean age values is reduced. With our new exTR–TR method, we are thus able to derive more realistic values of typical transport times in the LMS from in situ SF6 measurements. Absolute differences between both methods range from 0.3 to 0.4 years among the three campaigns. Interhemispheric differences in mean age are found when comparing seasonally overlapping campaign phases from the PGS and the SouthTRAC campaigns. On average, within the lowest 65 K potential temperature above the tropopause, the NH LMS is 0.5±0.3 years older around March 2016 than the Southern Hemispheric (SH) LMS around September 2019. The derived differences between results from the exTR–TR method and the TR-only method, as well as interhemispheric differences, are higher than the sensitivities of the exTR–TR method to parameter uncertainties, which are estimated to be below 0.22 years for all three campaigns.

Vb-cyclones propagating from the North-Western Mediterranean Sea (NWMS) into central Europe are often associated with extreme precipitation. This study explores the state and process chain linking the NWMS state and the Vb-cyclone precipitation in the Danube, Elbe, and Odra catchments in regional coupled atmosphere-ocean climate simulations with COSMO-CLM+NEMO. Two high-resolution simulations, an evaluation simulation (1951–2005) downscaling the centennial ERA-20C reanalysis and a continuous simulation (historical 1951–2005 + RCP8.5 future scenario 2006–2099) downscaling the EC-EARTH global climate data set are used for this purpose. The results show a good agreement in mean annual Vb-cyclone frequency between the evaluation (9.7 events/year) and the historical (10.1 events/year) simulations. But, there are significant discrepancies in the seasonal cycle. The mean cyclone intensity measured with minimum central pressure, track density, and precipitation rankings in the three catchments also show good agreement. The simulations for the future period show a basin-average SST warming of ≈ 2.5–3 K by the end of 21st century, but insignificant changes in Vb-cyclone frequency, mean intensity, and precipitation in the selected catchments. The NWMS sea surface temperature, evaporation, and wind speed anomalies corresponding to the Vb-cyclone precipitation rankings differ between the evaluation and historical simulations. In the evaluation simulation, Vb-cyclone precipitation rankings correspond with sea surface temperature, evaporation, and wind speed anomalies, while in the historical and the future simulation no such correspondence is seen. Especially the Adriatic and Ionian basins in the simulation driven by EC-EARTH show no sensitivity to the Vb-cyclone precipitation over the catchments. The change in the processes between evaluation and historical simulations might be due to the emergence of biases inherited from the driving EC-EARTH global simulation. The future simulation shows no significant process changes compared to the historical simulation.

22 pags., 10 figs., 3 tabs., Bromine released from the decomposition of short-lived brominated source gases contributes as a sink of ozone in the lower stratosphere. The two major contributors are CH2Br2 and CHBr3. In this study, we investigate the global seasonal distribution of these two substances, based on four High Altitude and Long Range Research Aircraft (HALO) missions, the HIAPER Pole-to-Pole Observations (HIPPO) mission, and the Atmospheric Tomography (ATom) mission. Observations of CH2Br2 in the free and upper troposphere indicate a pronounced seasonality in both hemispheres, with slightly larger mixing ratios in the Northern Hemisphere (NH). Compared to CH2Br2, CHBr3 in these regions shows larger variability and less clear seasonality, presenting larger mixing ratios in winter and autumn in NH midlatitudes to high latitudes. The lowermost stratosphere of SH and NH shows a very similar distribution of CH2Br2 in hemispheric spring with differences well below 0.1gppt, while the differences in hemispheric autumn are much larger with substantially smaller values in the SH than in the NH. This suggests that transport processes may be different in both hemispheric autumn seasons, which implies that the influx of tropospheric air ("flushing") into the NH lowermost stratosphere is more efficient than in the SH. The observations of CHBr3 support the suggestion, with a steeper vertical gradient in the upper troposphere and lower stratosphere in SH autumn than in NH autumn. However, the SH database is insufficient to quantify this difference. We further compare the observations to model estimates of TOMCAT (Toulouse Off-line Model of Chemistry And Transport) and CAM-Chem (Community Atmosphere Model with Chemistry, version 4), both using the same emission inventory of . The pronounced tropospheric seasonality of CH2Br2 in the SH is not reproduced by the models, presumably due to erroneous seasonal emissions or atmospheric photochemical decomposition efficiencies. In contrast, model simulations of CHBr3 show a pronounced seasonality in both hemispheres, which is not confirmed by observations. The distributions of both species in the lowermost stratosphere of the Northern and Southern hemispheres are overall well captured by the models with the exception of southern hemispheric autumn, where both models present a bias that maximizes in the lowest 40gK above the tropopause, with considerably lower mixing ratios in the observations. Thus, both models reproduce equivalent flushing in both hemispheres, which is not confirmed by the limited available observations. Our study emphasizes the need for more extensive observations in the SH to fully understand the impact of CH2Br2 and CHBr3 on lowermost-stratospheric ozone loss and to help constrain emissions., This research has been supported by the Bundesministerium für Bildung und Forschung (grant no. 01LG1908B), the Deutsche Forschungsgemeinschaft (grant nos. EN367/13-1, EN367/14-1, EN367/16-1, EN367/17-1), and DFG collaborative research program “The Tropopause Region in an Changing Atmosphere” TRR 301 – Project-ID 428312742, the National Center for Atmospheric Research (grant no. 1852977), the Consejo Nacional de Investigaciones Científicas y Técnicas (grant no. PICT 2019-2187), and the Natural Environment Research Council (grant no. NE/N014375/). This open-access publication was funded by the Goethe University Frankfurt.

Ambient ions play an important role in atmospheric processes such as ion-induced new particle formation. While there are several studies of ambient ions for different layers of the atmosphere, data coverage for the free troposphere and especially the upper troposphere and lower stratosphere (UTLS) region is scarce. Here, we present the first airborne measurements of ambient ions using a high-resolution atmospheric pressure interface time-of-flight mass spectrometer (HR-APi-TOF-MS) in the free troposphere and lower stratosphere above Europe on board the HALO aircraft during the CAFE-EU/BLUESKY campaign in May and June 2020. In negative measurement mode, we observed nitrate and hydrogen sulfate and their related ion clusters in an altitude range of 4.7 to 13.4 km. The horizontal profiles for those ions reveal an increasing count rate for NO3- and (HNO3)NO3- towards higher altitudes but no significant trend for HSO4−. From the count rates of the nitrate (NO3-) and hydrogen sulfate (HSO4-) core ions, we inferred the number concentration of gaseous sulfuric acid. The lowest average value was found to be 1.9×105 cm−3 at the maximum altitude bin, i.e. 13.4 km. The highest average value of 7.8×105 cm−3 was observed in the 8.7–9.2 km altitude bin. During the transit through a mixed-phase cloud, we observed an event of enhanced ion count rates and aerosol particle concentrations that can largely be assigned to nitrate ions and particles, respectively; this may have been caused by the shattering of liquid cloud droplets on the surface of the aircraft or the inlet. Furthermore, we report the proof of principle for the measurement of ambient cations and the identification of protonated pyridine.

The TWIN - Hemera stratospheric balloon flight took place on 12 - 13-Aug-2021 from the Esrange Space Center near Kiruna, Sweden (67°N).The project was supported by Hemera (www.hemera-h2020.eu) via the first call of proposals, and the flight was managed by the CNES (Centre national d'Etudes Spatiales) and SSC (Swedish Space Corporation). The scientific payload was developed in collaboration by several institutions from the Netherlands, Germany and France.The main objectives were: (1) to characterize the vertical structure of COS mole fraction and isotopic composition; (2) to characterize the CFCs, other ozone depleting substances and climate relevant trace gases in the present atmosphere, linked to their change over the past decade; and (3) to compare and evaluate several instruments and sampling techniques.The payload included several AirCores (U. Frankfurt, CIO and FZJ), two Pico-SDLA mid-infrared in-situ diode laser spectrometers (GSMA/DT-INSU), and devices for taking large whole air samples of stratospheric air for subsequent laboratory measurements: the BONBON whole-air cryosampler (U. Frankfurt) and LISA (CIO). IMAU is involved for the analysis of isotopic composition and mole fractions of samplers from the cryo-sampler. This approach allows obtaining a comprehensive dataset covering a range of spatial resolutions: from the multitude of gas species to be measured in the high-volume samples, to the subset of gases at higher vertical resolution from AirCores, and finally to the continuous in-situ CO2 and CH4 data from tunable diode laser spectroscopy. We expect this dataset to lead to novel and important knowledge on the trace gases in the stratosphere.In this presentation we will describe the overall setup of the scientific payload, the flight characteristics, and we will give an overview of the already performed and planned measurements.