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This paper presents measurements of ozone, water vapour and nitric acid (HNO 3) in the upper troposphere/lower stratosphere (UTLS) over North Atlantic and Europe. The measurements were acquired with the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) during the Wave Driven Isentropic Exchange (WISE) campaign in October 2017. GLORIA is an airborne limb imager capable of acquiring both 2-D data sets (curtains along the flight path) and, when the carrier aircraft is flying around the observed air mass, spatially highly resolved 3-D tomographic data. Here, we present a case study of a Rossby wave (RW) breaking event observed during two subsequent flights 2 d apart. RW breaking is known to steepen tracer gradients and facilitate stratosphere–troposphere exchange (STE). Our measurements reveal complex spatial structures in stratospheric tracers (ozone and nitric acid) with multiple vertically stacked filaments. Backward-trajectory analysis is used to demonstrate that these features are related to several previous Rossby wave breaking events and that the small-scale structure of the UTLS in the Rossby wave breaking region, which is otherwise very hard to observe, can be understood as stirring and mixing of air masses of tropospheric and stratospheric origin. It is also shown that a strong nitric acid enhancement observed just above the tropopause is likely a result of NO x production by lightning activity. The measurements showed signatures of enhanced mixing between stratospheric and tropospheric air near the polar jet with some transport of water vapour into the stratosphere. Some of the air masses seen in 3-D data were encountered again 2 d later, stretched to very thin filament (horizontal thickness down to 30 km at some altitudes) rich in stratospheric tracers. This repeated measurement allowed us to directly observe and analyse the progress of mixing processes in a thin filament over 2 d. Our results provide direct insight into small-scale dynamics of the UTLS in the Rossby wave breaking region, which is of great importance to understanding STE and poleward transport in the UTLS. [ABSTRACT FROM AUTHOR]

The intensive measurement campaign CoMet 1.0 (Carbon Dioxide and Methane Mission) took place during May and June 2018, with a focus on greenhouse gases over Europe. CoMet 1.0 aimed at characterising the distribution of CH4 and CO2 over significant regional sources with the use of a fleet of research aircraft as well as validating remote sensing measurements from state-of-the-art instrumentation installed on board against a set of independent in situ observations. Here we present the results of over 55 h of accurate and precise in situ measurements of CO2 , CH4 and CO mole fractions made during CoMet 1.0 flights with a cavity ring-down spectrometer aboard the German research aircraft HALO (High Altitude and LOng Range Research Aircraft), together with results from analyses of 96 discrete air samples collected aboard the same platform. A careful in-flight calibration strategy together with post-flight quality assessment made it possible to determine both the single-measurement precision as well as biases against respective World Meteorological Organization (WMO) scales. We compare the result of greenhouse gas observations against two of the available global modelling systems, namely Jena CarboScope and CAMS (Copernicus Atmosphere Monitoring Service). We find overall good agreement between the global models and the observed mole fractions in the free tropospheric range, characterised by very low bias values for the CAMS CH4 and the CarboScope CO2 products, with a mean free tropospheric offset of 0 (14) nmolmol-1 and 0.8 (1.3) µmolmol-1 respectively, with the numbers in parentheses giving the standard uncertainty in the final digits for the numerical value. Higher bias is observed for CAMS CO2 (equal to 3.7 (1.5) µmolmol-1), and for CO the model–observation mismatch is variable with height (with offset equal to -1.0 (8.8) nmolmol-1). We also present laboratory analyses of air samples collected throughout the flights, which include information on the isotopic composition of CH4 , and we demonstrate the potential of simultaneously measuring δ13C-CH4 and δ2H-CH4 from air to determine the sources of enhanced methane signals using even a limited number of discrete samples. Using flasks collected during two flights over the Upper Silesian Coal Basin (USCB, southern Poland), one of the strongest methane-emitting regions in the European Union, we were able to use the Miller–Tans approach to derive the isotopic signature of the measured source, with values of δ2H equal to -224.7 (6.6) ‰ and δ13C to -50.9 (1.1) ‰, giving significantly lower δ2H values compared to previous studies in the area. [ABSTRACT FROM AUTHOR]

Dropsonde observations from three research aircraft in the North Atlantic region, as well as several hundred additionally launched radiosondes over Canada and Europe, were collected during the international North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) in autumn 2016. In addition, over 1000 dropsondes were deployed during NOAA's Sensing Hazards with Operational Unmanned Technology (SHOUT) and Reconnaissance missions in the west Atlantic basin, supplementing the conventional observing network for several intensive observation periods. This unique dataset was assimilated within the framework of cycled data denial experiments for a 1-month period performed with the global model of the ECMWF. Results show a slightly reduced mean forecast error (1%–3%) over the northern Atlantic and Europe by assimilating these additional observations, with the most prominent error reductions being linked to Tropical Storm Karl, Cyclones Matthew and Nicole, and their subsequent interaction with the midlatitude waveguide. The evaluation of Forecast Sensitivity to Observation Impact (FSOI) indicates that the largest impact is due to dropsondes near tropical storms and cyclones, followed by dropsondes over the northern Atlantic and additional Canadian radiosondes. Additional radiosondes over Europe showed a comparatively small beneficial impact. [ABSTRACT FROM AUTHOR]

Taking to the skies to study the atmosphere, climate and planet: Funded by a consortium of major German research institutes, HALO has quickly become the most advanced research aircraft in Europe. With an array of modern and variable equipment, it can be used for demanding measurement campaigns from aerosol particles to air pollutants and clouds. [ABSTRACT FROM AUTHOR]

This study gives a summary of lessons learned during the absolute calibration of the airborne, high-power Ka-band cloud radar HAMP MIRA on board the German research aircraft HALO. The first part covers the internal calibration of the instrument where individual instrument components are characterized in the laboratory. In the second part, the internal calibration is validated with external reference sources like the ocean surface backscatter and different air- and spaceborne cloud radar instruments. A key component of this work was the characterization of the spectral response and the transfer function of the receiver. In a wide dynamic range of 70 dB , the receiver response turned out to be very linear (residual 0.05 dB). Using different attenuator settings, it covers a wide input range from -105 to -5 dBm. This characterization gave valuable new insights into the receiver sensitivity and additional attenuations which led to a major improvement of the absolute calibration. The comparison of the measured and the previously estimated total receiver noise power (-95.3 vs. -98.2 dBm) revealed an underestimation of 2.9 dB. This underestimation could be traced back to a larger receiver noise bandwidth of 7.5 MHz (instead of 5 MHz) and a slightly higher noise figure (1.1 dB). Measurements confirmed the previously assumed antenna gain (50.0 dBi) with no obvious asymmetries or increased side lobes. The calibration used for previous campaigns, however, did not account for a 1.5 dB two-way attenuation by additional waveguides in the airplane installation. Laboratory measurements also revealed a 2 dB higher two-way attenuation by the belly pod caused by small deviations during manufacturing. In total, effective reflectivities measured during previous campaigns had to be corrected by +7.6 dB. To validate this internal calibration, the well-defined ocean surface backscatter was used as a calibration reference. With the new absolute calibration, the ocean surface backscatter measured by HAMP MIRA agrees very well (<1 dB) with modeled values and values measured by the GPM satellite. As a further cross-check, flight experiments over Europe and the tropical North Atlantic were conducted. To that end, a joint flight of HALO and the French Falcon 20 aircraft, which was equipped with the RASTA cloud radar at 94 GHz and an underflight of the spaceborne CloudSat at 94 GHz were performed. The intercomparison revealed lower reflectivities (-1.4 dB) for RASTA but slightly higher reflectivities (+1.0 dB) for CloudSat. With effective reflectivities between RASTA and CloudSat and the good agreement with GPM, the accuracy of the absolute calibration is estimated to be around 1 dB. [ABSTRACT FROM AUTHOR]

An air pollution plume from Southern and Eastern Asia, including regions in India and China, was predicted by the FLEXPART particle dispersion model to arrive in the upper troposphere over Europe on 24-25 March 2006. According to the model, the plume was exported from Southeast Asia six days earlier, transported into the upper troposphere by a warm conveyor belt, and travelled to Europe in a fast zonal flow. This is confirmed by the retrievals of carbon monoxide (CO) from AIRS satellite measurements, which are in excellent agreement with the model results over the entire transport history. The research aircraft DLR Falcon was sent into this plume west of Spain on 24 March and over Southern Europe on 25 March. On both days, the pollution plume was found close to the predicted locations and, thus, the measurements taken allowed the first detailed characterization of the aerosol content and chemical composition of an anthropogenic pollution plume after a nearly hemispheric transport event. The mixing ratios of CO, reactive nitrogen (NOy) and ozone (O3) measured in the Asian plume were all clearly elevated over a background that was itself likely elevated by Asian emissions: CO by 17-34 ppbv on average (maximum 60 ppbv) and O3 by 2-9 ppbv (maximum 22 ppbv). Positive correlations existed between these species, and a ΔO3/ΔCO slope of 0.25 shows that ozone was formed in this plume, albeit with moderate efficiency. Nucleation mode and Aitken particles were suppressed in the Asian plume, whereas accumulation mode aerosols were strongly elevated and correlated with CO. The suppression of the nucleation mode was likely due to the large pre-existing aerosol surface of the transported larger particles. Supermicron particles, likely desert dust, were found in part of the Asian pollution plume and also in surrounding cleaner air. The aerosol light absorption coefficient was enhanced in the plume (average values for individual plume encounters 0.25-0.70Mm-1), as was the fraction of non-volatile Aitken particles. This indicates that black carbon (BC) was an important aerosol component. During the flight on 25 March, which took place on the rear of a trough located over Europe, a mixture of Asian pollution and stratospheric air was found. Asian pollution was mixing into the lower stratosphere, and stratospheric air was mixing into the pollution plume in the troposphere. Turbulence was encountered by the aircraft in the mixing regions, where the thermal stability was low and Richardson numbers were below 0.2. The result of the mixing can clearly be seen in the trace gas data, which are following mixing lines in correlation plots. This mixing with stratospheric air is likely very typical of Asian air pollution, which is often lifted to the upper troposphere and, thus, transported in the vicinity of stratospheric air. [ABSTRACT FROM AUTHOR]

During May and June 2018, an intensive campaign (CoMet: Carbon dioxide and Methane mission) made atmospheric measurements of greenhouse gases over Europe. CoMet aimed to characterise the distribution of CH4 and CO2 over significant regional sources with the use of a fleet of research aircraft, as well as to validate remote sensing measurements from state-of-the-art instrumentation installed on-board against a set of independent in-situ observations.Here we present in-situ measurements of CO2 and CH4 mixing ratios made during flights performed with the German research aircraft HALO with a cavity ring-down spectrometer. We also present laboratory analyses of air samples collected throughout the flights, which include information on isotopic composition of CH4. Emphasis is placed on the data collected in the atmosphere over the Upper Silesian Coal Basin (USCB, southern Poland), one of the strongest methane-emitting regions in the European Union, which is responsible for emissions of between 0.4 and 1.5 Tg CH4 annually.In order to link the observations to emission sources, high-resolution simulations with WRF-GHG v 3.9.1.1. (10 km x10 km Europe + nested 2 km x 2 km domain over USCB), driven by short-term meteorological forecasts from the ECMWF IFS model and chemical forecasts from CAMS MACC for initial and lateral tracer boundary conditions were performed. Biogenic fluxes of CO2 were calculated online using the VPRM model driven by MODIS indices. Anthropogenic emissions over Europe were taken from the database of TNO, Department of Climate, Air and Sustainability (7 km x 7 km) and from the internal emission database of CoMet. Detailed information about the location and strength of the most important point sources within the USCB allowed for tagged tracer simulations for selected sources to be performed. The results of source partitioning of the predicted signals are presented and compared against observations performed during the campaign. [ABSTRACT FROM AUTHOR]