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End date: 2021 × Start date: 2021 × End date: 2019 × Publisher: London : Springer Nature × WGL Institute: TROPOS ×

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    Impact of vertical air motions on ice formation rate in mixed-phase cloud layers
    (London : Springer Nature, 2019) Bühl, Johannes; Seifert, Patric; Engelmann, Ronny; Ansmann, Albert
    The relationship between vertical air velocity at cloud base and primary ice formation has been measured for shallow mixed-phase cloud layers (thickness <380 m) by means of ground-based cloud radar and Doppler lidar. For layers with a cloud-top temperature below −12 °C, an increase of vertical-velocity standard deviation from 0.1 to 1.0 m s−1 leads to an increase in the mass flux of ice water by two orders of magnitude. The cloud layers under study were selected in such a way that secondary ice-formation processes played a minor role, and primary ice formation was the dominant source of ice formation. Phenomenological parameterizations of the ice mass and the ice mass flux as functions of standard deviation of vertical air velocity are given.
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    Formation and composition of the UTLS aerosol
    (London : Springer Nature, 2019) Martinsson, Bengt G.; Friberg, Johan; Sandvik, Oscar S.; Hermann, Markus; van Velthoven, Peter F. J.; Zahn, Andreas
    Stratospheric aerosol has long been seen as a pure mixture of sulfuric acid and water. Recent measurements, however, found a considerable carbonaceous fraction extending at least 8 km into the stratosphere. This fraction affects the aerosol optical depth (AOD) and the radiative properties, and hence the radiative forcing and climate impact of the stratospheric aerosol. Here we present an investigation based on a decade (2005–2014) of airborne aerosol sampling at 9–12 km altitude in the tropics and the northern hemisphere (NH) aboard the IAGOS-CARIBIC passenger aircraft. We find that the chemical composition of tropospheric aerosol in the tropics differs markedly from that at NH midlatitudes, and, that the carbonaceous stratospheric aerosol is oxygen-poor compared to the tropospheric aerosol. Furthermore, the carbonaceous and sulfurous components of the aerosol in the lowermost stratosphere (LMS) show strong increases in concentration connected with springtime subsidence from overlying stratospheric layers. The LMS concentrations significantly exceed those in the troposphere, thus clearly indicating a stratospheric production of not only the well-established sulfurous aerosol, but also a considerable but less understood carbonaceous component. © 2019, The Author(s).