Preprints
https://doi.org/10.5194/acp-2020-1285
https://doi.org/10.5194/acp-2020-1285

  05 Jan 2021

05 Jan 2021

Review status: this preprint is currently under review for the journal ACP.

New particle formation inside ice clouds: In-situ observations in the tropical tropopause layer of the 2017 Asian Monsoon Anticyclone

Ralf Weigel1, Christoph Mahnke2,a, Manuel Baumgartner1,3, Martina Krämer1,4, Peter Spichtinger1, Nicole Spelten4, Armin Afchine4, Christian Rolf4, Silvia Viciani5, Francesco D'Amato5, Holger Tost1, and Stephan Borrmann1,2 Ralf Weigel et al.
  • 1Institut für Physik der Atmosphäre, Johannes Gutenberg Universität, Mainz, Germany
  • 2Partikelchemie, Max-Planck-Institut für Chemie, Mainz, Germany
  • 3Zentrum für Datenverarbeitung, Johannes Gutenberg University, Mainz, Germany
  • 4Institute of Energy and Climate Research (IEK-7), Forschungszentrum Jülich, Jülich, Germany
  • 5National Institute of Optics - National Research Council (CNR-INO), Florence, Italy
  • anow at: the Institute of Energy and Climate Research (IEK-8), Forschungszentrum Jülich, Jülich, Germany

Abstract. From 27 July to 10 August 2017 the airborne StratoClim mission took place in Kathmandu, Nepal where eight mission flights were conducted with the M-55 Geophysica up to altitudes of 20 km. New Particle Formation (NPF) was identified by the abundant presence of ultrafine aerosols, with particle diameters dp smaller than 15 nm, which were in-situ detected by means of condensation nuclei counting techniques. NPF fields in clear-skies as well as in the presence of cloud ice particles (dp > 3 µm) were encountered at upper troposphere/lowermost stratosphere (UT/LS) levels and within the Asian Monsoon Anticyclone (AMA). NPF-generated ultrafine particles in elevated concentrations (Nuf) were frequently found together with cloud ice (in number concentrations Nice of up to 3 cm−3) at heights between ~ 11 km and 16 km. From a total measurement time of ~ 22.5 hours above 10 km altitude, in-cloud NPF was in sum detected over ~ 1.3 hours (~ 50 % of all NPF records throughout StratoClim). Maximum Nuf of up to ~ 11000 cm−3 were detected coincidently with intermediate ice particle concentrations Nice of 0.05–0.1 cm−3 at comparatively moderate carbon monoxide (CO) contents of ~ 90–100 nmol mol−1. Neither under clear-sky nor during in-cloud NPF do the highest Nuf concentrations correlate with the highest CO mixing ratios, suggesting that an elevated pollutant load is not a prerequisite for NPF. Under clear-air conditions, NPF with elevated Nuf (> 8000 cm−3) occurred slightly less often than within clouds. In the presence of cloud ice, NPF with Nuf between 1500–4000 cm−3 were observed about twice as often as under clear air conditions. When ice water contents exceeded 1000 µmol mol−1 in very cold air (< 195 K) at tropopause levels NPF was not found. This may indicate a reduction of NPF once a strong overshoot is prevalent together with the presence of mainly liquid-origin ice particles. In the presence of in-situ cirrus near the cold point tropopause very recent NPF or events of remarkable strength (mixing ratios nuf > 5000 mg−1) were rarely observed (~ 6 % of in-cloud NPF data). For specifying the constraining mechanisms for NPF possibly imposed by the microphysical properties of the cloud elements, the integral radius (IR) of the ice cloud population was identified as the most practicable indicator. Neither of both, the number of ice particles or the free distance between the ice particles, is clearly related to the NPF-rate detected. The results of a numerical simulation indicates how the IR affects the supersaturation of a condensable vapour, such as sulphuric acid, and that IR determines the effective limitation of NPF rates due to cloud ice.

Ralf Weigel et al.

Status: open (extended)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2020-1285', Anonymous Referee #1, 07 Mar 2021 reply
  • RC2: 'RC1 correction', Anonymous Referee #1, 07 Mar 2021 reply
  • RC3: 'RC1 correction', Anonymous Referee #1, 07 Mar 2021 reply

Ralf Weigel et al.

Ralf Weigel et al.

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Short summary
In July and August 2017, the StratoClim mission took place in Nepal with 8 flights of the M-55 Geophysica up to 20 km in the Asian monsoon anticyclone. New particle formation (NPF) in and cloud ice were detected in-situ by the abundance of ultrafine aerosols (> 15 nm) together with ice particles (> 3 µm). NPF was most frequently observed below the tropopause (bottom TTL) with fractions of non-volatile residues of up to 15 %. Observed intra-cloud NPF indicates its importance for the TTL composition.
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