Preprints
https://doi.org/10.5194/egusphere-2023-450
https://doi.org/10.5194/egusphere-2023-450
28 Mar 2023
 | 28 Mar 2023

Water isotopic characterisation of the cloud-circulation coupling in the North Atlantic trades. Part 2: The imprint of the atmospheric circulation at different scales

Leonie Villiger and Franziska Aemisegger

Abstract. Water vapour isotopes reflect the history of moist atmospheric processes encountered by the vapour since evaporation from the ocean. This study focuses on water isotope variability in the winter trades near Barbados at cloud base, which has been identified as an important level for understanding the net radiative effects of shallow cumuli. The analyses are based on nested convection resolving COSMOiso simulations during the EUREC4A field campaign. The two main findings are that (i) the contrasting isotope and humidity characteristics in clear-sky versus cloudy cloud base environments emerge due to vertical transport on time scales of 12 hours associated with local, convective circulations and show a clear diel cycle; and (ii) the cloud base isotopes are, in addition, sensitive to variations in the large-scale circulation on time scales of several days, which shows on average a Hadley-type subsidence but occasionally much stronger descent related to extratropical dry intrusions. This investigation, based on high-resolution isotope-enabled simulations in combination with trajectory analyses, reveals how dynamical processes at different scales act in concert to produce the observed humidity variations at the base of trade-wind cumuli.

Leonie Villiger and Franziska Aemisegger

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-450', Anonymous Referee #1, 17 Apr 2023
  • RC2: 'Comment on egusphere-2023-450', Ann Kristin Naumann, 28 Apr 2023
  • AC1: 'Comment on egusphere-2023-450', Leonie Villiger, 20 Sep 2023

Leonie Villiger and Franziska Aemisegger

Leonie Villiger and Franziska Aemisegger

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Short summary
In this study, three numerical simulations performed with an isotope-enabled weather forecast model are used to investigate the cloud-circulation coupling between shallow trade-wind cumulus clouds and atmospheric circulations on different scales. It is shown that stable water isotopes near cloud base in the tropical reflect (1) the diel cycle of the atmospheric circulation which drives the formation and dissipation of clouds and (2) changes in the large-scale circulation over the North Atlantic.