Preprints
https://doi.org/10.5194/acp-2021-537
https://doi.org/10.5194/acp-2021-537

  12 Jul 2021

12 Jul 2021

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

The effect of marine ice nucleating particles on mixed-phase clouds

Tomi Raatikainen1, Marje Prank1, Jaakko Ahola1, Harri Kokkola2, Juha Tonttila2, and Sami Romakkaniemi2 Tomi Raatikainen et al.
  • 1Finnish Meteorological Institute, Helsinki, Finland
  • 2Finnish Meteorological Institute, Kuopio, Finland

Abstract. Shallow marine mixed-phase clouds are important for the radiative balance, but modelling their formation and dynamics is challenging. These clouds depend on boundary layer turbulence and cloud top radiative cooling, which is related to the cloud phase. The fraction of frozen droplets depends on the availability of suitable ice nucleating particles (INPs), which initiate droplet freezing. While desert dust is the dominating INP type in most regions, remote boundary layer clouds are dependent on local marine INP emissions, which are often related to biogenic sources including phytoplankton. Here we use high resolution large eddy simulations to examine the potential effects of marine emissions on boundary layer INP concentrations and their effects on clouds. Surface emissions have a direct effect on INP concentration in a typical well-mixed boundary layer whereas a steep inversion can block the import of background INPs from the free troposphere. The importance of the marine source depends on the background INP concentration, so that marine emissions become dominant with low background concentrations. For the INP budget it is also important to account for INP recycling. Finally, with the high-resolution model we show how ice nucleation hotspots and high INPs concentrations are focused on updraught regions. Our results show that marine INP emissions contribute directly to the boundary layer INP budget and therefore have an influence on mixed-phase clouds.

Tomi Raatikainen et al.

Status: open (until 23 Aug 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-537', Anonymous Referee #1, 27 Jul 2021 reply

Tomi Raatikainen et al.

Data sets

Brief description of the simulations and the data used in Raatikainen et al., ACPD, 2021 Raatikainen, T. https://a3s.fi/moac_marine_inp_ms/readme.txt

Model code and software

The source code of UCLALES-SALSA version used in Raatikainen et al., ACPD, 2021 Raatikainen, T., et al., https://github.com/UCLALES-SALSA/UCLALES-SALSA/tree/isdac_poa

Tomi Raatikainen et al.

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Short summary
Desert dust or similar ice nucleating particles are needed to initiate cloud droplet freezing at temperatures common in shallow clouds. In this work we examine how ice nucleating particles that are released from sea surface impact marine clouds. Our high-resolution simulations show that turbulent updraughts carry these particles up to the clouds, where they initiate cloud droplet freezing. Sea surface emissions become more important with decreasing background dust concentrations.
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