15 Jun 2023
 | 15 Jun 2023

Above Cloud CCN Concentrations Help to Sustain Some Arctic Low-Level Clouds

Lucas J. Sterzinger and Adele L. Igel

Abstract. Recent studies have reported observations of enhanced aerosol concentrations directly above the Arctic boundary layer, and it has been suggested that Arctic boundary layer clouds could entrain these aerosol and activate them. We use an idealized LES modeling framework where aerosol concentrations are kept low in the boundary layer, and increased up to 50x in the free troposphere. We find that the simulations with higher tropospheric aerosol concentrations persisted for longer and had higher liquid water path. This is due to direct entrainment of the tropospheric aerosol into the cloud layer which results in a precipitation suppression from the increase in cloud droplet number and in stronger radiative cooling at cloud top due to the higher liquid water content at cloud top, which causes stronger circulations maintaining the cloud in the absence of surface forcing. Together, these two responses result in a more well-mixed boundary layer with a top that does not move rapidly in time such that it remains in contact with the tropospheric aerosol reservoir and can maintain entrainment of those aerosol particles. The boundary layer aerosol and cloud droplet concentrations, however, remained low in all simulations. Surface based measurements in this case would not necessarily suggest the influence of tropospheric aerosol on the cloud, despite it being necessary for stable cloud persistence.

Lucas J. Sterzinger and Adele L. Igel

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-2023-1253', Anonymous Referee #1, 31 Jul 2023
  • RC2: 'Comment on egusphere-2023-1253', Anonymous Referee #2, 08 Aug 2023

Lucas J. Sterzinger and Adele L. Igel

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lsterzinger/sterzinger-igel-2023-scripts Lucas J. Sterzinger

Lucas J. Sterzinger and Adele L. Igel


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Short summary
We find in our study using idealized large eddy simulations that clouds forming in the Arctic in environments with low concentrations of aerosol particles may be sustained by mixing in new particles through cloud top. Observations show that higher concentrations of these particles regularly exist above cloud top in concentrations that are sufficient to promote this sustenance.