08 Nov 2021

08 Nov 2021

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

Stability dependent increases in liquid water with droplet number in the Arctic

Rebecca Jonette Murray-Watson and Edward Gryspeerdt Rebecca Jonette Murray-Watson and Edward Gryspeerdt
  • Space and Atmospheric Physics Group, Imperial College London, UK

Abstract. The effects of aerosols on cloud microphysical properties are a large source of uncertainty when assessing anthropogenic climate change. The aerosol-cloud relationship is particularly unclear in high-latitude polar regions due to a limited number of observations. Cloud liquid water path (LWP) is an important control on cloud radiative properties, particularly in the Arctic, where clouds play a central role in the surface energy budget. Therefore, understanding how aerosols may alter cloud LWP is important, especially as aerosol sources such as industry and shipping move further north in a warming Arctic.

Using satellite data, this work investigates the effects of aerosols on liquid Arctic clouds over open ocean by considering the relationship between cloud droplet number concentration (Nd) and LWP, an important component of the aerosol-LWP relationship. The LWP response to Nd varies significantly across the region, with increases in LWP with Nd observed at very high latitudes in multiple satellite datasets, with this positive signal observed most strongly during the summer months. This result is in contrast to the negative response typically seen in global satellite studies and previous work on Arctic clouds showing little LWP response to aerosols.

The lower tropospheric stability (LTS) was found to be the driving force behind the spatial variations in LWP response, strongly influencing the sign and magnitude of the Nd-LWP relationship, with increases in LWP in high stability environments. The influence of humidity varied depending on the stability, with little impact at low LTS but a strong influence at high. The background Nd state does not seem to dominate the LWP response, despite the non-linearities in the relationship. As the LTS is projected to decrease in a future, warmer Arctic, these results show that increases may produce lower cloud water paths, offsetting their shortwave cooling effect.

Rebecca Jonette Murray-Watson and Edward Gryspeerdt

Status: open (until 20 Dec 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-861', Anonymous Referee #1, 24 Nov 2021 reply
  • RC2: 'Comment on acp-2021-861', Anonymous Referee #2, 24 Nov 2021 reply

Rebecca Jonette Murray-Watson and Edward Gryspeerdt

Rebecca Jonette Murray-Watson and Edward Gryspeerdt


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Short summary
Clouds are important to the Arctic surface energy budget, but the impact of aerosols on their properties is largely uncertain. This work uses satellite data to measure the liquid water path-droplet number relationship, a key aspect of how aerosols affect clouds. The lower tropospheric stability (LTS) strongly influences the relationship, with lower cloud water at lower stability. As the Arctic warms, LTS is projected to decrease, potentially resulting in clouds with a weaker cooling effect.