Preprints
https://doi.org/10.5194/acp-2021-334
https://doi.org/10.5194/acp-2021-334

  30 Apr 2021

30 Apr 2021

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

What is Adiabatic Fraction in Cumulus Clouds: High-Resolution Simulations with Passive Tracer

Eshkol Eytan1, Ilan Koren1, Orit Altaratz1, Mark Pinsky2, and Alexander Khain2 Eshkol Eytan et al.
  • 1Department of Earth and Planetary Science, Weizmann Institute of Science, Rehovot, Israel
  • 2Institute of Earth Science, Hebrew University, Jerusalem, Israel

Abstract. The process of mixing in warm convective clouds and its effects on microphysics, is crucial for an accurate description of cloud fields, weather, and climate. Still, it remains an open question in the field of cloud physics. Adiabatic regions in the cloud could be considered as non-mixed areas and therefore serve as an important reference to mixing. Therefore, the adiabatic fraction (AF) is an important parameter that estimates the mixing level in the cloud in a simple way. Here, we test different methods of AF calculations using high-resolution (10 m) simulations of isolated warm Cumulus clouds. The calculated AFs are compared with a normalized concentration of a passive tracer, which is a measure of dilution by mixing. This comparison enables us to examine how well the AF parameter can determine mixing effects, and to estimate the accuracy of different approaches used to calculate it. The sensitivity of the calculated AF to the choice of different equations, vertical profiles, cloud base height, and its linearity with height are all tested. Moreover, the use of a detailed spectral bin microphysics scheme demonstrates that the accuracy of the saturation adjustment assumption depends on aerosol concentration, and leads to an underestimation of AF in pristine environments.

Eshkol Eytan et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-334', Anonymous Referee #1, 15 Jun 2021
  • RC2: 'Comment on acp-2021-334', Anonymous Referee #2, 19 Jun 2021

Eshkol Eytan et al.

Eshkol Eytan et al.

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Short summary
The adiabatic fraction of cloudy volumes is an important and commonly used variable, as mixing is still an open question in cloud physics. High-resolution simulations of single clouds with a passive tracer are used to test the accuracy of the different methods that were used in previous studies to calculate the adiabatic fraction. The results emphasize the limitation of adiabatic fraction and the errors that are introduced with different assumptions under some environmental conditions.
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