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Title: Comments on 'Do ultrafine cloud condensation nuclei invigorate deep convection?'

Abstract

Here we elaborated on the deficiencies associated with the theoretical arguments and model simulations in Grawbowski and Morrison (2020; GM20), and showed that the concept of convective invigoration by aerosols can be supported by both accurate theoretical analysis and explicit physics modeling with prognostic aerosols and supersaturation. Above the freezing level, droplet freezing itself does not change mass loading and the latent heat release resulting from freezing leads to an increase in the buoyancy. The derivation in GM20 is erroneous because of omitting the liquid water sink term. They also ignored the effect of enhanced latent heating from the subsequent growth processes (deposition and riming) after freezing. Regarding aerosol effect on condensational growth, the quasi-steady assumption for supersaturation as adopted in GM20 is invalidated especially when droplet number concentration is low and updraft is strong from both theoretical analysis and our bin microphysics modeling results. The quasi-steady assumption makes condensation independent of droplet number and size and therefore reduces the overall aerosol effects on cloud dynamics. Studying aerosol effects on clouds particularly deep convective clouds requires the exact solution of supersaturation. Any assumption imposed to supersaturation such as saturation adjustment and quasi-steady approximation leads to incorrect aerosol effects on diffusionalmore » growth. The exact supersaturation equation clearly shows that condensation depends on droplet number and size, and more droplets in the polluted clouds increase condensation (thus lower supersaturation), leading to enhanced buoyancy and updraft speeds.« less

Authors:
 [1];  [2]
  1. BATTELLE (PACIFIC NW LAB)
  2. Hebrew University of Jerusalem
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1767049
Report Number(s):
PNNL-SA-155536
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Journal of Atmospheric Sciences
Additional Journal Information:
Journal Volume: 78; Journal Issue: 1
Country of Publication:
United States
Language:
English
Subject:
Convective invigoration, deep convective clouds, aerosols

Citation Formats

Fan, Jiwen, and Khain, Alexander. Comments on 'Do ultrafine cloud condensation nuclei invigorate deep convection?'. United States: N. p., 2021. Web. doi:10.1175/JAS-D-20-0218.1.
Fan, Jiwen, & Khain, Alexander. Comments on 'Do ultrafine cloud condensation nuclei invigorate deep convection?'. United States. https://doi.org/10.1175/JAS-D-20-0218.1
Fan, Jiwen, and Khain, Alexander. Fri . "Comments on 'Do ultrafine cloud condensation nuclei invigorate deep convection?'". United States. https://doi.org/10.1175/JAS-D-20-0218.1.
@article{osti_1767049,
title = {Comments on 'Do ultrafine cloud condensation nuclei invigorate deep convection?'},
author = {Fan, Jiwen and Khain, Alexander},
abstractNote = {Here we elaborated on the deficiencies associated with the theoretical arguments and model simulations in Grawbowski and Morrison (2020; GM20), and showed that the concept of convective invigoration by aerosols can be supported by both accurate theoretical analysis and explicit physics modeling with prognostic aerosols and supersaturation. Above the freezing level, droplet freezing itself does not change mass loading and the latent heat release resulting from freezing leads to an increase in the buoyancy. The derivation in GM20 is erroneous because of omitting the liquid water sink term. They also ignored the effect of enhanced latent heating from the subsequent growth processes (deposition and riming) after freezing. Regarding aerosol effect on condensational growth, the quasi-steady assumption for supersaturation as adopted in GM20 is invalidated especially when droplet number concentration is low and updraft is strong from both theoretical analysis and our bin microphysics modeling results. The quasi-steady assumption makes condensation independent of droplet number and size and therefore reduces the overall aerosol effects on cloud dynamics. Studying aerosol effects on clouds particularly deep convective clouds requires the exact solution of supersaturation. Any assumption imposed to supersaturation such as saturation adjustment and quasi-steady approximation leads to incorrect aerosol effects on diffusional growth. The exact supersaturation equation clearly shows that condensation depends on droplet number and size, and more droplets in the polluted clouds increase condensation (thus lower supersaturation), leading to enhanced buoyancy and updraft speeds.},
doi = {10.1175/JAS-D-20-0218.1},
url = {https://www.osti.gov/biblio/1767049}, journal = {Journal of Atmospheric Sciences},
number = 1,
volume = 78,
place = {United States},
year = {2021},
month = {1}
}