skip to main content
DOE PAGES title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Comments on “A limited-area-model case study of the effects of sub-grid scale variations in relative humidity and cloud upon the direct radiative forcing of sulfate aerosol”

Abstract

HRD indicated that, because GCMs do not account for sub-grid scale variability in RH and its impact on water uptake and aerosol radiative properties, GCM estimates of direct radiative forcing are systematically too low. We suggest that, because water uptake is dominated by conditions that favor aerosol activation and produce cloud, the GCM estimates of direct radiative forcing may not be so far off. Direct radiative forcing within sub-grid scale clouds is likely to be negligible because so many of the aerosol particles in clouds are activated, and hence cannot contribute to direct radiative forcing (although activated aerosol material in cloud droplets still scatters sunlight, the effective radius of the cloud droplets is much larger than that of less than if the particles remained suspended aerosols).Correspondingly, however, there is the potential for indirect radiative forcing by these sub-grid scale clouds, and a GCM neglecting sub-grid scale clouds would neglect this contribution to indirect radiative forcing. The calculation of this indirect radiative forcing involves consideration of competition between natural and anthropogenic aerosol particles as cloud condensation nuclei and is beyond the scope of our comments. The reader should also consider that, because water uptake and aerosol activation are closely related processes,more » these conclusions depend little on the aerosol particle composition; although insoluble particles are less likely to be activated, water uptake is much less than for the more readily activated soluble particles. Thus, the conditions most likely to produce the greatest water uptake (high RH and large solubleable aerosol particles) are also those conditions most favorable for aerosol activation.« less

Authors:
ORCiD logo [1]; ORCiD logo [1]
  1. Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE; NASA Mission to Planet Earth Program
OSTI Identifier:
1511457
Report Number(s):
PNNL-SA-29414
Journal ID: ISSN 0094-8276
Grant/Contract Number:  
AC05-76RL01830; NAG5-4643
Resource Type:
Accepted Manuscript
Journal Name:
Geophysical Research Letters
Additional Journal Information:
Journal Volume: 25; Journal Issue: 7; Journal ID: ISSN 0094-8276
Publisher:
American Geophysical Union
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES

Citation Formats

Ghan, Steven J., and Easter, Richard C. Comments on “A limited-area-model case study of the effects of sub-grid scale variations in relative humidity and cloud upon the direct radiative forcing of sulfate aerosol”. United States: N. p., 1998. Web. doi:10.1029/98GL50357.
Ghan, Steven J., & Easter, Richard C. Comments on “A limited-area-model case study of the effects of sub-grid scale variations in relative humidity and cloud upon the direct radiative forcing of sulfate aerosol”. United States. doi:10.1029/98GL50357.
Ghan, Steven J., and Easter, Richard C. Wed . "Comments on “A limited-area-model case study of the effects of sub-grid scale variations in relative humidity and cloud upon the direct radiative forcing of sulfate aerosol”". United States. doi:10.1029/98GL50357. https://www.osti.gov/servlets/purl/1511457.
@article{osti_1511457,
title = {Comments on “A limited-area-model case study of the effects of sub-grid scale variations in relative humidity and cloud upon the direct radiative forcing of sulfate aerosol”},
author = {Ghan, Steven J. and Easter, Richard C.},
abstractNote = {HRD indicated that, because GCMs do not account for sub-grid scale variability in RH and its impact on water uptake and aerosol radiative properties, GCM estimates of direct radiative forcing are systematically too low. We suggest that, because water uptake is dominated by conditions that favor aerosol activation and produce cloud, the GCM estimates of direct radiative forcing may not be so far off. Direct radiative forcing within sub-grid scale clouds is likely to be negligible because so many of the aerosol particles in clouds are activated, and hence cannot contribute to direct radiative forcing (although activated aerosol material in cloud droplets still scatters sunlight, the effective radius of the cloud droplets is much larger than that of less than if the particles remained suspended aerosols).Correspondingly, however, there is the potential for indirect radiative forcing by these sub-grid scale clouds, and a GCM neglecting sub-grid scale clouds would neglect this contribution to indirect radiative forcing. The calculation of this indirect radiative forcing involves consideration of competition between natural and anthropogenic aerosol particles as cloud condensation nuclei and is beyond the scope of our comments. The reader should also consider that, because water uptake and aerosol activation are closely related processes, these conclusions depend little on the aerosol particle composition; although insoluble particles are less likely to be activated, water uptake is much less than for the more readily activated soluble particles. Thus, the conditions most likely to produce the greatest water uptake (high RH and large solubleable aerosol particles) are also those conditions most favorable for aerosol activation.},
doi = {10.1029/98GL50357},
journal = {Geophysical Research Letters},
number = 7,
volume = 25,
place = {United States},
year = {1998},
month = {4}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Citation Metrics:
Cited by: 8 works
Citation information provided by
Web of Science

Save / Share: