Remote Sensing of Droplet Number Concentration in Warm Clouds: A Review of the Current State of Knowledge and Perspectives

Reviews of Geophysics
Daniel P GrosvenorJohannes Quaas

Abstract

The cloud droplet number concentration (N d) is of central interest to improve the understanding of cloud physics and for quantifying the effective radiative forcing by aerosol-cloud interactions. Current standard satellite retrievals do not operationally provide N d, but it can be inferred from retrievals of cloud optical depth (τ c) cloud droplet effective radius (r e) and cloud top temperature. This review summarizes issues with this approach and quantifies uncertainties. A total relative uncertainty of 78% is inferred for pixel-level retrievals for relatively homogeneous, optically thick and unobscured stratiform clouds with favorable viewing geometry. The uncertainty is even greater if these conditions are not met. For averages over 1° ×1° regions the uncertainty is reduced to 54% assuming random errors for instrument uncertainties. In contrast, the few evaluation studies against reference in situ observations suggest much better accuracy with little variability in the bias. More such studies are required for a better error characterization. N d uncertainty is dominated by errors in r e, and therefore, improvements in r e retrievals would greatly improve the quality of the N d retrievals. Recommendations are made for how t...Continue Reading

References

Oct 3, 2015·Science·Matthew J BealsJeffrey L Stith
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Mar 6, 2016·Proceedings of the National Academy of Sciences of the United States of America·Daniel RosenfeldMeinrat O Andreae
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Citations

Jul 15, 2020·Proceedings of the National Academy of Sciences of the United States of America·Matthew W ChristensenPhilip Stier
Jul 29, 2020·Proceedings of the National Academy of Sciences of the United States of America·Isabel L McCoyHamish Gordon
Feb 7, 2020·Journal of Geophysical Research. Atmospheres : JGR·Dongwei FuGuangyu Zhao
Oct 11, 2019·Journal of Advances in Modeling Earth Systems·A Bodas-SalcedoG S Elsaesser
Aug 1, 2020·Reviews of Geophysics·N BellouinB Stevens
Oct 2, 2020·Journal of Advances in Modeling Earth Systems·Hugh MorrisonLulin Xue
Aug 2, 2019·Nature·Velle TollNicolas Bellouin
Dec 5, 2020·Journal of Geophysical Research. Atmospheres : JGR·Ali Hossein MardiArmin Sorooshian
Dec 5, 2020·Atmospheric Chemistry and Physics·Alexander B MacDonaldArmin Sorooshian
Jun 24, 2021·Journal of Geophysical Research. Atmospheres : JGR·Abdulmonam M AldhaifArmin Sorooshian

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Methods Mentioned

BETA
light scattering

Software Mentioned

ORAC
CLOUDSAT
CALIPSO
VOCALS
Cloudnet
HELIOS
ACTOS
CALIOP
POLDER
MODIS

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