How much can the vertical distribution of black carbon affect its global direct radiative forcing?

Colin Zarzycki, Tami C. Bond

Research output: Contribution to journalArticle

88 Citations (Scopus)

Abstract

Black carbon (BC) has an increased forcing per unit mass when it is located above reflective clouds. To explore sensitivity of forcing to aerosol vertical location, we used a column radiative transfer model to produce globally-averaged values of normalized direct radiative forcing (NDRF) for BC over and under different types of clouds. We developed a simple column-weighting scheme based on the mass fractions of BC that are over and under clouds in measured vertical profiles. The resulting NDRF is in good agreement with global 3-D model estimates, supporting the column-weighted model as a tool for exploring uncertainties due to diversity in vertical distribution. BC above low clouds accounts for about 20% of the global burden but 50% of the forcing. We estimate maximum-minimum spread in NDRF due to modeled profiles as about 40% and uncertainty as about 25%. Because models overestimate BC in the upper troposphere compared with measurements, modeled NDRF might need to be reduced by about 15%. Redistributing BC within the lowest 4 km of the atmosphere affects modeled NDRF by only about 5% and cannot account for very high forcing estimates.

Original languageEnglish (US)
Article numberL20807
JournalGeophysical Research Letters
Volume37
Issue number20
DOIs
StatePublished - Oct 1 2010

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radiative forcing
vertical distribution
black carbon
carbon
estimates
profiles
troposphere
vertical profile
radiative transfer
aerosols
aerosol
atmospheres
atmosphere
sensitivity

All Science Journal Classification (ASJC) codes

  • Earth and Planetary Sciences(all)
  • Geophysics

Cite this

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abstract = "Black carbon (BC) has an increased forcing per unit mass when it is located above reflective clouds. To explore sensitivity of forcing to aerosol vertical location, we used a column radiative transfer model to produce globally-averaged values of normalized direct radiative forcing (NDRF) for BC over and under different types of clouds. We developed a simple column-weighting scheme based on the mass fractions of BC that are over and under clouds in measured vertical profiles. The resulting NDRF is in good agreement with global 3-D model estimates, supporting the column-weighted model as a tool for exploring uncertainties due to diversity in vertical distribution. BC above low clouds accounts for about 20{\%} of the global burden but 50{\%} of the forcing. We estimate maximum-minimum spread in NDRF due to modeled profiles as about 40{\%} and uncertainty as about 25{\%}. Because models overestimate BC in the upper troposphere compared with measurements, modeled NDRF might need to be reduced by about 15{\%}. Redistributing BC within the lowest 4 km of the atmosphere affects modeled NDRF by only about 5{\%} and cannot account for very high forcing estimates.",
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How much can the vertical distribution of black carbon affect its global direct radiative forcing? / Zarzycki, Colin; Bond, Tami C.

In: Geophysical Research Letters, Vol. 37, No. 20, L20807, 01.10.2010.

Research output: Contribution to journalArticle

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AU - Zarzycki, Colin

AU - Bond, Tami C.

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