• Jacobson, M. Z., 2002: Control of fossil-fuel particulate black carbon and organic matter, possibly the most effective method of slowing global warming. J. Geophys. Res., 107 .4410, doi:10.1029/2001JD001376.

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  • Jacobson, M. Z., 2003a: Reply to comment by J. Feichter et al. on “Control of fossil-fuel particulate black carbon and organic matter, possibly the most effective method of slowing global warming.’’. J. Geophys. Res., 108 .4768, doi:10.1029/2002JD003299.

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  • Jacobson, M. Z., 2003b: Reply to comment by J. E. Penner on “Control of fossil-fuel particulate black carbon and organic matter, possibly the most effective method of slowing global warming.’’. J. Geophys. Res., 108 .4772, doi:10.1029/2003JD003403.

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  • Jacobson, M. Z., 2003c: Reply to comment by D. P. Chock et al. on “Control of fossil-fuel particulate black carbon and organic matter, possibly the most effective method of slowing global warming.’’. J. Geophys. Res., 108 .4770, doi:10.1029/2003JD003707.

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  • Jacobson, M. Z., 2004: Climate response of fossil-fuel and biofuel soot, accounting for soot’s feedback to snow and sea ice albedo and emissivity. J. Geophys. Res., 109 .D21201, doi:10.1029/2004JD004945.

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  • Johnson, B. T., 2005: The semidirect effect: Comparisons of a single-column model with large eddy simulation for marine stratocumulus. J. Climate, 18 , 119130.

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Comments on “The Semidirect Aerosol Effect: Comparison of a Single-Column Model with Large Eddy Simulation for Marine Stratocumulus’’

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  • 1 Department of Civil and Environmental Engineering, Stanford University, Stanford, California
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Corresponding author address: Dr. Mark Z. Jacobson, Terman Engineering Center, M-31, Stanford University, Stanford, CA 94305-4020. Email: jacobson@stanford.edu

Corresponding author address: Dr. Mark Z. Jacobson, Terman Engineering Center, M-31, Stanford University, Stanford, CA 94305-4020. Email: jacobson@stanford.edu

Johnson (2005) compared single-column model “semidirect’’ radiative forcing results from a large-eddy simulation (LES) model with those from the National Center for Atmospheric Research (NCAR) single-column community climate model (SCCM) and found that the SCCM gave positive forcings a factor of 5 smaller than those of the LES. I do not disagree with this general result.

However, in the article, Johnson cited three commentaries that criticized results from Jacobson (2002) for various reasons, yet he did not cite or discuss the responses to these commentaries, thereby leaving readers with a misleading impression that the criticisms were either correct or unanswered. In my opinion, when a commentary is cited to criticize someone else’s work, the response to the commentary should also be cited. The citations for the responses to the commentaries omitted by Johnson (2005) are provided herein (Jacobson 2003a, b,c).

Furthermore, Johnson (2005) concluded that “global studies into the influence of absorbing aerosols on clouds [citations omitted] have necessarily relied on numerically efficient models where the vertical resolution is restricted and cloud parameterizations are just as simple as in the SCMM.’’ Whereas this statement appears true for the studies cited, it is largely misleading with respect to Jacobson (2002, 2004), since those two studies also examined the effect of absorbing aerosols on climate through their feedback to clouds yet (a) treated cloud microphysics in more detail than in the others papers cited or in the LES model of Johnson (2005) and (b) treated subgrid clouds.

Whereas, Johnson (2005) did state, “Many state-of-the-art GCMs now have prognostic treatment of cloud water/ice [citations omitted], ’’ this specific statement ignored Jacobson (2002, 2004), even though these are the only global absorbing-aerosol studies to date to treat the evolution of size-resolved clouds from size-resolved aerosol particles (as opposed to treating cloud liquid and ice as bulk or modal parameters). Specifically, Jacobson treated the evolution of size-resolved liquid, ice, and graupel from size-resolved aerosol particles, accounting for size-resolved hydrometeor condensation/evaporation/deposition/sublimation, hydrometeor–hydrometeor coagulation (liquid–liquid, liquid–ice, liquid–graupel, ice–ice, ice–graupel, and graupel–graupel), aerosol–hydrometeor coagulation, large liquid drop breakup, settling, evaporative cooling during drop settling, evaporative freezing (freezing during drop cooling), heterogeneous–homogeneous freezing, contact freezing, melting, evaporation, sublimation, release of aerosol cores upon evaporation/sublimation, irreversible aqueous chemistry, gas washout, and lightning generation from size-resolved coagulation among ice hydrometeors. Johnson’s LES model, which had better spatial resolution, did not treat evolution of clouds from aerosol particles; it treated soot absorption by adding a slab soot layer to an atmospheric cloud layer. This brings up an interesting issue as to whether a high-resolution model with poor microphysics and limited boundary conditions can provide a better climate response than a course-resolution model with detailed microphysics.

In sum, whereas, global model results need improvement and will get better as resolution and treatment of physical processes are improved, significant differences already exist among global models, and such differences should be recognized and clarified explicitly and clearly, where possible, so that global models are not stereotyped to have largely the same weaknesses as each other.

REFERENCES

  • Jacobson, M. Z., 2002: Control of fossil-fuel particulate black carbon and organic matter, possibly the most effective method of slowing global warming. J. Geophys. Res., 107 .4410, doi:10.1029/2001JD001376.

    • Search Google Scholar
    • Export Citation
  • Jacobson, M. Z., 2003a: Reply to comment by J. Feichter et al. on “Control of fossil-fuel particulate black carbon and organic matter, possibly the most effective method of slowing global warming.’’. J. Geophys. Res., 108 .4768, doi:10.1029/2002JD003299.

    • Search Google Scholar
    • Export Citation
  • Jacobson, M. Z., 2003b: Reply to comment by J. E. Penner on “Control of fossil-fuel particulate black carbon and organic matter, possibly the most effective method of slowing global warming.’’. J. Geophys. Res., 108 .4772, doi:10.1029/2003JD003403.

    • Search Google Scholar
    • Export Citation
  • Jacobson, M. Z., 2003c: Reply to comment by D. P. Chock et al. on “Control of fossil-fuel particulate black carbon and organic matter, possibly the most effective method of slowing global warming.’’. J. Geophys. Res., 108 .4770, doi:10.1029/2003JD003707.

    • Search Google Scholar
    • Export Citation
  • Jacobson, M. Z., 2004: Climate response of fossil-fuel and biofuel soot, accounting for soot’s feedback to snow and sea ice albedo and emissivity. J. Geophys. Res., 109 .D21201, doi:10.1029/2004JD004945.

    • Search Google Scholar
    • Export Citation
  • Johnson, B. T., 2005: The semidirect effect: Comparisons of a single-column model with large eddy simulation for marine stratocumulus. J. Climate, 18 , 119130.

    • Search Google Scholar
    • Export Citation
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