Albrecht effect a.k.a. the second aerosol indirect effect

Differences in precipitation 

“efficiency” between continental and marine 

clouds

Battan, L. J., and R. R. Braham, 1956: A Study of Convective Precipitation Based on Cloud and Radar Observations. J. Meteorol., 13, 587–91

Squires, P., 1958: The Microstructure and Colloidal Stability of Warm Clouds. Tellus, 10, 262–71.Hudson, J. G., 1983: Effects of CCN Concentrations on Stratus Clouds. J. Atmos. Sci., 40, 480–86.

Hocking size limit

Later calculations for collision 

efficiency of small drops

A Short Course in Cloud Physics, Third Edition (International Series in Natural Philosophy), M K Yau, R R Rogers

• Sharp drop‐off in collision efficiency when small drop radius r < 8 m (the Hocking limit)

Albrecht “effect”• Mentions effect of drizzle on stabilizing PBL• Model: Albrecht trade‐Cu model, modified to include precip. Models cloud 

fractional cover using an RH‐based parameterization. 

Key processes controlling PBL clouds

Radiative (left) and latent (right) heating rates

Informed by aircraft 

observations

From Brost, R. A., J. C. Wyngaard, and D. H. Lenschow, 1982: Marine Stratocumulus Layers. Part II: Turbulence Budgets. J. Atmos. Sci., 39, 818–36.Also…Nicholls, S., and J. Leighton., 1986: An Observational Study of the Structure of Stratiform Cloud Sheets: Part I. Structure. Quart. J. Roy. Meteorol. Soc., 112, 431–60.

Albrecht (1989)

Key insights:• Drizzle formation in marine stratocumulus is sensitive to droplet size• Suppressed drizzle from increasing CCN/Nd can lead to more water 

retention, thereby extending the cloud lifetime/cloud cover and further increasing the albedo increases proposed by Twomey

Albrecht, Bruce A., 1989: Aerosols, Cloud Microphysics, and Fractional Cloudiness. Science, 245, 1227–30.

I suggest a 1989 Bourgogne from the Côte de Nuits region. Simple, light flavors belie a much more complex pallet of black fruit and spice. Similarly, Albrecht's relatively simple pallet of precipitation efficiency overlays a complex texture of interactions between large scale dynamical and thermodynamic changes, which are somewhat predictable and the changes in aerosol in a warmed climate as well as a complex network of feedbacks between aerosol, precipitation, and cloud fraction. The deep earthy texture of the Bourgogne compliments the subtle interplay of additional feedbacks on the cloud fraction, such as the enhanced stabilization of the boundary layer as precipitation evaporates into the subcloud layer.

A sharp cheddar or munster is a good side.

Post‐Albrecht

• Observations have clarified importance of CCN/Nd for suppressing precipitation in warm, stratiform cloud

• Evidence for suppression in warm convective clouds, and deeper clouds is lacking

• Cloud‐resolving models show similar effects, but do not always show cloud cover or condensate increases……later papers

• Appreciation of importance of cloud effects on aerosols

Cloud effects on aerosols

Twomey, S., and T. A. Wojciechowski, 1969: Observations of the Geographical Variation of Cloud Nuclei. J. Atmos. Sci., 26, 648–51.

Precipitation “susceptibility” metric

Analogous to albedo susceptibility, precipitation susceptibility expresses sensitivity of precipitation rate to cloud droplet concentration:

Feingold, G., and H. Siebert, Cloud-aerosol interactions from the micro to the cloud scale. Chapter 14 in Strungmann Forum report, vol. 2. Cambridge, MA: The MIT press., 2009.

Mann, Julian A. L., J. Christine Chiu, Robin J. Hogan, Ewan J. O’Connor, Tristan S. L’Ecuyer, Thorwald H. M. Stein, and Anne Jefferson, 2014: Aerosol Impacts on Drizzle Properties in Warm Clouds from ARM Mobile Facility Maritime and Continental Deployments. J. Geophys. Res. 119, 2013JD021339.

Present day: understanding various 

observations of precipitation 

susceptibility and reconciling with models