Cloud microphysical response to entrainment and mixing is locally inhomogeneous and globally homogeneous: Evidence from the lab
- Department of Physics and Atmospheric Sciences Program, Michigan Technological University, Houghton, MI 49931
- Department of Physics and Atmospheric Sciences Program, Michigan Technological University, Houghton, MI 49931, Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder Chemical Sciences Lab, National Oceanic and Atmospheric Administration, Boulder, CO 80309
- Brookhaven National Laboratory, Upton, NY 11973
Entrainment of dry air into clouds strongly influences cloud optical and precipitation properties and the response of clouds to aerosol perturbations. The response of cloud droplet size distributions to entrainment–mixing is examined in the Pi convection-cloud chamber that creates a turbulent, steady-state cloud. The experiments are conducted by injecting dry air with temperature (T e ) and flow rate (Q e ) through a flange in the top boundary, into the otherwise well-mixed cloud, to mimic the entrainment–mixing process. Due to the large-scale circulation, the downwind region is directly affected by entrained dry air, whereas the upwind region is representative of the background conditions. Droplet concentration (Cn) and liquid water content (L) decrease in the downwind region, but the difference in the mean diameter of droplets (D m ) is small. The shape of cloud droplet size distributions relative to the injection point is unchanged, to within statistical uncertainty, resulting in a signature of inhomogeneous mixing, as expected for droplet evaporation times small compared to mixing time scales. As T e and Q e of entrained air increase, however, Cn, L, and D m of the whole cloud system decrease, resulting in a signature of homogeneous mixing. The apparent contradiction is understood as the cloud microphysical responses to entrainment and mixing differing on local and global scales: locally inhomogeneous and globally homogeneous. This implies that global versus local sampling of clouds can lead to seemingly contradictory results for mixing, which informs the long-standing debate about the microphysical response to entrainment and the parameterization of this process for coarse-resolution models.
- Research Organization:
- Brookhaven National Laboratory (BNL), Upton, NY (United States); Michigan Technological University, Houghton, MI (United States); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); University of Colorado Boulder, CO (United States)
- Sponsoring Organization:
- USDOE; USDOE Office of Science (SC), Biological and Environmental Research (BER)
- Grant/Contract Number:
- SC0012704; SC0022128
- OSTI ID:
- 2008121
- Alternate ID(s):
- OSTI ID: 2202460
OSTI ID: 2204130
OSTI ID: 2148220
- Report Number(s):
- BNL--224916-2023-JAAM; e2307354120
- Journal Information:
- Proceedings of the National Academy of Sciences of the United States of America, Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Issue: 42 Vol. 120; ISSN 0027-8424
- Publisher:
- Proceedings of the National Academy of SciencesCopyright Statement
- Country of Publication:
- United States
- Language:
- English