EGU25-18274, updated on 15 Mar 2025
https://doi.org/10.5194/egusphere-egu25-18274
EGU General Assembly 2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
Novel measures for diagnosing and evaluating entrainment-mixing in warm and mixed-phase clouds using airborne, in situ measurements
John Dalessandro1, Robert Wood2, Peter Blossey3, and Greg McFarquhar4,5
John Dalessandro et al.
  • 1University of Lille, Laboratoire d'Optique Atmosphérique, France (jdallas223@gmail.com)
  • 2University of Washington, Department of Atmospheric and Climate Science, Seattle, US (robwood2@uw.edu)
  • 3University of Washington, Department of Atmospheric and Climate Science, Seattle, US (pblossey@uw.edu)
  • 4University of Oklahoma, School of Meteorology, Norman, US (mcfarq@ou.edu)
  • 5Cooperative Institute for Severe and High-Impact Weather Research and Operations, University of Oklahoma/NOAA, Norman, US (mcfarq@ou.edu)

Multiple methods using in situ observations exist to evaluate cloud microphysical characteristics associated with entrainment-mixing. These include comparing average drop sizes with drop concentrations, comparing these quantities weighted by their adiabatically derived values, as well as computing theoretically derived mixing parameters (e.g., Damköhler number [Dimotakis 2005] and transition length scale [Lehmann et al. 2009]). Although multiple methods exist to quantify entrainment-mixing, observational studies often incorporate a number of these methods due to a wide range of variability in the methods’ output. Further, multiple uncertainties exist when computing these parameters, ranging from required assumptions for determining adiabatic values to sampling limitations preventing the diagnosis of the entrained air’s humidity. For these reasons, most observational studies only evaluate a select number of flight legs due to the diligent analysis required case-by-case.

To compensate for such discrepancies, we introduce a novel method to diagnose the presence of entrainment by using the variance of drop concentrations on the order of ~100 m as a proxy variable. Drop concentrations are acquired using a commonly deployed cloud droplet probe (CDP) at ~10 m spatial resolutions. These basic factors allow for the dissemination of entrainment-mixing characteristics amongst hundreds of hours of cloud measurements acquired during numerous field campaigns.

Findings using this proxy variable suggest that the greatest ice crystal sizes in low-level mixed-phase clouds over the Southern Ocean are found in cloud samples associated with relatively weak entrainment (D’Alessandro and McFarquhar 2023). The methodology is further developed to evaluate how drop size distributions evolve in the presence of entrainment-mixing, revealing greater frequencies of inhomogeneous (homogeneous) mixing associated with high (low) aerosol environments and non-precipitating (precipitating) clouds in subtropical marine environments (D’Alessandro et al. submitted). Occurrence frequencies of inhomogeneous and homogenous mixing are approximately similar amongst four field campaigns, which sampled cloud regimes ranging from low-level warm and mixed-phase marine clouds to terrestrial, convective clouds. Additionally, the methodology in conjunction with measurements from the HOLODEC probe suggest the potential of droplet growth in the “bottleneck” size range (diameters ~25–50 µm) in the presence of entrainment.

 

Bibliography

D’Alessandro, J. J., and G. M. McFarquhar, 2023: Impacts of Drop Clustering and Entrainment-Mixing on Mixed Phase Shallow Cloud Properties Over the Southern Ocean: Results From SOCRATES. Journal of Geophysical Research: Atmospheres, 128, e2023JD038622, https://doi.org/10.1029/2023JD038622.

D’Alessandro, J. J., R. Wood, and P. N. Blossey, submitted: Evaluating entrainment-mixing characteristics through direct comparisons of drop size distributions using in situ observations from ACE-ENA. J. Atmos. Sci.

Dimotakis, P. E., 2005: TURBULENT MIXING. Annual Review of Fluid Mechanics, 37, 329–356, https://doi.org/10.1146/annurev.fluid.36.050802.122015.

Lehmann, K., H. Siebert, and R. A. Shaw, 2009: Homogeneous and inhomogeneous mixing in cumulus clouds: Dependence on local turbulence structure. Journal of the Atmospheric Sciences, 66, 3641–3659, https://doi.org/10.1175/2009JAS3012.1.

 

How to cite: Dalessandro, J., Wood, R., Blossey, P., and McFarquhar, G.: Novel measures for diagnosing and evaluating entrainment-mixing in warm and mixed-phase clouds using airborne, in situ measurements, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18274, https://doi.org/10.5194/egusphere-egu25-18274, 2025.