U.S. Department of Energy Office of Biological and Environmental Research

BER Research Highlights

Broadening of Cloud Droplet Spectra through Turbulent Eddy Hopping
Published: April 24, 2017
Posted: January 23, 2018

New turbulent eddy hopping methodology produces realistically broad cloud droplet distributions.

The Science
Clouds are made up of droplets of a range of sizes; the “spectrum” or distribution of the droplet sizes has important implications for how clouds reflect solar radiation and the development of precipitation. Two of the key parameters describing cloud droplet spectra are the mean radius and the spectrum width. Spatial variability of the mean radius in clouds developing in different environments is relatively well understood and it is predominantly determined by the characteristics of small aerosol particles on which cloud droplets formed (called cloud condensation nuclei, or CCN) and by the bulk thermodynamic properties (such as the temperature and moisture as well as cloud dilution). The width of the spectrum remains poorly understood.

The Impact
A novel methodology is being developed to represent the impact of unresolved turbulent eddies on the width of the droplet spectrum. The methodology follows the concept of eddy hopping--that is, variable trajectories and growth histories of cloud droplets arriving at a given location inside a turbulent cloud. The eddy-hopping mechanism needs to be accounted for in large-eddy simulations (LES) of turbulent clouds because it has a potentially significant impact on rain formation through collision/coalescence and on radiative transfer through a cloudy atmosphere.

This study investigates spectral broadening of droplet size distributions through a mechanism referred to as “turbulent eddy hopping”. The key idea, suggested several decades ago, is that droplets arriving at a given location within a turbulent cloud follow different trajectories and thus different growth histories, and that this leads to a significant spectral broadening. In this study, a parcel model is used to contrast growth of cloud droplets with and without turbulence. As expected, parcels without turbulence produce extremely narrow droplet spectra. In contrast, the impact for the parcel model with turbulence is significant, with the width of the distribution increasing several times when compared to the spectrum without turbulence. High-resolution cloud model simulations using this methodology are ongoing.

Contacts (BER PM)
Shaima Nasiri
Atmospheric System Research

Ashley Williamson
Atmospheric System Research

(PI Contact)
Wojciech W. Grabowski
National Center for Atmospheric Research

This work was partially supported by the Polish National Science Center (NCN) “POLONEZ 1” Grant 2015/19/P/ST10/02596 and by the U.S. ASR Grant DE-SC0016476. The POLONEZ 1 grant has received funding from the European Union’s Horizon 2020 Research and Innovation Program under the Marie Sklodowska-Curie Grant Agreement 665778.

Grabowski, W. and G. Abade, "Broadening of Cloud Droplet Spectra through Eddy Hopping: Turbulent Adiabatic Parcel Simulations." Journal of the Atmospheric Sciences, 74: 1485-1493 (2017). [DOI: 10.1175/JAS-D-17-0043.1]

Related Links
ASR Highlight: Broadening of Cloud Droplet Spectra Through Turbulent Eddy Hopping

Topic Areas:

  • Research Area: Atmospheric System Research

Division: SC-23.1 Climate and Environmental Sciences Division, BER


BER supports basic research and scientific user facilities to advance DOE missions in energy and environment. More about BER

Recent Highlights

May 10, 2019
Quantifying Decision Uncertainty in Water Management via a Coupled Agent-Based Model
Considering risk perception can improve the representation of human decision-making processes in age [more...]

May 09, 2019
Projecting Global Urban Area Growth Through 2100 Based on Historical Time Series Data and Future Scenarios
Study provides country-specific urban area growth models and the first dataset on country-level urba [more...]

May 05, 2019
Calibrating Building Energy Demand Models to Refine Long-Term Energy Planning
A new, flexible calibration approach improved model accuracy in capturing year-to-year changes in bu [more...]

May 03, 2019
Calibration and Uncertainty Analysis of Demeter for Better Downscaling of Global Land Use and Land Cover Projections
Researchers improved the Demeter model’s performance by calibrating key parameters and establi [more...]

Apr 22, 2019
Representation of U.S. Warm Temperature Extremes in Global Climate Model Ensembles
Representation of warm temperature events varies considerably among global climate models, which has [more...]

List all highlights (possible long download time)