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

BER Research Highlights


Comparing Model Simulations of Arctic Mixed-Phase Clouds: Importance of Ice Size Distribution
Published: March 14, 2014
Posted: August 11, 2014

To improve understanding and model representation of processes in mixed-phase Arctic clouds, a team of researchers, led by U.S. Department of Energy scientists at Pacific Northwest National Laboratory, analyzed simulations of these clouds in 11 different high-resolution, large-eddy simulation (LES) models. Using simulations guided by observations from the Indirect and Semi-Direct Aerosol Campaign (ISDAC), they explored the processes that controlled cloud structure and evolution in the numerical simulations. In contrast to previous intercomparison studies, all 11 numerical models used the same ice particle properties and a common radiation parameterization. This constrained setup exposed the importance of ice particle size distributions (PSDs) in influencing cloud evolution in the simulations.

Numerical models use two different approaches (bin or bulk) to represent ice PSDs. In the more accurate, but computationally more expensive bin approach, the models predict how the number of particles within a given size range (or bin) changes as the cloud evolves. This approach results in an explicit size distribution that can be used to calculate variables such as ice water path, particle fall speeds, and cloud mass. In the computationally cheaper bulk approach, which is the method used in large-scale climate models, a fixed shape is assumed for PSD and the models predict higher-order moments of the distribution to calculate the necessary cloud variables.

In this study, researchers found a clear separation in liquid water path (LWP) and ice water path (IWP) predicted by models with bin and bulk microphysical treatments. This difference was attributed primarily to the assumed shape of the ice PSD used in bulk schemes. Compared to the bin schemes that explicitly predict PSD, bulk schemes assuming exponential ice PSD underestimate ice growth by vapor deposition and overestimate mass-weighted fall speed leading to an under-prediction of IWP by a factor of two in the considered case. Sensitivity tests indicated LWP and IWP are much closer to the bin model simulations when a modified shape factor, which is similar to that predicted by the bin model simulation, is used in the bulk scheme. These results demonstrate the importance of ice PSD representation in determining liquid and ice partitioning and the longevity of mixed-phase clouds. The authors suggest that future work to improve modeling of mixed-phase clouds in climate models should focus on methods for predicting the shape and width of ice PSD for use in bulk schemes.

Reference: Ovchinnikov, M., A. S. Ackerman, A. Avramov, A. Cheng, J. Fan, A. M. Fridlind, S. Ghan, J. Harrington, C. Hoose, A. Korolev, G. M. McFarquhar, H. Morrison, M. Paukert, J. Savre, B. J. Shipway, M. D. Shupe, A. Solomon, and K. Sulia. 2014. “Intercomparison of Large-Eddy Simulations of Arctic Mixed-Phase Clouds: Importance of Ice Size Distribution Assumptions,” Journal of Advances in Modeling Earth Systems 6(1), 223-48. DOI:10.1002/2013MS000282. (Reference link)

Contact: Sally McFarlane, SC-23.1, (301) 903-0943, Rickey Petty, SC-23.1, (301) 903-5548
Topic Areas:

  • Research Area: Atmospheric System Research
  • Facility: DOE ARM User Facility

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

Aug 24, 2019
New Approach for Studying How Microbes Influence Their Environment
A diverse group of scientists suggests a common framework and targeting of known microbial processes [more...]

Aug 08, 2019
Nutrient-Hungry Peatland Microbes Reduce Carbon Loss Under Warmer Conditions
Enzyme production in peatlands reduces carbon lost to respiration under future high temperatures. [more...]

Aug 05, 2019
Amazon Forest Response to CO2 Fertilization Dependent on Plant Phosphorus Acquisition
AmazonFACE Model Intercomparison. The Science Plant growth is dependent on the availabi [more...]

Jul 29, 2019
A Slippery Slope: Soil Carbon Destabilization
Carbon gain or loss depends on the balance between competing biological, chemical, and physical reac [more...]

Jul 15, 2019
Field Evaluation of Gas Analyzers for Measuring Ecosystem Fluxes
How gas analyzer type and correction method impact measured fluxes. The Science A side- [more...]

List all highlights (possible long download time)