Representing ice in microphysics models is important not only to study the effects of ice on cloud dynamics and cloud lifetime, but also for accurate quantitative precipitation forecasts. Traditional microphysics parameterizations artificially separate ice into categories such as cloud ice, snow, and graupel. These models assume that for each category ice crystal size varies with mass, but they do not account for ice crystal shape evolution. In nature, ice crystal shape, or habit, is temperature dependent and evolves as ice moves through a cloud. Ice crystal shape significantly affects vapor growth rates by varying the gradients in the encompassing vapor field. Ice crystal shape also influences riming rates and fall speed. Traditional models are not able to capture this ice crystal shape sensitivity.
This project will study the impact of ice crystal shape evolution on different cloud systems. Simulations will be conducted using the Weather Research and Forecasting (WRF) model to look at how ice crystal habit evolution impacts orographic precipitation, tropical cyclone dynamics and precipitation, and squall lines. A 2-dimensional modeling framework will also be used to explore the effects of evolving ice crystal shape on phase partitioning in mixed-phase clouds. Finally, how representing lightly-rimed ice crystals, which is now possible by evolving ice crystal shape, impacts mixed-phase cloud stability will be studied.
Intellectual Merit: The research provides a unique opportunity to study how ice crystal habit evolution impacts different cloud systems. At present, the degree to which ice particle shape evolution influences cloud evolution is unknown. With the new microphysics parameterization, the influence evolving ice crystal shape has on cloud system properties can be explored. How light riming affects mixed-phase clouds can also be examined for the first time.
Broader Impacts: Modeling ice crystal fall speed evolution which is partially determined by ice crystal shape is crucial for quantitative precipitation forecasts. Also, cirrus cloud properties and lifetime are incredibly sensitive to ice crystal fall speeds. Cirrus cloud radiative properties depend on ice crystal shape as well, meaning ice crystal shape could have important influences on climate. Because the microphysical methods in this study can, in principle, be used in any modeling framework, the research has the potential to impact modeling ranging from operational forecasting through climate studies of ice clouds. Being able to more accurately forecast precipitation, especially heavy or persistent precipitation that could cause flooding in general makes this research relevant to society.
