A novel, multiple liquid and ice hydrometeor species, hybrid-bulk/bin, three-moment microphysics parameterization scheme

A novel bulk microphysics scheme is introduced that combines what are known to be essential and cutting-edge elements: a hybrid-bulk/bin framework, a three-moment distribution, shape discriminating parameterization, and multiple species for both liquid and ice hydrometeors. Recent work has shown that only by using a three-moment scheme in conjunction with hybrid-bulk/bin does the correct time-evolving distribution shape result in processes such as fallout for a bulk type parameterization. Recent work has shown that only by using a three-moment scheme in conjunction with hybrid-bulk/bin does the correct time-evolving distribution shape result in processes such as fallout for a bulk type parameterization.

The most significant motivation for this novel work is that it is essential for a microphysics parameterization to have the capability to not only predict the amount and number of hydrometeors, but also the species of the hydrometeors. Thus, one of the many of the theses of this work is that multiple ice crystal and mixed ice crystal habits are required to simulate the many different type of events of ice and snowfalls that occur in nature. The new model does this without any tuning unlike most other models. In addition, density variation of mid-size ice species is essential for accurate growth and differential sedimentation. The model also has various liquid categories ranging from cloud and drizzle to various rain species from different sources. In all, 22 ice habits (13 are crystal habits, four of which are mixed habits) and five liquid habits are used. For future efforts the model also contains four categories of aerosols and a category for ice nuclei.

Much effort also has been put forth in this work in developing new conversion parameterization in hybrid-bulk/bin space. In particular those with the difficult auto conversions within a species (cloud to drizzle to rain) and even more difficult conversion between different species. All of the microphysical processes in the new model make use of the latest physics found in the literature and use hybrid-bulk/bin parameterizations for their calculation. Every attempt is made to keep the physics as consistent as possible with observations from laboratory or insitu observation.

Finally. the new parameterization also is a means to avoid the huge memory and computational cost of bin-parameterization models (e.g., those costs associated with advection, diffusion, filters etc.) yet embrace the comprehensiveness of the physics that can be incorporated with bin-parameterization models.