Electromagnetic modeling of pristine ice crystals with multiple mass-dimensional relationships

Description

Advances in electromagnetic scattering techniques for arbitrary objects (e.g., Draine and Flatau 1994, Xu 1995) have led to the creation of accurate models for complex ice particles such as pristine ice crystals (e.g., Liu 2008, Botta et al. 2011). These types of models have the potential to successfully constrain cloud models through comparisons with radar measurements, representing the missing link between the two (e.g., Avramov et al. 2011). Therefore particular care is necessary when approaching this modeling problem.

A very common approach to complex electromagnetic modeling of pristine ice crystals consists in characterizing a particular type of crystal (e.g., stellar, dendrite, or planar) in terms of a single mass-dimensional (M-D) relationship (e.g., Liu 2008). However, the literature provides many different M-D relationships (e.g., Pruppacher and Klett 1997, Mitchell and Heymsfield 2005) for the same type of crystal, making the single M-D relationship approach substantially limited.

An overview of the many M-D relationships available in the literature shows that a given class of crystals can cover a relatively big region in the M-D plane. Ideally, electromagnetic models of pristine ice crystals should be able to appropriately sample a significant set of points in this region in order to provide cloud modelers with appropriate scattering computations that match the desired microphysical parameters (i.e., the shape of the crystals and their M-D relationship). In an effort to close the gap between electromagnetic and cloud models, several electromagnetic models of different classes of pristine ice crystals (dendrites, plates, columns, etc.) were developed using the generalized multiparticle Mie (GMM) method for scattering computations (Xu 1995, Botta et al. 2011). These models were tailored to cover as much area of the M-D plane region defined by the multiple M-D relationships available for each class. Electromagnetic back-scattering computations at vertical and side incidence for pristine ice crystals modeled using this approach are presented.