NASA Center for Climate Simulation

Abstract 

One of the most fundamental and crucial quantities for accurate precipitation retrievals is the single-scattering property (SSP) of each individual hydrometeor in the precipitating volume. Thus, an important step in minimizing retrieval uncertainty is to ensure that the particles used for single-scattering calculations resemble those that occur in nature, allowing the SSPs to be computed precisely with numerical techniques.

Hydrometeors with rotational symmetry (axial symmetry) are most efficiently computed using the T-Matrix methods. For hydrometeors with a uniform dielectric, the Extended Boundary Condition Method (EBCM) is the most efficient. However, for mixed-phase hydrometeors with non-uniform dielectrics EBCM is not applicable. In these cases, we can use the Invariant Imbedded T-Matrix (IITM), which we developed for this purpose. It is also noted that hydrometeors with more extreme aspect ratios can be computed with IITM than EBCM and that such hydrometeors are found in precipitating systems. For hydrometeors without any rotational symmetry, however, volume integral methods like Discrete Dipole Approximation (DDA) and the Method of Moments (MoM) must be employed.