A Physically-based, Meshless Lagrangian Approach to Simulate Melting
Precipitation
Abstract
An outstanding challenge in modeling the radiative properties of
stratiform rain systems is an accurate representation of the mixed-phase
hydrometeors present in the melting layer. The use of ice spheres coated
with meltwater or mixed-dielectric spheroids have been used as rough
approximations, but more realistic shapes are needed to improve the
accuracy of the models. Recently, realistically structured synthetic
snowflakes have been computationally generated, with radiative
properties that were shown to be consistent with coincident airborne
radar and microwave radiometer observations. However, melting such
finely-structured ice hydrometeors is a challenging problem, and most of
the previous efforts have employed heuristic approaches. In the current
work, physical laws governing the melting process are applied to the
melting of synthetic snowflakes using a meshless-Lagrangian
computational approach henceforth referred to as the Snow Meshless
Lagrangian Technique (SnowMeLT). SnowMeLT is capable of scaling across
large computing clusters, and a collection of synthetic aggregate
snowflakes from NASA’s OpenSSP database with diameters ranging from
2–10.5 mm are melted as a demonstration of the method. To properly
capture the flow of meltwater, the simulations are carried out at
relatively high resolution (15 μm), and a new analytic approximation is
developed to simulate heat transfer from the environment without the
need to simulate the atmosphere explicitly.