Hail embryo differences between simulated High Plains and Oklahoma storms

Previous observational studies have shown that marked differences exist in the embryo composition of hailstones collected at the ground between hailstorms of the High Plains and Oklahoma. [Hail embryos can be either from frozen drops or graupel.] In particular, collected hailstones from Oklahoma contained more frozen drop embryos than those of the High Plains. Although past researchers have postulated explanations for this behavior, observations of the in-cloud microphysics do not exist for confirmation. This study attempts to explain this behavior using a numerical cloud model with sophisticated microphysics.

The microphysics scheme used in the current study is only one of two in existence that are capable of testing the scientific hypotheses herein because it includes a separate hailstone category in addition to separate frozen drop and graupel categories. This scheme was designed for use in both NWP forecasting and research; therefore, microphysical processes needed to be as simple as possible for computational efficiency. Accordingly, this scheme must be tested to determine whether the processes are adequate representations. Thus, the first objective is to test whether this new microphysics parameterization is able to sufficiently capture this difference in hailstorm behavior through simulation of the different environments. If so, then the second objective is to understand why this difference in hailstorm behavior exists.

The environments are defined using proximity soundings: those observed in close time/space proximity to observed hailstorms. Using the numerical simulations, hail embryo composition is analyzed within the entire cloud and contrasted to the more limited ground observations. Preliminary analyses of the depth of the cloud layer between the cloud's base and freezing level and the mass flux through the freezing level will be shown to lend insight as to why hailstone composition differs between the High Plains and Oklahoma. These analyses are cast in the form of testable scientific hypotheses and statistical “means testing” (with Student's t-test) is used to determine the significance of the differences between regions.