The kinematic and thermodynamic structures of convective storms have profound implications on their severe weather potential (e.g., surface wind intensity, precipitation intensity). However, kinematic and thermodynamic retrieval from radars are often only available in field campaign settings. Furthermore, even the most sophisticated retrieval algorithms (e.g., Foerster and Bell 2017; Liou et al. 2019) provide no information on what microphysical processes induce the thermodynamic changes.

This project asks the following question:
Can we use the spatial separation of rain size and concentration in the low level to diagnose hard-to-observe storm thermodynamic and microphysical characteristics?

The hypothesis is simple: Low level rain size-concentration separation will occur when either smaller hydrometeor are advected further away (stronger updraft and front-to-rear flow), or graupel can grow more easily (more large particles are produced).

If our hypothesis is true, the magnitudes of rain diameter-concentration spatial separation may give us extra information on the updraft strength and the amount of heat released through graupel growth!

Statistical analysis on 74.5 hours of radar observations on 10 boreal continental MCSs showed a positive correlation between separation magnitudes and convective depth. After evaluating the WRF simulation on one of the 10 MCSs, we further conclude that the amount of heat released through water freezing over ice hydrometeor (riming) and the melting of graupel/hail are the two microphysical processes that are statistically most correlated to low-level separation magnitudes. In other word, low-level rain diameter-concentration separations may have predicting values on how deep can convection get, and how much heat is released/absorbed during phase change.

The main novelty of this work is that it highlights the relationship between low-level separation, vertical motion, and diabatic heating/cooling, rather than storm-relative inflows.