Date of Award
Doctor of Philosophy (PhD)
Atmospheric and Earth Science
Snow--Remote sensing, Lightning--Remote sensing
Much of the research using lightning, satellite, and numerical weather prediction model dataset involves the observation and prediction of warm season convection, whereas studies with regards to winter weather and heavy snowfall are sparse and nearly non-existent for electrified snowfall events. Single channel and multispectral composite satellite imagery were analyzed prior to lightning initiation in snowfall (i.e., thundersnow). Objectively tracked cloud features exhibited similar cloud-top brightness temperature and reflectance value changes – prior to thundersnow initiation – compared to cloud features associated with summertime lightning. Multispectral composite imagery – particularly the day cloud phase distinction – demonstrated consistent color changes (i.e., cyan to yellow/green) prior to thundersnow initiation. Furthermore, two nor’easters – sampled during the NASA Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) field campaign – were examined to quantify the in-cloud microphysics in relation to the underlying electrification processes within wintertime stratiform regions. More specifically, these cases were examined with in-situ microphysics probe data and simulated with a numerical weather prediction model with explicit electrification parameterization. The non-inductive charging mechanism was determined to be the primary charging mechanism within wintertime stratiform regions sampled during the two cases from an observation and modeling perspective. However, supercooled liquid water and graupel may not play a large role in weakly electrified environments; the strongest observed electric fields were associated with a non-riming, low liquid water content environment, and large hydrometeor collisions. Lastly, a thundersnow outbreak event associated with an extratropical cyclone was simulated to explicitly resolve thundersnow and provide context to the electrification processes that occur within winter storms. For the first time, thundersnow was explicitly resolved using the NASA Unified Weather Research and Forecasting with electrification (NU-WRF-ELEC). More specifically, the simulation produced 1,733 thundersnow flashes but was still less than the 19,677 thundersnow flashes observed by the Geostationary Lightning Mapper. A conceptual model was developed to provide an explanation as to why thundersnow initiation tended to be spatially separated from the heaviest surface snowfall rates within the main snowband. Lastly, a new thermodynamic instability parameter was developed (i.e., isentropic convective available potential energy) to provide insight into environments that were conducive to thundersnow.
Harkema, Sebastian S., "Microphysical examination of electrified snowfall events using GOES ABI/GLM and NU-WRF" (2023). Dissertations. 350.
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