Date of Award
Master of Science (MS)
David J. Delene
The process of melting snow as clouds precipitate is important for storm evolution. The atmospheric layer where melting occurs has largely been studied with radar observations that investigate the bright band region; however, in-situ observations are necessary to improve and verify these radar observations. In-situ observations during recent NASA field campaign are reviewed to obtain aircraft profiles of the melting layer. A total of thirty-three melting layer cases are analyzed for changes in area ratio and particle size distribution from above, within, and below the melting layer. Additionally, the effect relative humidity in the melting layer is analyzed. The area ratio begins to increase when the ice-bulb temperature is above 0 °C, which indicates the area ratio can depict the melting layer top. Only two of the thirty-three cases analyzed have a 0 °C quasi-isothermal layer nearby the melting layer, which indicates diabatic cooling from melting does not frequently produce such a layer as has been commonly reported. Additionally, there is a lack of enhanced aggregation within the melting layer, which has been hypothesized as a potential cause of the radar bright band signal. Large hydrometeors concentration decreases from above to below the melting layer; however, the small hydrometeors concentration does not commonly increase, which suggests that hydrometeors evaporate and the concentration is shifted to hydrometeors smaller than 500 µm. Exponential spectrum fits to the particle size distribution are largely variable; however, the slope parameter commonly increases in the melting layer, which suggests there is no enhanced aggregation. Still, there is occasionally a small increase in the maximum hydrometeor diameter within the melting layer. Additional analysis could compare radar reflectivity changes to the melting layer observed particle spectrum changes.
Twohey, Logan John, "Melting Layer Analysis Of In-Situ Observations Obtained From Multiple Field Projects" (2022). Theses and Dissertations. 4379.