Date of Award
Doctor of Philosophy (PhD)
The first part of this dissertation investigates natural small-scale microphysical and dynamical mechanisms identified in a winter orographic snowstorm over the Sierra Madre mountain range of Wyoming during the AgI Seeding Clouds Impact Investigation (ASCII). A turbulent shear layer was observed in a cold post-frontal environment that was created by a mid-level cross-barrier jet riding over a decoupled Arctic air mass. Similar turbulent shear layers have been observed over blocked low-level air masses along coastal maritime mountain ranges, but little research has focused on inland continental ranges. The multi-instrument analysis suggests 1) shear-induced turbulent overturning cells do exist over cold continental mountain ranges like the Sierra Madre, 2) the presence of cross-barrier jets favor these turbulent shear zones, 3) this turbulence is a key mechanism in enhancing snow growth, and 4) snow growth enhanced by turbulence primarily occurs through deposition and aggregation in these cold (< -15°C) post-frontal continental environments.
The second part of this dissertation utilizes a high-resolution observational network from the Integrated Precipitation and Hydrology Experiment (IPHEx) to document the orographic modification of a prefrontal squall line that passed over the southern Appalachian Mountains. Little previous research exists documenting the interaction of squall lines with mountainous terrain, especially observationally, so this study is one of the first. The squall line studied was embedded within an Atmospheric River (AR), where southerly low-level moisture transport was impeded by the southern Appalachian Mountains, favoring rapid fallout of precipitation on its southeastern slopes. A growing research interest exists in the role ARs play in extreme precipitation events over the eastern US, and this study highlights the importance of small-scale terrain and convective features within AR environments in generating heavy rainfall.
The third part of this dissertation describes i) my first-of-its-kind NOAA G-IV tail Doppler radar analysis over the Pacific Ocean aimed at documenting cloud and precipitation structures within an offshore AR during the CalWater-2 field project, and ii) my role in collecting ground-breaking radar data during the SNOWIE field project that is being used to document the formation and fallout of snow initiated by man-made airborne glaciogenic cloud seeding.
Aikins, Joshua Daniel, "Investigating Small-Scale Microphysical and Dynamical Mechanisms Within a Winter Orographic Snowfall Event and a Spring Squall Line Interacting with Mountains" (2018). Atmospheric & Oceanic Sciences Graduate Theses & Dissertations. 72.