Mesoscale Controls on the Shasta County Convergence Zone [thesis]

Matthew Thomas Roberts
MESOSCALE CONTROLS ON THE SHASTA COUNTY CONVERGENCE ZONE Matthew T. Roberts The Shasta County Convergence Zone (SCCZ) is a poorly understood terrain-forced convergence zone that develops at the northern terminus of California's Sacramento Valley during cool season (Oct.-Apr.) trough passages. While terrain-flow interactions clearly factor into the SCCZ development, the nature of these interactions is unknown as are the mesoscale processes affecting event duration and orientation. Level-II
more » ... ion. Level-II NEXRAD radar data are used to examine the onset, duration, orientation, geographical extent, and precipitation rate of 23 SCCZ events during the 2016-2017 cool season. The analyses reveal distinct event morphologies including (1) isolated convective bands over the topography, (2) isolated convective bands displaced off of the topography over the Sacramento Valley, and (3) linear convective bands embedded within broader regional precipitation. Event duration ranges from 1 hour to more than 9 hours, and single event estimated rainfall is as high as 100 mm in some locations. Additionally, RAP model analyses, WRF simulations and in situ observations are used to investigate stability parameters and vertical wind and moisture profiles between different cases. These data indicate that location of convective bands is dependent on wind speed and direction in the low and middle levels of the atmosphere. Linearity and orientation of convective lines appear to be linked to the low level shear profile and mean winds. The non-dimensional mountain height is also examined as a control parameter, showing some utility in distinguishing between convective initiation locations. v ACKNOWLEDGEMENTS First and foremost, I would like to thank my advisor Dr. Neil Lareau for his insight, motivation and patience throughout the research process. This research would not be the same without his guidance. Second, I would like to acknowledge Drs. Craig Clements and Sen Chiao for serving on my thesis committee and providing invaluable feedback on my work. I would also like to thank the faculty and my colleagues in the SJSU department of meteorology for their support. Lastly, I would like to thank my friends and family for their motivation and support during my time at SJSU. Special thanks to my girlfriend Alexis for her constant encouragement despite the moments of grumpiness, stress and long nights that came with completing this research. Finally, I can't forget an important thank you to my parents for their support throughout my life. vi
doi:10.31979/etd.sq5w-e3a9 fatcat:3lfbpeqz3fe6pfsrhhrqbtzqwq