Kristine Tofte, Meteorology Masters Thesis Defense

October 28, 9:00am - 10:30pm
Mānoa Campus, Pacific Ocean Science and Technology (POST) 414 Add to Calendar

Title: Large-scale weather patterns favorable for vog occurrences on Oahu, Hawaii


The Kilauea Volcano is one of the most active volcanoes in the world, and the volcano releases more SO2 than the dirtiest power plant on the U.S. mainland. During the time of this study, the two vents released approximately 3,700 tons of SO2 per day. When SO2 is released into the atmosphere, the gas reacts with sunlight, dust, and moisture to create sulfuric aerosols or what most people know as vog. The vog is usually blown out to sea by the prevailing trade winds, but when the wind shifts to a southerly direction the vog can affect the air quality across the entire island chain. This study focuses on this wind shift and the large-scale weather patterns that bring vog to especially Oahu, since this is the most heavily populated island. The Department of Health hourly PM2.5 data from April 2009 throughout 2014 were used to find vog days. The total number of 101 vog days was found. The vog days were studied in further detail by using time-series of the PM2.5 data along with the ERA-Interim data to infer that the 101 vog days were actually apart of 57 vog events. Each vog event had duration from one to four days. The 57 events were further subjectively categorized into three large-scale weather patterns: 37 pre-cold fronts, 3 Kona lows, and 17 upper-level disturbances. The majority of the events were pre-cold front events. The pre-cold front events also had a distinction between duration, where some events lasted hours while other events lasted four days. The long-duration events also had higher values of PM2.5. The ERA-Interim reanalysis data of the four different weather patterns were then downscaled in the Weather Research and Forecasting model to a resolution of 3.3 km. The WRF output was ran in the Hybrid Single-Particle Lagrangian Integrated Trajectory model to produce both trajectory and concentration plots. This methodology, relating elevated PM2.5 measurement from station Honolulu to ERA-Interim reanalysis data, reveals the large-scale weather patterns that bring vog to Oahu. In the future, this methodology can provide a climatology perspective on these large-scale patterns. The HYSPLIT model allows for a visual representation of how the vog plume follow the large-scale wind patterns.

Event Sponsor
Department of Atmospheric Sciences, Mānoa Campus

More Information
Francis Mai, (808) 956-8775,,

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