Large-Scale Weather Patterns Favorable for Vog Occurrences on Oahu, Hawaii

Tofte, Kristine
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[Honolulu] : [University of Hawaii at Manoa], [December 2015]
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Kilauea Volcano is one of the most active volcanoes in the world, and its two vents (Halemaumau and Puu Oo) release more sulfur dioxide (SO2) than major power plants. During the time of this study (April 2009 – December 2014), the two vents released approximately 3,700 tons of SO2 per day. Within the atmosphere, the SO2 is oxidized and converted to sulfuric acid aerosols through reactions with OH radicals and H2O molecules in clear sky and cloud reactions. This sulfuric aerosol is commonly referred to as volcanic smog (vog) in Hawai'i. During prevailing trade winds conditions, the vog emitted from Kilauea volcano is advected towards the southwest of the Big Island of Hawai'i. However, when winds shift to a southeast or southwest direction, then vog can be carried up the island chain affecting all the Hawaiian Islands. This study focuses on the largescale Weather patterns that cause this wind shift and specifically, on conditions that bring the vog to the island of Oahu, the most heavily populated island. In order to identify large-scale weather patterns that bring vog to Oahu, two datasets were used. Firstly, the Hawai'i Department of Health maintains a record of hourly aerosol mass concentrations in size ranges below 10 μm (PM10) and below 2.5 μm (PM2.5). The volcanic plume consists of accumulation mode sulfuric acid aerosols below 1μm in diameter and therefore, the PM2.5 measurements will capture information about vog concentrations. As part of this study, Hawai'i Department of Health PM2.5 measurements were used to identify elevated vog conditions. Secondly, European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim reanalysis data were used to determine weather patterns occurring prior and during Oahu vog events. As part of this effort, the ERA-Interim reanalysis data, for different weather patterns, were downscaled to a resolution of 3.3 km using the Weather Research and Forecasting (WRF) model. The WRF output was run in the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model to produce both trajectory and concentration plots. The HYSPLIT model allowed for a visual representation of how the vog plume follows the large-scale wind patterns. Data from April 2009 throughout 2014 were analyzed and the total number of vog days was found to be 101. These 101 vog days were the result of 57 distinct vog events lasting from hours up to four days. The 57 events were further categorized into three large-scale weather patterns: precold fronts (37 cases), upper-level disturbances (17 cases) and Kona lows (3 cases). The pre-cold front events had variable duration lasting up to four days and it was found that the largest vog concentrations (PM2.5 values) occurred during long duration pre-cold front events.
M.S. University of Hawaii at Manoa 2015.
Includes bibliographical references.
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Theses for the degree of Master of Science (University of Hawaii at Manoa). Meteorology
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