Developing a Long Record of Extreme South Pacific Cyclones

Jeff Donnelly, Geology & Geophysics

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Abstract

Efforts to understand the driving mechanisms responsible for modulating tropical cyclone activity are significantly hampered by a short instrumental record of tropical cyclone occurrence.  The brief observational record does not permit the identification and characterization of climate modes that may influence storm activity on centennial and longer timescales, including climate conditions for which there are not analogous historic observations.  Instrumental archives in the Pacific only extend back to the middle 20th century.  Over the past decade, paleo-records have been developed elucidating multi-decadal and centennial-scale patterns in tropical cyclone activity.  Coarse-grained storm-induced deposits, preserved in deep coastal embayments, are particularly effective proxies for intense tropical cyclone occurrences at a site.  Deep depressions present in the coastal zone record the passage of intense tropical cyclones by preserving coarse grained event beds transported to the basin by high energy waves and currents during the tropical cyclones passage.  These extraordinary sedimentary basins contain highly resolvable records that provide a means of extending documentary records of tropical cyclone strikes back several millennia, and allow for i) the examination of climate/tropical cyclones interactions that lack modern analogs, ii) the generation of more accurate reoccurrence rate estimates, and iii) and assessment of variations in storm activity on sub-millennial time scales.  In order to build on our previous work I propose to collect preliminary data from sites in Fiji and Vanuatu, which were each hit by extreme tropical cyclones in the past 15 months.  Cyclone Pam struck the Vanuatu archipelago in March 2015 with sustained winds over 155 mph.  Cyclone Winston struck the Fiji Islands with sustained winds of about 185 mph in February 2016.  Winston and Pam are the most intense and third most intense cyclones observed in the South Pacific, respectively, and their occurrence provide a critical opportunity to determine how extreme cyclones are recorded in the targeted sedimentary basins.  Using geophysical techniques we will map the basins, including their subbottom architecture, to target coring.  The resulting preliminary data will be essential for leveraging a large-scale National Science Foundation project to develop these archives and others like them from the tropical Pacific.