Global Identification of Previously Undetected Pre-Satellite-Era Tropical Cyclone Candidates in NOAA/CIRES Twentieth-Century Reanalysis Data

Abstract

rior to the satellite era, limited synoptic observation networks led to an indefinite number of tropical cyclones (TCs) remaining undetected. This period of decreased confidence in the TC climatological record includes the first two-thirds of the twentieth century. While prior studies found that this undersampling exists, disagreement regarding its magnitude has caused difficulties in interpreting multidecadal changes in TC activity. Previous research also demonstrated that reanalyses can be used to extend TC climatology, utilizing the NOAA/Cooperative Institute for Research in Environmental Sciences (CIRES) Twentieth-Century Reanalysis to manually identify previously unknown Atlantic Ocean basin potential TCs. This study expands the spatiotemporal scope of the earlier work by presenting a filtering algorithm that dramatically improves the efficiency with which candidate events are identified in the reanalysis. This algorithm was applied to all tropical basins for the years 1871?1979, resulting in the first quantitative and objective global TC candidate event counts for the decades prior to formal recordkeeping. Observational verification performed on a subset of these events indicates that the algorithm identifies potential missing TCs at a success rate approximating that of earlier work with a significant decrease in the amount of time required. Extrapolating these proportions to all of the candidate events identified suggests that this method may help to locate hundreds of previously unknown TCs worldwide for future study and cataloging. As such, the dataset produced by this research is a source of independent guidance for use in ongoing and future TC climatology revision efforts to produce a more complete historical record more quickly than with current methods.