Tropical Cyclone Interactions Within Gyre Circulations

Presentation Type: 
Philippe Papin (University at Albany: State University of New York)
Lance Bosart (University at Albany/SUNY)
Ryan D. Torn (University at Albany/SUNY/DAES)

Central American (CA) gyres are broad (~1000 km diameter) low-level cyclonic circulations that organize over CA during the boreal summer and fall months of the year. Little research has been conducted on CA gyres, with the vast majority of previous work focusing on similar type systems in the western Pacific, monsoon gyres (MGs) and monsoon depressions (MDs), which are also characterized by broad low-level cyclonic circulations that occur on a variety of spatial scales (1000-2500 km). A key difference between MGs and MDs is related to the organization of vorticity around the low-level circulation. MGs are comprised of embedded mesovorticies south and east of the center, which rotate cyclonically along the outer periphery of the larger circulation. Some of these mesovorticies can develop into small tropical cyclones (TCs). MDs, characterized by a symmetrical vorticity pattern and manifest by vorticity accumulation near the circulation center over time, can sometimes evolve into large TCs near the end of their lifecycle. A noteworthy CA gyre observed during the 2010 PREDICT field project served as a sink of TC Matthew and a source for TC Nicole. Heavy rainfall produced devastating flooding across CA, Jamaica, and Cuba in association with this gyre between 25-30 September 2010. The absence of prior research on CA gyres, the apparent scale differences of vortices that comprise these gyre circulations, and the association of these gyre circulations with high-impact weather motivates this presentation.

This presentation focuses on the mutual interaction and propagation of vortices of different scale embedded in the larger-scale cyclonic flow comprising the CA gyre circulation. A circulation framework will be used to illustrate the relationship between vortices embedded in the gyre circulation and the larger-scale gyre circulation by means of case studies. We will compare CA gyres that contain only a few intense cyclonic vorticity elements (possibly TCs) comprising the majority of the gyre circulation with gyre cases where many weaker cyclonic vorticity strips comprise the larger scale circulation. Some CA gyres fit the MD-like classification, where cyclonic vorticity accumulates and axis-symmetrizes at a particular point, ultimately evolving into a large TC. Other CA gyres manifest themselves as MG-like disturbances, where cyclonic vorticity occurs asymmetrically along the outer circulation periphery and rotates cyclonically around the broader gyre center. The latter disturbance occurrences are less likely to result in the formation of one large TC but rather smaller mesovorticies that comprise the larger-scale gyre circulation. A circulation analysis framework aids in the diagnosis of the interaction between different scale cyclonic vortices, and can be used in other complex interaction scenarios (e.g. Fujiwara interaction, trough TC interaction). Observational analyses of distinct CA gyre categories are then used to build gyre conceptual models that can be beneficial in forecasting applications.

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