Collaborative Research: On the Intensity and Size Relationship of Tropical Cyclones

Tropical cyclones (TCs) are the most destructive natural phenomena, causing many casualties and enormous economic loss every year. Their intensity and size are the two most important matrics for assessing TC severity and potential hazards but their relation is not well understood and challenging to be predicted. The improved understanding of TC intensity-size relation will shed insights into how operational forecasts for TC intensity and size could be further improved.

These improvements will in turn help coastal communities to prepare for the maximum potential damage and lead to saving lives and minimizing the losses of properties. This project will train two Ph.D. students and a postdoc in fields of atmospheric dynamics, modeling, and data science, and support STEM education by working with an undergraduate student to launch experimental forecasts for TC intensity and size based on the knowledge gained from the project.

The research findings and experimental forecasts will be communicated to the science community via peer-reviewed publications, to college students via classroom teaching and curriculum development, and to general public via website and twitter accounts.

This project is built on the knowledge and insights gained from a previously NSF-funded EAGER project, which put forward a radial invariant model of “effective absolute angular momentum” (eAAM) for radial profiles of TC surface winds by combining the absolute angular momentum (AAM) and the loss of AAM due to surface drags. The main goal of this project is to explore the dependencies of radial loss of AAM and eAAM values on environment factors so that the eAAM model would better explain the observed complexity and rich diversity of TC intensity-size relation.

This research is guided by the central hypothesis substantiated by three process-based working hypotheses. Under this framework, different eAAM values result from differences in the inward radial loss of AAM that depends environment conditions. The central question of how the inward radial loss rate of AAM and eAAM are related to environment conditions is investigated through 6 sets of A-B series numerical experiments using the Cloud Model Version 1 (CM1) model for the A-series and cloud-permitting version of the Weather Research and Forecast (WRF) model for the B-series.

The resultant environment-dependent eAAM model will be validated by requiring that both the eAAM-predicted TC winds using observed size information and the eAAM-predicted TC sizes using observed wind information are highly in agreement (within observation uncertainties) with their observational counterparts

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.