Toward Understanding the Climatic Role of Tropical Cyclones Using an Atmospheric General Circulation Model: Experiment Design, Model Evaluation, and Preliminary Results

A formal assessment and an identification for the global circulation impact of a tropical cyclone (TC) remains in the developmental stages. This area of research was first suggested by Bengtsson et al., [1982], when questions were posed regarding the role of TCs with respect to the poleward transport of heat, moisture, and momentum. To date, much attention has been paid to the role of oceanic heat transport [Emanuel, 2001; Sriver and Huber, 2007; Hart et al., 2007; Liu et al., 2008; Hu and Meehl, 2009]. Fewer studies, however, have identified an explicit role for the TC within the atmosphere, although recent work has begun to quantify the magnitude of that atmospheric footprint from reanalysis datasets [Hart et al., 2007; Schenkel and Hart, 2011].

A recent study by Hart [2011] deduced a statistical relationship between northern hemisphere TC activity (evaluated using both TC count and power dissipation [Emanuel, 2007]) and the subsequent winter climate. Hart [2011] ascertained that there exists a strong (statistical) inverse relationship between the amount of pole-ward TC power-dissipation (e.g., recurving TCs) and the 500-hPa extratropical stationary eddy-temperature flux, and speculated on the physical (and potential nonphysical) explanations for such a relationship. Indeed, the relationship was so strong that it was the most robust predictor of this measure of wind activity amidst all known teleconnection indices. These prior works provide the foundation on which to further explore the TC role in climate. Accordingly, in this study, we diagnose the climatic impact of TCs upon the Earth's general circulation using the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM) and the TC vortex removal procedure discussed by Winterbottom and Chassignet [2011].

A series of experiments with and without TCs will be compared. We will evaluate the mean and transient eddy fluxes as a function of a simulation with TCs and a simulation without. We will also analyze the tropical wave characteristics and the position and strength of the Hadley Cell also as functions of TC presences. Finally, we will present the initial results from this ongoing study and will provide a hypothesis for the climatic role of TCs within the Earth's general circulation.