Characterizing the Energetics of Vortex-Scale and Sub-Vortex-Scale Asymmetries during Tropical Cyclone Rapid Intensity Changes

Abstract

Our collective understanding of azimuthally-asymmetric features within the coherent structure of a tropical cyclone (TC) continues to improve with the availability of more detailed observations and high-resolution model outputs. However, a precise understanding of how these asymmetries impact TC intensity changes is lacking. Prior attempts at investigating the asymmetric impacts follow a mean-eddy partitioning that condenses the effect of all the asymmetries into one term and fails to highlight the differences in the role of asymmetries at different scales. In this study, we present a novel energetics-based approach to analyze the asymmetric impacts at multiple lengthscales during periods of TC rapid intensity changes. Using model outputs of TCs under low and high shear, we compute the different energy pathways that enhance/suppress the growth of multiscale asymmetries in the wavenumber (WN) domain. We then compare and contrast the energetics of the mean flow field (WN 0) with that of the persistent, coherent vortex-scale asymmetric structures (WNs 1,2) and the more local, transient, sub-vortex-scale asymmetries (WNs ≥ 3). We find in our case-studies that the dominant mechanisms of growth/decay of the asymmetries are the baroclinic conversion from available potential to kinetic energy at individual scales of asymmetries, and the transactions of kinetic energy between the asymmetries of various length-scales; rather than the barotropic mean-eddy transactions as is typically assumed. Our case-study analysis further shows that the growth/decay of asymmetries is largely independent of the mean. Certain aspects of eddy energetics can potentially serve as early-warning indicators of TC rapid intensity changes.

Land‐Surface Diurnal Effects on the Asymmetric Structures of a Postlandfall Tropical Storm

“…Since land-surface and atmospheric radiation can interact with each other, future work should also address the importance of radiative diurnal effects on storm evolution. Moreover, with a tropical cyclone case over the ocean, Bhalachandran et al (2020) revealed that asymmetries of a tropical cyclone could grow or decay independent of the symmetric component of the vortex. Therefore, to better understand the land-surface's diurnal effects on asymmetric structures of a tropical cyclone, the interaction between vortex-scale and subvortex-scale waves under strong environment-vortex influences should be investigated for postlandfall tropical storms.…”

Correcting biases in tropical cyclone intensities in low-resolution datasets using dynamical systems metrics

“…Such inverse cascades are associated with potential-kinetic energy conversions and are particularly notable for intense storms (Bhalachandran et al, 2020).…”

Impacts of model resolution and ocean coupling on mean and eddy momentum transfer during the rapid intensification of super‐typhoon Muifa (2011)

“…RI is usually associated with intense inner‐core (eyewall) convective bursts (Steranka et al ., 1986 ; Sanger et al ., 2014 ) and asymmetric convective structures (Zhang et al ., 2001 ; Montgomery et al ., 2006 ; Van Sang et al ., 2008 ; Fang and Zhang, 2011 ; Persing et al ., 2013 ; Kilroy and Smith, 2016 ). The asymmetric eddy processes can change a TC′s intensity through the barotropic and baroclinic energy cascade (Bhalachandran et al ., 2020 ). Agradient wind forcing in the friction layer contributes to the spin‐up of RI (Montgomery et al ., 2020 ).…”