Abstract
Abstract. It is well known that rapid changes in tropical-cyclone motion occur during interaction with extratropical waves. While the translation speed has received much attention in the published literature, acceleration has not. Using a large data sample of Atlantic tropical cyclones, we formally examine the composite synoptic-scale patterns associated with tangential and curvature components of their acceleration. During periods of rapid tangential acceleration, the composite tropical cyclone moves poleward between an upstream trough and downstream ridge of a developing extratropical wave packet. The two systems subsequently merge in a manner that is consistent with extratropical transition. During rapid curvature acceleration, a prominent downstream ridge promotes recurvature of the tropical cyclone. In contrast, during rapid tangential deceleration or near-zero curvature acceleration, a ridge is located directly poleward of the tropical cyclone. Locally, this arrangement takes the form of a cyclone–anticyclone vortex pair. On average, the tangential acceleration peaks 18 h prior to extratropical transition, while the curvature acceleration peaks at recurvature. These findings confirm that rapid acceleration of tropical cyclones is mediated by interaction with extratropical baroclinic waves. Furthermore, the tails of the distribution of acceleration and translation speed show a robust reduction over the past 5 decades. We speculate that these trends may reflect the poleward shift and weakening of extratropical Rossby waves.
Highlights
The track and movement of tropical cyclones (TCs) are known to be governed by the background environment (e.g., Hodanish and Gray, 1993)
The composite for rapid tangential acceleration shows a poleward-moving tropical cyclone straddled by an upstream trough and a downstream ridge
The subsequent merger of the tropical cyclone and the developing extratropical wave packet is consistent with the process of extratropical transition
Summary
The track and movement of tropical cyclones (TCs) are known to be governed by the background environment (e.g., Hodanish and Gray, 1993). Moon et al (2019) and Lanzante (2019) argued that the historical record of tropicalcyclone track data, prior the advent of the satellite era around the mid-1960s, is likely incomplete They showed that annual-mean tropical-cyclone translation speed exhibits step-like changes and questioned the existence of a true monotonic trend. In a large ensemble of simulations with an atmospheric general circulation model, Zhang et al (2020) found a robust slowdown of tropical-cyclone motion in the extratropics in response to a warming climate. They attributed it to the poleward shift in the midlatitude westerlies. We focus on the region 20–50◦ N, wherein tropical cyclones are more likely to interact with extratropical baroclinic waves
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