Possible Steering flows from SAR-derived surface wind asymmetry over
loop track of Typhoon Saola (2023)
Abstract
Typhoon Saola’s (2023) anti-clockwise loop track was monitored by six
spaceborne synthetic aperture radar (SAR) images, offering a unique
opportunity to investigate the physical factor known as steering flow, a
widely accepted concept for studying tropical cyclone (TC) movement and
storm surges. Despite its importance, direct observations of steering
flows are limited. To address the complex movements observed during the
loop track, we propose a novel method to decompose the SAR-derived
high-resolution surface wind field into: 1) symmetric rotational winds,
2) general steering flow across three consecutive SAR cases within
~24 hours, and 3) the remaining steering flow. Our
analysis reveals that the newly determined remaining steering flows from
north effectively explain the loop track associated with two general
steering flows, identified as the western North Pacific summer monsoon
(WNPSM) from southeast and Indian summer monsoon (ISM) from southwest.