Tropical Cyclone Multiscale Wind Features from Spaceborne Synthetic Aperture Radar
This study presents multi-scale wind features observed in space-borne synthetic aperture radar (SAR) images in tropical cyclones. Examples of eyewall mesovotices, spiral rainbands, fine-scale-band features, arc clouds, and boundary layer rolls are documen
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Tropical Cyclone Multiscale Wind Features from Spaceborne Synthetic Aperture Radar Jun A. Zhang and Xiaofeng Li
Abstract This study presents multi-scale wind features observed in space-borne synthetic aperture radar (SAR) images in tropical cyclones. Examples of eyewall mesovotices, spiral rainbands, fine-scale-band features, arc clouds, and boundary layer rolls are documented. Although these wind features are strongly tied to tropical cyclone dynamics and intensity based on previous numerical studies, they are not well-observed due to high rainfall and cloudiness that limits remote sensing instrument and severe environment for in-situ observations to survive. Since SAR images view the actual ocean surface responses to the storm-forced winds, they provide clear evidence for the presence of these wind features below clouds and their interaction with the sea surface. Analyses of the characteristics of boundary layer rolls based on SAR images show good agreement with in-situ aircraft observations, suggesting that a SAR image has a great potential to be utilized to study tropical cyclone low-level structure.
2.1 Introduction Hurricanes account for a significant portion of damage, injury and loss of life from natural hazards, and are the most expensive natural catastrophes in the US [1]. The threat of high winds and storm surge has been known for intense storms. Multiscale wind features such as the “eyewall mesovortices”, spiral band features, and boundary layer wind streaks or rolls are believed to largely contribute to the hurricane induced damage during landfalls. These features are also strongly tied to hurricane dynamics according to previous observational and numerical modeling studies. J.A. Zhang (B) National Oceanic and Atmospheric Administration (NOAA)/AOML/Hurricane Research Division, University of Miami/CIMAS, Miami, FL, USA e-mail: [email protected] X. Li GST, National Oceanic and Atmospheric Administration (NOAA)/NESDIS, College Park, MD, USA e-mail: [email protected] © Springer Nature Singapore Pte Ltd. 2017 X. Li (ed.), Hurricane Monitoring With Spaceborne Synthetic Aperture Radar, Springer Natural Hazards, DOI 10.1007/978-981-10-2893-9_2
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J.A. Zhang and X. Li
Previous observations have shown that intense transient vorticity features usually exist close to the inside edge of eyewalls of numerous intense hurricanes. Marks and Houze [2] reported the first example of eyewall mesovortices in Hurricane Debby (1982) using airborne Doppler radar data. Mesovortices were also seen in satellite images in Hurricane Isabel (2003) by Kossin and Schubert [3] and analyzed in Doppler radar data in Hurricane Guillermo (1997) by Reasor et al. [4]. Such vortical features are also clearly shown in several recent high-resolution cloudrepresenting numerical model simulations [5, 6], as well as in two-dimensional turbulence-resolving numerical models [7, 8]. The mesovortices are tied to the combined baratropic-baroclinic instability that is associated with the annulus of high potential vorticity near and within
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