Dual-Doppler radar analysis of a near-shore line-shaped convective system on 27 July 2011, Korea: a case study

The interaction between waves, surges and tides is one of the main drivers of coastal total water levels (TWL). &#160;Understanding this interaction is crucial for studying high TWL formation near shore, and to do this it is important to not only evaluate how high the TWL is but also when and where it occurs.In this study we use a high resolution (1.5 km) three-way coupled (waves-atmosphere-ocean) numerical model developed by the MetOffice (UKC4) to study coastal conditions at the UK coast during the extreme events of winter 2013, which was chosen as case study because of the amount of flooding that occurred in relation to storms and surges during this period.For each coastal grid point the ten strongest storms of that winter, ranked by the significant wave height (Hs) magnitude, were selected. During these storm periods, the number of hours in which Hs and surges exceeded the 90th percentile of winter 2013 were evaluated considering what tidal stage they occurred on. The same was done for instances where high Hs and surges occurred simultaneously. The aim is to understand if specific areas were predominantly affected by one of the TWL components and how Hs and surges interacted with the tide. What was the spatial distribution of the waves, surges, and tides during winter 2013? Did extreme Hs and Surges occur more often over specific stages of the tidal cycle? Did they occur simultaneously?&#160;In this study we show that during the winter 2013, Hs and surges above the 90th percentile value did occur simultaneously at all stages of the tidal cycle. They more often occurred together over the rising tide with in average 8.7% and 8.6% of instances found two and three hours before high tide. In 7.7% of cases high wave and surges also concurred at high tide.

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Reintensification and Eyewall Formation in Strong Shear: A Case Study of Typhoon Noul (2015)

Monthly Weather Review ◽

10.1175/mwr-d-18-0035.1 ◽

2018 ◽

Vol 146 (9) ◽

pp. 2799-2817 ◽

Cited By ~ 2

Author(s):

Udai Shimada ◽

Takeshi Horinouchi

Keyword(s):

Doppler Radar ◽

Vertical Wind Shear ◽

Vertical Shear ◽

Tangential Wind ◽

Strong Shear ◽

Vertically Aligned ◽

Mean Structure ◽

Convection Dominated ◽

Left Quadrant

Abstract Strong vertical wind shear produces asymmetries in the eyewall structure of a tropical cyclone (TC) and is generally a hostile environment for TC intensification. Typhoon Noul (2015), however, reintensified and formed a closed eyewall despite 200–850-hPa vertical shear in excess of 11 m s−1. Noul’s reintensification and eyewall formation in strong shear were examined by using Doppler radar and surface observations. The evolution of the azimuthal-mean structure showed that the tangential wind at 2-km altitude increased from 30 to 45 m s−1 in only 5 h. During the first half of the reintensification, the azimuthal-mean inflow penetrated into the ~40-km radius, well inside the radius of maximum wind (RMW), at least below 4-km altitude, and reflectivity inside the RMW increased. As for the asymmetric evolution, vigorous convection, dominated by an azimuthal wavenumber-1 asymmetry, occurred in the downshear-left quadrant when shear started to increase and then moved upshear. A mesovortex formed inside the convective asymmetry on the upshear side. The direction of vortex tilt between the 1- and 5-km altitudes rotated cyclonically from the downshear-left to the upshear-right quadrant as the vortex was vertically aligned. In conjunction with the alignment, the amplitude of the wavenumber-1 convective asymmetry decreased and a closed eyewall formed. These features are consistent with the theory that a vortex can be vertically aligned through upshear precession. The analysis results suggest that the vortex tilt, vigorous convection, and subsequent intensification were triggered by the increase in shear in a convectively favorable environment.

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