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Estimates of Drag Coefficients and S...

Hsu, Je-Yuan.

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Estimates of Drag Coefficients and Surface Waves under Tropical Cyclones Using Subsurface EM-APEX Floats.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Estimates of Drag Coefficients and Surface Waves under Tropical Cyclones Using Subsurface EM-APEX Floats./
Author:	Hsu, Je-Yuan.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2017,
Description:	177 p.
Notes:	Source: Dissertation Abstracts International, Volume: 79-05(E), Section: B.
Contained By:	Dissertation Abstracts International79-05B(E).
Subject:	Physical oceanography. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10686902
ISBN:	9780355597165

Estimates of Drag Coefficients and Surface Waves under Tropical Cyclones Using Subsurface EM-APEX Floats.
Hsu, Je-Yuan.

Estimates of Drag Coefficients and Surface Waves under Tropical Cyclones Using Subsurface EM-APEX Floats. - Ann Arbor : ProQuest Dissertations & Theses, 2017 - 177 p.

Source: Dissertation Abstracts International, Volume: 79-05(E), Section: B.

Thesis (Ph.D.)--University of Washington, 2017.

Nineteen autonomous EM-APEX floats were air-launched from aircraft to measure the profiles of ocean current velocity, temperature, salinity, and high-frequency velocity variance sigmau2 under five different tropical cyclones. In the first part of this work, the surface wind stress tau is estimated by integrating the float velocity measurements in the vertical, assuming a linear momentum budget balance. The biases and uncertainties of estimated tau are studied carefully, using the simulations of tropical cyclone-induced ocean response in the Price--Pinkel--Weller (PWP3D) model. The results are reliable only before passage of the storms' eyes. At wind speeds |U10| = 25--40 m s --1 the downwind drag coefficient C&par; is 1.1 --3.1 x 10--3 in the front-right sector of tropical cyclones and 0.8--1.7 x 10--3 in the front-left sector. At wind speeds |U10| > 40 m s--1, the C&par; is ~ 1.6 x 10 --3. The angle &phis; of drag tau is mostly clockwise from the wind U10 in the front-right sector of storms. A new parameter, the nondimensional effective wind duration zeta *, is proposed as a function of wind forcing, storm translation, and fetch length. The value of zeta* is shown to predict the values of C&par; and &phis;. C&par; increases with decreasing zeta *. We propose that surface waves with larger amplitude are forced more efficiently by the wind under faster storms, resulting in stronger surface wave breaking and thus higher C&par;. In the second part of this work, the peak frequency fp and significant wave height H s of surface waves are estimated under Typhoon Fanapi using a nonlinear least-squared fit of the modeled profiles to the profiles of sigma u2 measured by the floats, assuming the Joint North Sea Wave Project (JONSWAP) surface wave spectrum. The fp is 0.08--0.10 Hz, with the maximum fp (0.10 Hz) in the rear-left quadrant of Fanapi. The Hs is 6--12 m with the maximum in the rear sector of Fanapi. The results are then assessed and compared to the simulations in the WAVEWATCH III surface wave model. The contributions of this work, including the improvements to previous methods for estimating tau and surface waves using subsurface EM-APEX floats, the estimates of drag coefficients and &phis; under five tropical cyclones, and the data-based parameterization of drag coefficients in terms of surface waves' effects, are all important to future studies of tropical cyclone--wave--ocean interactions.

ISBN: 9780355597165Subjects--Topical Terms:

3168433
Physical oceanography.

Estimates of Drag Coefficients and Surface Waves under Tropical Cyclones Using Subsurface EM-APEX Floats.
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245 1 0 $a Estimates of Drag Coefficients and Surface Waves under Tropical Cyclones Using Subsurface EM-APEX Floats.
260 1 $a Ann Arbor : $b ProQuest Dissertations & Theses, $c 2017
300 $a 177 p.
500 $a Source: Dissertation Abstracts International, Volume: 79-05(E), Section: B.
500 $a Advisers: Ren-Chieh Lien; Eric A. D'Asaro.
502 $a Thesis (Ph.D.)--University of Washington, 2017.
520 $a Nineteen autonomous EM-APEX floats were air-launched from aircraft to measure the profiles of ocean current velocity, temperature, salinity, and high-frequency velocity variance sigmau2 under five different tropical cyclones. In the first part of this work, the surface wind stress tau is estimated by integrating the float velocity measurements in the vertical, assuming a linear momentum budget balance. The biases and uncertainties of estimated tau are studied carefully, using the simulations of tropical cyclone-induced ocean response in the Price--Pinkel--Weller (PWP3D) model. The results are reliable only before passage of the storms' eyes. At wind speeds |U10| = 25--40 m s --1 the downwind drag coefficient C&par; is 1.1 --3.1 x 10--3 in the front-right sector of tropical cyclones and 0.8--1.7 x 10--3 in the front-left sector. At wind speeds |U10| > 40 m s--1, the C&par; is ~ 1.6 x 10 --3. The angle &phis; of drag tau is mostly clockwise from the wind U10 in the front-right sector of storms. A new parameter, the nondimensional effective wind duration zeta *, is proposed as a function of wind forcing, storm translation, and fetch length. The value of zeta* is shown to predict the values of C&par; and &phis;. C&par; increases with decreasing zeta *. We propose that surface waves with larger amplitude are forced more efficiently by the wind under faster storms, resulting in stronger surface wave breaking and thus higher C&par;. In the second part of this work, the peak frequency fp and significant wave height H s of surface waves are estimated under Typhoon Fanapi using a nonlinear least-squared fit of the modeled profiles to the profiles of sigma u2 measured by the floats, assuming the Joint North Sea Wave Project (JONSWAP) surface wave spectrum. The fp is 0.08--0.10 Hz, with the maximum fp (0.10 Hz) in the rear-left quadrant of Fanapi. The Hs is 6--12 m with the maximum in the rear sector of Fanapi. The results are then assessed and compared to the simulations in the WAVEWATCH III surface wave model. The contributions of this work, including the improvements to previous methods for estimating tau and surface waves using subsurface EM-APEX floats, the estimates of drag coefficients and &phis; under five tropical cyclones, and the data-based parameterization of drag coefficients in terms of surface waves' effects, are all important to future studies of tropical cyclone--wave--ocean interactions.
590 $a School code: 0250.
650 4 $a Physical oceanography. $3 3168433
690 $a 0415
710 2 $a University of Washington. $b Oceanography. $3 2101461
773 0 $t Dissertation Abstracts International $g 79-05B(E).
790 $a 0250
791 $a Ph.D.
792 $a 2017
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10686902