In situ Measurements of Momentum Fluxes in Typhoons

Potter, Henry; Graber, Hans C.; Williams, Neil J.; Collins, Clarence O.; Ramos, Roberto; Drennan, William M.

doi:10.1175/jas-d-14-0025.1

Cited by 49 publications

(45 citation statements)

References 41 publications

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“…French et al (2007) found a roll-off at a much lower wind speed of about 21 ms −1 using direct observations from an aircraft, although they claimed to remain uncertain. A similar result obtained by Potter et al (2015) showed evidence of a rolloff C D at a wind speed of 22 ms −1 with the direct buoy observations in typhoons. Based on the wind profile measured from a tower, Zhao et al (2015) revealed that C D begins to decrease at wind speeds of 24 ms −1 .…”

Section: Discussionsupporting

confidence: 85%

“…Based on the wind profile measured from a tower, Zhao et al (2015) revealed that C D begins to decrease at wind speeds of 24 ms −1 . However, with the high-resolution wind profiles collected with GPS drop sondes, reported that C D begins to decrease at a wind speed of about 40 ms −1 , which is much greater than those of French et al (2007), Potter et al (2015) and Zhao et al (2015). It is clear that the critical wind speeds for maximum C D need to be investigated further.…”

Section: Discussionmentioning

confidence: 99%

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Drag coefficients derived from ocean current and temperature profiles at high wind speeds

Zou

Zhao

Tian

et al. 2018

Tellus A: Dynamic Meteorology and Oceanography

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Two bottom-up methods based on the turbulence closure and bulk model were utilised to estimate drag coefficients at high wind speeds based on ocean current and temperature profiles observed by two subsurface buoys during Typhoon Megi in the South China Sea. A numerical experiment was conducted using the turbulence closure model to test the impact of missing measurements in the upper mixed layer on the wind stress estimate and reconstruction of the upper ocean current. The results were sufficiently robust after several time steps. The wind stresses derived from the two methods were consistent with each other. Wind stress increased quickly with increasing wind force, and then was constant. A parametric typhoon wind model was applied to obtain the wind field and estimate the corresponding drag coefficient. The results showed that the drag coefficient increased to a maximum at a critical wind speed of about 30 m s −1 , and then levelled off with increasing wind speed. The uncertainty of the maximum drag coefficient was about ±0.5 due to neglect of nonlinear terms, the uncertainty of the model wind speeds and the drag coefficient. The critical wind speed for the maximum drag coefficient varied by at least ±5 m s −1 . The uncertainty of the drag coefficient parameterisation was about 24% due to wind speed. These results indicate that a bottom-up method can be used to estimate drag coefficients at the forced stage during the passage of typhoons or hurricanes.

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Section: Discussionsupporting

confidence: 85%

Section: Discussionmentioning

confidence: 99%

Drag coefficients derived from ocean current and temperature profiles at high wind speeds

Zou

Zhao

Tian

et al. 2018

Tellus A: Dynamic Meteorology and Oceanography

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“…The coupling resulted in more uniform peak and HF wave directions which no longer pointed in the wind direction. The high frequency waves were pulled away from the wind direction, ostensibly through interaction with the peak waves, and steered a shift in wind stress away from the wind direction as observed in Potter et al ().…”

Section: Resultsmentioning

confidence: 99%

Directional Wave Spectra Observed During Intense Tropical Cyclones

et al. 2018

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Two deep‐sea moorings were deployed 780 km off the coast of southern Taiwan for 4–5 months during the 2010 typhoon season. Directional wave spectra, wind speed and direction, and momentum fluxes were recorded on two Extreme Air‐Sea Interaction buoys during the close passage of Severe Tropical Storm Dianmu and three tropical cyclones (TCs): Typhoon Fanapi, Super Typhoon Megi, and Typhoon Chaba. Conditions sampled include significant wave heights up to 11 m and wind speeds up to 26 m s−1. Details varied for large‐scale spectral structure in frequency and direction but were mostly bimodal. The modes were generally composed of a swell system emanating from the most intense storm region and local wind‐seas. The peak systems were consistently young, meaning actively forced by winds, when the storms were close. During the peaks of the most intense passages—Chaba at the northern mooring and Megi at the southern—the bimodal seas coalesced. During Chaba, the swell and wind‐sea coupling directed the high frequency waves and the wind stress away from the wind direction. A spectral wave model was able reproduce many of the macrofeatures of the directional spectra.

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“…The spectra of discarded samples deviated from −5/3 power law, which indicated that the similarity theory was not satisfied [ Kaimal et al ., ]. If the temporal variation of the cumulative summation affects the total momentum flux sharply, the samples were also rejected [ French et al ., ; Potter et al ., ]. Only if the ogive curve approaches asymptotically a single value, the corresponding data can meet the stationary condition for the measurement and would be accepted [ French et al ., ; Potter et al ., ].…”

Section: Methodsmentioning

confidence: 99%

Investigation of turbulent momentum flux in the typhoon boundary layer

Duan¹,

Yao

Li³

et al. 2017

JGR Oceans

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Turbulent momentum flux in the typhoon boundary layer was measured at a turbulent flux tower in Southeast China using an eddy covariance technique during the passage of typhoons Fanapi and Megi in 2010. The anemometers were mounted on the cantilever bracket at the height of 26.6, 42.4, 60.4, and 82.9 m. The momentum flux in the typhoon boundary layer decreased with increasing height during the two typhoon passages. The decrease was nearly linear during the passage of the Typhoon Fanapi. However, in the boundary layer of the Typhoon Megi, the momentum flux at 26.6 m height was much greater than that at 42.4 m height. The cospectra of wind components showed that the enhanced flux at the bottom of the boundary layer was caused by small‐scale turbulence with frequency in the range of 0.1–1 Hz and can be explained by the turbulent energy accumulation of small‐scale turbulence.

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In situ Measurements of Momentum Fluxes in Typhoons

Cited by 49 publications

References 41 publications

Drag coefficients derived from ocean current and temperature profiles at high wind speeds

Drag coefficients derived from ocean current and temperature profiles at high wind speeds

Directional Wave Spectra Observed During Intense Tropical Cyclones

Investigation of turbulent momentum flux in the typhoon boundary layer

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