Turbulent Transport Mechanism in the Surface Layer over the Tropical Ocean

Abstract

Turbulent flux measurements by the eddy correlation method were performed on board a ship in the tropical western Pacific during the summer MONEX field phase.The turbulent fluxes of momentum, sensible heat, and latent heat were estimated for three different stages, -the disturbed period influenced by the ITCZ, the equatorial doldrums, and the undisturbed period. The average Bowen ratio was 0.068 for the undisturbed period and 0.136 for the disturbed period. The Bowen ratio also varied significantly during the passage of a local convective disturbance.The reduced bulk transfer coefficients were 1.04*10-3 for momentum, 1.50*10-3 for sensible heat, and 0.91*10-3 for latent heat. These bulk transfer coefficients were mostly consistent with other results obtained over the tropical oceans. The drag coefficient was almost constant in the moderate wind speed range (1.5 < U < 8 m/s).In unstable conditions, */u*, */u*, */T*, and *q/q* were well expressed by the universal functions of z/L predicted by the Monin-Obukhov similarity theory. The proportional constants, Cu, C*, CT, and Cq were 2.37, 1.78, 1.82, and 1.36, respectively, and neutral values were *u/u* =2.53 and aw /u* =1.68, respectively.The u spectrum displayed the -2/3 fall-off for f > 0.2, and agreed well with Kaimal's unstable limit for f <0.2. The w spectrum had the expected -2/3 fall-off, and also showed a marked bimodal shape. However, the whole shape agreed approximately with Kaimal's unstable limit. The temperature spectrum had a plateau between 0.2 <f<2.0, and agreed well with Kaimal's unstable limit for f< 0.2. The humidity spectrum agrees approximately with Kaimal's temperature spectrum, and was similar to the horizontal velocity spectrum.A flatter shape was apparent in the uw cospectrum, and the wT cospectrum exhibited a plateau for 0.2<f<1. The wq cospectrum approximately followed Kaimal's generalized form of the wT cospectrum for f<2.

Bulk parameterization of air‐sea fluxes for Tropical Ocean‐Global Atmosphere Coupled‐Ocean Atmosphere Response Experiment

“…Because 1-hour average point winds of less than 4 m S -1 OCCUr about half of the time in the COARE region, particular attention must be paid to this problem. Recent experimental studies in the COARE region have shown unequivocally that the scalar fluxes do not go to zero in the limit of eero mean wind Fujitani, 1992;Young et al, 1992;Bradley etal., 1993; Greenhut and Khalsa, 1995…”

Shipborne Wind Measurement and Motion-induced Error Correction of a Coherent Doppler Lidar over the Yellow Sea in 2014

“…There are a number of studies on the turbulent fluxes measurement over the sea surface. Various motion sensing techniques on the moving platform have been developed in the field of airborne (Axford, 1968), spaceborne (Hawley et al, 1993), and shipborne observations (Fujitani, 1992;Song et al, 1996;Edson et al, 1998;Miller et al, 2008;Tucker et al, 2009). Many shipborne field experiments have been widely carried out over Pacific Ocean (Mitsuta and Fujitani, 1974;Bradley et al, 1991;Shao, 1995;Tsukamoto et al, 1995;Tucker et al, 2009).…”

“…One of the most common direct techniques for measuring surface fluxes is eddy correlation, which utilizes the covariance of mixing ratios and vertical wind velocity (Lenschow et al, 1981;Anctil et al, 1994;Fairaill et al, 2000), but wind velocity retrieval is complicated by contamination due to platform motion, representing a major source of uncertainty in measurement of turbulence and air-sea interaction. Several techniques have been used to correct the wind vector measured at sea for the influence of platform motion (Fujitani, 1992;Dunckel et al, X. Zhai et al: Shipborne Wind Measurement and Motion-induced Error Correction 1974;Song et al, 1996;Edson et al, 1998;Schulz et al, 2005). Fujitani (1985) used a stable platform System (SPS) consisting of a vertical, gyro-stabilized system and three accelerometers to measure the turbulent flux on the ship, and concluded that this system was applicable to measurement under rough sea surface conditions.…”

Shipborne Wind Measurement and Motion-induced Error Correction by Coherent Doppler Lidar over Yellow Sea in 2014

“…There are many studies on the turbulent fluxes measurement over the sea surface (Axford, 1968;Mitsuta et al, 1974;Bradley et al, 1991;Fujitani, 1992;Hawley et al, 1993;Shao, 1995;Tsukamoto et al, 1995;Song et al, 1996;Edson et al, 1998;Miller et Atmos. Meas.…”

“…One of the most direct techniques for measuring surface fluxes is eddy-correlation, which utilizes the covariance of mixing ratios and vertical wind velocity (Lenschow et al, 1981;Anctil et al, 1994;Fairaill et al, 2000), but the wind velocity is complicated by the contamination due to platform motion, representing a major source of uncertainty in measurement of turbulence and air-sea interaction. Several techniques have been used to correct the wind vector measured at sea for the efforts of platform motion (Fujitani, 1992;Dunckel et al, 1974;Song et al, 1996;Edson et al, 1998;Schulz et al, 2005). Fujitani 5 (1985) used a Stable Platform System (SPS) consisting of a vertical gyro-stabilized system and three accelerometers to measure the turbulent flux on the ship, and concluded that this system was applicable to measurement under the rough sea surface condition.…”