Vertical Eddy Motion and Energy Transfer at Very Low Altitudes Over the Tropical Atlantic Ocean

We analyze gust probe measurements obtained in the convective boundary layer over the central equatorial Pacific as part of the Equatorial Pacific Ocean Climate Studies (EPOCS) program. From the lowest level flights, the bulk transfer coefficients are found to be 1.1 x 10e3 and 1.4~ 10m3 for latent and sensible heat fluxes, respectively. Vertical profiles of water vapor density, potential temperature and wind velocity are obtained as are the profiles of the fluxes of latent and sensible heat and momentum. From the extrapolated profiles, we obtain surface fluxes of 120 W m-s and 13 W m-' for latent and sensible heat, respectively, and 0.11 N m-* for momentum. The 10 m drag coefficient is 1.5 x 10m3. Two convergence boxes, north and south of the ITCZ, are analyzed. Enhanced convergence is found in the northern trades relative to the southern trades. The advective acceleration is found to be comparable in magnitude to the other terms in the horizontal equations of motion. B G CET CH Cur Cpd CW Boundary-Layer Meteorology 20 (1981) 221-241.

Section: Introductionmentioning

confidence: 99%

Aircraft measurements of boundary-layer turbulence over the central Equatorial Pacific Ocean

Greenhut¹,

Bean²

1981

“…Earlier papers by Riehl et al (1978) and Reinking (1980) have analyzed the vertical profiles of latent and sensible heat fluxes and the power spectra and cospectra of the relevant variables obtained from the DC-6 gust probe measurements. The present paper extends these analyses to momentum flux in the subcloud layer.…”

Section: Introductionmentioning

confidence: 99%

“…Although in the ideal situation all flight lengths are approximately equal, it appears that the fluxes and variances are relatively uncorrelated with flight leg length and therefore that the eddy parameters from each leg can be considered on an equal basis. Reinking (1980) has found that the correlation coefficient between length of flight leg and the variance of w', p: or T' or the fluxes of latent or sensible heat for a set of 35 GATE cases lies in the range 0 to 0.5. Thus, at most, only 30% of the variance of these parameters can be explained by a linear relationship with path length.…”

Section: Introductionmentioning

confidence: 99%

“…The correlation coefficient is 0.08. The corresponding equations obtained by Reinking (1980) for latent and sensible heat in clear conditions during GATE are:…”

Section: Introductionmentioning

confidence: 99%

“…This implies that weighting by flight length interval is not necessary when obtaining averages of the various eddy parameters at different height intervals. As a final piece of evidence, Reinking (1980) finds that using the chi-square 78 G. K. GREENHUT statistic, the 95% confidence intervals for at are nearly equal when weighted and unweighted averages are used. The height interval averages taken in the remainder of this paper will therefore be unweighted, each individual sample being treated equally.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of aircraft measurements of momentum flux in the subcloud layer over the tropical atlantic ocean during gate

Greenhut¹

1981

The momentum flux data obtained by the gust probe aboard the NOAA DC-6 aircraft during GATE are analyzed. Vertical profiles are obtained for Phases I and III and correlated with vertical wind velocity profiles using the geostrophic departure method. Reasonable agreement is obtained using the horizontal equations of motion with negligible advective acceleration. The vertical profiles of momentum flux and wind speed variance compare well with the numerical model results of Deardorff (1972) and Wyngaard et al. (1974). Vertical distributions of power spectra for vertical eddy motion and cospectra corresponding to the momentum flux components are obtained along with the height variation of the dominant length scales of vertical eddy motion and the dissipation rate of turbulence kinetic energy. When normalized by mixed-layer similarity, these results agree well with previous determinations in the boundary layer over tropical oceans and over land.

A comparison of tropical oceanic heat fluxes determined by airborne eddy correlation and shipboard bulk aerodynamic techniques

Reinking¹,

Barnes

1981

Vertical turbulent transports of latent and sensible heat through the tropical marine boundary layer were measured with ship and airborne instruments in the GATE experimental area. The measurements from the two systems are compared for cases of simultaneous sampling in the same locations during undisturbed weather and during the wakes of convective disturbances. The paired average fluxes from the airborne eddy correlation measurements and the shipboard bulk aerodynamic measurements, for undisturbed weather, are related with correlation coefficients in the range of 0.6 to 0.9; the correlations depend primarily on stratifications of the aircraft data according to sampling altitude (15-153 m msl) and flight pattern relative to the mean wind. The agreement between the two types of measurements is best for ship data paired with aircraft samples from the lowest altitudes (15 and 30 m) and from alongwind rather than crosswind Rights, as is appropriate since the stationary ships monitor the alongwind characteristics of the turbulence. The use of long (l-3 hr) versus short (10 min) ship samples did not significantly affect the comparability with the aircraft samples during undisturbed periods.The good baseline comparability demonstrated by the undisturbed-weather comparisons was applied to interpret the results from the wakes behind showers. Although these paired measurements were few, not only the sensible heat, but also the latent heat flux was shown to decrease substantially with altitude from 10 m to at least 150 m in the wakes, where the mixing was relatively intense. Variations in the fluxes were much greater at the higher level than nearer the sea surface.