Atmospheric Boundary Layer Turbulence in the Presence of Swell: Turbulent Kinetic Energy Budget, Monin–Obukhov Similarity Theory, and Inertial Dissipation Method

Turbulence over the mobile ocean surface has distinct properties compared to turbulence over land. Thus, findings that are based on the turbulent kinetic energy (TKE) budget and Monin–Obukhov similarity theory (MOST) over land may not be applicable to conditions over ocean partly because of the existence of a wave boundary layer (the lower part of atmospheric boundary layer including effects of surface waves; we used the term “WBL” in this article for convenience), where the total stress can be separated into turbulent stress and wave coherent stress. Here the turbulent stress is defined as the stress generated by wind shear and buoyancy, while the wave coherent stress accounts for the momentum transfer between ocean waves and atmosphere. In this study, applicability of the turbulent kinetic energy (TKE) budget and the inertial dissipation method (IDM) in the context of the MOST within the WBL are examined. It was found that turbulent transport terms in the TKE budget should not be neglected when calculating the total stress under swell conditions. This was confirmed by observations made on a fixed platform. The results also suggested that turbulent stress, rather than total stress, should be used when applying the MOST within the WBL. By combining the TKE budget and MOST, our study showed that the stress computed by the traditional IDM corresponds to the turbulent stress rather than the total stress. The swell wave coherent stress should be considered when applying the IDM to calculate the stress in the WBL.

Atmospheric boundary layer turbulence in the presence of swell: turbulent kinetic energy budget, Monin-Obukhov similarity theory and inertial dissipation method

<p><span>Turbulence over the mobile ocean surface has distinct properties compared to turbulence over land. This raises the issue of whether functions such as the turbulent kinetic energy (TKE) budget and Monin-Obukhov similarity theory (MOST) determined over land are directly applicable to ocean surfaces because of the existence of a wave boundary layer (the lower part of atmospheric boundary layer including effects of surface waves. We used the term “WBL” in this article for convenience), where the total stress can be separated into turbulent stress and wave coherent stress. Here the turbulent stress is defined as the stress generated by wind shear and buoyancy, and wave coherent stress accounts for the momentum transfer between ocean waves and atmosphere. In this study, applications of the turbulent kinetic energy (TKE) budget and the inertial dissipation method (IDM) in the context of the Monin-Obukhov similarity theory (MOST) within the WBL are examined. It was found that turbulent transport terms in the TKE budget should not be neglected when calculating the total stress under swell conditions. This was confirmed by observations made on a fixed platform. The results also suggested that turbulent stress, rather than total stress should be used when applying the MOST within the WBL. By combing the TKE budget and MOST, our study showed that the stress computed by the traditional IDM corresponds to turbulent stress rather than total stress. The swell wave coherent stress should be considered when applying the IDM to calculate the stress in the WBL.</span></p>

Measured and Parameterized Energy Fluxes Estimated for Atlantic Transects of R/V Polarstern

Sensible and latent heat fluxes were estimated from turbulence measurements gathered during several Atlantic Ocean transects of the research vessel (R/V) Polarstern. The inertial dissipation method was used to analyze the data. Resulting bulk transfer coefficients were then applied to the data from the ship’s meteorological system to get continuous time series of the heat fluxes. Combined with the measured downward solar and longwave radiation fluxes it allows for an estimate of the total energy budget at the air–sea interface. Comparing these parameterized energy fluxes to those based on the Coupled Ocean–Atmosphere Response Experiment, version 3 (COARE3.0), bulk flux algorithm shows very strong agreement.

Characteristics of the near-surface turbulence during a bora event

During a bora event, the turbulence is strongly developed in the lee of the Dinaric Alps at the eastern Adriatic coast. In order to study its properties, a 3-D ultrasonic anemometer operating at 4 Hz sampling frequency was placed in the town of Senj at 13 m above ground. The strong bora case that occurred on 7 January and lasted till 11 January 2006 is analyzed here. This data set is used for evaluation of the turbulent kinetic energy, TKE, and its dissipation rate, ε. The computation of ε is performed using the inertial dissipation method. The empirical length scale parameter for this event is estimated with respect to ε and TKE. Some considerations about defining turbulent perturbations of the bora wind velocity are also pointed out.

Application of Coherent ADCP for Turbulence Measurements in the Bottom Boundary Layer

This paper presents a novel approach for estimating the rate of turbulent kinetic energy dissipation from pulse-coherent acoustic Doppler current profiler (ADCP) measurements using the inertial dissipation method. Although the inertial dissipation technique is widely accepted and used in oceanographic and atmospheric research, its application to ADCP data is limited by the loss of directional information for high-wavenumber velocity fluctuations. However, measurements in the bottom boundary layer of a lake revealed astonishing agreement between dissipation rates estimated from temperature microstructure profiles and those estimated by applying the inertial dissipation method to data from two different brands of ADCPs.