Wind stress: primary dynamic force for the upper layer turbulence and circulation : A Part from the Book Chapter : Seasonal Variability of Mixed Layer Depth in the Red Sea

The oceanic heat loss cools the mixed layer and weakens the stratification, leading to strong mixing and a deeper MLD. Similarly, the heat gain warms the mixed layer and strengthens the stratification, leading to weak mixing and shallow MLDs. The fresh-water loss makes the surface water denser, leading to enhanced mixing and deeper MLDs, while the fresh-water gain makes the surface water lighter, leading to diminished mixing and shallow MLDs. The momentum transmitted to the ocean through the wind stress acts as the primary dynamic force for the upper layer turbulence and circulation. The shear and stirring generated by the wind stress enhance the vertical mixing and play a major role in controlling the deepening of the oceanic mixed layer. In some regions, the mixed layer variability is mainly controlled by wind stress.

Author(s) Details:

P. Abdulla
Applied Research Center for Environment and Marine Studies, Research Institute, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia.

A. Alsaafani
Department of Marine Physics, King Abdulaziz University, Jeddah 80200, Saudi Arabia

M. Alraddadi
Department of Marine Physics, King Abdulaziz University, Jeddah 80200, Saudi Arabia

T. M. Asharaf
Applied Research Center for Environment and Marine Studies, Research Institute, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia.

M. Albarakati
Department of Marine Physics, King Abdulaziz University, Jeddah 80200, Saudi Arabia

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Recent Global Research developments in Seasonal Variability of Mixed Layer Depth in the sea

1. Mixed Layer Deepening due to Wind-Induced Shear-Driven Turbulence and Scaling of the Deepening Rate in the Stratified Ocean

• In this study, researchers investigated the deepening of the mixed layer (ML) in the stratified ocean due to wind-induced shear-driven turbulence.
• Key findings include:
  • The ML deepens rapidly until one-half inertial period (0.5 Tf), after which the deepening rate slows down but continues gradually.
  • The MLD at 0.5 Tf is approximately 1.6–1.7 times the friction velocity divided by the square root of the product of the Brunt-Väisälä frequency and the Coriolis parameter (U∗/√(Nf)).
  • The deepening rate depends on the Rossby number and the Froude number.
  • Time-dependent scaling of MLD is necessary for more accurate estimates than classical theories [1].

2. Quantifying the Role of Ocean Dynamics in Ocean Mixed Layer Temperature Variability

• This study quantifies the contributions of ocean dynamical processes to mixed layer temperature variability globally.
• The research spans various time scales and uses available measurements and two different methods to assess the role of ocean dynamics [2].

3. On Leakage of Energy from Turbulence to Internal Waves in the Oceanic Mixed Layer

• This study addresses the energy leakage from turbulence to internal waves (IWs) in the oceanic mixed layer (OML).
• Understanding this process is crucial for comprehending energy transfer and mixing in the upper ocean [3].

References:

1. Ushijima, Y., & Yoshikawa, Y. (2020). “Mixed layer deepening due to wind-induced shear-driven turbulence and scaling of the deepening rate in the stratified ocean.” Ocean Dynamics, 70(4), 505–512. DOI: 10.1007/s10236-020-01344-w
2. Thompson, P. R., & Patrizio, V. (2021). “Quantifying the Role of Ocean Dynamics in Ocean Mixed Layer Temperature Variability.” Journal of Climate, 34(7), 2667–2682. DOI: 10.1175/JCLI-D-20-0476.1
3. Polzin, K. L., & Lvov, Y. V. (2007). “On Leakage of Energy from Turbulence to Internal Waves in the Oceanic Mixed Layer.” Ocean Dynamics, 57(1), 1–8. DOI: 10.1007/s10236-006-0100-3

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