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A Versatile Laboratory Approach to Reproduce and Analyze Internal Ocean Wave Dynamics

Vohn Jacquez, Zachary Phan, Zachary Taebel, Dylan Brunei, Pierre-Yves Passaggia, Alberto Scotti

Abstract

Internal waves, or waves that propagate within a stratified fluid, may break and cause mixing. While each individual mixing event may be small, collectively, internal wave breaking drive processes in the ocean that are critical to understanding the maritime climate and biosphere. In this paper we show how to set up an experiment, suitable for an undergraduate-level lab, that illustrates a common generation and breaking mechanism in the ocean. In particular, we show how the process changes in response to a non dimensional parameter, the buoyancy Reynolds number, that can be easily varied. This parameter highlights the role of viscous vs. inertial/buoyancy forces. We outline our methods of creating a linear stratification, injecting energy with a forced topography, and analyzing the resulting dynamics with Background Oriented Schlieren and energy spectra from a conductivity probe. By altering our forcing to accommodate three values of the buoyancy Reynolds, three distinct internal wave regimes can be observed: no turbulence, slight turbulence, and extreme turbulence. Our methods aim to increase the accessibility to studying these internal waves in future experimental work, ocean modeling, and math and physics undergraduate learning.

A Versatile Laboratory Approach to Reproduce and Analyze Internal Ocean Wave Dynamics

Abstract

Internal waves, or waves that propagate within a stratified fluid, may break and cause mixing. While each individual mixing event may be small, collectively, internal wave breaking drive processes in the ocean that are critical to understanding the maritime climate and biosphere. In this paper we show how to set up an experiment, suitable for an undergraduate-level lab, that illustrates a common generation and breaking mechanism in the ocean. In particular, we show how the process changes in response to a non dimensional parameter, the buoyancy Reynolds number, that can be easily varied. This parameter highlights the role of viscous vs. inertial/buoyancy forces. We outline our methods of creating a linear stratification, injecting energy with a forced topography, and analyzing the resulting dynamics with Background Oriented Schlieren and energy spectra from a conductivity probe. By altering our forcing to accommodate three values of the buoyancy Reynolds, three distinct internal wave regimes can be observed: no turbulence, slight turbulence, and extreme turbulence. Our methods aim to increase the accessibility to studying these internal waves in future experimental work, ocean modeling, and math and physics undergraduate learning.
Paper Structure (12 sections, 27 equations, 6 figures, 1 table)

This paper contains 12 sections, 27 equations, 6 figures, 1 table.

Table of Contents

  1. Introduction
  2. Theory
  3. Characterizing the Abyssal Ocean Interior
  4. Parameters of Nonlinearity
  5. Deriving a novel buoyancy Reynolds number
  6. Methods
  7. Materials Used
  8. Setup and Procedure
  9. Data Collection
  10. Results and Discussion
  11. Conclusions
  12. Author Declarations

Figures (6)

  • Figure 1: Schematic of the 'two-bucket' method. Pump 1 pumps freshwater from tank F into tank S (which has been previously filled with saltwater) at rate $R_1$. A bilge pump (not shown in the schematic) in Tank S mixes the tank vigorously. Pump 2 simultaneously moves the mixed solution through the diffuser and into the tank at rate $R_2=2R_1$.
  • Figure 2: Experimental setup utilizing the 'two-bucket' method. Pumps 1 and 2 (BT-300EA JIHPUMP) move water through Tanks S and F as bilge pumps (Maxzone Bilge Pump 1100GPH Mod. A01-111001) mix water in Tank S. Diffuser is made of sponge and floats on the water level as water is pumped into tank.
  • Figure 3: Wavetank apparatus for internal wave generation and measurement. Casting conductivity probe (left) yields a pre-experiment BV frequency. Waves are formed by oscillating the topography (center) with a stepper motor. Stationary conductivity probe (right) identifies energetic frequencies.
  • Figure 4: Magnitude of buoyancy gradient squared $|\nabla b|$ (in s$^{-2}$) obtained from BOS for Configuration 1, $Re_b = 0.0076$. The superimposed vector represents the expected angle $\phi = 48.689^{\circ}$ from the dispersion relation. Data taken from 452 seconds after the onset of forcing and smoothed using splinesgarcia2010robust,gargett1981composite.
  • Figure 5: Magnitude of buoyancy gradient $|\nabla b|$ (in s$^{-2}$) obtained from BOS for (a) $Re_b = 0.0076$. (b) $Re_b = 0.0752$, and (c) $Re_b = 0.7256$. Topographic shape is superimposed. Data taken from 1835 s after the onset of forcing, and smoothed using splinesgarcia2010robust,gargett1981composite.
  • ...and 1 more figures