Seasonal and regional variability in turbulence below the mixed layer in the North Pacific Ocean
Open Access
- Author:
- Creedon, Ryan P
- Area of Honors:
- Meteorology
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Raymond Gabriel Najjar Jr., Thesis Supervisor
Johannes Verlinde, Thesis Honors Advisor - Keywords:
- meteorology
oceanography
turbulence
diffusivity
mixed layer
Richardson number - Abstract:
- Closures of upper-ocean heat budgets at National Oceanic and Atmospheric Administration North Pacific moorings KEO (32.3°N, 144.6°E) and Papa (50.1°N ,144.9°W) suggest seasonal and regional variability in turbulent diffusion below the mixed layer. Motivated by this variability, this investigation combines two years of hourly Acoustic Doppler Current Profiler velocities with subsurface density profiles at KEO and Papa to estimate hourly Richardson numbers (Ri) below the mixed layer. Prevalence of shear-based turbulence PSBT, defined as the number of hours per day when Ri < 1 below the mixed layer, indicates potential occurrence of shear-based turbulence below the mixed layer from early to late spring at KEO and Papa. Moreover, PSBT at KEO is found to be larger than at Papa throughout the investigation and may be attributed to enhanced velocity shears below mixed layer at KEO, particularly in spring. Such seasonal and regional variability in PSBT resembles seasonal and regional variability found previously in diffusivities below the mixed layer. In particular, relatively large diffusivities during spring at KEO and Papa coincide with relatively large PSBT, and large diffusivities at KEO year-round relative to those at Papa are reflected in higher PSBT at KEO year-round. PSBT is also found to be enhanced during early to late fall at KEO and Papa, distinct from seasonal variability in diffusivities. However, evidence of similar weekly variability between peaks in diffusivities and PSBT is found at KEO during this time. In a separate analysis, diffusivities below the mixed layer are also found to correlate negatively with surface heat flux and positively with wind stress at KEO and Papa. These correlations are statistically significant at the 5% level and suggest local meteorological forcings on the ocean could present additional understanding of seasonal and regional variability observed in diffusivities below the mixed layer.