Direct Mixing Measurements using χpods in IWISE Profiling Dissipation Measurements using

1. Direct Mixing Measurements using χpodsin IWISE Profiling Dissipation Measurements using χpods on Moored Profilers (Moum/Nash) Shipboard LADCP/χpod profiling of Internal Wave Structure (Nash/Moum) Jonathan D. Nash & James N. Moum College of Earth, Ocean and Atmospheric Sciences Oregon State University with help from: Byungho Lim (OSU), Andy Pickering and Matthew Alford (APL-UW)and thanks to Ming-Huei Chang, Maarten Buijsman, Luc Rainville, Alexander Perlin, Ray Kreth, Mike Neeley-Brown, John Mickett, Eric Boget, Amy Waterhouse, Zoe Parsons, Jen MacKinnon, Harper Simmons

2. Objectives • General • quantify turbulence dissipation where large amplitude internal waves are generated • Particular • capture the energetics of the largest scales that directly extract energy from the barotropic tides • while simultaneously measuring mixing associated with the turbulence that occurs at millimeter and millisecond scales. • through direct observation, to assess the means by which waves form and break, elucidate the structure/evolution of the wave breaking, and quantify the dissipation that induces irreversible mixing

3. Methods • χpodson moorings Stablemoor

4. Methods • χpodson moorings • χpod-like devices on moored profilers

5. Methods χpod-LADCP • χpodson moorings • χpod-like devices on moored • χpod on shipboard CTD for full • ocean depth turbulence profiling

6. Methods • χpodson moorings • χpod-like devices on moored profilers • χpod on shipboard CTD for full ocean depth turbulence profiling • fabricated and deployed 5-component array of moorings to capture the 2D evolution of the larger-scale dynamics MP χpods

7. Profiling Dissipation Measurements using χpods on Moored Profilers data example fast thermistors on APL MP Kraichnan theoretical spectrum εχ=N2χ/(2 Γ Tz2) Products → LTThorpe (overturn) scales χT temperature variance dissipation rate KT turbulence diffusivity (Osborn-Cox) ε TKE dissipation rate (indirect) Km turbulence viscosity Tested – Puget Sound 2009 Refined for 2010 (MPN) Deployed 2011 on N1, N2 all data returned • 1st continuous deep-ocean profiling experiment • mesoscale current (Kuroshio?) dominates 2nd half • elevated turbulence at base of current • is this friction on a western boundary current?

8. New mean speed / dissipation sensor for use on χpods and in general on moorings inexpensive, lightweight, low power, standalone velocity sensor χpod compensated pitot tube mooring N1 – χpod at 2000 m 1 day time series leading to a new GustT combination probe dissipation sensor at high f speed sensor at low f not acoustic, hence requires no scatterers quiet ε=2x10-7 m2s-3 • characterization of sensor includes tests in • wind tunnel • tidal channel • P / T chambers

9. 2nd continuous deep turbulence profiling time series N2 (1830m water depth) 2011 2 units constructed and deployed – both worked – only 1 MP profiled

10. Above: TKE dissipation rate from LADCP/chipods (green) and Thorpe analyses (blue) at one of the most energetic stations sampled during IWISE. fast-T 3-axis accel 3-axis gyro compass USB-data inferred turbulence (blue) direct turbulence (green) Nash & Moum • OSU Ocean Mixing χ-pod/LADCP • direct measurements of abyssal turbulence from standard shipboard CTD. • permits rapid deep profiling • direct turbulence differs from that inferred from overturns • low noise-floor (but N2-dependent) Chipod-LADCP-CTD

11. contrasting structures from detailed measurements at 2 ridges 1) broadly-distributed dissipation on the east ridge 2) big breaking lee waves on the west ridge MP chipods east west

12. mid-column dissipation not dominated by a single breaking wave… A1 – mid-column dissipation at the generation site 1440 m water depth Byungho Lim

13. similar tidal fields, but water-column instabilities are not captured by MITgcm and model dissipation is mostly near the bottom. A1 – mid-column dissipation at the generation site observation / model comparison (MITgcm / Buijsman) Byungho Lim

14. eastward westward west Jonathan Nash Buijsman et al T2 T1 N2 T3 T4 • 30-50 m sensor spacing to detect overturns • 2-sec sampling to capture inertial subrange • Vertical synopticity(test sampling schemes of other platforms) •  3 months data 500 m overturns east T-Chains on the West Ridge 700 m waves

15. T-Chains on the West Ridge spring tides / diurnal inequality T2 T1 N2 T3 T4 Mooring T3 during spring + diurnal inequality

16. T-Chains on the West Ridge neap tides / semidiurnal period T2 T1 N2 T3 T4 Mooring T3 during neap/semidiurnal period

17. Time – mean structure / east ridge T2 T1 N2 T3 T4 Springs (diurnal) • Dissipation tied to lee waves • Strong spring/neap changes • Isopycnals displaced down in the mean? • Lee-wave shifts closer to ridge crest during neaps? Neaps (semidiurnal)

18. Dissipation evolution and scaling ε~ u3bt T2 T2 T1 T1 N2 N2 T3 T3 T4 T4 • dissipation scales with u3bt(nonlinear!) • consistent with Klymak et al (2010)’s “recipe” for ε over a supercritical ridge … u3 because flux into trapped lee waves ~( ubtx u2bt ) …

19. Summary Results • 1st continuous turbulence profiling away from ship-based upper ocean measurements • χpod-CTD measurements have led to beginning of contribution to Global Repeat Hydrogaphy Program • NEW VELOCITY SENSOR - speed + turbulence • leading way to new possibilities • observational confirmation of Klymaketal (2010) ε scaling • breaking waves: vertically-integrated εO(1 W/m2) • comparable to flux divergence 5 kW/5 km • suggests significant local dissipative losses • vertically-distributed turbulence may be difficult to model but significant to water mass mixing through vertical flux divergence

20. Summary Results • continued contributions to NRL field science • MORT Mixing Over Rough Topography • BWE Breaking Wave Effects in High Winds • technological: • loan of OSU-developed instrumentation • technical-level analysis • scientific: • participation in science-level analysis • contribution to publications

21. Moored profiler χpod estimates of turbulence dissipation rate, ε LT – large-eddy length scale statistic simply computed from 1D profiles - but an imperfect statistic in an evolving 3D field Lo – large-eddy length scale defining buoyancy limit on turbulence Lo = √(ε/N3) if LT = Lo, then ε = LT2 N3 is LT = Lo?

22. Moored profiler χpod estimates of turbulence dissipation rate, ε same data – different definition of N2 LT – large-eddy length scale statistic simply computed from 1D profiles - but an imperfect statistic in an evolving 3D field Lo – large-eddy length scale defining buoyancy limit on turbulence Lo = √(ε/N3) if LT = Lo, then ε = LT2 N3 is LT = Lo?

25. pod How do we know χpods work? Equatorial Internal Wave Experiment 2008 7χpods on EQUIX mooring yields 7 time series of χ, ε 16-day experiment at 0, 140W Oct/Nov 2008 24h continuous profiling of χ, ε 6-10 profiles/h 5 χpods on TAO mooring yields 5 time series of χ, ε Perlin & Moum, 2012 JAOTech

26. pod How do we know χpods work? χ ε profiler χpods χpods Perlin & Moum, 2012 JAOTech

27. Comparison of ε computed from χpod and from pitot tube

28. A1 – mid-column dissipation at the generation site

29. Observation / model comparison at T3 Observation / Model comparison at T3 Andy Pickering

30. model does a pretty good job with the vertical distribution and daily-averages details are a little different Andy Pickering

31. T2 T2 T1 T1 N2 N2 T3 T3 T4 T4 MITgcm / Buijsmann et al 2013 Dissipation evolution / compare to MITgcm

32. First continuous deep turbulence profiling time series MP-N 2010 mesoscale current (Kuroshio?) dominates 2nd half elevated turbulence at base of current is this friction on a western boundary current?

33. T-Chains on the West Ridge spring diurnals vs. neap semidiurnals diurnal composite / spring semidiurnal composite / neap

34. Summary Results Buijsman et al • Distributed Mixing(detached from bottom) is difficult to model ε~ u3bt • Can models accurately capture mid-column ε and its vertical distribution? • Can we assign errorbounds on model ε? Conclusions ε~ u3bt log10ε observed Integrated Dissipation from big breaking waves contributes O(1 W/m2) vertically-integrated ε this suggests ΔFε= 5 kW/m in 5km… εis significant to FE!