1. Estimating Diffusivity from the Mixed Layer Heat and Salt Balances Meghan F Cronin 1, et al. 1 NOAA Pacific Marine Environmental Laboratory 4 April 2013 - Station P Science Workshop - NOAA PMEL, Seattle WA 4 April 2013 - Station P Science Workshop - NOAA PMEL, Seattle WA A companion paper to: Cronin et al., 2013: Formation and erosion of the seasonal thermocline in the Kuroshio Extension recirculation gyre. DSR II, 85, 62-74.

2. KEO Papa KEO Papa KEO Large Sfc Heat Loss Large CO 2 Uptake Fronts & Eddies Typhoons Deep wintertime mixed layer Mode water Papa Weak Sfc Heat Gain Weak CO 2 Uptake Subsfc Fronts & Eddies? Shallow halocline

3. Wind ATRH http://www.pmel.noaa.gov/ocs/ UV at 15m, & 35m http://www.pmel.noaa.gov/ocs/disdel/disdel.html TS Seacat strapped to release (Starting 2012) T upper 300m S upper 200m SWR-LWR Rain Wind ATRH BP SST&SSS Longranger ADCP at 835m (2008-2010) Narrowband ADCP at ~150m (2007-2010)

4. Q0= Net Surface Heat Flux (+ = into Ocean) Q0 = Qsw – Qlw – Qsen - Qlat

5. Q0= Net Surface Heat Flux (+ = into Ocean) Q0 = Qsw – Qlw – Qsen - Qlat Surface Heat Flux Warms Ocean Surface Heat Flux Cools Ocean

6. Wind ATRH http://www.pmel.noaa.gov/ocs/ UV at 15m, & 35m http://www.pmel.noaa.gov/ocs/disdel/disdel.html TS Seacat strapped to release (Starting 2012) T upper 300m S upper 200m SWR-LWR Rain Wind ATRH BP SST&SSS Longranger ADCP at 835m (2008-2010) Narrowband ADCP at ~150m (2007-2010)

7. Mixed Layer Depth Isothermal Layer Depth

8. Methodology For h = mixed layer depth, i.e. where Sfc MooringSfc +ADCP Moorings + satellite or glider Sfc Mooring + satellite Residual Sfc Mooring Rate of ML T change Due to SFC heat flux Due to horiz advection Due to entrainment (diapycnal w) Due to diffusion

9. Methodology w -h is Ekman balance with turbulent stress vanishing at z=-h=MLD small Assume steady state linear momentum equation… assume negligible

10. Methodology For h = mixed layer depth, i.e. Sfc MooringSfc +ADCP Moorings + glider (or as residual) Sfc Mooring + satellite Residual (or using κ T ) Sfc Mooring Rate of ML S change Due to Evap & Precp Due to horiz advection Due to entrainment (diapycnal w) Due to diffusion If salinity gradients can be estimated directly from glider data, then the residual of the salt budget provides an independent estimate of diffusivity.

11. Heat Budget Salt Budget

12. The correspondence between the diffusivity estimate from the heat & salt budgets gives us confidence that it can be used for other mixed layer budgets.

13. Papa diffusivity is 1x10 -4 m 2 /s during summer, 3x10 -4 m 2 /s during fall, and higher during spring. Diffusivity at Base of Mixed Layer inferred from mixed layer temperature budget KEO Papa THIS IS BIG !

14. At Papa, strong Near Inertial Oscillation (NIO) shear is observed during winter. Winter 2010 was stronger than 2009. At KEO, strong NIO shear is observed from May- March due to typhoons and winter storms.

15. Diffusivity at base of ML (weak advective periods) + Diffusivity at base of ML (weak advective periods) Error Error Inferred κ at Papa Inferred κ at KEO is 10 1 higher during summer and 10 1 -10 2 higher during winter

16. Relation between diffusivity and stratification KEO Papa Both sites show an approximate N -2 relationship for diffusivity. Slope = -1.9 Slope = -2.5

17. Summaryhttp://www.pmel.noaa.gov/OCS Heat gained through the surface by solar warming at Papa is exported into the deeper ocean, where it is presumably transported away. Diffusivity is not as large as at KEO. At KEO during summer κ ≈ 3x10 -4 m 2 /s. During winter, κ is > 5x10 -2 m 2 /s. Papa diffusivity is roughly 1x10 -4 m 2 /s during summer and 3x10 -4 m 2 /s during fall. Salinity advection appears to be an order 1 process in the mixed layer.