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Estimating Diffusivity from the Mixed Layer Heat and Salt Balances Meghan F Cronin 1 , et al.

Estimating Diffusivity from the Mixed Layer Heat and Salt Balances Meghan F Cronin 1 , et al. 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.

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Estimating Diffusivity from the Mixed Layer Heat and Salt Balances Meghan F Cronin 1 , et al.

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  1. Estimating Diffusivity from the Mixed Layer Heat and Salt BalancesMeghan F Cronin1, et al. 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. 1NOAA Pacific Marine Environmental Laboratory 4 April 2013 - Station P Science Workshop - NOAA PMEL, Seattle WA

  2. Papa Weak Sfc Heat Gain Weak CO2 Uptake Subsfc Fronts & Eddies? Shallow halocline KEO Large Sfc Heat Loss Large CO2 Uptake Fronts & Eddies Typhoons Deep wintertime mixed layer Mode water Papa KEO Papa KEO

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

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

  7. Mixed Layer Depth Isothermal Layer Depth

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

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

  10. Methodology For h = mixed layer depth, i.e. Due to Evap & Precp Rate of ML S change Due to horiz advection Due to diffusion Due to entrainment (diapycnal w) Sfc Mooring Sfc Mooring Sfc +ADCP Moorings + glider (or as residual) Sfc Mooring + satellite Residual (or using κT) 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. Diffusivity at Base of Mixed Layer inferred from mixed layer temperature budget Papa KEO THIS IS BIG ! Papa diffusivity is 1x10-4 m2/s during summer, 3x10-4 m2/s during fall, and higher during spring.

  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. Inferred κ at Papa + Diffusivity at base of ML (weak advective periods) Error Inferred κ at KEO is 101 higher during summer and 101-102 higher during winter

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

  17. Summary http://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 m2/s. During winter, κ is > 5x10-2 m2/s. Papa diffusivity is roughly 1x10-4 m2/s during summer and 3x10-4 m2/s during fall. Salinity advection appears to be an order 1 process in the mixed layer.

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