Geophysical Fluid Dynamics Laboratory ReviewOctober 29‐31, 2019
Mixing for the ocean surface boundary layer and
WAVEWATCH III model
B. Reichl
1Geophysical Fluid Dynamics Laboratory ReviewOctober 29‐31, 2019
Focus: Improving representation of air‐sea interface physics in GFDL’s climate models
• Developed an energetic Planetary Boundary Layer (ePBL)ocean surface mixing framework for climate simulation
• Used a process level approach to introduce Langmuir turbulence to ePBL, reducing bias in ocean vertical mixing
• Examining wave coupled models at GFDL and NCEP to enhance NOAA weather and climate simulation capabilities
Introduction
2Geophysical Fluid Dynamics Laboratory ReviewOctober 29‐31, 2019
Upper Ocean Mixing For Climate Models‐ Parameterized mixing schemes should be efficient & robust‐ ePBL uses 1st order approach trained with 2nd moment & LES results
Simplicity:(Physics)
Cost:(Numerics)
LES2nd Moment
ClosureTKE
Closure1st Order Schemes
Bulk Boundary layer
Constant mixing coefficients
Cheap Expensive
Simple Complex
3Geophysical Fluid Dynamics Laboratory ReviewOctober 29‐31, 2019
ePBL uses an implicit, non‐local energeticmixing constraintWhy? Robust to numeric constraints (grid & time step)
ePBL: Implicit Numerics
Reichl and Hallberg, 2018, OMLarge et al., 1994Rodi, 1987
ΔZ = 1 m, ΔT = 30 s ΔZ = 20 m, ΔT = 30 s ΔZ = 1 m, ΔT = 7200 s ΔZ = 20 m, ΔT = 7200 s
4Geophysical Fluid Dynamics Laboratory ReviewOctober 29‐31, 2019
ePBL: Accurate Physics‐ Mixing constraints for ePBL validated from Large Eddy Simulations‐ LES also used to add wave effects on mixing (ePBL ePBL‐LT)
Reichl and Hallberg, 2018 OM; Reichl and Li, 2019, JPO
Turbulent vertical buoyancy flux
Time 2π/f0
Dep
th [m
]
0
-60
Includes Waves
Langmuir Turbulence
Thorpe, 2004
Large Eddy Simulation, with waves
Dep
th [m
]
0
-60
Large Eddy Simulation, no waves
Increasing mixing
Para
met
eriz
ed M
ixin
g
Mixing in LES
ePBL
ePBL
Para
met
eriz
ed M
ixin
g
Mixing in LES
WithWaves
[m3 s-3]
[m3 s-3]
[m3 s-3]
[m3 s-3]
ePBL-LT
Para
met
eriz
ed M
ixin
g
Mixing in LES
WithWaves
[m3 s-3]
[m3 s-3]
5Geophysical Fluid Dynamics Laboratory ReviewOctober 29‐31, 2019
Ocean Mixing in GFDL Climate ModelsePBL helps improve simulated ocean mixed layer depth
Adcroft et al., 2019, JAMES Held et al., 2019, JAMES Dunne et al. (in prep)
Obs: Obs: Obs:
Obs: Obs: Obs:
10 50 7030
Summer MLDObs
OM2RMS: 5.48 m r2 = 0.70
OM4RMS: 3.06 m r2 = 0.73
CM3RMS: 4.98 m r2 = 0.64
ESM2MRMS: 5.21 m r2 = 0.48
CM4RMS: 3.21 m r2 = 0.70
ESM4RMS: 3.46 m r2 = 0.68
6Geophysical Fluid Dynamics Laboratory ReviewOctober 29‐31, 2019
ePBL helps improve simulated ocean mixed layer depth
Ocean Mixing in GFDL Climate Models
Adcroft et al., 2019, JAMES Held et al., 2019, JAMES Dunne et al. (in prep)
Obs: Obs: Obs:
Obs: Obs: Obs:
10 100 1000
ObsWinter MLD
OM2RMS: 68.60 m r2 = 0.34
OM4RMS: 44.34 m r2 = 0.41
CM3RMS: 91.37 m r2 = 0.24
ESM2MRMS: 70.53 m r2 = 0.24
CM4RMS: 45.34 m r2 = 0.54
ESM4RMS: 43.78 m r2 = 0.51
7Geophysical Fluid Dynamics Laboratory ReviewOctober 29‐31, 2019
GFDL‐NCEP Collaboration & WAVEWATCH III
Atmosphere
Land
Ocean
Imag
es: 1
-usr
a.ed
u, 2
-yal
e.ed
u, 3
-mit.
edu,
4-n
sidc
.org
, 5-n
oaa.
gov
Wind & Stokes Drift Correlation CoefficientJRA-55 + WAVEWATCH III, 2004‐ Ocean waves are critical
component of air‐sea physics‐ Yet, waves are not explicitly represented routinely in models
‐ Wave coupled models are critical to understand their impacts in Earth System Models
1.00.5
Increase of Summer MLD w/ wave mixing (ePBL-LT) 10m
-10m
8Geophysical Fluid Dynamics Laboratory ReviewOctober 29‐31, 2019
SummaryImproved representation of upper ocean physics
• ePBL in GFDL “4th generation” models (OM4, CM4, ESM4)• Implicit numerics w/ realistic physics• Wave‐driven mixing for realistic Southern Ocean
• WAVEWATCH III coupling for surface wave simulationFuture Work
• Apply ePBL principles continuously through water column• Bottom boundary layers• Breaking internal gravity waves• Internal tides
• Wave coupling• Improve air‐sea flux parameterizations (e.g. momentum, gases [CO2, Reichl and Deike, in revision], heat, mass)
• Represent wave/cryosphere interactions (sea ice, icebergs)• Sea‐state dependent sea‐salt aerosols• Weather vs climate scale: Wave variability and extremes