Jian-Wen BaoChristopher W. Fairall
Sara A. MichelsonLaura Bianco
NOAA/ESRL/Physical Sciences Division
in collaboration with N. Surgi, Y. Kwon and V. Tallapragada of NCEP/EMC
Impact of Sea Spray on the Balance of Turbulent Kinetic
Energy in the Hurricane Surface Boundary Layer
Presented atThe 63rd Interdepartmental Hurricane Conference
Saint Petersburg, FL, March 4, 2009
Outline• A Two-Phase Flow Problem
- Thermal effects: release of sensible and latent heat
- Mechanical effects: suspension against gravitation
• 1-D Modeling of Equilibrium SBL Flow- Balance of turbulent kinetic energy (TKE)
• Parameterization in NWP Models - Extension of the Monin-Obukhov similarity theory
• Summary of the HWRF Model Testing
Ocean
Atmosphere Sea Spray
by P. Black
Ocean surface whitecaps and foam streaks in a hurricane at wind speeds of ~46 m/s
1-D Spray–Laden Atmospheric Boundary Layer Model (Kepert, Fairall and Bao, 1999)
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Left: Mass averaged droplet radius as a function of the 10-m wind speed.Right: Mass of the droplets as a function of the 10-m wind speed
Fairall et al. (2008) Fairall et al. (2008)
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Flux Richardson Number at 12 M
Droplet Richardson Number at 12 M
Summary of the 1-D Simulations
• The suspension of sea-spray droplets reduces the buoyancy and makes the surface layer more stable, reducing the friction velocity and the downward turbulent mixing of momentum.
• Sea-spray droplets tend to cool and moisten the surface boundary layer at winds below 35 ms-1 , but they tend to warm and moisten the surface boundary layer at winds above 50 ms-1.
• The sign of the flux Richardson number is opposite to the droplet Richardson number at hurricane-strength winds.
• The effect of the flux Richardson number is smaller than that of the droplet Richardson number at hurricane-strength winds, rendering the overall effect of sea-spray to be that the vertical mixing of both momentum and heat are enhanced.
The NOAA/ESRL Parameterization Scheme of Sea Spray in the HWRF Model
• A physical model of sea-spray generation function consistent with wave breaking dynamics
• An extension of the Monin-Obukhov similarity framework to take into account the feedback effects
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HWRF Evaluation: Dennis (2005)
Track Error Comparison, 2005 Atlantic Hurricanes: DENNIS
0
20
40
60
80
100
120
140
160
0 12 24 36 48 60 72 84 96 108 120Forecast Hour
Ave
rage
Tra
ck E
rror
(nm
)
Benchmark 2008
Sea SprayParameterization
Intensity Error Comparison, 2005 Atlantic Hurricanes: DENNIS
0
5
10
15
20
25
30
35
40
0 12 24 36 48 60 72 84 96 108 120Forecast Hour
Ave
rage
Inte
nsity
Err
or (k
ts)
Benchmark 2008
Sea SprayParameterization
#cases(13) (13) (13) (13) (13) (11) (9) (7) (13) (13) (13) (13) (13) (11) (9) (7)
Track Error Comparison, 2005 Atlantic Hurricanes: DENNIS
0
20
40
60
80
100
120
140
160
0 12 24 36 48 60 72 84 96 108 120Forecast Hour
Ave
rage
Tra
ck E
rror
(nm
)
Benchmark 2008
Sea SprayParameterization
Intensity Error Comparison, 2005 Atlantic Hurricanes: DENNIS
0
5
10
15
20
25
30
35
40
0 12 24 36 48 60 72 84 96 108 120Forecast Hour
Ave
rage
Inte
nsity
Err
or (k
ts)
Benchmark 2008
Sea SprayParameterization
HWRF Evaluation: Katrina (2005)
Track Error Comparison, 2005 Atlantic Hurricanes: KATRINA
0
50
100
150
200
250
300
350
0 12 24 36 48 60 72 84 96 108 120Forecast Hour
Ave
rage
Tra
ck E
rror
(nm
)
Benchmark 2008
Sea SprayParameterization
Intensity Error Comparison, 2005 Atlantic Hurricanes: KATRINA
0
10
20
30
40
50
60
0 12 24 36 48 60 72 84 96 108 120Forecast Hour
Ave
rage
Inte
nsity
Err
or (k
ts)
Benchmark 2008
Sea SprayParameterization
#cases(13) (13) (12) (11) (10) (8) (6) (4) (13) (13) (12) (11) (10) (8) (6) (4)
Track Error Comparison, 2005 Atlantic Hurricanes: KATRINA
0
50
100
150
200
250
300
350
0 12 24 36 48 60 72 84 96 108 120Forecast Hour
Ave
rage
Tra
ck E
rror
(nm
)
Benchmark 2008
Sea SprayParameterization
Intensity Error Comparison, 2005 Atlantic Hurricanes: KATRINA
0
10
20
30
40
50
60
0 12 24 36 48 60 72 84 96 108 120Forecast Hour
Ave
rage
Inte
nsity
Err
or (k
ts)
Benchmark 2008
Sea SprayParameterization
Summary of the HWRF Testing
• For strong storms (such as Katrina and Rita), the scheme tends to produce a greater positive bias of intensity during the first 48-72 hours than the control runs, while the impact on track is negligible.
• For weak storms (such as Dennis), the scheme tends to produce an intensity bias that varies around that of the control runs, while the track is degraded slightly after 72 hours.
• The storm structure is affected by the sea-spray mediated momentum and heat fluxes, suggesting a strong connection between the surface fluxes and the vortex dynamics through the convection in the eyewall (not shown).
• The performance of the scheme can be improved by tuning the source function and the degree of feedback effects.
Vertical profiles of absolute change in wind speed for: 10-m wind speed = 50 ms-1,droplet radius = 450 mm, mass of the droplets = 4.8*10-2 Kg/m2/s,
potential evaporation = 120000 (W m-2)
Vertical profiles of heat fluxes for: 10-m wind speed = 50 ms-1, droplet radius = 450 mm, mass of the droplets = 4.8*10-2 Kg/m2/s,
potential evaporation = 120000 (W m-2)
