ocean: wind-driven circulation - github pages · last time • ocean circulation • hydrostatic...
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![Page 1: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/1.jpg)
Ocean: wind-driven circulation
ATM2016
![Page 2: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/2.jpg)
Last time
• Ocean circulation
• Hydrostatic balance
• Geostrophic balance
• Thermal wind relationship
• Sea level and isopycnal (lines with the same density)
![Page 3: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/3.jpg)
Today
• Wind stress
• Wind-driven circulation
• Ekman transport
• Upwelling / Downwelling
• Ekman pumping
• Convergence / divergence
![Page 4: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/4.jpg)
Averaged wind speed
![Page 5: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/5.jpg)
Averaged wind stress
![Page 6: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/6.jpg)
Wind and wind stress
Wind = wind stress ?
Weak stress
![Page 7: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/7.jpg)
Wind and wind stress
Moderate stress
Wind = wind stress ?
![Page 8: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/8.jpg)
Wind and wind stress
Strong stress
Wind = wind stress ?
![Page 9: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/9.jpg)
Wind and wind stress
Wind stress = cD ρair |uair - uwater| (uair - uwater)
Crag coefficient
Wind stress ∝ uair2
![Page 10: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/10.jpg)
How does the ocean feel the wind stress?
Fx =1
⇢ref
@⌧x@z
Fy =1
⇢ref
@⌧y@z
![Page 11: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/11.jpg)
How does the ocean feel the wind stress?
Wind stress decreases rather rapidly with depth.
Ekman layer
![Page 12: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/12.jpg)
Dynamics in the Ekman layer
�fv +1
⇢ref
@p
@x=
1
⇢ref
@⌧x@z
�f(vg + va) +1
⇢ref
@p
@x=
1
⇢ref
@⌧x@z
�fva =1
⇢ref
@⌧x@z
�fv +1
⇢ref
@p
@x= Fx
![Page 13: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/13.jpg)
Dynamics in the Ekman layer
�fva =1
⇢ref
@⌧x@z
fua =1
⇢ref
@⌧y@z
f⇢ref
Z 0
��uadz = ⌧y,wind
�f⇢ref
Z 0
��vadz = ⌧x,wind
![Page 14: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/14.jpg)
Dynamics in the Ekman layer
f⇢ref
Z 0
��uadz = ⌧y,wind
�f⇢ref
Z 0
��vadz = ⌧x,wind
WindW
ind
Ocean currentO
cean
cur
rent
North hemisphere
![Page 15: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/15.jpg)
• Transport of the water in the Ekman layer is to the right of the wind stress direction in the northern hemisphere
• Transport of the water in the Ekman layer is to the left of the wind stress direction in the southern hemisphere.
• Ekman spiral
Dynamics in the Ekman layer
![Page 16: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/16.jpg)
Ekman spiral
![Page 17: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/17.jpg)
Wind stress structure
![Page 18: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/18.jpg)
Wind stress structure
@⌧x@y
> 0@⌧x@y
< 0
- Northern H. : divergence - Southern H. : convergence
- Northern H. : convergence - Southern H. : divergence
![Page 19: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/19.jpg)
Wind stress structure
@⌧y@x
< 0@⌧y@x
> 0
- Northern H. : divergence - Southern H. : convergence
- Northern H. : convergence - Southern H. : divergence
![Page 20: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/20.jpg)
Wind stress structure
- Northern H. : divergence - Southern H. : convergence
- Northern H. : convergence - Southern H. : divergence
@⌧y@x
� @⌧x@y
> 0@⌧y@x
� @⌧x@y
< 0
![Page 21: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/21.jpg)
Wind stress structure
![Page 22: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/22.jpg)
Sea level
![Page 23: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/23.jpg)
Ekman pumping / suction
Anticyclonic applied stress
Cyclonic applied stress
Convergenceand
Downwelling
Divergenceand
Upwelling
![Page 24: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/24.jpg)
Ekman pumping / suction
![Page 25: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/25.jpg)
Ekman pumping at the equator
![Page 26: Ocean: wind-driven circulation - GitHub Pages · Last time • Ocean circulation • Hydrostatic balance • Geostrophic balance • Thermal wind relationship • Sea level and isopycnal](https://reader036.vdocuments.site/reader036/viewer/2022081611/5f02ea4d7e708231d406a430/html5/thumbnails/26.jpg)
Ekman pumping / suction and temperature