niklas schneider , bunmei taguchi , masami nonaka and akira … · 2016. 5. 24. · linear rossby...
TRANSCRIPT
Characterization of frontal air-sea interaction by spectral transfer functions
Niklas Schneider1, Bunmei Taguchi2, Masami Nonaka2 and Akira Kuwano-Yoshida21International Pacific Research Center, University of Hawaii, Honolulu, USA
2Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan
Imprint of ocean mesoscale on extratropical atmospherewarm SST associated with high wind speed
SST
con
tour
inte
rval
1K
Chelton and X
ieO
ceanography, 2010
July 2002, monthly average, spatially high pass filtered
win
d sp
eed
m/s
International Ocean Vector Winds Science Team Meeting, Hokkaido University, Sapporo, Japan, May 17-19, 2016
Air-sea interaction at weak SST frontsSchneider and Qiu, JAS, 2015
BackgroundEkman spiral
inversion
2
SST perturbation
Air-sea interaction at weak SST frontsSchneider and Qiu, JAS, 2015
BackgroundEkman spiral
inversion
warm
2
Vertical mixing mechanism (Wallace et al. 1989, Hayes et al. 1989, Samelson et al. 2006)
SST perturbation
Air-sea interaction at weak SST frontsSchneider and Qiu, JAS, 2015
BackgroundEkman spiral
inversion
warm
2
Vertical mixing mechanism (Wallace et al. 1989, Hayes et al. 1989, Samelson et al. 2006)
SST perturbation
Air-sea interaction at weak SST frontsSchneider and Qiu, JAS, 2015
BackgroundEkman spiral
inversion
warm
2
Vertical mixing mechanism (Wallace et al. 1989, Hayes et al. 1989, Samelson et al. 2006)
SST perturbation
Air-sea interaction at weak SST frontsSchneider and Qiu, JAS, 2015
BackgroundEkman spiral
inversion
warm
2
Pressure effect (Lindzen and Nigam 1987)
Vertical mixing mechanism (Wallace et al. 1989, Hayes et al. 1989, Samelson et al. 2006)
SST perturbation
Air-sea interaction at weak SST frontsSchneider and Qiu, JAS, 2015
BackgroundEkman spiral
inversion
warm
2
Wind&inversion responseadvection rotation
back pressure vertical mixing
continuity
Pressure effect (Lindzen and Nigam 1987)
Air-sea interaction at weak SST frontsSchneider and Qiu, JAS, 2015
BackgroundEkman spiral
inversion
warm
weak SST perturbation
3
wind&inversion responseadvection rotation
back pressure vertical mixing
continuity
Air-sea interaction at weak SST frontsSchneider and Qiu, JAS, 2015
BackgroundEkman spiral
inversion
warm
weak SST perturbation
3
advection by background winds only
wind&inversion responseadvection rotation
back pressure vertical mixing
continuity
Air-sea interaction at weak SST frontsSchneider and Qiu, JAS, 2015
BackgroundEkman spiral
inversion
warm
weak SST perturbation
3
vertical mixing mechanism acts on background shear onlybackground mixing acts on frontally induced winds
advection by background winds only
wind&inversion responseadvection rotation
back pressure vertical mixing
continuity
Air-sea interaction at weak SST frontsSchneider and Qiu, JAS, 2015
weak SST perturbation
4
vertical mixing mechanism acts on background shear onlybackground mixing acts on frontally induced winds
advection by background winds only
A! !k Φ! !k = D! !k T! !kdynamics u, v, w, h, Θ SST forcing
linear Rossby adjustment problem with coefficients constant in x, y
Air-sea interaction at weak SST frontsSchneider and Qiu, JAS, 2015
weak SST perturbation
4
vertical mixing mechanism acts on background shear onlybackground mixing acts on frontally induced winds
advection by background winds only
A! !k Φ! !k = D! !k T! !kdynamics u, v, w, h, Θ SST forcing
linear Rossby adjustment problem with coefficients constant in x, y
Φ! !k = A! !k−1D! !k T! !k
Transfer functiondependent on background wind speed, direction
mixing formulation
Transfer function for surface wind speed
Transfer function for surface wind speed
background surface wind direction
Transfer function for surface wind speed
downwind wave-number /Rossby Radius-1
background surface wind direction
Transfer function for surface wind speed
downwind wave-number /Rossby Radius-1
cros
swin
d w
ave-
num
ber
/Ros
sby
Radi
us-1
background surface wind direction
Transfer function for surface wind speed
downwind wave-number /Rossby Radius-1
cros
swin
d w
ave-
num
ber
/Ros
sby
Radi
us-1
Ug /gravity wave speed
Transfer function for surface wind speed
downwind wave-number /Rossby Radius-1
cros
swin
d w
ave-
num
ber
/Ros
sby
Radi
us-1
… in phase with SST
Frontally induced surface wind speed …
Ug /gravity wave speed
Transfer function for surface wind speed
downwind wave-number /Rossby Radius-1
cros
swin
d w
ave-
num
ber
/Ros
sby
Radi
us-1
… in phase with SST
… 90° phase-shifted with SST
Frontally induced surface wind speed …
Ug /gravity wave speed
Surface wind speed, best fit linear model
downwind wave-number/Rossby Radius-1
cros
swin
d w
ave-
num
ber
/Ros
sby
Radi
us-1
Surface wind speed, best fit linear model
downwind wave-number/Rossby Radius-1
cros
swin
d w
ave-
num
ber
/Ros
sby
Radi
us-1
downwind wave-number/Rossby Radius-1
cros
swin
d w
ave-
num
ber
/Ros
sby
Radi
us-1
Surface wind speed, best fit linear model
/0.1
ms-
1 K-1
QuikSCAT
downwind wave-number/Rossby Radius-1
cros
swin
d w
ave-
num
ber
/Ros
sby
Radi
us-1
Conclusions
• A linearized model for the atmospheric boundary layer response to ocean mesoscale sea surface temperatures is tested.
• Spectral transfer functions of the linear model and based on an AGCM (AFES) and QuikSCAT observations compare favorably in the Southern Ocean, and suggest that the linear model captures the underlying physics.
• Additional physics can be tested to improve fit between linear model, AGCMs and observations.
Schneider, N. and B. Qiu, 2015: The atmospheric response to weak sea surface temperature fronts. J. Atmos. Sci., 72, 3356-3377.
Cross-wind
downwind wave-number/Rossby Radius-1
cros
swin
d w
ave-
num
ber
/Ros
sby
Radi
us-1
QuikSCAT
/0.1
ms-
1 K-1
downwind wave-number/Rossby Radius-1
cros
swin
d w
ave-
num
ber
/Ros
sby
Radi
us-1
Cross-wind