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Coupled Atmosphere-Ocean Feedbacks
ICTP-CLIVAR Summer School on EBUS
July 17, 2019
Art Miller
Scripps Institution of Oceanography
University of California, San Diego
Eddy-Wind Interaction in the California Current System:
Dynamics and Impacts
ICTP-CLIVAR Summer School on EBUS
July 17, 2019
Hyodae Seo1, Art Miller2 and Joel Norris2
1Woods Hole Oceanographic Institution 2Scripps Institution of Oceanography
Journal of Physical Oceanography (2016)
Coupled Atmosphere-Ocean Feedbacks
Outline
1) Ocean Eddy Influences on Surface Fluxes- SST effects and Current effects
2) Regional Coupled Modeling Experiments for the CCS- Isolating the effects of SST and U
3) Dynamical Diagnostics of the Eddy-Stress interaction- EKE and Ekman Pumping
4) Further Work- Ocean Influence on Atmospheric States
Coupled Atmosphere-Ocean Feedbacks
Initial Considerations….
1. Observations indicate mesoscale SST alters surface fluxes
2. Atmospheric response to these ocean-mediated fluxes is not obvious
3. Oceanic response to these ocean-mediated fluxes is not obvious
4. Regional coupled ocean-atmosphere modeling
may help shed on light on possible feedbacks
Driving Question
• What impact do mesoscale-eddy generated
surface flux anomalies have on the
atmosphere and ocean?
Our previous work involved modeled
mesoscale-SST anomaly influences on
surface fluxes
SST gradient impact on wind stress curl
and divergence
Scripps Coupled Ocean-Atmosphere Regional
(SCOAR) Model
Ocean
(Regional Ocean Modeling
Systems - ROMS)
Atmosphere
(Regional Spectral Model -
RSM)
SST-Flux Coupler
Mesoscale Air-sea
Coupling Experiment
Control
SCOAR
Control run
composed of fully-
coupled SCOAR
run for 2005-2010
Smoothed
SCOAR
SCOAR run with
daily, mesoscale
smoothing of SST
and/or U-ocean at
every coupling step Putrasahan et al. 2013
Seo, Miller and
Norris, 2016
Seo, Miller and Roads
J. Climate, 2007
Regional Coupled Ocean-Atmosphere Feedbacks in the
California Current Sector
Wind Stress
divergence
Latent
heat fluxSST, winds
Wind Stress
curl
• Coupling of SST
with Atmospheric
Boundary Layer is
observed and
modeled in the
CCS region over
eddy scales
•How does this
coupling affect
statistics of
ocean eddies,
and the
overlying
atmospheric
flows?
RSM
Atmos
model:
16 km
ROMS
Ocean
model:
7 km
SCOAR simulation
Seo, Miller and Roads
(2007, J. Climate)
Peru-Humboldt Current System:
Do coupled feedbacks of SST-anomaly-induced
mesoscale surface fluxes (wind stress, heat)
alter eddy statistics?
Putrasahan, Miller and Seo (2013, Ocean Dynamics)
Very small impacts – perhaps SST gradients are simply too weak
RMS SST
Peru-Humboldt Current System:
Do coupled feedbacks of SST-anomaly-induced
mesoscale surface fluxes (wind stress, heat)
alter eddy statistics?
Putrasahan, Miller and Seo (2013, Ocean Dynamics)
Very small impacts – perhaps SST gradients are simply too weak
RMS surface vorticity
Driving Question
• What impact do mesoscale-eddy generated surface flux anomalies have on the atmosphere and ocean?
Today, focus is on mesoscale eddy surface velocity impacts on surface stress, relative to the mesoscale eddy SST effects in the California Current System
Mean State Differences: JJAS SST vs. Obs and Smoothed Cases
- Upwelling too strong + Interesting patterns of eddies
Rectified SST patterns when turning off eddy coupling effects:
Downscaled
equatorward
wind stress
too strong
Mean State Differences: JJAS Wind stress vs. Obs and Smoothed Cases
- Stress patterns match interesting patterns of eddy-induced SST
Pattern of rectified SST difference spatially positively correlated with the wind stress difference
Mean State Differences: JJAS Latent Heat Flux
vs. Obs and Smoothed Cases
- Latent heat flux
is a response to SST
(not atmospheric state)
- Patches of SST difference associated with changes insemi-permanent eddies and filaments and associatedlateral eddy heat advection
Drifter Obs, rms:
Centurioni et al.
Cross-shore distribution of EKE:
- Peaks at 150 km offshore
- Remains high without inclusion of eddy current feedback on stress
Summary
• Examined the relative importance of τSST vs τcur in EKE and Ekman pumping
velocity in the CCS using a regional coupled model.
• Surface EKE is weakened (~25%) due to mesoscale current effects on τ
- Mesoscale SST has very little direct impact on EKE
• In the EKE budget: eddies both enhance eddy drag (by zonal current)
and weaken the wind work (by meridional current).
• Eddies modify the Ekman pumping velocity.
- via eddy SST through positive relationship between crosswind SST gradient and
wind stress curls
- via eddy Current through the gradient of surface vorticity
• SST- and Current-induced Ekman pumping have comparable spatial scales and
amplitudes but different patterns, indicative of their different feedback processes
Further Work (unpublished)
• Ocean eddy influences on Atmospheric statistics
• Ocean anomalous state influences on Atmospheric
Rivers (deterministic effects)
• Ocean anomalous state influences on the diurnal
cycle, sea breeze, and marine layer
DJF averaged rainfall
2005-2010
DJF mean precipitation
mm/day
DJF mean precipitation difference
mm/day
DJF mean precipitation percent difference (%)
e.g., (CTL-noTe)/CTL X 100
DJF Mean SST Difference
Deg C
Rainfall response to eddies
• Rectified mean SST difference (due to
eddies) drives changes in mean rainfall up
to 10% of the winter mean
• Some signatures of oceanic patterns extend
over land (coastal ranges, ~100km)
• Mainly convective precip, not large-scale
Coupled Atmosphere-Ocean Feedbacks
Outline
1) Ocean Eddy Influences on Surface Fluxes- SST effects and Current effects
2) Regional Coupled Modeling Experiments for the CCS- Isolating the effects of SST and U
3) Dynamical Diagnostics of the Eddy-Stress interaction- EKE and Ekman Pumping
4) Further Work- Ocean Influence on Atmospheric States
Thanks!
Art Miller
SIO/UCSD
La Jolla, CA
ICTP-CLIVAR Summer School on EBUS
July 17, 2019
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