Title: Regional OceanAtmosphere Interactions in the Eastern Pacific: TIWs, Mesoscale Eddies and Gap Winds
1Regional Ocean-Atmosphere Interactions in the
Eastern Pacific TIWs, Mesoscale Eddies and Gap
Winds
Arthur J. Miller Scripps Institution of
Oceanography University of California, San
Diego Based on the Ph.D. Dissertation of Mr.
Hyodae Seo (SIO) Including collaboration with
John Roads (SIO) Ragu Murtugudde
(Maryland) Markus Jochum (NCAR)
Woods Hole Oceanographic Institution Ocean
Engineering Seminar Series April 26, 2006
2 Outline
- Background
- Regional Ocean-Atmosphere Coupled Model
- Research Topics
- TIWs and Air-Sea Interaction
- Atmospheric Response to TIWs
- - Stability adjustment of ABL ?
Thermal and dynamic response - Effect of Atmospheric Feedback on TIWs
frequency-wavenumber - California Current Eddies and Air-Sea
Interaction - Gap Winds and Air-Sea Interaction
- Wind-induced forcing ? Thermocline doming
?
Suppression of atmospheric deep convection - Summary
3Background
- Important component of large-scale atmospheric
and oceanic circulation - Atmospheric deep convection over the eastern
Pacific warm pool and Equatorial Current system - Coastal upwelling and equatorial cold tongue
- Equatorial SST front and TIWs
- Influence by land and coastline
- Different cloud response to SSTs
- ? All involve interactions among air, sea and
land. Studying the nature of such coupling is
important for regional climate, and large-scale
climate as well.
? Consider a new high-resolution regional coupled
model.
4Scripps Coupled Ocean-Atmosphere Regional (SCOAR)
Model
- Bulk formulae or RSM physics in ABL for
momentum, heat and fresh-water fluxes
Atmosphere
Ocean
- Wind stress relative to ocean currents
- Sequential Coupling
- ? 3 hourly or daily coupling
Seo, Miller and Roads (2006) J. Climate, sub
judice
5Eastern equatorial Pacific domain example
Evolving SST and wind-stress vector in 1999-2000
45 km ROMS 50 km RSM
- Coupled system
- ITCZ / Eastern Pacific Warm Pool
- Cross-equatorial trade winds
- Gap Winds
- Tropical Depressions and Hurricanes
- Equatorial and Coastal Upwelling
- Tropical Instability Waves
Tehuantepec
Papagayo
6Model domains in the eastern Pacific sector
- (a) Eastern Tropical Pacific TIWs
- (b) California Current System Eddies
- (c) Central American Coast Gap Winds
7Tropical Instability WavesHow do Feedbacks
Between SST and the Atmospheric Boundary
LayerAffect TIW stability characteristics?
8TIW Domain in the Eastern Tropical Pacific
9EOF analysis of SST
EOF from September to December, 1999 over
1?S-6?N, 130?W-100?W.
CLM EOF 1 34.2
PC 1
- 1st and 2nd EOFs and PCs are paired and directly
related to TIWs, explaining more than 60 of the
total variance.
CLM EOF 2 30.5
PC 2
CLM EOF 3 9.3
- We are interested in....
- from EOFs, changes in amplitude and wavelength
of zonal temperature fluctuations by TIWs. - from PCs, changes in frequency of TIWs.
PC 3
CLM EOF 4 6.6
PC 4
10Stability Changes in ABL due to SST
17(15) warm(cold) phases during 2-4 Sep. 1999
Atmospheric Temperature
U-Wind
Stronger shear
- ? Weaker stratification of ABL over warm phase of
TIWs. - ?
- Stronger surface winds over warmer
Weaker shear
Ocean Temp. Profile
Ocean Temperature
11Modification of heat and momentum flux
Change in dynamic state
Change in thermal state
Coupling of SST and Wind stress
WSD
WSC
LH anomaly ?20W / m2 Div and curl anomaly ?
2N/m2 per 100km
- Turbulent heat flux damps the SST a negative
feedback - Feedback from wind stress perturbation remains
largely unknown
12Observed -40-50 W/m2/K
Comparable to observed values
13Effects of atmospheric feedbacks on TIWs
? How do the perturbation heat fluxes and wind
stresses affect the characteristics of TIWs? ?
Additional experiments sensitivity test for the
year of 1999
temporally smoothed using 120-day moving mean
- Analysis using the first two EOFs and PCs of
ocean temperature - We are interested in....
- EOFs changes in wavelength of zonal temperature
fluctuations by TIWs. - PCs changes in frequency of the TIWs.
14Changes in amplitude of SST fluctuations
mean of 1st and 2nd modes
- TIWs occur under climatological forcing.
- Heat flux coupling damps the fluctuations of SST
by TIWs. - Wind coupling yields a stronger damping also
increases wavelength. (cf. Pezzi et al., 2002) - Full-coupling results in weakest fluctuations of
SST over the TIW region.
EOF from September to December, 1999 over
1?S-6?N, 130?W-100?W.
15Changes in vertical distribution
Average over 1?N-6?N
Zonal STD of temperature
Depth (m)
Zonal STD of temperature (?C)
- Heat flux coupling thermal damping increases
baroclinicity in the mixed layer - Wind coupling damping increase in wavelength.
- Full-coupling mixture of effects from wind and
heat feedback
CLM EOF-1 41 (2nd 35, Total ? 76)
Depth (m)
Longitude
16Changes in wavenumber and frequency
characteristics
Average of 1st and 2nd PCs Average of 1?N-6?N
- Coupling increases the period of waves.
- Dynamic coupling increases the wavelength of the
wave.
17Air-Sea Coupling in the California Current Region
- Similar coupling of SST with dynamics and
thermodynamics of ABL is also seen in CCS region
over various spatial and temporal scales. - But model coupling strength in midlatitudes is 3
- 5 times weaker than observed
RSM 16 km ROMS 7 km
18Gap Winds and Air-Sea Interactions
- Gap winds are driven by pressure gradient across
narrow gaps or by intrinsic variability of the
trades.
- Gap Winds produce cold tongues due to
evaporative cooling and entrainment, plus
windstress curl forcing. - Affect the atmospheric deep convection and
precipitation.
19Wind Stress and Ekman Pumping Velocity
- Ekman Pumping Velocity Unit
- 10-6m/s
- Low-level wind jets through mountain gaps
95W 85W
- Wind-induced vorticity forcing leads to dynamic
response in the ocean thermocline.
95W 85W
RSM 27 km ROMS 25 km
20Thermocline Doming by Ekman Forcing Costa Rica
Dome
95W 85W
- Ekman pumping (above) causes thermocline
shoaling (left), which further cools SST and
supports a productive ecosystem. - MLD is 10 m and thermocline is 30 m deep over
Costa Rica Dome, both in obs and model.
21SST Response to Gap Winds
- Cold tongues off the major mountain gaps (due
to wind-induced mixing, evaporative cooling, and
Ekman pumping)
Cold bias in CRD
22Rainfall Suppression of Precipitation by Eddies
- Costa Rica Dome and cold tongues by gap winds
suppress atmospheric deep convection and
precipitation, shifting the ITCZ southward (Xu et
al., 2005)
Region of rain deficit within ITCZ
23Summary of TIW feedbacks
- Coupled model simulates the observed atmospheric
response to TIWs - Evolving SST induces ABL
stability adjustment and changes in heat flux and
wind stress.
- Series of fully coupled, partially coupled, and
uncoupled experiment show that ... - 1) as expected, heat flux feedback suppresses
amplitude of SST fluctuation by TIWs a negative
feedback - 2) dynamic feedback provides even stronger
damping to SST fluctuation (cf. Pezzi et al.,
2002) - 3) surface damping of temperature by heat flux
results in stronger baroclinicity of zonal
temperature fluctuation. - 4) dynamic feedback also increases the wavelength
of TIW
24Summary of Gap Winds Feedbacks
- Coupled model simulates observed mean structure
and seasonal variability of gap winds and their
influences on upper ocean hydrography (Xie et al.
2005). - Shoaling of thermocline and colder SST over Costa
Rica Dome results in suppression and displacement
of atmospheric deep convection and rainfall (Xie
et al. 2005 Xu et al. 2005).
25Future work.
-
- Bering Sea
- - Add Sea Ice
- - Bering Ecosystem Study (BEST)
- 2) VOCALS
- - Peru-Humboldt Upwelling SST - Stratocumulus
- 3) North Pacific Decadal Variability
- - KOE Aleutian Low feedbacks 1948-2005
26Thanks!