Regional Ocean-Atmosphere Interactions in the Eastern Pacific: TIW’s, Mesoscale Eddies and Gap...
-
Upload
dennis-holt -
Category
Documents
-
view
216 -
download
3
Transcript of Regional Ocean-Atmosphere Interactions in the Eastern Pacific: TIW’s, Mesoscale Eddies and Gap...
Regional Ocean-Atmosphere Interactions in the Eastern Pacific:
TIW’s, Mesoscale Eddies and Gap Winds
Regional Ocean-Atmosphere Interactions in the Eastern Pacific:
TIW’s, Mesoscale Eddies and Gap Winds
Woods Hole Oceanographic InstitutionOcean Engineering Seminar Series
April 26, 2006
Woods Hole Oceanographic InstitutionOcean Engineering Seminar Series
April 26, 2006
Arthur J. MillerScripps Institution of OceanographyUniversity of California, San Diego
Based on the Ph.D. Dissertation ofMr. Hyodae Seo (SIO)
Including collaboration with John Roads (SIO)
Ragu Murtugudde (Maryland)Markus Jochum (NCAR)
OutlineOutline• Background
• Regional Ocean-Atmosphere Coupled Model
• Research Topics
TIWs and Air-Sea InteractionAtmospheric 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
• Background
• Regional Ocean-Atmosphere Coupled Model
• Research Topics
TIWs and Air-Sea InteractionAtmospheric 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
BackgroundBackground
• 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.
• 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.
• Air-sea interaction in the Eastern Pacific
Consider a new high-resolution regional coupled model….
Latitude
Deep CumulusShallow Stratocumulus
Scripps Coupled Ocean-Atmosphere Regional (SCOAR) ModelScripps Coupled Ocean-Atmosphere Regional (SCOAR) Model
• Sequential Coupling 3 hourly or daily coupling
• Bulk formulae or RSM physics in ABL for momentum, heat and fresh-water fluxes
• Wind stress relative to ocean currents:
IC and Lateral BC: NCEP/DOE Reanalysis
SST
Boundary Layer Variables
Ocean Atmosphere
Bulk Formulaeor RSM BL
physics
Regional Spectral Model (RSM)
Lateral BC: Ocean Analysis (JPL/ECCO) or Climatology
Regional Ocean Modeling System
(ROMS)
Schematic of Ocean-Atmosphere Coupled Model
Seo, Miller and Roads (2006) J. Climate, sub judice
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
Eastern equatorial Pacific domain exampleEastern equatorial Pacific domain example
Tehuantepec
Papagayo
Model domains in the eastern Pacific sector
Model domains in the eastern Pacific sector
(a) Eastern Tropical Pacific: TIW’s
(b) California Current System: Eddies
(c) Central American Coast: Gap Winds
(a) Eastern Tropical Pacific: TIW’s
(b) California Current System: Eddies
(c) Central American Coast: Gap Winds
Tropical Instability Waves:How do Feedbacks Between SST and
the Atmospheric Boundary LayerAffect TIW stability characteristics?
Tropical Instability Waves:How do Feedbacks Between SST and
the Atmospheric Boundary LayerAffect TIW stability characteristics?
TIW Domain in the Eastern Tropical PacificTIW Domain in the Eastern Tropical Pacific
Tropical Instability Waves 20 km ROMS + 30 km RSM
Galapagos Is.
RSM: 28 layers (6 below 900mb)ROMS: 30 layers (9 in top 100m)
EOF analysis of SSTEOF analysis of SST
• 1st and 2nd EOFs and PCs are paired and directly related to TIWs, explaining more than 60% of the total variance.
• 1st and 2nd EOFs and PCs are paired and directly related to TIWs, explaining more than 60% of the total variance.
CLM EOF 1; 34.2%
CLM EOF 2; 30.5%
CLM EOF 3; 9.3%
CLM EOF 4; 6.6%
PC 1
PC 2
PC 3
PC 4
EOF from September to December, 1999 over 1S-6N, 130W-100W.
• We are interested in....1) from EOFs, changes in
amplitude and wavelength of zonal temperature fluctuations by TIWs.
2) from PCs, changes in frequency of TIWs.
• We are interested in....1) from EOFs, changes in
amplitude and wavelength of zonal temperature fluctuations by TIWs.
2) from PCs, changes in frequency of TIWs.
Stability Changes in ABL due to SSTStability Changes in ABL due to SST
Weaker stratification of ABL over warm phase of TIWs.
• Stronger surface
winds over warmer
Weaker stratification of ABL over warm phase of TIWs.
• Stronger surface
winds over warmer
Atmospheric Temperature
Ocean Temperature
U-Wind
Ocean Temp. Profile
Stronger shear
Weaker shear
17(15) warm(cold) phases during 2-4 Sep. 1999
Modification of heat and momentum fluxModification of heat and momentum flux
• Turbulent heat flux damps the SST; a negative feedback• Feedback from wind stress perturbation remains largely unknown• Turbulent heat flux damps the SST; a negative feedback• Feedback from wind stress perturbation remains largely unknown
CEOF 1 of SST and Latent Heat Flux
WSC
WSD
Coupling of SST and Wind stress
LH anomaly : 20W / m2
Div and curl anomaly : 2N/m2 per 100km
Change in thermal state
Change in dynamic state
Observed: -40-50 W/m2/K
Comparable to observed values
Effects of atmospheric feedbacks on TIW’sEffects of atmospheric feedbacks on TIW’s
How do the perturbation heat fluxes and wind stresses affect the characteristics of TIW’s?
Additional experiments: sensitivity test for the year of 1999
How do the perturbation heat fluxes and wind stresses affect the characteristics of TIW’s?
Additional experiments: sensitivity test for the year of 1999
wind stress heat flux
CPL coupled coupled fully coupled
DYNM coupled smoothed* CPLdynamically
coupled
THERM smoothed CPL coupledthermally
coupled
CLM smoothed CPL smoothed CPL uncoupled
* : temporally smoothed using 120-day moving mean
• Analysis using the first two EOFs and PCs of ocean temperature • We are interested in....1) EOFs: changes in wavelength of zonal temperature fluctuations by TIWs.2) PCs: changes in frequency of the TIWs.
• Analysis using the first two EOFs and PCs of ocean temperature • We are interested in....1) EOFs: changes in wavelength of zonal temperature fluctuations by TIWs.2) PCs: changes in frequency of the TIWs.
Changes in amplitude of SST fluctuationsChanges in amplitude of SST fluctuations
• 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.
• 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.
std of SST (C)
Reduction wrt CLM (%)
CPL 1.1 35
DYNM 1.3 23
THERM 1.5 11
CLM 1.7 -
mean of 1st and 2nd modesCPL EOF-1 37% (2nd: 26%, Total 63%)
DYNM EOF-1 31% (2nd 19%, Total 50%)
THERM EOF-1 37% (2nd 30%, Total 67%)
CLM EOF-1 34% (2nd 30%, Total 64%)
Longitude
Latit
ude
EOF from September to December, 1999 over 1S-6N, 130W-100W.
Changes in vertical distributionChanges in vertical distribution
• 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
• 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%)
Longitude
THERM EOF-1 40% (2nd 37%, Total 77%)
DYNM EOF-1 32% (2nd 28%, Total 60%)
CPL EOF-1 40% (2nd 31%,Total 71%)Zonal STD of temperature
Dep
th (
m)
De
pth
(m
)
Zonal STD of temperature (C)
Average over 1N-6N
Changes in wavenumber and frequency characteristicsChanges in wavenumber and frequency characteristics
wavelength ( long.)
period (day)
phase speed (m s-1)
CPL 12 36 0.4
DYNM 18 36 0.6
THERM 12 36 0.4
CLM 12 27 0.5
Coupling increases the period of waves.
Dynamic coupling increases the wavelength of the wave.
Frequency spectra
Spe
ctra
l den
sity
[(
C)2
/cp
d]
~ 0.04 cycle / day
~ 0.03 cycle / day
Frequency (cycle per day)
Average of 1st and 2nd PCsAverage of 1N-6N
Wavenumber (cycle per long.)
Spe
ctra
l den
sity
[(
C2//c
p
long
.]
~ 0.1 cycle / long.
~0.07cycle / long.
Wavenumber spectra
Air-Sea Coupling in the California Current RegionAir-Sea Coupling in the California Current Region
WSD
LHSST & WS
WSC
• 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
RSM: 16 km
ROMS: 7 km
• Gap Winds produce cold tongues due to evaporative cooling and entrainment, plus windstress curl forcing. • Affect the atmospheric deep convection and precipitation.
• Gap winds are driven by pressure gradient across narrow gaps or by intrinsic variability of the trades.
AVHRR Satellite SST Image; Jan 1999
Tehuantepec
Papagayo
Panama
OBS; Chelton et al., 2000
Gap Winds and Air-Sea InteractionsGap Winds and Air-Sea Interactions
Wind Stress and Ekman Pumping VelocityWind Stress and Ekman Pumping Velocity
• Wind-induced vorticity forcing leads to dynamic response in the ocean thermocline.
• Low-level wind jets through mountain gaps
• Ekman Pumping Velocity Unit :10-6m/s
Xie et al., 2005
Winter
Summer
OBSERVATION
Winter
MODEL: 1999-2003
95W 85W
95W 85W
Summer
RSM: 27 km ROMS: 25 km
Thermocline Doming by Ekman Forcing; Costa Rica DomeThermocline Doming by Ekman Forcing; Costa Rica Dome
OBSERVATION MODEL: 1999-2003
Along 8.5°N
Along 90°W
Costa Rica
DomeAlong 90°W
Along 8.5°N
• 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.
95W 85W
SST: Response to Gap WindsSST: Response to Gap Winds
• Cold tongues off the major mountain gaps (due to wind-induced mixing, evaporative cooling, and Ekman pumping)
OBSERVATION
Winter
Winter
MODEL: 1999-2003
Summer
Costa Rica
Dome
Cold bias in CRD
Rainfall: Suppression of Precipitation by EddiesRainfall: 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)
OBSERVATION
Xie et al., 2005
Summer
WinterMODEL
Summer
Region of rain deficit
within ITCZ
Winter
Summary of TIW feedbacksSummary 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.
• 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
• 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
Summary of Gap Winds FeedbacksSummary 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).
• 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).
Future work…. Future work….
1) 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
1) 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
Thanks!Thanks!