imprints of coastal mountains on ocean circulation and ... · imprints of coastal mountains on...
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Imprints of Coastal Mountains on Ocean Circulation and Variability
Shang-Ping Xie1
with C.-H. Chang1, W. Zhuang2, with C.-H. Chang1, W. Zhuang2, N. Schneider1, J. Small3, B. Taguchi4, and H. Sasaki4
1 IPRC, University of Hawaii2 South China Sea Institute of Oceanology
3 Naval Research Laboratory4 Earth Simulator Center, Japan
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Orographic jets � Ocean circulation (We) & SST
South China Sea: orog. forcing from the west
Eastern Pacific: orog. forcing from the east
Comparative study at similar latitudes>500 m
1
2
L
Jul-Aug wind & SST Jan-Mar wind & SST
H
Xie et al. (2003, 2007, JGR)
Xie et al. (2005, JC)
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-3
-2
-1
0
1
2
3WSCisv spatial mode 1
o
8oN
12oN
16oN
Summer (Jun-Sept)
TP spatial mode 1
8oN
12oN
16oN
(a)
SSH EOF (17%)Wind curl EOF (41%)
-3 108oE 112oE 116oE 120oE
4oN
(c)
• Max correlation ~ 0.5 when wind curl leads SSH by 2 weeks MJO, wind-forced Rossby wave adjustment (Xie et al. 2007, JGR-Oceans)
• Max SSH response on the gyre boundary organization along the inertial jet (e.g., localized increase of beta on the gyre boundary)
108oE 112oE 116oE 120oE 4oN
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Curl (color)SSH (contour)
Winter Mean Circulation in Sverdrup Balance
Ocean circulation in Sverdrup balance with wind curls
• Tehuantepec BowlTehuantepec jet
Sverdrup relation τβ curlV = Winter Wind + Spring Circulation
Tehuantepec jetAntiCyclonic gyre (SSH high ~72cm)
• Costa Rica DomeZonal Papagayo JetCyclonic gyre (SSH low ~ 48cm)
• Panama CirculationMeridional Panama jet Cyclonic gyre (SSH low ~ 57 cm)
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Gap Wind Season (Nov-Feb) SSH Variability
STD: Wind (contour) & SSH (color)
Spatial relationship b/w Wind & SSH (color)�SSHA variability may be forced by wind via Ekman pumping mechanism
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Standard deviations of intraseasonal variability in
SSH (contour) & Wind Stress Curl (color)
Tehuantepec
SSH_STD vs Curl
Wind forced, westward propagation along the high-variance band
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Coherent Eddy-train Structure in High Variance Band
STD (color) & Correlation (contour)
SSHA Lag Correlation w/ Action Centers
Lag Correlation
w/ Action Centers
near Three Gaps
Action Center
=: local max SSHA STD
Nov-Feb
=: local max SSHA STD
(marked by squares)
Correlation in contours
Black: w/ Tehuantepec AC
Blue: w/ Papagayo AC
Pink w/ Panama AC
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Oct.2000-Jun.2001 Oct.2002-Jun.2003
Tehuantepec Time-Distant Diagram
SSHA vs Wind Stress Curl (2000-01; 2002-03)
Still
SSHA clearly responding to wind forcing:offshore propagation of Positive SSHA signal seen right after strong coastal negative Wind Stress Curl
Still
along
the
same
axis
(will
change
later)
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SSH (color) & Wind Curl(con)
High-wind composites
lag0
Obs
SSH (color) & Wind speed
Tim
e la
g (w
eeks
)
Distance along High Variance Band
lag1
lag2
Tim
e la
g (w
eeks
)
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Phase velocity of Rossby waves; wavelengths set by the dispersion given intraseasonal frequency
kkkk
llllTehuantepec
High variance band (con)
Cph(green)
Tehuantepec
L 660 km
R 87 km
ωωωω-1 85 days
High variance band (con)
SSHA from Tehuantepec high wind composite (col) at lag +4
2
22
2 1
22 Rlk −
=+
+ω
βω
β
Rossby Wave Dispersion Relation
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Dec.10, 2003
SST, SSH & Wind
Eddy train on the northwest flank of the cool SST band, causing meanders & cusps
Dec.17, 2003causing meanders & cusps of the SST front.
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High-wind Composite of SSHA
Obs (color) vs model (contour)Obs (color) vs OFES ISV
Global, eddy-resolving (0.1o) hindcast (OFES) forced by QuikSCAT winds (1999 -)
20-120-day SSHA STD (Nov-Feb)
• Obs (col) (1993—2005)
• OfES(con) (Jul.1999—Dec.2005)
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Wind Work
Oct-Apr Mean
SSHA std (cm, contour)
Ug (m/s, vector)
Wind Work
(shade, upper panel)
Energeticsbased on OFES
Instability (T2+T4)
(shade, upper panel)
Instability (BCC+BTC)
(shade, lower panel)
(integrate over entire water column)
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• Pronounced intraseasonal variability in SSH off Tehuantepec and Papagayo, producing cusps on the northwest flank of the cool SST band.
• Organized into eddy train in the high-variance band, its wavelength set by intraseasonal frequency and phase propagation consistent with Rossby waves. (The mean response to wind jets propagates westward as long waves.)
• Wind variability is important for eddy shedding off Tehuantepec, a
Summary
• Wind variability is important for eddy shedding off Tehuantepec, a mechanism supported by QuikSCAT-forced, high-resolution ocean simulation.
• Dynamical instabilities contribute to downstream development.
• Intraseasonal variability of SSH is also high off Papagayo but is not highly correlated with wind variability: why?
Enhanced variability and predictability of orographical-induced upwelling � Fisheries applications
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Winter SSHM (contour) SSH.STD (shade)
obsSix features in winter circulationsseen in OfES-QSCAT (from north):
Tehuantepec BowlTehuantepec Bump
Papagayo Anticyclonic circulationCosta Rica Dome
6oN Anticyclonic circulationPanama Single Cyclonic Circulation
In OfES-NECP only Tehuantepec Bowland Costa Rica Dome are seen in winter
OfES-NCEP OfES-QSCA
and Costa Rica Dome are seen in winter circulation (below)
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High Wind Composite—Observation
Tehuantepec Composite
lag-1 lag 1
lag 3lag 4
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Correlation SSHA btw Obs and Model
The Tehuantepec jet-forced eddy generation is some
captured but simulated eddies deviate in phase from obs.
SSH Variance (col) during Nov-Feb
Corr b/w Obs and Model (20-120-dy)