Imprints of Coastal Mountains on Ocean Circulation and Variability

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Ernest Johnson
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1 Imprints of Coastal Mountains on Ocean Circulation and Variability Shang-Ping Xie 1 with C.-H. Chang 1, W. Zhuang 2, N. Schneider 1, J. Small 3, B. Taguchi 4, and H. Sasaki 4 1 IPRC, University of Hawaii 2 South China Sea Institute of Oceanology 3 Naval Research Laboratory 4 Earth Simulator Center, Japan

2 Orographic jets Ocean circulation (We) & SST 1 South China Sea: orog. forcing from the west >500 m Comparative study at similar latitudes 2 Eastern Pacific: orog. forcing from the east L H Jul-Aug wind & SST Jan-Mar wind & SST Xie et al. (2003, 2007, JGR) Xie et al. (2005, JC)

3 16 o N Wind curl EOF (41%) WSCisv spatial mode 1 Summer (Jun-Sept) 3 16 o N SSH EOF (17%) TP spatial mode 1 2 (a) 12 o N 1 12 o N 0 8 o N -1 8 o N -2 4 o N 108 o E 112 o E 116 o E 120 o E -3 4 o N 108 o E 112 o E 116 o E 120 o E (c) Max correlation ~ 0.5 when wind curl leads SSH by 2 weeks MJO, windforced 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)

4 Winter Mean Circulation in Sverdrup Balance Sverdrup relation βv = curlτ Winter Wind + Spring Circulation Ocean circulation in Sverdrup balance with wind curls Tehuantepec Bowl Tehuantepec jet AntiCyclonic gyre (SSH high ~72cm) Costa Rica Dome Zonal Papagayo Jet Cyclonic gyre (SSH low ~ 48cm) Panama Circulation Meridional Panama jet Cyclonic gyre (SSH low ~ 57 cm) Curl (color) SSH (contour)

5 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

6 Standard deviations of intraseasonal variability in SSH (contour) & Wind Stress Curl (color) Tehuantepec Wind forced, westward propagation along the high-variance band SSH_STD vs Curl

7 Coherent Eddy-train Structure in High Variance Band SSHA Lag Correlation w/ Action Centers STD (color) & Correlation (contour) Lag Correlation w/ Action Centers near Three Gaps Action Center =: local max SSHA STD (marked by squares) Nov-Feb Correlation in contours Black: w/ Tehuantepec AC Blue: w/ Papagayo AC Pink w/ Panama AC

8 Tehuantepec Time-Distant Diagram SSHA vs Wind Stress Curl ( ; ) Oct.2000-Jun.2001 Oct.2002-Jun.2003 Still along the same axis (will change later) SSHA clearly responding to wind forcing: offshore propagation of Positive SSHA signal seen right after strong coastal negative Wind Stress Curl

9 High-wind composites SSH (color) & Wind speed Obs SSH (color) & Wind Curl(con) lag0 lag1 Time lag (weeks) lag2 Distance along High Variance Band

10 Phase velocity of Rossby waves; wavelengths set by the dispersion given intraseasonal frequency C ph (green) Tehuantepec l k High variance band (con) SSHA from Tehuantepec high wind composite (col) at lag +4 L R ω -1 Tehuantepec 660 km 87 km 85 days Rossby Wave Dispersion Relation k + 2 β 2 β 1 + l = 2 ω 2 ω R 2 2

11 Dec.10, 2003 SST, SSH & Wind Dec.17, 2003 Eddy train on the northwest flank of the cool SST band, causing meanders & cusps of the SST front.

12 Global, eddy-resolving (0.1 o ) hindcast (OFES) forced by QuikSCAT winds (1999 -) Obs (color) vs OFES ISV High-wind Composite of SSHA Obs (color) vs model (contour) day SSHA STD (Nov-Feb) Obs (col) ( ) OfES(con) (Jul.1999 Dec.2005)

13 Energetics based on OFES Wind Work Oct-Apr Mean SSHA std (cm, contour) Ug (m/s, vector) Wind Work (shade, upper panel) Instability (BCC+BTC) (shade, lower panel) (integrate over entire water column) Instability (T2+T4)

14 Summary 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 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

15 Six features in winter circulations seen in OfES-QSCAT (from north): Winter SSHM (contour) SSH.STD (shade) obs Tehuantepec Bowl Tehuantepec Bump Papagayo Anticyclonic circulation Costa Rica Dome 6 o N Anticyclonic circulation Panama Single Cyclonic Circulation In OfES-NECP only Tehuantepec Bowl and Costa Rica Dome are seen in winter circulation (below) OfES-NCEP OfES-QSCA

16 High Wind Composite Observation Tehuantepec Composite lag-1 lag 1 lag 4 lag 3

17 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 ( dy)

Intraseasonal Variability in Sea Level Height in the Bay of Bengal: Remote vs. local wind forcing & Comparison with the NE Pacific Warm Pool

Intraseasonal Variability in Sea Level Height in the Bay of Bengal: Remote vs. local wind forcing & Comparison with the NE Pacific Warm Pool Shang-Ping Xie 1,3, Xuhua Cheng 2,3, Julian P. McCreary 3 1.