1 / 30

Central America: A conduit for Atlantic-to-Pacific influences Shang-Ping Xie

Central America: A conduit for Atlantic-to-Pacific influences Shang-Ping Xie Timmermann, Y. Okumura * , S. de Szoeke, H. Xu, J. Small, T. Miyama + , Y. Wang International Pacific Research Center, University of Hawaii *UCAR; + FRCGC, JAMSTEC, Japan. Water hosing experiments (GCMs)

mareo
Download Presentation

Central America: A conduit for Atlantic-to-Pacific influences Shang-Ping Xie

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Central America: A conduit for • Atlantic-to-Pacific influences • Shang-Ping Xie • Timmermann, Y. Okumura*, • S. de Szoeke,H. Xu, J. Small, T. Miyama+, Y. Wang • International Pacific Research Center, University of Hawaii • *UCAR;+FRCGC, JAMSTEC, Japan • Water hosing experiments (GCMs) • Regional model results • AR4 CMIP • Orographic effects

  2. ITCZ Shift Pan-Atlantic Pattern SST & wind NAO  subtropical wind Xie & Tanimoto (1998, GRL) WES feedback Tropical meridional mode  Shift in ITCZ A model for interpreting paleo variability? (Chiang 2004, Hadley circulation book)

  3. Close connection between the subpolar and tropical North Atlantic Cariaco Basin north of South America Wet tropical South America Warm Greenland Peterson et al. (2000, Science) Chiang (2004, Hadley circulation book)

  4. Annual mean response (Yr 81-100) A. Timmermann, Y Okumura, et al. 2006 SST & wind stress GFDL_CM2.1 NCAR CCSM2 ECHAM5/MPI-OM HadCM3 • Meridional (WES) mode in ATL • Cross-Central American winds • Reduced NS asymmetry in EP

  5. Use Regional Models to resolve the narrow and mountainous Central America January Wind (QSCAT) h (km)

  6. Ocean spin-up Coupled 1990 – 1995 1996 – 2003 IPRC Regional Ocean-Atmosphere Model (iROAM) on Earth Simulator Atmosphere: IPRC-RAM 0.5°×0.5°, L 28 GFDL Modular Ocean Model 2 0.5°×0.5°, L 35 Prescribed OISST Land surface model Ocean forced by NCEP reanalysis Interactive

  7. Annual-mean climatology SST, precipitation & surface wind iROAM Obs: TRMM, OISST & QSCAT 25 25 Northward-displaced ITCZ and equatorial cold tongue

  8. ITCZ’s meridional migration Precip (gray shade), surface wind & SST (contours) in 125-95W IROAM TRMM obs 20N 10N EQ 10S 20N Jan Mar May Jul Sep Nov Jan Mar May Jul Sep Nov Double ITCZ for a brief period of Mar-Apr

  9. Mesoscale Features February: Gap wind jets < 40 m Sfc wind, Z20(m) & orography

  10. Response to a 2oC cooling in the North Atlantic • Large equatorial cooling in Jan-Apr  Reduced annual cycle • Bjerknes feedback, instead of WES, is triggered. Implications for water-hosing experiments of relevance to Younger Dryas Xie et al. (2007, JC, in press)

  11. -2oC -2oC Dec Jan • Seasonality • Cooling begins in the Gulf of Panama in response to an intensified Panama jet. • Panama cooling coincides with the seasonal shoaling of the thermocline there. • The cooling intensifies and extends to the equator along the thermocline ridge. -2oC Feb

  12. Response to a 2oC cooling in the North Atlantic SST & Wind difference -2oC -2oC January - March July - September Atmospheric adjustment mostly through the Panama gap. The thermocline ridge in the Gulf of Panama helps spread the SST cooling to the equator, triggering the Bjerknes feedback. Wind anomalies are larger, but with a smaller SST response.  Deepened thermocline in the Gulf of Panama.

  13. Seasonality of the Pacific Response 1: Mean state • Why is the coupled response favor the warm than the cold season? • Mean northeasterlies in Feb  increased wind speed in response to Atl cooling  increased evaporation (wind speed & dry advection) & mixing. • Shoaling thermocline in Feb (by > 20 m) •  Stronger air-sea coupling in Feb than in July. February Sfc wind, Z20(m) & orography August > 60 m < 40 m

  14. du & q at 100W, Eq Seasonality of the Pacific Response (2) Wind, Pressure & Precip (July) Pressure 850 mb • During the cool season (Jun-Oct), strong easterlies on the equator at 850 mb, but not at the surface  seasonal SST cooling and stable ABL? • Anomalies patterns similar to the observed mid-summer drought: suppressed convection & intensified cross-Central American wind (Small et al. 2006). cf. Rowan’s talk 1000 mb

  15. Feb • Factors for strong equatorial response during the cool season (Jan-May) • Pros • Mean NE wind • Shoaling thermocline • Strong vertical coupling in wind • Con • Stronger atmospheric response in boreal summer

  16. Common among GCMs: • Reduced annual cycle • cooling north/on the equator during Jan-May • +LBM-POP(Axel et al.) • FOAM (L. Wu et al.) iROAM

  17. Why does the meridional mode develop subsequently in some models?  Prolonged southern/double ITCZ in some GCMs  stronger WES feedback involving convective heating Equator Wind-Evaporation-SST (WES) Feedback

  18. Intercomparison of AR4 models cf. Mechoso et al. (1995), Devay et al. (2002) by Simon de Szoeke • Meridional asymmetry • Role of the eastern Pacific warm pool

  19. latitude EP climate in AR4 models SST, rain & eq wind

  20. NE trades over the EP warm pool vs. meridional asymmetry GCM #c

  21. r=-0.55 29 0 C) 28 ° e 1 cccma cgcm3.1 27 6 9 2 cnrm cm3 f a 8 FMA SST ( b 1 3 csiro mk3.0 5 26 4 c 7 4 gfdl cm2.0 d 5 gfdl cm2.1 3 2 25 6 iap fgoals1.0g 0 5 7 inmcm3.0 -1 DJF CA wind speed (m s ) 8 ipsl cm4 9 miroc3.2 hires a miroc3.2 medres b mri cgcm2.3.2a c ncar ccsm3.0 d ncar pcm1 e ukmo hadcm3 f iroam 0 Observed NE wind off Central America vs. Meridional asymmetry r=-0.87 4 ) -1 2 b 0 (m s e 1 0 f 2 6 9 a EQ 4 3 8 5 -2 FMA v c -4 d 7 0 2 4 6 8 m DJF CA wind speed ( s-1)

  22. Westward and disconnected equatorial cold tongue bias SST Obs GCM #5 Latitude West Longitude

  23. 30 r=–0.60 28 6 8 d SST (° C) 9 26 5 c 3 4 a 1 7 b 24 e f 2 22 2 4 v (m s-1) Niño 1+2 meridional windcools SST Nino 1+2: 80-90° W, 0-10°S

  24. Orographic Effects by Haiming Xu, Justin Small • EP warm pool convection • Moisture transport from the Atlantic to Pacific • Basin-scale climate

  25. Winter SST & wind ITCZ displaced on the south edge of EP warm pool TMI SST & precip; QuikSCAT wind (Jan-Feb)

  26. Cross-Central American moisture transport Hypothesized to hold the key to the preference for AMOC Mexico (<27N) – Panama (Jan-Feb ‘02) 0.25o orog T42 orog Xu et al. (2005, JC) 0.323 0.309 January Wind (QSCAT) h (km)

  27. Summary • Tropical response to a MOC shutdown • Robust response in the tropical Atlantic: the WES feedback and a meridional dipole; • Weakened meridional asymmetry in the eastern Pacific in some models but the zonal mode triggered in other; • The equatorial annual cycle weakens, and cooling north/on the equator during Jan-May. Response during May-Dec varies among models. • AR4 CMIP &CGCM run without mountains: NE wind through Panama during Dec-Feb influences the subsequent development of meridional asymmetry (ITCZ displacement) • Tropical Pacific response may be sensitive to the treatment of narrow and mountainous Central America. • How can paleo data help constrain models?

  28. Upon coupling, the model SST tracks observations closely.  Air-sea feedback Nino3 SST MOM2 OISST iROAM Ocean spin-up Coupled

  29. Role of internal air-sea feedback Suppressed cloud radiative effect south of the equator ITCZ moves back and forth across the equator Double ITCZ 20N 10N EQ 10S 20N Jan Mar May Jul Sep Nov Precip (shade), SST & sfc wind

  30. q (g/kg) 0.25o orog Wind speed (m/s) Panama Mexico T42 orog

More Related