WPGM2008-PNG_Coastal_Upwelling_and_ElNino

258 views
193 views

Published on

WPGM2008講演スライド
パプアニューギニア沖沿岸湧昇とエルニーニョ発生

Published in: Business, News & Politics
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
258
On SlideShare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
3
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

WPGM2008-PNG_Coastal_Upwelling_and_ElNino

  1. 1. Takuya Hasegawa, Kentaro Ando, Keisuke Mizuno (JAMSTEC/IORGC) & Roger Lukas (University of Hawaii) Relationship between SST Cooling over the Western Part of the Pacific Warm Pool and Coastal Upwelling along the North Coast of Papua New Guinea Prior to the 2002/03 El Nino 2008 WPGM Cairns
  2. 2. -Background- Western equatorial Pacific Coastal upwelling along PNG can contribute to generate positive zonal gradient of SST Warm SST related to Pacific warm pool Onset of El Nino Coastal upwelling (Rotschi et al. 1973 Lukas1988; Tsuchiya et al. 1989; Kuroda 2000; Webster & Lukas 1992; Ueki et al. 2003) WWB Papua New Guinea (PNG) Eastward movement of Pacific warm pool Positive zonal gradient of SST negative zonal gradient of SLP High SLP Low SLP Enhancement of westerly wind
  3. 3. SST horizontal map (NOAA OI-SST) Dec 1981 Mar 1997 Dec 2001 Cold SST along the north coast of PNG before onset of El Nino Coastal cooling before onset of El Nino events Papua New Guinea El Nino events after 1980s: 1982/83 1986/87 1991/92 1997/98 2002/03 2006/07 El Nino events after 1980s: 1982/83 (1986/87) (1991/92) 1997/98 2002/03 2006/07 (but weak signal) Half of El Nino events after 1980s: Cold SST along the north coast of Papua New Guinea However, role of coastal oceanic variation in SST cooling over the western part of the Pacific warm pool, is not clear at present
  4. 4. western part of the Pacific warm pool (WPWP) -Target- SST cooling in WPWP Papua New Guinea (PNG) This study: # Exploring mechanism of SST cooling in WPWP # With special reference to coastal upwelling along the north coast of PNG # Discuss an onset mechanism of El Nino ?
  5. 5. Satellite data -Data- # Sea surface temperature (SST): TMI satellite data # Sea surface wind (SSW): QuikSCAT satellite data # T, S, current velocity, air-temp., etc.: TRITON moored buoy data # CTD & ADCP data: KY0111 cruse of R/V Kaiyo # Data period: 1999~present Focus the oceanic variation in WPWP prior to onset of 2002/03 El Nino event WPWP PNG CTD data from R/V Kaiyo TRITON mooring buoy data
  6. 6. Upper ocean temperature structure observed by R/V Kaiyo 2.7˚S EQ CTD stations 28˚C Coastal upwelling in 2001 boreal winter with cold SST along PNG coast Shallower near the coast Latitude-depth diagram of CTD-observed temperature 80m 20m CTD-observation of the R/V Kaiyo for 21-23 December 2001 (Prior to onset of 2002/03 El Nino) Snapshot of daily SST on 22 December 2001 SSTs in the upwelling region: Lower than those around it Shows coastal upwelling -Results- Cold SST area along coast
  7. 7. 22 Dec 2001 Snapshot of SSW Cold SST North coast of PNG: ・Northwesterly SSW → Coastal upwelling (Lukas1988; Webster & Lukas 1992) Snapshot of TMI SST (color) & QuikSCAT SSW (arrow) Northwesterly wind parallel to the coast
  8. 8. TMI-SST 20Dec2001  10Jan2002  30Dec2001  Cold SST area: Extension from the coastal area toward the equator [℃] Extension of the cold SST area from the coast
  9. 9. Cooling mechanism in WPWP Using four TRITON buoys in BOX (daily data): # Horizontal heat advection; from box-averaged zonal current velocity at 10m depth (U) & horizontal gradient of mixed layer temperature (MLT) # Net surface heat flux: from buoy meteorological data # Vertical heat advection, entrainment cooling, diffusion; Residual # Daily data; tide-killer & 7-day running mean filtered Cooling period of MLT Dec 2001 MLT Cooling: -0.7 (℃) (Explaining 50% of MLT cooling) (℃/day) Large contribution of zonal heat advection to MLT cooling, as compared to the net surface heat flux Temporal change rate of observed MLT Due to zonal heat advection Due to net surface heat flux (℃) Heat budget analysis TRITON buoys Due to meridional heat advection 1 JAN 2002
  10. 10. onset of 2002/03 El Nino -Summary and discussion- eastward shift of warm pool zonal heat advection Schematic diagram explaining the proposed mechanism for onset of 2002/03 El Nino SST cooling ●About half of El Nino events after 1980s: Coastal SST cooling before onset ●Case study of the 2002/03 El Nino using buoy data etc.: [Western edge of Pacific warm pool] PNG positive zonal gradient of SST & strong westerly SSW Newly shows a role of coastal upwelling in SST cooling over the western edge of the Pacific warm pool. It may also contribute to onset of El Nino. To explore a relationship between SST cooling and enhancement of westerly wind is next target. Northwesterly wind
  11. 11. END
  12. 12. -Background- Onset of El Nino: # Various mechanisms/hypotheses  ・Eastward movement of Pacific warm pool (Wyrtki 1975, etc.) Western equatorial Pacific Eastward movement of Pacific warm pool → Air-sea coupled instability mode/slow mode ・ Positive zonal gradient of SST & westerly wind over the western side of Pacific warm pool (Yamagata 1985; Philander et al. 1984) ・Westerly Wind Burst (WWB) related to MJO→SST cooling→Positive SST gradient →low-level zonal pressure gradient (negative pressure gradient) →enhancement of westerly wind→eastward movement of Pacific warm pool (Kessler et al. 1995; Kessler and Kleeman 2000; Yu et al. 2003; Tziperman et al. 2007 ) Eastern equatorial Pacific Warm SST related to Pacific warm pool Onset of El Nino WWB SST cooling in the western edge of Pacific warm pool High pressure Low pressure Eastward movement of Pacific warm poolPositive zonal gradient of SST Negative zonal gradient of low-level pressure
  13. 13. Time series of SSW component parallel to north coast of PNG Uwin (raw) Vwin (raw) Parallel component (Positive: Northwesterly wind) (raw & 7-day running mean filtered) CTD Observation by R/V Kaiyo Coastal upwelling period: Strong northwesterly wind
  14. 14. TRITON-buoys ADCP current velocities at depth of 40m during 13-23 December 2001 Cooling Mechanism? Eastward & Northeastward ADCP-measured 40m-depth current velocities Cold temperature; transported to the equatorial region, by eastward/northeastward advection

×