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- C. Gnanaseelan
Indian Ocean warming: possible causes, feedbacks and impact C. - - PowerPoint PPT Presentation
Indian Ocean warming: possible causes, feedbacks and impact C. - - PowerPoint PPT Presentation
Indian Ocean warming: possible causes, feedbacks and impact C. Gnanaseelan Indian Institute of Tropical Meteorology, Pune Collaborators: S. Rahul, J.S. Deepa ESM modelling workshop at IITM, 26 July 2016 OUTLINE Possible mechanisms for Indian
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(in oC/decade)
1958 to 2008
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(in oC/decade)
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Heat flux trends (W/m2/year) Net heat flux (W/m2) Large bias in heat flux products but they all agree in the negative heat flux trends
Rahul & Gnanaseelan, 2013, GSRL
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MOM5 experiments
Cooling in the western IO due to changing ocean dynamics is
- vercome by positive net heat flux
Trends in the model wind stress Annual mean net heat flux in model
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Gnanaseelan et al. (2016)
SODA 1958 to 2008 ORAS4 1958 to 2015
Courtesy: Rashmi per decade TRENDS IN CURRENTS
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Rahul & Gnanaseelan, 2015, CD
- C per decade
Trends in annual SST and winds
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Annual mean southeasterly trade in south IO and westerlies at equator induces a cyclonic curl in SWIO which manifests a unique
- pen
- cean
upwelling zone in SWIO (5o to 15oS and 50o to 80oE) and characterized by Shallow thermocline (Known as thermocline ridge in Indian ocean).
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SSHA trend for Indian Ocean based on SODA,ORA, and MOM5 (1959-2008)
HYCOM SSHA trend for 1961-2008 (Han et.al,2010)
SODA
ORAS4
MOM5
HYCOM Ocean response (in thermocline depth or SSHA)
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Upwelling in the north Upwelling in the south
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Courtesy: Rahul Watterson, 2001
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Rahul & Gnanaseelan, 2016, Clim Dyn Concides with the global mean surface temperature hiatus
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First EOF of stream function (after applying a 7 year running mean) First EOF of velocity potential (after applying a 7 year running mean) Rahul & Gnanaseelan, 2016, Clim Dyn MOM5 Model captures these epochal changes ….
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SST and winds regressed with the first PC of stream Function, and their trends are shown in the right panels SODA ORAS4
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Coupled feedback mechanism
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Ueda et al. 2015, nature comm.
Correlation between Nino3.4 index with Indo-Pacific SSTA
Hiatus anomaly La Nina anomaly comp
1999 to 2014
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North Indian Ocean warming
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Global ocean heat content (700m) Indian Ocean heat content Pacific Ocean heat content
Lee et al. 2015, nature geos. ITF transport
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Vertical structure of temperature trends
Model simulated the pattern well, but most of the CMIP coupled models fail to represent the subsurface pattern
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Indonesian Through Flow can modulate Indian Ocean temperature
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Lee et al. 2015 Deepa et al. 2016
ITF in MOM5
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Sea level anomaly trend(mm/year) 1959-2008
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Meridional Volume transport across the Equator
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Meridional Volume transport across 20oS
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SUMMARY
Indian Ocean warming trends can not be explained by net heat flux Recent Indian Ocean warming pattern is not associated with the atmospheric teleconnections, and ocean dynamics plays an important role Changing surface circulation patterns explains the recent IO warming trends to a large extent Cooling in the western IO due to changing ocean dynamics is overcome by positive net heat flux Recent increase in ITF explains subsurface warming trends in the southern TIO The equatorial Indian Ocean forcing affects ITF and then to the subsurface warming in the south
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Thank You
We need a good model to understand the Indian Ocean warming
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Ueda et al. 2015, nature comm Roxy et al. 2015, nature comm
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