Indian Ocean Warming and its Impact on Indian Summer Monsoon and - - PowerPoint PPT Presentation

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Indian Ocean Warming and its Impact on Indian Summer Monsoon and - - PowerPoint PPT Presentation

Aug 29, 2022 371 likes •762 views

Indian Ocean Warming and its Impact on Indian Summer Monsoon and Global Hiatus Suryachandra A. Rao Associate Mission Director, Monsoon Mission Indian Institute of Tropical Meteorology Collaborators: H.S.Chaudari, S. Pokhrel, Asish Dhakate,

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Indian Ocean Warming and its Impact on Indian Summer Monsoon and Global Hiatus

Suryachandra A. Rao Associate Mission Director, Monsoon Mission Indian Institute of Tropical Meteorology

Collaborators: H.S.Chaudari, S. Pokhrel, Asish Dhakate, Kiran Solunke, S. Saha and others

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Outline

  • 1. Why Indian Ocean is Warming Consistently?
  • 2. What is its impact on Indian Summer

Monsoon

  • a. Seasonal Mean
  • b. Intraseasonal Oscillations
  • c. Extreme Rainfall Events
  • d. Global warming Hiatus
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Data and Model

  • TMI & Reynolds SST
  • Merged Sea Surface Height data
  • NCEP/NCAR and SODA/GODAS/ECCO

reanalysis

  • ECHAM-5 AGCM (T106L19)
  • Data from CMIP5 Models
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Indian Ocean Warm Pool

70% of the World Ocean Heat gain is in IO

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Relative Role of surface heat fluxes and Ocean Dynamics for warming/expansion of warm pool

Role of net surface heat fluxes

  • n SST trend

Role of latent heat fluxes

  • n SST trend

Net heat Fluxes (dominated by latent heat flux) try to cool the Ocean, particularly in the central tropical IO

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Reynolds area anomalies

  • Vs. Merged SSH anomalies

TMI area anomalies

  • Vs. Merged SSH anomalies
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Relation between area anomalies and other parameters

SSHA OLRA Qnet Winds

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Rao et al., (2012). Climatic Change

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Roxy et al., (2014)

11th March 2010. INCOIS, HYderabad

CMIP5 Models get much less warming than Observed in the Rest of the Indian Ocean. WIO warming is Overestimated.

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Indian Ocean Warming, Walker Circulation & El Nino: Skewness

El Nino warms Western IO significantly, however Lan Nina do not cool the WIO with Same magnitude.

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2008 Indian Monsoon Rainfall anomalies and deviations from normal IOD

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Indian Ocean Dipole and Its influence on Indian Summer Monsoon SST ANOMALIES

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SST Differences in 2008

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Indian Ocean warming trend and Monsoon Rainfall

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IOD run IOD +SIO Warming run SIO response

Model response to different SSTA forcings

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Modulation of Local Hadley Circulation (Vertical Velocities averaged between 70oE-90oE)

Observations Model Rao et al., (2010). Journal of Climate

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Indian Ocean Warming weakens Monsoon

Roxy et al., (2014)

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CMIP5 Models Projections

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Observations Model Expt.

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ISO Variance Trend (1970-2012)

ISO variance is increasing over Indian land mass and eastern Indian Ocean

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Space-Time Spectra of Rainfall (10oS- 30oN, 65oE-95oE)

ISO variance is increasing & Propagation speed is slightly decreasing

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Space-Time Spectra of Rainfall (10oS- 30oN, 65oE-95oE) in Model Expts.

ISO variance is increasing & Propagation speed is slightly decreasing

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Mechanism to modulate ISO variance

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CMIP5 Model Projections of ISO

JJAS Mean Rainfall Bias in CMIP5 models. Dry Bias over India and Eastern Indian Ocean is a common feature

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CMIP5 Model Projections of ISO Variance

JJAS ISO Variance bias in CMIP5 models. Dry Bias over India and Eastern Indian Ocean is a common feature

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CMIP5 Model Projections of MISO Propagation

JJAS MISO Variance bias in CMIP5 models. Dry Bias over India and Eastern Indian Ocean is a common feature

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Number of Heavy Rainfall Events

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Correlation between number of heavy rainfall events and SST(SSH) anomalies

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Correlation between Extreme Rainfall events with SLP, Moisture Divergence and vorticity

Ajayamohan and Rao , (2008). JMSJ

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Global Warming Hiatus

Trend in SST/Air. Temp SST Trend during hiatus

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Global Warming Hiatus

Indian Ocean vs Pacific Relation weakening? AGCM expt.

11-year running correlation between Nino 3.4 and IO SST

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Other Aspects of Indian Ocean Warming and recent trends

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Indian Ocean Warming and Primary productivity

Roxy et al., (2016)

Primary productivity is decreasing rapidly in recent periods.

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Jin & Wang, 2017 Monsoon Rainfall Decreasing trend is Revived after 2002

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I950-2002 Trends 2002-2012 Trends

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Conclusions

  • Indian Ocean is warming consistently for last 50

years

  • Coupled Positive feedback is responsible for the

above observation

  • Monsoon rainfall over central India may reduce

considerably in the above scenario

  • Monsoon Intraseasonal Oscillations are

modulated considerably under warming.

  • Number of extreme rainfall events may increase

due to Indian Ocean warming

  • Global warming Hiatus is partially due to IO

warming

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