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Impact of Air Pollution on the South Asian Monsoon

Impact of Air Pollution on the South Asian Monsoon. A Paper Review Siv Balachandran 04/26/07. Overview. Motivation South Asian Monsoon Aerosols/Haze in South Asia Impact of Air Pollution on Monsoon UNEP 2002 Ramanathan et al 2005 Chung et al 2006 Conclusions. Motivation. India

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Impact of Air Pollution on the South Asian Monsoon

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  1. Impact of Air Pollution on the South Asian Monsoon A Paper Review Siv Balachandran 04/26/07

  2. Overview • Motivation • South Asian Monsoon • Aerosols/Haze in South Asia • Impact of Air Pollution on Monsoon • UNEP 2002 • Ramanathan et al 2005 • Chung et al 2006 • Conclusions

  3. MODIS Satellite picture from wikepedia

  4. Motivation • India • 1 Billion and growing • Emissions are increasing • South Asia • Also growing • Monsoon = survival • Health Impacts • Globally • Transport of pollution • Climate Change Impacts UNEP 2002

  5. 2 monsoons June - September: SW December - April: NE SW monsoon predominant for most of South Asia 1856 - 1997 30 El Nino, with 10 drought 16 La Nina, with 7 flood Studies suggest weakening due to global warming Anthropogenic aerosol load October to June Peaks in Feb/March May is transition period Winds change from NE to SW April/May - warmest The South Asian Monsoon

  6. UNEP 2002

  7. Aerosol/Haze Composition • Natural vs. Anthropogenic • INDOEX • Brown Cloud in dry winter months due to aerosols • Monsoons wash out aerosols UNEP 2002

  8. Aerosol Composition Carrico 2003

  9. UNEP 2002

  10. 8 major impacts • Aerosol forcing • Dimming • Reduction in surface evaporation • Surface cooling • Weakening of latitudinal SST Gradients • Stabilization of the troposphere • Decrease in monsoon rainfall • ABC induced droughts Ramanathan et al 2005

  11. Aerosol Impact on Climate • Direct Effects • Changes to Radiative Forcing • Indirect Effects • Cloud albedo • Cloud lifetime • Semi-Direct • Reduction in cloud cover and albedo due to aerosol induced increase in solar heating

  12. Papers Reviewed • Ramanathan et al 2005 • Coupled ocean - atmospheric GCM • Cases • GHGs+SO4_2050 (business as usual) • ABC_1998 (GHGs, SO4, ABC @1998) • ABC_2050 (increases in GHGs and SO4 and extrapolates ABC forcing) • ABC_2050_1 (GHGs and SO4 held at 1998) • Chung et al 2006 • CCM3

  13. Aerosol Forcing Ramanathan et al 2005

  14. Radiative Forcing Impacts UNEP 2002

  15. Dimming Ramanathan et al 2005

  16. Impact of SST Changes • Atmospheric heating  Surface Cooling • Indian Ocean SST changes • NIO cools • Equatorial IO warms • SST gradient affects pressure gradient • Pressure gradient affects circulation • Net effect = monsoon is disturbed

  17. Stabilization of the Troposphere • In the first 5km: dT/dz = -5 to -6 K/km • Unstable to moist convection • Instability coupled with low-level moisture convergence  deep convection • Aerosols/haze confined to ~ 4km • Heating of aerosol-loaded inhibits instability via differential warming of the atmosphere

  18. Pressure Gradients • Surface pressure late spring/early summer • NIO is warmer • SOE > 1015 mb • NIO < 1005 mb • Cross equatorial pressure gradient drives moisture from SIO to South Asia • Cooling of NIO causes SST gradient that reverses pressure gradient • Mid to upper troposphere • Cooler NIO  less deep convection in NIO • N to S circulation is disrupted

  19. Circulation Impacts Ramanathan et al 2005

  20. Rainfall Trends Ramanathan et al 2005

  21. Chung et al 2006

  22. Chung et al 2006

  23. Increased Droughts Ramanathan et al 2005

  24. Conclusions • Aerosol/haze impacts • Direct and indirect effects • SST changes affect circulation • Droughts • Transport of pollution • More than 1 billion people directly dependent on South Asian monsoon • Impacts to agriculture/health/global

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