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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 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 • 1 Billion and growing • Emissions are increasing • South Asia • Also growing • Monsoon = survival • Health Impacts • Globally • Transport of pollution • Climate Change Impacts UNEP 2002
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
Aerosol/Haze Composition • Natural vs. Anthropogenic • INDOEX • Brown Cloud in dry winter months due to aerosols • Monsoons wash out aerosols UNEP 2002
Aerosol Composition Carrico 2003
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
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
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
Aerosol Forcing Ramanathan et al 2005
Radiative Forcing Impacts UNEP 2002
Dimming Ramanathan et al 2005
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
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
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
Circulation Impacts Ramanathan et al 2005
Rainfall Trends Ramanathan et al 2005
Increased Droughts Ramanathan et al 2005
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