of Impact Air Pollution on the South Asian Monsoon
A Paper Review Siv Balachandran 04/26/07
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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
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MODIS Satellite picture from wikepedia
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Motivation
India
1 Billion and growing Emissions are increasing Also growing Monsoon = survival Health Impacts Transport of pollution Climate Change Impacts
South Asia
Globally
UNEP 2002
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The South Asian Monsoon
2 monsoons
June - September: SW December - April: NE SW monsoon predominant for most of South Asia 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 Winds change from NE to SW
1856 - 1997
May is transition period
April/May - warmest
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UNEP 2002
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Aerosol/Haze Composition
Natural vs. Anthropogenic INDOEX
Brown Cloud in dry winter months due to aerosols
Monsoons wash out aerosols
UNEP 2002
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Aerosol Composition
Carrico 2003
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UNEP 2002
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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 Cloud albedo Cloud lifetime Reduction in cloud cover and albedo due to aerosol induced increase in solar heating
Indirect Effects
Semi-Direct
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Papers Reviewed
Ramanathan et al 2005
Coupled ocean - atmospheric Cases
GCM 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
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Aerosol Forcing
Ramanathan et al 2005
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Radiative Forcing Impacts
UNEP 2002
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Dimming
Ramanathan et al 2005
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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
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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
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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
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Circulation Impacts
Ramanathan et al 2005
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Rainfall Trends
Ramanathan et al 2005
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Chung et al 2006
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Chung et al 2006
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Increased Droughts
Ramanathan et al 2005
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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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