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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

Impact of Air Pollution on the South Asian Monsoon

A Paper Review

Siv Balachandran

04/26/07

overview
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
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

the south asian monsoon
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
Aerosol/Haze Composition
  • Natural vs. Anthropogenic
  • INDOEX
    • Brown Cloud in dry winter months due to aerosols
  • Monsoons wash out aerosols

UNEP 2002

8 major impacts
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
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
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
Aerosol Forcing

Ramanathan et al 2005

dimming
Dimming

Ramanathan et al 2005

impact of sst changes
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
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
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
Circulation Impacts

Ramanathan et al 2005

rainfall trends
Rainfall Trends

Ramanathan et al 2005

increased droughts
Increased Droughts

Ramanathan et al 2005

conclusions
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