Impact of air pollution on the south asian monsoon
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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

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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


Impact of air pollution on the south asian monsoon

MODIS Satellite picture from wikepedia


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


Impact of air pollution on the south asian monsoon

UNEP 2002


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


Aerosol composition

Aerosol Composition

Carrico 2003


Impact of air pollution on the south asian monsoon

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


Radiative forcing impacts

Radiative Forcing Impacts

UNEP 2002


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


Impact of air pollution on the south asian monsoon

Chung et al 2006


Impact of air pollution on the south asian monsoon

Chung et al 2006


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


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