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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


Aerosol composition
Aerosol Composition

Carrico 2003



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


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