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The other Harvard 3-D model: CACTUSChemistry, Aerosols, Climate: Tropospheric Unified
Simulation
Objective: to improve understanding of the interaction between chemistry, aerosols, and climate
GISS
Harvard
CalTech
UC Irvine
Carnegie Mellon
(Goddard)
Anatomy of a Unified Model
GISS GCM II’
calculates meteorology
GHG concentrations, solar flux, land surface characteristics
CalTech aerosol module
Harvard chemistry module
aerosoltropospheric ozone
temperature, humidity, wet dep, clouds, winds, etc
precursor emissions
aerosol, gases
What follows: Alternative, practical approaches, with tie-in to GEOS CHEM
Fully coupling a model is ambitious and CPU-intensive!
(wallclock time: 10 days/model year)
Equilibrium climate simulations: 75-100 years, including spin-up
Transient simulations: 50 years just for ocean spin-up
Chapter 1: Calculate radiative forcing due to increase in tropospheric ozone (Mickley et al., 1999, 2001)
GISS GCM II’
GHG concentrations, solar flux, land surface characteristics
Harvard chemistry module
meteorology
Specified aerosol. Present-day & preindustrial precursor emissions (run twice)
ozone
Forcing calculation
Calculated ozone does not influence climate
Uncertainty of radiative forcing due to O3 is quite large.
Standard simulation,F = 0.44 Wm-2
Test simulation with natural emissions within range of uncertainty
F = 0.80 Wm-2
(about 1/2 F of CO2)
obs, late 1800s
test model
std model
Mickley et al., 2001Preindustrial ozone monthly means
Chapter 1 continued: Do same forcing calculation for sulfate aerosol (Adams et al., 1999)
GISS GCM II’
GHG concentrations, solar flux, land surface characteristics
CalTech aerosol module
aerosol
meteorology
precursor emissions
nitric acid
Forcing calculation
Harvard offline chemistry
Nitrate forcing may have large impact over 21st century
F preindustrial to present-day for sulfate+nitrate =
-1.14 Wm-2
F preindustrial to 2100 for sulfate+nitrate =
-2.13 Wm-2
2100 annual averaged forcing due to sulfate+nitrate aerosolAdams et al., 2001
Chapter 2: Begin to unify model (Liao et al., 2003)
GISS GCM II’
GHG concentrations, solar flux, land surface characteristics
CalTech aerosol module
Harvard chemistry module
aerosol ozone
meteorology
precursor emissions
oxidants, nitric acid
Forcing calculation
Forcing calculation
Heterogeneous chemistry decreases ozone at the surface
Ratio of annual mean mixing ratios of ozone:
With het chem / without hem chem
Includes ozone uptake on mineral dust.
Liao et al., 2003
Chapter 3: Calculate equilibrium climate response to changing tropospheric ozone (Mickley et al., 2003)
GISS GCM II’
calculates meteorology
GHG concentrations, solar flux, land surface characteristics
Harvard chemistry module
archived monthly mean ozone fields
precursor emissions
Calculate preindustrial and present-day ozone fields beforehand, using present-day climate.
Results from GCM equilibrium simulation with present-day vs. preindustrial tropospheric ozone
T = 0.3oC
F = 0.49 W m-2
Preindustrial ozone
equilibriumclimate Present-day ozone
Mickley et al., 2003
Inhomogeneity of climate response to tropospheric ozone change over 20th century
Greater warming in northern hemisphere (due to more ozone and albedo feedback in Arctic)
Strong cooling in stratosphere (>1oC in Arctic winter):
Surface
Troposphericozone
9.6 m
Stratosphericozone
Global
SH
NH
Chapter 3 continued (Chung et al., in progress)
Do same with Caltech aerosol:
Feed monthly mean preindustrial and present-day aerosol fields into GISS GCM.
Chapter 4: Build interface between GISS GCM and GEOS CHEM to study past and future climates
GISS GCM II’
GHG concentrations, solar flux, land surface characteristics
GEOS CHEM
calculates chemistry, aerosol
precursor emissions
archived temperatures, humidity, winds, etc
First application: investigate effect of future climate change on US air quality (Mickley, Shiliang Wu)
Chapter 4 continued: Diagnose effect of changing climate on US air quality (transient simulation)
1950 2000 2025 2050 2075 2100
GISS GCM, with changing GHGs
Spin-up of ocean
GEOS-CHEM
Calculate chemistry, aerosol
present-day precursor emissions
archived temperatures, humidity, winds, etc
Chapter 5: Investigate effect of aerosol and tropospheric ozone on future climate
precursor emissions
1950 2000 2025 2050 2075 2100
GISS GCM, with changing GHGs + ozone, aerosol
Spin-up of ocean
GEOS-CHEM
Calculate chemistry, aerosol
archived temperatures, humidity, winds, etc
1950 2000 2025 2050 2075 2100
Develop 100-year forecast of ozone, aerosol
Chapter 6: Investigate indirect effect of aerosols (Adams, DelGenio)
Acknowledgments:
Brendan Field, David Rind, Jean Lerner, Reto Ruedy, Gavin Schmidt, Drew Shindell, Andy Lacis, Prashant Murti, Bob Yantosca
