Radiative Transfer Modeling: Deriving Forcing on Climate in Support of GMI Don Wuebbles Department of Atmospheric Sciences University of Illinois, Urbana, IL November, 2003

Effect of Gases and Particles on Climate Determined by its radiative forcing relative to other forcings on climate Increase in Radiative Forcing on Climate since 1750 – Driven by CO 2 and other GHG

Calculation of Radiative Forcing  RF (for an externally imposed perturbation) = Change in the radiative balance of the climate system IPCC Definition Globally- and annually-averaged change in net irradiance at the tropopause after allowing for the adjustment of stratospheric temperatures to reach radiative equilibrium but with surface & tropospheric temperature held fixed at the unperturbed values (IPCC).  RF is defined without dynamical or other feedbacks on the climate system

Factors Important in Direct Radiative Forcing Calculations Strength of longwave radiation absorption and location of absorbing wavelength –Absorption is important in “window region” (8-12  m) Background distributions of H 2 O, O 3, CO 2, N 2 O, CH 4 Distribution of Clouds –Cloud fraction, location, cloud type, optical depth, cloud liquid water, effective drop radii Distribution of concentrations of given GHGs and/or aerosols –Depends on atmospheric lifetime and emissions

UIUC Narrow Band Model Developed for radiative forcing and energy balance climate by Atul Jain –Component in the ISAM Integrated Climate System Model Initially developed to use seasonal and latitudinal variations in UIUC 2-D CTM –Very fine altitude structure in UTLS –3 levels of clouds (based on ISCCP data and other observations) –netCDF inputs from 2-D model

Calculation Methodology for Radiative Forcing and Concentration Infrared (IR) fluxes are calculated using Malkumus Random Narrow Band (NBM) radiative transfer model (Jain et al., 2000). uIncludes IR opacity by CO 2, CH 4, N 2 O,O 3, H 2 O, and Halocarbons. uSpectral Range – cm -1. uSpectral Width – 5 cm -1 (CO 2, CH 4, N 2 O, O 3 ), and 10 cm -1 (H 2 O and other gases). uRadiance calculated over 24 Gaussian angles using 12 point Gaussian quadrature. Short-Wave fluxes are calculated using the Delta Eddington model (Briegleb, 1992) with 18 spectral intervals (0.2 to 5 micron).

NBM-Derived Infrared Fluxes for the Top-of- Atmosphere Jain et al. (2000) Note that the NCEP Reanalysis compares very closely with ERBE data

Greenhouse Gases Studied (Jain et al., 2000) CO 2, CH 4, N 2 O Chloroflurocarbons (CFCs) and other Halocarbons  CFC-11, -12, -13, -113, -114, -115  CCl 4, CH 3 CCl 3  HCFC-22, -123, -124, -141, -142b, -225ca, -225cb  HFC-23, -32, -125, -134, -134a, -143, -143a, -152a, -161, -227ea, -236fa, - 245ca  H-1201, -1311, CF 2 ClBr, CF 3 Br, CH 3 Br, CH 2 Br 2, CHF 2 Br  CF 3 I, CF 3 CF 2 I Perfluorocompounds (PFCs)  SF 6, CF 4

Sensitivity Studies in Jain et al. (2000) NBM vs. BBM Radiative Forcings Clear Sky vs. Cloudy Sky Radiative Forcings Constant Vertical Profile-Based vs. Realistic Vertical Profile-Based Radiative Forcings Global Average-based vs. Latitudinal and Seasonal Average-based Radiative Forcings

Estimated Seasonal and Latitudinal Dependent Changes in Radiative Forcing (Wm -2 ) for the Period for CO2, CH4, N2O, and Halocarbons Jain et al. (JGR 2000)

100-Year GWP Calculations Jain et al (2000) vs. WMO (1999)

ISAM-Estimated Forcing & Climate Changes from Pre-Industrial Times to Present ( ) Direct SO 2 Aerosols GHGs Direct SO 2 Aerosols +GHGs

Recent Analysis of HFC-134a for IPCC October 2003 Radiative Forcing: Clear sky constant profile UIUC (constant diffusivity) Wm -2 UIUC (variable diffusivity) Wm -2 Reading Univ Wm -2 Oslo Univ Wm -2 NOAA Wm -2

2. Changes in Atmospheric Constituents and in Radiative Forcing · Introduction · Definition and Utility of Radiative Forcing · Recent Changes in Greenhouse Gases · Aerosols – Direct and Indirect Radiative Forcing · Radiative Forcing due to Land Use Changes · Contrails and Aircraft-Induced Cirrus · Variability in Solar and Volcanic Radiative Forcing · Synthesis of Radiative Forcing Factors · GWPs and Other Metrics for Comparing Different Emissions IPCC AR4

Using the UIUC NBM for GMI Studies Convert NBM to use netCDF files from GMI –Transfer to use MOZART-3 files is currently in process –Will use cloudiness, grid structure, etc. from GMI –Will use atmospheric composition fields from GMI (gases, aerosols) Testing NBM –E.g., with additional particle types –For perturbations to ozone, water vapor (e.g., Ponater et al., 2002) Tests and studies with GMI inputs –Radiative forcing calculations for (interim and) 2006 aircraft assessment –Radiative forcing calculations for IPCC

Climate Sensitivity Traditional definition  T s =  RF  = climate sensitivity parameter  varies from ~ with different GCMs  reasonably constant within a given model for homogeneously distributed perturbations  Recent studies: varies for spatially inhomogeneous changes in gases (e.g., ozone) or aerosols  Larger for higher latitude changes  Larger for lower stratospheric O 3 than upper tropospheric O 3  Indirect effects of aerosols require special calculations 1. Change in cloud albedo (due to change in droplet concentration) 2. Change in cloud-amount and liquid water content (associated with changes in precipitation efficiency)

 Propose an “alternative” definition, particularly for comparing GCMs, called “adjusted tropospheric and stratospheric forcing”   RF ats uses fixed surface temperature (land, ocean)  Allows changes in lapse rate, clouds, water vapor  Includes many of the climate feedbacks  Run GCM to steady-state (a few years with fixed SST) Resulting is nearly constant for for all forcings

Modified Plan Radiative forcing –Continues to be a useful concept Much more efficient than GCM Comparisons easier; not subject to differences in GCMs Easier to isolate error and uncertainties in radiative aspects At same time, we will evaluate the new concepts for  RF ats –Which GCM?

The End

Temperature, Cloud Fractions, H2O, and O3 Used in Radiative Calculations for September-October Pre-industrial and Contemporary Time Periods Jain et al. (2000)

Comparison of Latitudinal and Seasonal Average ISAM vs. WMO Radiative Forcing Calculations

ISAM