# Presentation: 841800

## 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 H2O, O3, CO2, N2O, CH4
- 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).
- Includes IR opacity by CO2, CH4, N2O,O3, H2O, and Halocarbons.
- Spectral Range – 0-3000 cm-1.
- Spectral Width – 5 cm-1 (CO2, CH4, N2O, O3), and 10 cm -1 (H2O and other gases).
- Radiance 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
- CCl4, CH3CCl3
- HCFC-22, -123, -124, -141, -142b, -225ca, -225cb
- HFC-23, -32, -125, -134, -134a, -143, -143a, -152a, -161, -227ea, -236fa, -245ca
- H-1201, -1311, CF2ClBr, CF3Br, CH3Br, CH2Br2, CHF2Br
- CF3I, CF3CF2I
**Perfluorocompounds (****PFCs****)**
- SF6, CF4

## 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 1750-1992 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 (1765-2000)

## Recent Analysis of HFC-134a for IPCCOctober 2003

**Radiative Forcing: Clear sky constant profile**
**       **UIUC (constant diffusivity)        0.193 Wm-2
- UIUC (variable diffusivity)        0.202 Wm-2
- Reading Univ.                             0.205 Wm-2
- Oslo Univ.                                   0.200 Wm-2
- NOAA                                         0.212 Wm-2

## IPCC AR4

- ·  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

## 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 ~0.4-1.2 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 O3 than upper tropospheric O3
- Indirect effects of aerosols require special calculations
- Change in cloud albedo (due to change in droplet concentration)
- 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”

- RFats 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 RFats
- 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

***ISAM***