AeroCom Prescribed

From Earth Science Information Partners (ESIP)

Proposed AeroCom Prescribed Experiment

Introduction

The simulated AeroCom forcings show significant diversity that can partly be attributed to processes in the host models. To isolate the host model contribution we propose a simple AeroCom experiment with prescribed aerosol fields derived from the median of the AeroCom models.

Motivation

Even for the case of identical aerosol emissions, the simulated direct aerosol radiative forcings show significant diversity among the AeroCom models (Schulz et al., 2006).

Our analysis of the absorption in the AeroCom models (Presentation at the 2006 AeroCom meeting , Poster at the AGU Fall Meeting 2006) indicates a larger diversity in the translation from given aerosol radiative properties (absorption optical depth) to actual atmospheric absorption than in the translation of a given atmospheric burden of black carbon to the radiative properties (absorption optical depth). The large diversity is caused by differences in the simulated cloud fields, radiative transfer, the relative vertical distribution of aerosols and clouds, and the effective surface albedo. This indicates that differences in the host model (GCM or CTM hosting the aerosol model) parameterizations contribute significantly to the simulated diversity of atmospheric absorption and consequently of the TOA forcing. The magnitude of these effects cannot be estimated from the diagnostics of the first AeroCom forcing experiment.

To quantify the contribution of differences in the host models to the simulated aerosol radiative forcing and absorption we propose a simple AeroCom experiment with prescribed aerosol fields. The simulated forcing variability among the models is then a direct measure of the host model contribution to the uncertainty in the assessment of the aerosol radiative effects.

Experimental Setup

  • Global 3D aerosol distributions are provided as monthly-mean field of aerosol extinction, single scattering albedo, and asymmetry factor derived from the AeroCom median model.
  • The aerosol radiative properties are provided on 24 SW bands that can be mapped to the bands of the individual host model radiation schemes.
  • The 3D fields of radiative properties need to be interpolated to the respective model levels. An interpolation tool should be provided (cdo tools?).
  • Quality checks, such as diagnostic output of the 3D aerosol fields as implemented in each model, ensure the comparability of the aerosol implementation in the models

Diagnostics

(To be completed)

Aerosols

  • 3D aerosol radiative properties as implemented in the model
  • Separate diagnostics for in-cloud and clear-sky radiative properties as applied also in the forcing experiment. If aerosol are neglected in clouds, submit fields as zero.
  • ?

Clouds

  • 3D fractional cloud cover
  • 3D cloud optical depth
  • ?

Radiation

  • Forcing protocol as in the AeroCom Forcing experiment
  • Explicit in-cloud and clear-sky contributions?
  • ?

General model parameters

  • Prescribed surface albedo
  • Effective surface albedo as applied in the model (including effects of snow cover, moisture, etc.)
  • Information on radiation scheme (bands, key assumptions)
  • ?

Timeframe

  • The implementation of the experimental setup is simple and the results could guide future AeroCom experiments. Thus, we could propose a short timeframe of less than 6 months. To be discussed.

Intended Participation

Discussion

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See http://meta.wikimedia.org/wiki/Help:Talk_page for more help. Philip Stier (PhilipStier)


--Philip Stier (PhilipStier) 13:57, 14 December 2006 (EST)