Dear Colleague,
The objective of the Direct Aerosol Radiative Forcing (DARF) Activity of the Focus on Atmospheric Aerosols (FAA) of the International Global Atmospheric Chemistry Project (IGAC) is
to determine, primarily through observations, the magnitude, uncertainty, chemical sources, and temporal and spatial variations of the direct radiative climate forcing by aerosols of various types (e.g., sulfates, organics, mineral dust).
Achieving this goal requires a coordinated effort of several subdisciplines of atmospheric science, including radiative transfer, remote sensing, aerosol chemistry, and aerosol physics.  Our hope is that IGAC's Focus on Atmospheric Aerosols can provide the mechanism that will bring together researchers from many nations and disciplines to reach this goal.  The necessary components of this coordinated effort can be broken into five tasks:
Task 1.	Satellite-based remote inference of aerosol radiative properties;
Task 2.	Surface-based remote observations of aerosol radiative properties;
Task 3.	In-situ observations of aerosol radiative, chemical, and microphysical properties;
Task 4.	Closure studies to test the combined ability of measurements and models to describe aerosol radiative properties and aerosol-induced radiative flux perturbations;
Task 5.	Integration of the multi-platform observations to determine the direct aerosol radiative forcing.
The purpose of this letter is to introduce the DARF activity to a wide community of atmospheric scientists, and to encourage interested parties to contact one of the members of the coordinating committee.  To succeed, DARF will require the active involvement of leaders and team members for each of the five tasks.  At present, most of DARF is in the planning stage, so now is the time for interested parties to express their interest and contribute suggestions for specific research projects within the various tasks of DARF.  If you are interested, please let us know what role you would like to take within the activity (task leader, team member, liason with related national/international programs, etc.) and include a short summary of the research that you would like to contribute.
The coordinating committee of DARF consists of
T. Nakajima (Japan)	teruyuki@ccsr.u-tokyo.ac.jp	(co-convenor)
J. Ogren (USA)	johno@cmdl.noaa.gov	(co-convenor)
H. Gordon (USA)*	gordon@phyvax.ir.miami.edu
R. Hoff (Canada)**	rhoff@dow.on.doe.ca
M. King (USA)*	king@climate.gsfc.nasa.gov
P. Pilewskie (USA)	pil@ra.arc.nasa.gov
P. Russell (USA)	philip_russell@qmgate.arc.nasa.gov
G.-Y. Shi (China)*	shigy@bepc2.ihep.ac.cn
L. Stowe (USA)*	lstowe@orbit1i.nesdis.noaa.gov
D. Tanre (France)*	Didier.Tanre@univ-lille1.fr
M. Wendisch (Germany)*	wendisch@tropos.de
* pending formal approval of the IGAC Executive Committee
** invited
Enclosure:	Summary of IGAC/DARF activity