AtmoHEAD is an independently-organized workshop but follows on the heels of a few prior meetings with similar themes:
Astroparticles and Atmosphere (AA) Workshop - 2003, Paris
Atmospheric Monitoring for Astroparticle Physics (ATMON) - 2008, Prague
Atmospheric Monitoring in Astroparticle Physics & Astronomy (ATMON) - 2010, Madison
The slides from these three meetings are all available online*.
They provide a very nice historical record of progress in this field over the last 11 years.
*Thanks to Michael Punch for resurrecting the old AA workshop slides.