Atmosphere-Climate Working Group General remarks… Issues of importance to climate community require climatological (long time scale) data analysis rather than focus on individual events Therefore, studies of sun/climate connections must, in general, rely on decadal or multi-decadal data But, there are also a number of sun/atmosphere studies that can be carried out or initiated in the time frame of IHY2007 …all with attention to coordination with ongoing (e.g., CAWSES, SPARC) programs and prior (e.g., EPIC, PSMOS) programs

Long-term projects In the form of assessments of scientific understanding of the following areas: TSI and SRI (photons) reconstructions, especially over time scales longer than the solar cycle (multi-century time scale) Establish solar minimum irradiance value and change from earlier solar minimum observations Role of the sun in producing tropospheric/stratospheric climate variability (statistical significance of observations; theoretical “proof” via numerical simulation) – sensitivity of climate to solar variability Response of stratospheric ozone to solar variability (solar cycle) Cosmogenic proxies as an indicator of solar activity (solar cycle to milennia)

Long-term datasets Insofar as multi-year data is essential to the study of sun/climate interactions… Support allocation of resources to continue measurements by space- based instruments (e.g., TIMED, SORCE, ACRIM, etc.) Continue taking measurements through IHY. Promote the development of comprehensive databases of solar and atmospheric parameters, covering long time scales (integration of existing satellite, ground-based observations)

Short-term projects (potential campaigns) Studies that could be carried out during the time span of IHY2007 Response of atmosphere to impulsive and periodic solar events (e.g., REP, SPE…) Response to the 27-day solar rotation –inferences for longer term variability Response of the ionosphere to upward-propagating wave activity (“meteorological variability” to be distinguished from solar) Effect of cosmic rays on ion nucleation, aerosols, clouds, and climate (theoretical, observational, numerical, and laboratory studies; study Forbush decreases and ground-level enhancements as test cases for longer term changes) Radar/lidar/rocketsonde observations of stratosphere/lower mesosphere tropical winds (Tropical winds affect the link between solar forcing and atmospheric response below) Ozonesonde network for the lower tropical stratosphere Modeling of atmospheric response to solar variability, including model intercomparison UV effects on the biosphere (including humans).