Forcing in the long-wave spectrum due to aerosol-cloud interactions: satellite and climate modelling vs. HALO (FLASH)

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The radiative forcing by anthropogenic aerosols via aerosol-cloud interactions is the main uncertainty in quantifying current forcing of climate change. While some progress has been achieved for liquid water clouds that dominate the forcing in the short-wave (solar) part of the electromagnetic spectrum, for the forcing in the long-wave (terrestrial) spectrum only crude estimates from general circulation models exist. In preliminary work, we have developed a suggestion how active satellite remote sensing might be used to characterise ice crystal number concentrations and co-incident aerosol concentrations, and thus might allow for an assessment of the aerosol forcing in the terrestrial spectrum. However, the satellite remote sensing data are highly uncertain and need to be validated using reference data. In FLASH, we propose to (i) validate the satellite ice crystal concentration and its sensitivity to temperature, vertical wind, cloud regime, and aerosol conditions using the large statistics now available from HALO (ACRIDICON, ML-CIRRUS), (ii) verify the spaceborne retrievals with airborne retrievals using the lidar and radar onboard HALO (NARVAL, NARVAL-II, NAWDEX) that have better spatiotemporal resolution, (iii) make use of climate model simulations for interpretation of the statistical relationships and (iv) work towards an estimate and uncertainty characterisation of the aerosol radiative forcing in the long-wave spectrum. Within SPP 1294, FLASH is intends to exploit the exiting data and work with upcoming data from multiple campaigns in an integrative way, towards the goals of achieving a better quantification of the aerosol-climate forcing, a validation of innovative and crucial satellite retrievals, as well as an evaluation and improvement of essential parameterisations in climate models.