Combining Tried-and-True Strategies for Reducing Uncertainties in Aerosol-Cloud-Precipitation-Radiation Interactions in Climate Models (Invited Presentation)

The objective of reducing uncertainties in aerosol and cloud microphysical processes in Earth system models (ESMs) remains urgent owing to its leading relevance to both reducing large uncertainties in Earth's climate sensitivity and estimating the potential efficacy of some proposed geoengineering strategies to offset Earth's anthropogenically forced radiative imbalance. Here we highlight recent progress that links several well-established pathways to reducing uncertainty in specific and collective processes, as well as first steps along a pathway to estimate the impact of propagated uncertainties on model projections. Use of bespoke data collected during the DOE AEROICESTUDY field campaign demonstrates extension of the well-known point closure approach to evaluate primary ice nucleation schemes as a function of size-dependent aerosol composition. Such an aerosol-ice nucleation closure test is similarly applied at the beginning and end of a Lagrangian model intercomparison project (MIP) study period, based on measurements during a cold-air outbreak over the Norwegian sea during the DOE COMBLE field campaign. Within the COMBLE-MIP framework, primary ice formation becomes one process among several that are now evaluated at once along marine boundary layer trajectories (including sea spray emission at high wind speeds, warm rain, aerosol scavenging by collision-coalescence, and secondary ice production within a deepening turbulent boundary layer). COMBLE-based Lagrangian modeling cases are constrained by near-surface in situ aerosol data upwind and downwind, as well as several classes of remote sensing data (see Tornow et al. at this meeting). The NASA CAMP2Ex campaign provides a small ensemble of case studies with detailed in situ aerosol and hydrometeor measurements that are more suitable for testing droplet activation, warm rain formation and ice multiplication within terminal congestus (see Stanford et al. at this meeting). Both COMBLE and CAMP2Ex ensemble case studies are suitable for large-eddy simulation (LES) and ESMs in single-column model (SCM) mode side-by-side. Taken together, multiple LES-SCM case studies enable estimation of ESM aerosol and cloud state and process parameter uncertainties for input to a combined optimization against global measurements in one-year fixed-aerosol atmosphere-only simulations, demonstrating proof-of-concept for future multi-parameter optimization in coupled simulations with interactive aerosol. Finally, evaluation of key processes is made using one-year to decadal simulations using diverse ESM configurations that are found to provide equally good agreement with a range of satellite data. Detailed evaluations benefit from advancement of forward-simulation and budget analysis approaches to more robustly establish the occurrence frequency of light precipitation and supercooled liquid against ground-based and satellite measurements, as well as emergent convectively coupled equatorial wave behaviors such as the Madden-Julian oscillation.