Understanding when hydrometer formation is driven by aerosol variation

Abstract:

Αerosol-cloud interactions constitute the largest source of uncertainty in assessments of anthropogenic climate change. Key towards improved predictions is understanding and capturing the relative importance of aerosol and vertical velocity variations as drivers of hydrometer (droplet number, ice crystal) formation. Towards this, we present analysis of global model output and ambient observational datasets from different parts of the globe that link aerosol with hydrometer concentrations, and determine the sensitivity of droplet and ice crystal concentrations to aerosol and vertical velocity variations. By comparing the hydrometer formation “regime” (aerosol- or velocity-limited) we then determine where global models are correctly sensitive to aerosol variations – or if biases in vertical velocity predictions dominate the aerosol-droplet link. Given that model assessments of aerosol–cloud-climate interactions do not routinely evaluate for overall turbulence or its covariance with other parameters, datasets and analyses such as the one presented here are of the highest priority to address unresolved sources of hydrometeor variability, bias, and the response of droplet number to aerosol perturbations.