Addressing a High-Altitude Cirrus Deficit in the Thompson Aerosol-Aware Microphysics Scheme

Cloud droplet activation and ice nucleation are both dependent on aerosol number concentration in the Thompson and Eidhammer (2014) aerosol-aware microphysics scheme. Several sensitivity tests were conducted with WRF for ice nucleation and droplet freezing using the dust aerosol due to an identified issue noted by NOAA of a deficit in the representation of high-altitude ice clouds as compared to satellite observations. The case study we focus on for these sensitivity tests was an atmospheric river event over the northeastern Pacific Ocean and western United States, on 15-16 February 2011 during the CalWater 2011 campaign. We find that replacing the existing heterogeneous freezing schemes (Phillips et al. (2008) and DeMott et al. (2015)) with DeMott et al. (2010) freezing improves both overall results and the sensitivity to dust concentration, while also simplifying the code. Additional work remains, however, to resolve this cirrus deficit more fully. This research is in response to requirements and funding by the Federal Aviation Administration (FAA). The views expressed are those of the authors and do not necessarily represent the official policy or position of the FAA.