Polar Stratospheric Clouds
Polar Stratospheric Clouds (PSCs) consist of liquid binary H2SO4/H2O droplets (background stratospheric aerosol), liquid ternary HNO3/H2SO4/H2O droplets, solid nitric acid trihydrate (NAT) and H2O ice particles. PSCs play a crucial role in stratospheric ozone chemistry by providing surfaces for heterogeneous reactions, which active reactive chlorine species and lead to a denitrification of the stratosphere.
Despite several decades of research the exact PSC formation processes are still not well understood, and these uncertainties limit the representation of PSCs in global models and a variety of parameterizations exist. In SOCOLv3, the formation of ternary solution droplets (STS) follows the work by Carslaw et al. (1995). NAT particles form at TNAT with a mean radius of 5 µm and a maximum number density of 5e-4 cm-3, while for ice clouds we assume a fixed number density of 0.01 cm-3. Continuous satellite observations since the early 2000s provide now a long-enough observational record to evaluate the representation of PSCs in global models (for more information see the external pageSPARC Polar Stratospheric Cloud Initiative PSCicall_made).
In an ongoing MSc project by Michael Steiner we compare the parameters like occurrence frequency, total PSC volume or composition of the modelled PSCs.