Investigation of potential sources of widespread high ice water content in deep convection anvil outflow, Part I: Quasi-steady properties of precipitating stratiform regions in observations and simulations

Occurrences of jet engine malfunction have been in recent years increasingly associated with extended flight through widespread deep convection anvils at flight levels corresponding to ambient temperatures of –10 to –50°C, associated with fully glaciated icing conditions rather than supercooled water. Malfunctions commonly occur with radar reflectivity less than 20–30 dBZ at flight elevation in the presence of light to moderate turbulence. Airbus airborne measurements in several regions were obtained with the sole objective of seeking and characterizing regions of substantial ice water content (in excess of ~3 g m-3) in the absence of strong radar reflectivity (less than 30 dBZ) in large, cold-topped storm systems. Measurements of particle size distribution and particle shape properties reveal generally consistent signatures of ice evolution associated with substantial ice water content. In part one of this two-part work, we employ simulations with size-resolved microphysics that are informed by observations in order to evaluate the consistency of size distribution signatures with ground-based radar measurements and rain rate retrievals obtained under similar, quasi-steady stratiform rain conditions in the tropics. We find that the signatures of substantial ice water content appear generally consistent with remote-sensing measurements, capable of reproducing observed features of quasi-steady, heavy stratiform rain.