Aircraft-induced hole punch and canal clouds: Inadvertent cloud seeding

The ice crystals can be produced by both turboprop and jet aircraft in and around supercooled liquid cloud layers. The crystals are produced by local adiabatic expansion at propeller tips at temperatures as warm as -8°C or over wing surfaces at temperatures <-20°C, and the resultant cooling chills droplets to a temperature of -37°C or below, causing the supercooled droplets to freeze through homogeneous nucleation. During research flights that measured cloud properties, the production of ice crystals from the passage of propeller aircraft at temperatures as warm as -8°C was documented. The production of aircraft-produced ice particles (APIP) by a turboprop passenger aircraft flying through a stratus layer at a temperature of about -10°C has been observed. The volume extinction coefficient σ in 2D probe sizes is also relatively high in the line echo compared to those found in the streamers. Wake turbulence is sufficient to produce holes of the size initially seen, but is unable to induce further spread.