The effect of artificially induced Crow instability on contrail radiative forcing*

Aircraft contrails are believed to have a net warming effect on the earth that is greater than that due to aviation CO₂, albeit with a large uncertainty.  This is because on average they absorb more upward longwave radiation from the earth's surface than they reflect downward shortwave solar radiation back to space.  We perform time-developing simulations in a stratified atmosphere to assess whether artificially inducing the Crow instability of trailing vortices via out-of-phase deflection of two ailerons on each wing (so as to maintain a constant lift) can reduce contrail radiative forcing.  The initial condition consists of (a) a vortex sheet with an axially varying strength to mimic the effect of aileron deflection; (b) hot vapor laden jets that are initially perturbed; and (c) Lagrangian particles in the jets that subsequently grow due to ice deposition.  Separate simulations are performed with the compressible CharLES code and the incompressible Vortex Particle-Mesh (VPM) code.  Radiative forcing is assessed using a parameterization in terms of optical depth.  We find that for a range of surface albedos and zenith angles of the sun, particle redistribution by the Crow instability in the forced case, leads to increased radiative forcing.  This is due to an increased spanwise extent of the contrail where vortex reconnection occurs.