Evaluation of Climate Impacts from Different Models for Aviation-Induced Contrails for Trans-Atlantic Flights

A contrail or condensation vapor trail is a long and thin man-made cloud, formed when water vapor is condensed and frozen on aerosols from the exhaust of aircraft engine in upper troposphere and lower stratosphere (UTLS) at which ambient air temperature is below typically -40°C. The contrail may persist for hours and spread to be several kilometers wide, depending on meteorological conditions like temperature, humidity, and wind shear at a place in UTLS where it is formed. This eventually results in climate impact due to a change in radiative forcing (RF) by reflecting and trapping both incoming shortwave and outgoing longwave radiation on Earth. In this study, contrail RF is calculated using Schumann's parametric methodology that computes both positive and negative contrail RF values for given Earth-atmospheric condition. Here we use input as provided from the Modern-Era Retrospective Analysis for Research and Application (MERRA) data. In addition to the Earth-atmospheric condition, the Schumann's method uses contrail properties like optical depth and ice particle size and habit as input for the calculation of the contrail RF. These properties can be either assumed to be the representative values or computed with further assumptions from a dynamic contrail model. From an operational air traffic management perspective, sensitivity tests to the contrail RF values from different contrail models are necessary to assess the dependency of the results on contrail model details. In this study, we calculated the different climate impacts based on four different versions of the contrail model: 1) EXP-1; a simple Schmidt-Appleman criterion (SAC) for temperature and a criterion for ice saturation from humidity with a single RF value for each contrail segment, 2) EXP-2; the same simple SAC with local RF values from the Schumann's method for each contrail segment, 3) EXP-3: a dynamic contrail model with a single RF value, and 4) EXP-4: the dynamic contrail model with local RF values from the Schumann's method. Here, the dynamic contrail model developed at NASA Ames Research Center includes four steps: 1) Potential areas of the contrail formation according to the SAC and ambient relative humidity for ice greater than 100%, 2) Horizontal and vertical advection of contrail ice particles by wind, and 3) Spread by turbulence diffusion and growth of ice particle in contrail depending on ambient humidity, and 4) computing the contrail RF by Schumann's parametric model. We tested this for wind-optimal trans-Atlantic flight routes (i.e., time-minimal path with presence of winds) using MERRA data. The results show differences of climate impacts from the different models along the flight routes. This work is ongoing and the results presented will be preliminary.