On the fidelity of numerical weather prediction model forecasts to identify ice supersaturated regions for aircraft contrail management

The potential atmospheric warming and impact on climate by aircraft contrails may be similar in magnitude to the direct effect from carbon dioxide emissions across all aviation.  Contrail management via optimized flight planning considering aircraft performance and CO₂ emissions, and the presence of ice supersaturated regions (ISSR), could mitigate any potential climate impacts.  The success of aircraft deviations depends on accurate predictions of the water vapor in the upper troposphere and lower stratosphere (UTLS). 

To evaluate the performance of two global numerical weather prediction (NWP) models (the US Global Forecast System, GFS; and the European Integrated Forecast System, IFS), one reanalysis model (the European fifth generation ECMWF atmospheric reanalysis, ERA5), and one research-grade mesoscale model to predict UTLS moisture and ISSR, we compared humidity forecasts to observations from 383 aircraft flights and radiosondes from 168 launch times over Europe and the Middle East for 10 months in 2022.

The research model mirrored observed distributions of relative humidity with respect to ice (RH_ice)  at all locations above 25,000 ft AMSL, while GFS and IFS forecasts poorly reproduced the observed distribution, and ERA 5 reanalysis only slightly improved on the skill of the IFS. Furthermore, ISSR validation was performed using near equal-area neighbourhoods to compute the Matthew Correlation Coefficient and F1-score and demonstrated a higher model score (F1=0.66) than IFS (F1=0.62), while the GFS score is close to zero (F1≈0) due to an absence of predictions of RH_ice greater than 100% in stark contrast to observations.  Importantly, the research model also correctly predicts RH_ice<100% in 92% of model-observation comparisons, identifying where atmospheric conditions are not conducive to persistent contrail formation. 

In summary, NWP model skill is adequate, when configured for the use case, to identify both ISSR and dry atmosphere locations and ensure a mitigation of the atmospheric warming caused by aircraft contrails through aircraft routing to reduce non-CO₂ climate impact of aviation.