Insights into Potential Contrail Cirrus Regions During Surface Temperature Extremes from Three Decades of Airborne Measurements

Contrails and contrail cirrus, induced by civil aviation and posing a radiative warming threat to the climate, form and persist at high altitudes in the upper troposphere in regions characterized by low temperatures and high relative humidity with respect to ice (RH_ice). Both temperature and humidity are critical variables controlling the formation of contrails and contrail cirrus. Variability in RH_ice in the upper troposphere is intrinsically associated with changes in ambient temperature. Recent years have seen record-breaking surface temperatures, particularly across continental regions. However, the relationship between upper-tropospheric temperature and humidity and surface temperatures remains poorly understood.

This work uses 30 years of airborne temperature and relative humidity measurements from the European Research Infrastructure IAGOS to investigate changes in Potential Contrail Cirrus Regions (PCCRs) in relation to surface temperature extremes (heatwaves and cold waves) over Europe. Surface temperature extremes are identified for each season using temperature measurements in the planetary boundary layer (<1.5–2 km altitude), applying statistical methods and significance tests. This classification provides the basis for examining the seasonal variability of RH_ice and PCCRs during heatwaves and cold waves. This study aims to improve understanding of how an increasingly warming world may affect the formation of contrails and contrail cirrus.