Does surface warming over Western Europe affect the occurrence frequency of contrail forming regions?

The decade, 2012 to 2021, was the warmest on record, with the global mean near-surface air temperature in the most recent seven years, 2015 to 2021, keeping hitting record high. Europe, with an increase of 1.94 to 2.01 °C in the mean annual temperature since pre-industry level, is warming much faster than the global average (1.11 to 1.14 °C) (https://www.eea.europa.eu/ims/global-and-european-temperatures). Surface warming disrupts upper-air temperature, which will affect the humidity fields in the upper troposphere. Both ambient temperature and relative humidity with respect to ice (RH_ice) are key factors determining the formation and persistence of contrail cirrus clouds, which exert a net warming radiative forcing among aviation emissions (Lee et al., 2009; Lee et al., 2021).

Previous studies have provided insights into the long-term trend and seasonal variability of upper-air temperature and relative humidity using airborne, radiosonde and reanalysis datasets (Petzold et al., 2020; Chen et al., 2015; Philandras et al., 2017; Essa et al., 2022). The variation of RH_ice in relation to the changing upper tropospheric temperature because of surface warming has, however, rarely been investigated.

In this work, we use the temperature and RH_ice measurements over Western Europe from the European research infrastructure IAGOS (In-Service Aircraft for a Global Observing System; www.iagos.org) to study how the upper-air temperature and RH_ice distributions in the warmest seven years have changed seasonally and regionally compared to the IAGOS-MOZAIC period, 1995 to 2010, when the surface warming was not so drastic. We will focus on whether the occurrence frequency of contrail forming regions, i.e., slightly ice subsaturated to supersaturated regions in the upper troposphere, would be affected by the increasing warming climate, which could promote our understanding of contrail mitigation.

[Note: This work is carried out under the frame of EU H2020 Research and Innovation Action “Advancing the Science for Aviation and Climate (ACACIA)”, Grant Agreement No. 875036.]