Raman lidar water vapor observations to assess the uncertainty of MLS and ERA5 at the upper troposhere

Water vapor information in the upper troposphere (UT) is crucial for understanding the thermodynamic conditions leading to the formation of cirrus clouds and persistent contrails. Both phenomena significantly contribute to aviation-induced radiative forcing, driving global mitigation efforts. Raman lidars provide high-resolution humidity profiles, describing altitudes prone to ice supersaturation—conditions that are challenging to detect and accurately represent in current models.

In this study, Raman lidar Water Vapor Mixing Ratio (WVMR) measurements from various sites in France were used to evaluate the performance of the ERA5 model in assessing humidity at typical aircraft altitudes. Additionally, the uncertainties in Microwave Limb Sounder (MLS) WVMR measurements at the same altitudes were assessed. Raman lidar profiles were aggregated into pseudo-monthly datasets to facilitate comparison with the limited number of MLS overpasses at each site, enabling validation of spatio-temporal pseudo-monthly lidar-matched MLS and ERA5 WVMR profiles.

The MLS dataset offers one of the longest records of WVMR, making it a valuable resource for trend assessment. This investigation enables the validated use of these datasets for studying UT humidity trends and variability on seasonal and annual scales over the past decade.