Relative humidity over ice as a key variable for Northern Hemisphere midlatitude tropopause inversion layers

Abstract

The tropopause inversion layer (TIL) is a prominent feature of the midlatitude tropopause region, constituting a transport barrier. Adiabatic and diabatic processes might contribute to the formation and sharpening of the inversion. For both types of processes, relative humidity over ice is ideal for attribution; from theory and former model case studies, we expect enhanced relative humidity values with a sharp TIL.

We use high-resolution radiosonde and ERA5 reanalysis data to show very good qualitative and quantitative agreement in terms of TIL features; thus, coarser ERA5 data can be used for further investigations. Next, we investigate the connection between TIL features and relative humidity measures in both radiosonde and ERA5 data, revealing a clear relationship. Moister profiles, on average, exhibit significantly higher maximum values of the Brunt–Väisälä frequency (N2), indicating a more stable stratification of the tropopause in these cases. This result holds true in both radiosonde measurements and