Ice-supersaturated air masses in the northern mid-latitudes from regular in situ observations by passenger aircraft: vertical distribution, seasonality and tropospheric fingerprint

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Petzold, Andreas, Neis, Patrick, Wahner, Andreas, Rütimann, Mihal, Rohs, Susanne, Berkes, Florian, Smit, Herman G. J., Krämer, Martina, Spelten, Nicole, Spichtinger, Peter, Nédélec, Philippe
• Format: Article in Journal/Newspaper
• Language: English
• Published: EGU 2020
• Subjects: info:eu-repo/classification/ddc/550; North Atlantic
• Online Access: https://juser.fz-juelich.de/record/884280; https://juser.fz-juelich.de/search?p=id:%22FZJ-2020-03172%22

The vertical distribution and seasonal variation of water vapour volume mixing ratio (H2O VMR), of relative humidity with respect to ice (RHice) and particularly of regions with ice-supersaturated air masses (ISSRs) in the extratropical upper troposphere and lowermost stratosphere are investigated at northern mid-latitudes over the eastern North American, North Atlantic and European regions for the period 1995 to 2010. Observation data originate from regular and continuous long-term measurements on board instrumented passenger aircraft in the framework of the European research programme MOZAIC (1994–2010), which continues as the European research infrastructure IAGOS (from 2011). Data used in our study result from collocated observations of O3 VMR, RHice and temperature, as well as H2O VMR deduced from RHice and temperature data. The in situ observations of H2O VMR and RHice with a vertical resolution of 30 hPa (< 750 m at the extratropical tropopause level) and a horizontal resolution of 1 km resolve detailed features of the distribution of water vapour and ice-supersaturated air relative to the thermal tropopause, including their seasonal and regional variability and chemical signatures at various distances from the tropopause layer. Annual cycles of the investigated properties document the highest H2O VMR and temperatures above the thermal tropopause in the summer months, whereas RHice above the thermal tropopause remains almost constant in the course of the year. Over all investigated regions, upper tropospheric air masses close to the tropopause level are nearly saturated with respect to ice and contain a significant fraction of ISSRs with a distinct seasonal cycle of minimum values in summer (30 % over the ocean, 20 %–25 % over land) and maximum values in late winter (35 %–40 % over both land and ocean). Above the thermal tropopause, ISSRs are occasionally observed with an occurrence probability of 1.5 ± 1.1 %, whereas above the dynamical tropopause at 2 PVU (PVU: potential vorticity unit), the ...