IAGOS (In-service Aircraft for a Global Observing System) performs long-term routine in-situ observations of atmospheric chemical composition (O3, CO, NOx, NOy, CO2, CH4), water vapour, aerosols, clouds, and temperature on a global scale by operating compact instruments on board of passenger aircraft. The unique characteristics of the IAGOS data set originate from the global scale sampling on air traffic routes with similar instrumentation such that the observations are truly comparable and well suited for atmospheric research on a statistical basis. Here, we present the analysis of 15 months of simultaneous observations of relative humidity with respect to ice (RHice) and ice crystal number concentration in cirrus (Nice) from July 2014 to October 2015.

- "Andreas Petzolda,*, Martina Krämerb, Patrick Neisa,e, Christian Rolfb, Susanne Rohsa, Florian Berkesa, Herman G.J. Smit, Martin Gallagher, Karl Beswick, Gary Lloyd, Darrel Baumgardner, Peter Spichtinger, Philippe Nédéle, Volker Ebertg, Bernhard Buchholzg, Martin Riese, Andreas Wahner"