Both, the analysis of polar climate change on the basis of observations and the validation of weather and climate prediction in polar regions are challenging since only few observations are available. In the inner arctic regions in-situ observations are available only from buoys, ship cruises and aircraft campaigns with large temporal differences and spatial separations. In the present contribution we compare near-surface meteorological observations and rawinsonde soundings from Arctic cruises with the German icebreaker RV Polarstern during August 1996, 2001, and 2007 with each other and with ERA-Interim reanalyses. Although the used observations are usually applied in the reanalysis, they differ considerably from ERA data. ERA overestimates the relative humidity and temperature in the atmospheric boundary layer and the base height of the capping inversion. Warm biases of ERA near-surface temperatures amount up to 2K. The melting point of snow is the most frequent near-surface temperature in ERA, while the observed value is the sea water freezing temperature. While this points to general drawbacks in the models, it shows also that the quantification of trends based on reanalyses is problematic especially when only one reanalysis is considered.