ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-10925-2012 A multi-instrument comparison of integrated water vapour measurements at a high latitude site Buehler S. A. 1 Östman S. 1 Melsheimer C. 2 Holl G. 1 Eliasson S. 1 John V. O. 3 Blumenstock T. 4 Hase F. 4 Elgered G. 5 Raffalski U. 6 Nasuno T. 7 Satoh M. 8 Milz M. 1 Mendrok J. 1 Department of Computer Science, Electrical and Space Engineering, Luleå University of Technology, Kiruna, Sweden Institute of Environmental Physics, University of Bremen, Bremen, Germany Met Office Hadley Centre, Exeter, UK Karlsruhe Institute of Technology (KIT), Institute for Meteorology and Climate Research (IMK-ASF), Karlsruhe, Germany Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, Onsala, Sweden The Swedish Institute of Space Physics, Kiruna, Sweden Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan Atmosphere and Ocean Research Institute, University of Tokyo, Tokyo, Japan 20 11 2012 12 22 10925 10943 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/10925/2012/acp-12-10925-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/10925/2012/acp-12-10925-2012.pdf

We compare measurements of integrated water vapour (IWV) over a subarctic site (Kiruna, Northern Sweden) from five different sensors and retrieval methods: Radiosondes, Global Positioning System (GPS), ground-based Fourier-transform infrared (FTIR) spectrometer, ground-based microwave radiometer, and satellite-based microwave radiometer (AMSU-B). Additionally, we compare also to ERA-Interim model reanalysis data. GPS-based IWV data have the highest temporal coverage and resolution and are chosen as reference data set. All datasets agree reasonably well, but the ground-based microwave instrument only if the data are cloud-filtered. We also address two issues that are general for such intercomparison studies, the impact of different lower altitude limits for the IWV integration, and the impact of representativeness error. We develop methods for correcting for the former, and estimating the random error contribution of the latter. A literature survey reveals that reported systematic differences between different techniques are study-dependent and show no overall consistent pattern. Further improving the absolute accuracy of IWV measurements and providing climate-quality time series therefore remain challenging problems.

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