ACP Atmospheric Chemistry and Physics ACP Atmos. Chem. Phys. 1680-7324 Copernicus Publications Göttingen, Germany 10.5194/acp-14-7533-2014 Technical Note: 30 years of HIRS data of upper tropospheric humidity Gierens K. https://orcid.org/0000-0001-6983-5370 1 Eleftheratos K. https://orcid.org/0000-0001-8897-3867 2 Shi L. 3 Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany Faculty of Geology and Geoenvironment, University of Athens, Athens, Greece National Climatic Data Center, NOAA, Asheville, NC, USA 28 07 2014 14 14 7533 7541 Copyright: © 2014 K. Gierens et al. 2014 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://acp.copernicus.org/articles/14/7533/2014/acp-14-7533-2014.html The full text article is available as a PDF file from https://acp.copernicus.org/articles/14/7533/2014/acp-14-7533-2014.pdf

We use 30 years of intercalibrated HIRS (High-Resolution Infrared Radiation Sounder) data to produce a 30-year data set of upper tropospheric humidity with respect to ice (UTH<sub>i</sub>). Since the required brightness temperatures (channels 12 and 6, <i>T</i><sub>12</sub> and <i>T</i><sub>6</sub>) are intercalibrated to different versions of the HIRS sensors (HIRS/2 and HIRS/4) it is necessary to convert the channel 6 brightness temperatures which are intercalibrated to HIRS/4 into equivalent brightness temperatures intercalibrated to HIRS/2, which is achieved using a linear regression. Using the new regression coefficients we produce daily files of UTH<sub>i</sub>, <i>T</i><sub>12</sub> and <i>T</i><sub>6</sub>, for each NOAA satellite and METOP-A (Meteorological Operational Satellite Programme), which carry the HIRS instrument. From this we calculate daily and monthly means in 2.5° &times; 2.5° resolution for the northern midlatitude zone 30–60° N. As a first application we calculate decadal means of UTH<sub>i</sub> and the brightness temperatures for the two decades 1980–1989 and 2000–2009. We find that the humidity mainly increased from the 1980s to the 2000s and that this increase is highly statistically significant in large regions of the considered midlatitude belt. The main reason for this result and its statistical significance is the corresponding increase of the <i>T</i><sub>12</sub> variance. Changes of the mean brightness temperatures are less significant.

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