ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-5-2019-2005 Retrieval of upper tropospheric water vapor and upper tropospheric humidity from AMSU radiances Houshangpour A. 1 John V. O. 1 Buehler S. A. 1 Institute of Environmental Physics, University of Bremen, Bremen, Germany 05 08 2005 5 8 2019 2028 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/5/2019/2005/acp-5-2019-2005.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/5/2019/2005/acp-5-2019-2005.pdf

A regression method was developed to retrieve upper tropospheric water vapor (UTWV in kg/m<sup>2</sup>) and upper tropospheric humidity (UTH in % <i>RH</i>) from radiances measured by the Advanced Microwave Sounding Unit (AMSU). In contrast to other UTH retrieval methods, UTH is defined as the average relative humidity between 500 and 200hPa, not as a Jacobian weighted average, which has the advantage that the UTH altitude does not depend on the atmospheric conditions. The method uses AMSU channels 6-10, 18, and 19, and should achieve an accuracy of 0.48 kg/m<sup>2</sup> for UTWV and 6.3% <i>RH</i> for UTH, according to a test against an independent synthetic data set. This performance was confirmed for northern mid-latitudes by a comparison against radiosonde data from station Lindenberg in Germany, which yielded errors of 0.23 kg/m<sup>2</sup> for UTWV and 6.1% <i>RH</i> for UTH.