Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Journal topic

Journal metrics

Journal metrics

  • IF value: 5.509 IF 5.509
  • IF 5-year value: 5.689 IF 5-year 5.689
  • CiteScore value: 5.44 CiteScore 5.44
  • SNIP value: 1.519 SNIP 1.519
  • SJR value: 3.032 SJR 3.032
  • IPP value: 5.37 IPP 5.37
  • h5-index value: 86 h5-index 86
  • Scimago H index value: 161 Scimago H index 161
Discussion papers
https://doi.org/10.5194/acp-2018-1129
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-1129
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 11 Dec 2018

Research article | 11 Dec 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Determination and significance of upper-tropospheric humidity

Klaus Gierens1 and Kostas Eleftheratos2 Klaus Gierens and Kostas Eleftheratos
  • 1Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
  • 2Department of Geology and Geoenvironment, National and Kapodistrian University of Athens, Athens, Greece

Abstract. We present a novel retrieval for upper-tropospheric humidity (UTH) from HIRS channel 12 radiances that successfully bridges the wavelength change from 6.7 to 6.5µm that occurred from HIRS 2 on NOAA 14 to HIRS 3 on NOAA 15. The jump in average brightness temperature (T12) that this change caused (about −7K) could be fixed with a statistical intercalibration method (Shi and Bates, 2011). Unfortunately, the retrieval of UTHi based on the intercalibrated data was not satisfying at the high tail of the distribution of UTHi. Attempts to construct a better intercalibration in the low T12 range (equivalent to the high UTHi range) were either not successful (Gierens et al., 2018) or required additional statistically determined correctionsto the measured brightness temperatures (Gierens and Eleftheratos, 2017).

The new method presented here is based on the original one (Soden and Bretherton, 1993; Stephens et al., 1996; Jackson and Bates, 2001), but it extends linearisations in the formulation of water vapour saturation pressure and in the temperature-dependence of the Planck function to second order. To achieve the second-order formulation we derive the retrieval from the beginning, and we find that the most influential ingredient is the use of different optical constants for the two involved channel wavelengths (6.7 and 6.5µm). The result of adapting the optical constant is an almost perfect match between UTH data measured by HIRS 2 on NOAA 14 and HIRS 3 on NOAA 15 on 1004 common days of operation. The method is applied to both UTH and UTHi, the upper-tropospheric humidity with respect to ice. For each case retrieval coefficients are derived.

We present a number of test applications, e.g. on computed brightness temperatures based on high-resolution radiosonde profiles, on the brightness temperatures measured by the satellites on the mentioned 1004 common days of operation. Further we present time series of the occurrence frequency of high UTHi cases and we show the overall probability distribution of UTHi. The two latter applications expose clear indications of moistening of the upper troposphere over the last 35 years.

Finally, we discuss the significance of UTH. We state that UTH algorithms cannot be judged for their correctness or incorrectness, since there is no true UTH. Instead, UTH algorithms should fulfil a number of usefulness-postulates, that we suggest and discuss. In the course of this discussion an alternative method to estimate the weighting function is presented.

Klaus Gierens and Kostas Eleftheratos
Interactive discussion
Status: open (until 05 Feb 2019)
Status: open (until 05 Feb 2019)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
[Subscribe to comment alert] Printer-friendly Version - Printer-friendly version Supplement - Supplement
Klaus Gierens and Kostas Eleftheratos
Klaus Gierens and Kostas Eleftheratos
Viewed  
Total article views: 316 (including HTML, PDF, and XML)
HTML PDF XML Total BibTeX EndNote
272 42 2 316 0 0
  • HTML: 272
  • PDF: 42
  • XML: 2
  • Total: 316
  • BibTeX: 0
  • EndNote: 0
Views and downloads (calculated since 11 Dec 2018)
Cumulative views and downloads (calculated since 11 Dec 2018)
Viewed (geographical distribution)  
Total article views: 183 (including HTML, PDF, and XML) Thereof 182 with geography defined and 1 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Cited  
Saved  
No saved metrics found.
Discussed  
No discussed metrics found.
Latest update: 20 Jan 2019
Publications Copernicus
Download
Short summary
We derive a new method to retrieve Upper-Tropospheric Humidity (UTH) from HIRS channel 12 brightness temperatures. With the new method we solve an old problem, namely that the wavelength change that occurred between HIRS 2 on NOAA 14 and HIRS 3 on NOAA 15 lead to retrieval of much more events with high UTH, that is, the time series shows strong jumps at high UTH values. This old problem is solved with the new retrieval.
We derive a new method to retrieve Upper-Tropospheric Humidity (UTH) from HIRS channel 12...
Citation
Share