Journal cover Journal topic
Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
Journal topic

Journal metrics

Journal metrics

  • IF value: 3.248 IF 3.248
  • IF 5-year value: 3.650 IF 5-year 3.650
  • CiteScore value: 3.37 CiteScore 3.37
  • SNIP value: 1.253 SNIP 1.253
  • SJR value: 1.869 SJR 1.869
  • IPP value: 3.29 IPP 3.29
  • h5-index value: 47 h5-index 47
  • Scimago H index value: 60 Scimago H index 60
Discussion papers | Copyright
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 17 Oct 2018

Research article | 17 Oct 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).

Tropospheric water vapor profiles obtained with FTIR: comparison with balloon-borne frost point hygrometers and influence on trace gas retrievals

Ivan Ortega1, Rebecca Buchholz1, Emrys Hall2,3, Dale Hurst2,3, Allen Jordan2,3, and James W. Hannigan1 Ivan Ortega et al.
  • 1Atmospheric Chemistry Observations & Modeling, National Center for Atmospheric Research, Boulder, Colorado, USA
  • 2Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA
  • 3NOAA Earth System Research Laboratory, Global Monitoring Division, Boulder, Colorado, USA

Abstract. Retrievals of vertical profiles of key atmospheric gases provide a critical long-term data record from ground-based Fourier Transform InfraRed (FTIR) solar absorption measurements. However, the characterization of the retrieved vertical profile structure can be difficult to validate, especially for gases with large vertical gradients and spatial-temporal variability such as water vapor. In this work, we evaluate the accuracy of the most common water vapor isotope (H216O, hereafter WV) FTIR retrievals in the lower and upper troposphere – lower stratosphere. Coincident high-quality vertically resolved WV profile measurements obtained from 2010 to 2016 with balloon-borne NOAA Frost Point Hygrometers (FPH) are used as reference to evaluate the performance of the retrieved profiles at two sites: Boulder, Colorado and in the mountain top observatory of Mauna Loa, Hawaii. For a meaningful comparison, the spatial-temporal variability has been investigated. Additionally, we evaluate the quantitative impact of different a priori profiles in the retrieval of WV vertical profiles using un-smoothed comparisons. An orthogonal linear regression analysis shows the best correlation among all layers using ERA-Interim (ERA-I) a priori profiles. In Boulder, we found a negative bias of 0.02±1.9% and precision of 3.7% (r=0.95) for the 1.5–3km layer. A larger negative bias of 11.1±3.5% and precision of 7.0% was found in the lower free troposphere layer of 3–5km (r=0.97) attributed to rapid vertical change of WV, which is not always captured by the retrievals. The bias improves in the 5–7.5km layer (1.0±5.3%) and the precision worsens to about 10%. The bias remains at about 13% and the precision remains to about 10% for layers above 7.5km but below 13.5km. At MLO the spatial mismatch is significantly larger due to the launch of the sonde being farther from the FTIR location. Nevertheless, we estimate a negative biases of 5.9±4.6% for the 3.5–5.5km layer (r=0.93) and 9.9±3.7% for the 5.5–7.5km layer (r=0.93), and positive biases of 6.2±3.6% for the 7.5–10km layer (r=0.95), and 12.6% and greater values above 10km. The agreement for the first layer is significantly better at BLD likely that the air masses are similar for both FTIR and FPH. Furthermore, for the first time we study the influence of different sources of WV profiles in the retrieval of selected gas profiles. Using NDACC standard retrievals we present results for hydrogen cyanide (HCN), carbon monoxide (CO), and ethane (C2H6) by taking NOAA FPH profiles as the ground-truth and evaluate the impact of other WV profile sources. We show that the effect is minor for C2H6 (bias <0.5% for all WV sources) among all vertical layers. However, for HCN we found significant biases between 6% for layers close to the surface to 2% for upper troposphere depending on WV profile source. The best results (lowest bias/precision and r-values closer to unity) are always found for pre-retrieved WV. Therefore, we recommend to first retrieve WV to use in subsequent retrieval of gases.

Ivan Ortega et al.
Interactive discussion
Status: open (until 12 Dec 2018)
Status: open (until 12 Dec 2018)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
[Subscribe to comment alert] Printer-friendly Version - Printer-friendly version Supplement - Supplement
Ivan Ortega et al.
Ivan Ortega et al.
Total article views: 237 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
183 48 6 237 9 3 2
  • HTML: 183
  • PDF: 48
  • XML: 6
  • Total: 237
  • Supplement: 9
  • BibTeX: 3
  • EndNote: 2
Views and downloads (calculated since 17 Oct 2018)
Cumulative views and downloads (calculated since 17 Oct 2018)
Viewed (geographical distribution)
Total article views: 237 (including HTML, PDF, and XML) Thereof 233 with geography defined and 4 with unknown origin.
Country # Views %
  • 1
No saved metrics found.
No discussed metrics found.
Latest update: 13 Nov 2018
Publications Copernicus
Short summary
In this work we evaluate the accuracy of water vapor ground-based FTIR retrievals in the lower and upper troposphere using coincident high-quality vertically resolved balloon-borne NOAA FPH measurements. Our results suggest that highly structured water vapor vertical gradients are captured with the FTIR and found a negligible bias in the immediate layer above the instrument altitude accounting for a water vapor time variability of less than 2 %.
In this work we evaluate the accuracy of water vapor ground-based FTIR retrievals in the lower...