Preprints
https://doi.org/10.5194/amt-2022-98
https://doi.org/10.5194/amt-2022-98
 
22 Apr 2022
22 Apr 2022
Status: this preprint is currently under review for the journal AMT.

The impact of aerosol fluorescence on water vapor long-term monitoring by Raman lidar and the evaluation of a potential correction method

Fernando Chouza1, Thierry Leblanc1, Mark Brewer1, Patrick Wang1, Giovanni Martucci2, Alexander Haefele2, Hélène Vérèmes3, Valentin Duflot3, Guillaume Payen4, and Philippe Keckhut5 Fernando Chouza et al.
  • 1Laboratory Studies and Atmospheric Observations, Jet Propulsion Laboratory, California Institute of Technology, 92397 Wrightwood, USA
  • 2Federal Office of Meteorology and Climatology, MeteoSwiss, CH-1530 Payerne, Switzerland
  • 3Laboratoire de l’Atmosphère et des Cyclones (LACy, UMR 8105 CNRS, Université de la Réunion, Météo-France), Université de La Réunion, 97400 Saint-Denis de La Réunion, France
  • 4Observatoire des Sciences de l’Univers de La Réunion (OSU-Réunion), UAR 3365, Université de la Réunion, CNRS, Météo-France, 97400 Saint-Denis de La Réunion, France
  • 5LATMOS/IPSL, UVSQ Université Paris-Saclay, Sorbonne Université, CNRS, 75000 Paris, France

Abstract. The impact of aerosol fluorescence on the measurement of water vapor by UV (355 nm emission) Raman lidar in the upper troposphere and lower stratosphere (UTLS) is investigated using the long-term records of three high-performance Raman lidars contributing to the Network for the Detection of Atmospheric Composition Change (NDACC). Comparisons with co-located radiosondes and aerosol backscatter profiles indicate that laser-induced aerosol fluorescence in smoke layers injected into the stratosphere by pyrocumulus events can introduce very large and chronic wet biases above 15 km, thus impacting the ability of these systems to accurately estimate long-term water vapor trends in the UTLS.

In order to mitigate the fluorescence contamination, a correction method based on the addition of an aerosol fluorescence channel was developed and tested on the water vapor Raman lidar TMWAL located at the JPL Table Mountain Facility, in California. The results of this experiment, conducted between 27 August and 4 November 2021 and involving 22 co-located lidar and radiosonde profiles, suggest that the proposed correction method is able to effectively reduced the fluorescence-induced wet bias. After correction, the average difference between the lidar and co-located radiosonde water vapor measurements was reduced to 5 %, consistent with the difference observed during periods of negligible aerosol fluorescence interference.

The present results provide confidence that, after a correction is applied, water vapor long-term trends can be reasonably well estimated in the upper troposphere, but they also call for further refinements, or the use of alternate Raman lidar approaches (e.g., 308 nm or 532 nm emission) to confidently detect long-term trends in the lower stratosphere. These findings may have important implications on NDACC’s water vapor measurements strategy in the years to come.

Fernando Chouza et al.

Status: open (until 28 May 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2022-98', Anonymous Referee #1, 25 Apr 2022 reply
  • RC2: 'Comment on amt-2022-98', Jens Reichardt, 22 May 2022 reply

Fernando Chouza et al.

Fernando Chouza et al.

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Short summary
The comparison of water vapor lidar measurements with co-located radiosondes and aerosol backscatter profiles indicate that laser-induced aerosol fluorescence in smoke layers injected into the stratosphere can introduce very large and chronic wet biases above 15 km, thus impacting the ability of these systems to accurately estimate long-term water vapor trends. The proposed correction method presented in this work is able to reduce this fluorescence-induced bias from 75 % to under 5 %.