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
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
Received: 18 Mar 2022 – Discussion started: 22 Apr 2022
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.
The smoke layers in the low stratosphere, in contrast to dust or volcanic ash, can provide strong fluorescence. The smoke fluorescence, in particular, was analyzed, in recent publication:
Veselovskii, I., Hu, Q., Ansmann, A., Goloub, A., Podvin, T., Korenskiy, M.: Fluorescence lidar observations of wildfire smoke inside cirrus: A contribution to smoke-cirrus - interaction research, Atmos. Chem. Phys., 22, 5209–5221, 2022.
In the manuscript presented, the authors analyze the influence of smoke fluorescence on Raman water vapor measurements in stratosphere. They demonstrate that smoke contribution is significant and suggest the scheme to correct corresponding contamination. Comparison of lidar and zonde measurements convincingly demonstrate, that their approach allows significantly to decrease the uncertainty of vapor measurements inside the smoke layers. Manuscript is well and clearly written, and is suitable for publication in AMT. I have just several technical comments.
Fig.1. Green letters M-09 at the top of the figure probably mean MOHAVE-2009. This should be explained in the capture.
Influence of fluorescence on the vapor measurements discussed also in:
Reichardt, J.: Cloud and aerosol spectroscopy with Raman lidar, J. Atm. Ocean. Tech., 31, 1946-1963, 2014.
Fig.5c. From the title of left axis it is not clear, that this is the ratio of the channels
Fig.6c. I am a bit confused by the explanation of increase of uncertainty at high altitudes after correction. If we measure the sum of water vapor and fluorescence signal, does it mean that statistical uncertainty of vapor measurements becomes lower? I think uncertainty of vapor signal should stay the same…Correct me if I am wrong.
Ln.438. “ but kis substantially more difficult to quantify and much more variable as it depends on the composition of the interfering aerosols”
Why does this coefficient depends on aerosol type? I think only absolute value of fluorescence signal depends, but not kð¹.
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 %.
The comparison of water vapor lidar measurements with co-located radiosondes and aerosol...
