Speaker
Description
Measuring water vapor concentration in the Upper Troposphere/Lower Stratosphere (UTLS) region presents significant challenges due to complex atmospheric conditions and low densities. The current study sheds light on several Raman lidar systems with promising capabilities for providing high-resolution and accurate water vapor profiles, namely: the IPRAL Raman lidar (25 km south of Paris) and the Lid1200 Raman lidar (La Réunion Island in the Indian Ocean). Many years of nocturnal atmospheric observations are analyzed from both sites. This research represents the first comprehensive effort to evaluate the IPRAL lidar system, focusing particularly on the Raman channels used to derive hourly Water Vapor Mixing Ratio (WVMR) profiles at aircraft cruising altitudes. On the other hand, we show recent efforts to retrieve near-monthly Lid1200 water vapor densities up to lower stratospheric altitudes. The Lid1200 lidar system, being coaxial, is calibrated using GNSS Total Column Water Vapor measurements at 5-minute intervals (Vérèmes et al., 2019). Meanwhile, we have calibrated 6 years of biaxial IPRAL WVMR using co-located ERA5 water vapor profiles between 4 and 6 km altitude. A unique IPRAL WVMR calibration factor on an hourly basis is calculated, and a full-night calibration coefficient is obtained as the median of hourly factors over the night. Daily calibrations are inspected to detect any instrumental changes, and final generalized scaling factors are applied for quasi-stationary periods.
Both lidar WVMR profiles are compared to the most spatially and temporally coincident ERA5 profiles. The IPRAL/ERA5 comparison aims to evaluate ERA5's ability to detect supersaturation events in the upper Troposphere. ERA5 water vapor concentrations are found to be about 20% lower than those measured by IPRAL at cruising altitudes (9-11 km). An assessment and potential correction of ERA5 data were also performed and examined.
The Lid1200/ERA5 comparison provides an opportunity to examine ERA5's capacities and limitations at higher altitudes (LS domain up to 20 km) following the Lid1200 capacities in near-monthly screenings.
The newly developed upper tropospheric midnight-calibrated IPRAL WVMR profiles are also compared to midnight-launched radiosonde data, including Meteomodem M10 and GRUAN-corrected M10. Results indicate a high degree of agreement between data sources, with significant correlation coefficients exceeding 90%. Notably, there is excellent concordance with GRUAN-corrected M10 radiosondes up to 10.5 km altitude. Below 8 km, a negative bias of approximately 10% is observed when comparing IPRAL with the standard M10. This bias is thought to be linked to the radiosondes' time lag effect.
This comprehensive study aims to enhance the accuracy of UT water vapor measurements by IPRAL. The newly developed software from this study is intended to improve atmospheric models and, consequently, better understand contrail contributions in future air traffic regulations, as part of the European project BeCoM.
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