Evaluation of Arctic Water Vapor Profile Observations from a Differential Absorption Lidar

Abstract

The continuous measuring of the vertical profile of water vapor in the boundary layer using a commercially available differential absorption lidar (DIAL) has only recently been made possible. Since September 2018, a new pre-production version of the Vaisala DIAL system has operated at the Iqaluit supersite (63.74°N, 68.51°W), commissioned by Environment and Climate Change Canada (ECCC) as part of the Canadian Arctic Weather Science project. This study presents its evaluation during the extremely dry conditions experienced in the Arctic by comparing it with coincident radiosonde and Raman lidar observations. Comparisons over a one year period were strongly correlated (r > 0.8 at almost all heights) and exhibited an average bias of +0.13 ± 0.01 g/kg (DIAL-sonde) and +0.18 ± 0.02 g/kg (DIAL-Raman). Larger differences exhibiting distinct artifacts were found between 250 and 400 m above ground level (AGL). The DIAL’s observations were also used to conduct a verification case study of operational numerical weather prediction (NWP) models during the World Meteorological Organization’s Year of Polar Prediction. Comparisons to ECCC’s global environmental multiscale model (GEM-2.5 km and GEM-10 km) indicate good agreement with an average bias < 0.16 g/kg for the higher-resolution (GEM-2.5 km) models. All models performed significantly better during the winter than the summer, likely due to the winter’s lower water vapor concentrations and decreased variability. This study provides evidence in favor of using high temporal resolution lidar water vapor profile measurements to complement radiosonde observations and for NWP model verification and process studies.

Evaluation of a Prototype Broadband Water-Vapour Profiling Differential Absorption Lidar at Cardington, UK

“…The Vaisala BB-DIAL used in this study was the same as that described by Mariani et al 2021 [17] and similar with the prototype described by Newson et al [16]. It uses diode laser transmitters to produce eye-safe pulsed infrared laser radiation.…”

“…The method to retrieve the water vapour profile followed the general method described by Newsom et al [16]. It requires use of line-by-line absorption model using the HITRAN data base [22] and the precise the knowledge of the near and farfield laser spectral widths [17]. For the BB-DIAL used in Newson et al [16] these widths were estimated using radiosondes over several field experiments, adjusting them until a good fit with the radiosondes was obtained.…”

“…In its earlier version (Newson et al [16]), the instrument was calibrated using radiosondes. A more recent prototype (Mariani et al 2021 [17]) does not require a radiosonde calibration which makes this instrument an independent measurement of the water vapour. This instrument could complement other measurements.…”

“…Yeung 2020, Newson 2020, Roininen and Münkel 2017, and Mariani 2021 [16][17][18][19] have published evaluations of very similar Vaisala prototypes in a range of climatic conditions. It was first evaluated [19] in Finland in clean air situations with a low particle density within the boundary layer against radiosonde, and in Germany versus radiosonde and Raman Lidar.…”

“…Another comparison with a Raman Lidar and radiosonde measurements in Canada in an urban area is described in Mariani, 2020 [20]. Recently, Mariani et al 2021 [17] evaluated it over a year in artic condition.…”