Abstract
For a one-month period in summer 2020, a prototype Vaisala broadband differential absorption lidar (BB-DIAL) was deployed at a Met Office research site. It was compared with in-situ observations of humidity (93 radiosonde ascents and 27 of uncrewed aerial vehicle flights) and the Met Office 1.5 km resolution numerical weather prediction (NWP) model: UK Variable resolution model (UKV). The BB-DIAL was able to collect data up to the cloud base, in all-weather situations including rain, when it was possible to reach 3 km. The average maximum height was 1300 m, with 75% of the data reaching 1000 m and 35% extending to 1500 m. Compared with radiosondes, the standard deviation for the water vapour is between 5% and 10%. The comparison with the UKV is very encouraging, with a correlation of 0.90. The error against the radiosonde is smaller than against the UKV, which is encouraging for assimilation the BB-DIAL data in UKV. Some data quality issues, such as an increase in error and variable bias in the region of overlap between the far field and close field, spurious oscillations and an unrealistic dry layer above fog are identified. Despite these issues, the overall results from this assessment are promising in terms of potential benefit, instrument reliability and capturing significant humidity changes in the boundary layer.
Highlights
The World Meteorological Organization (WMO), via its rolling requirements review process, identifies five priorities for narrowing the gap between requirements and capabilities of observation networks for high resolution numerical weather predication (NWP)
Even the high-resolution Infrared Sounder (IRS) on the Meteosat 3rd generation geostationary satellite will not give the required vertical resolution needed in the planetary boundary layer (PBL) [3]
At the Southern Great Plains (SGP) site [16], the broadband DIAL (BB-DIAL) was evaluated by comparing it to coincident observations from a Raman lidar, radiosondes, and an infrared interferometer
Summary
The World Meteorological Organization (WMO), via its rolling requirements review process, identifies five priorities for narrowing the gap between requirements and capabilities of observation networks for high resolution NWP. Until recent years use of Lidar technology (Raman or differential absorption) was mainly restricted to research applications [12,13,14], and was too expensive to be deployed in an operational network and required radiosondes to calibrate their measurements. At the Southern Great Plains (SGP) site [16], the BB-DIAL was evaluated by comparing it to coincident observations from a Raman lidar, radiosondes, and an infrared interferometer It was evaluated in very high humidity subtropical weather conditions in Hong Kong [18]. Another comparison with a Raman Lidar and radiosonde measurements in Canada in an urban area is described in Mariani, 2020 [20]. A number of data quality issues are highlighted and avenues that could be investigated to mitigate these issues are suggested, before concluding remarks on the usefulness of such an instrument in operational observing networks in future
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