Articles | Volume 8, issue 3
Atmos. Meas. Tech., 8, 1617–1625, 2015
https://doi.org/10.5194/amt-8-1617-2015
Atmos. Meas. Tech., 8, 1617–1625, 2015
https://doi.org/10.5194/amt-8-1617-2015

Research article 28 Mar 2015

Research article | 28 Mar 2015

Performance of WVSS-II hygrometers on the FAAM research aircraft

A. K. Vance1, S. J. Abel1, R. J. Cotton1, and A. M. Woolley2 A. K. Vance et al.
  • 1Met Office, Exeter, UK
  • 2FAAM, Cranfield, UK

Abstract. We compare the performance of five hygrometers fitted to the Facility for Airborne Atmospheric Measurement's (FAAM) BAe 146-301 research aircraft using data from approximately 100 flights executed over the course of 2 years under a wide range of conditions. Bulk comparison of cloud free data show good agreement between chilled mirror hygrometers and a WVSS-II fed from a modified Rosemount inlet, but that a WVSS-II fed from the standard flush inlet appears to over-read compared to the other instruments, except at higher humidities.

Statistical assessment of hygrometer performance in cloudy conditions is problematic due to the variable nature of clouds, so a number of case studies are used instead to investigate the performance of the hygrometers in sub-optimal conditions. It is found that the flush inlet is not susceptible to either liquid or solid water but that the Rosemount inlet has a significant susceptibility to liquid water and may also be susceptible to ice. In all conditions the WVSS-II responds much more rapidly than the chilled mirror devices, with the flush inlet-fed WVSS-II being more rapid than that connected to the Rosemount.

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Short summary
Comparisons on the FAAM BAe 146-301 aircraft show good agreement between chilled mirror hygrometers and a WVSS-II fed from a modified Rosemount inlet (wvssR) in coud-free conditions, but a WVSS-II fed from the standard flush inlet (wvssF) over-reads, except at higher humidities. Case studies in cloudy conditions show that wvssF is immune to liquid water and ice, whilst wvssR is susceptible to both. Both WVSS-II inlets respond much more rapidly than the chilled mirror devices, especially wvssF.