PSE4

A chilled-mirror hygrometer (CMH) prototype for in-situ UAS (unmanned aircraft system) measurements has been developed and compared against industrial state-of-the-art alternative light-weight humidity sensors. It is shown that the newly developed sensor resolves dew-point measurements up to 10 Hz at a sampling frequency of 50 Hz, and can therefore resolve turbulent dew-point fluctuations, measured by UAS. The CMH sensor is relatively low cost, and easy to maintain. The latest version of the sensor combines an in-house made housing and circuit board and is tuned to fit in the MASC-3 (multi-purpose airborne sensor carrier) research UAS of the University of Tübingen. However, the sensor can be modified to compliment EC (eddy-covariance) stations that monitor turbulent surface fluxes (e.g. turbulent vertical humidity or momentum fluxes) where the CMH sensor would substitute expensive equipment.
The proposal substantiates further how the sensor can be used for several meteorological applications, e.g. an installation of a low-cost EC-stations network, studying the CBL (convective boundary layer) or buoyancy-driven flows in general, since the sensor is able to resolve turbulent density fluctuations once combined with pressure and temperature readings. It is shown that the CMH sensor supports a comprehensive evaluation of turbulence in the atmosphere, including the hard to measure structure parameter for humidity C²_q that quantifies turbulent eddies and structures in the lower atmosphere.
Field campaigns and validation measurements against i.a. scintillometers and meteorological mast measurements have been conducted and new ones are planned for the future, together with the German Meteorological Service (DWD). Constant development of the CMH continuously improves the sensor and motivates a secondary goal; the possibility to offer a commercially available product to the meteorological community and the humidity sensor industry in the future. The market situation and a realistic reception of such a sensor have previously been assessed and has evolved in two business plans.

How to cite: Mauz, M.: A high-frequency chilled-mirror hygrometer for turbulent stationary and airborne dew point measurements, EMS Annual Meeting 2021, online, 6–10 Sep 2021, EMS2021-508, https://doi.org/10.5194/ems2021-508, 2021.

From the early stages of hailstone growth to the ground-impact finale, a trajectory is taken by each hailstone through the parent hailstorm. Larger hailstones form as their trajectory takes them into regions of the storm that are more favorable for growth, while others may miss out entirely. Simulation-based studies have shown that interactions between the hailstone fall speed, aerodynamics, storm winds (which continue to change along the trajectory and with new growth) can take hailstones on a myriad of different trajectories. Despite improvements in radar technology over the last 20 years, operational hail analysis techniques have changed little, and do not consider trajectories, leaving a high degree of uncertainty when estimating ground impact.

Case studies have demonstrated that trajectory information provides significant improvements to hail impact mapping and nowcasting services, but the lack of robust
observational datasets to leverage new radar technology and verify trajectories prevents the transition of this new science into operations. The follow proposal presents an innovative approach to measuring trajectories within a hailstorm using hailstone-shaped probes called “HailSondes”. Recent advances in low-energy telemetry, battery technology and electronics miniaturization are combined to make this new sensor possible, which, until recently, was the realm of fantasy for meteorologists (e.g., the 1996 Hollywood classic “Twister” imagined a similar sensors for observing tornadoes). The design challenges, simulations, prototype development and deployment of HailSondes are discussed.

HailSonde measurements will provide critical validation for the practical application radarderived trajectories for hailstorm analysis and nowcasting, supporting the transition to future hail services and benefiting a wide range of sectors from aviation, risk management, transport and public safety. This transition from science fiction into real science signifies extraordinary potential for further remote micro-sensor applications in the future. 

How to cite: Soderholm, J.: Observing the impossible – in situ observations of hail trajectories using the HailSonde, EMS Annual Meeting 2021, online, 6–10 Sep 2021, EMS2021-509, https://doi.org/10.5194/ems2021-509, 2021.