1. The Use of Tethered Balloons to Measure the Evaporation Duct
LEUT R. Phillips, RAN
OC3570

2. Purpose of Study
To assess the suitability of using a tethered balloon to carry a rawinsonde to sample the surface layer for evaporation duct height measurements

3. Measurements Six flights with rawinsonde attached to kite/balloon
Rawinsonde measured Tair, RH, P & Tdew every two seconds
Serial ASCII Interface Loop (SAIL) data from R/V Pt Sur measured corresponding surface observations Tair, wind speed, RH, P & SST

4. Problems and Assumptions
Skill level required in flying kite at low-levels
Kite needs at least ~10kts wind to fly
Balloon is easy to control at low-levels and is good for < 10kts wind
Difficult to sample data at low levels
Contamination of data whilst initialising rawinsonde on deck

5. Analysis
Removed initial data from rawinsonde files (probably contamination by ship whilst on deck)
Matlab code (written by Paul Frederickson and LT Mabey):
Modified refractivity profile from Kite data
Modified refractivity profile using Bulk Methods and SAIL data
Plots of Tair, q,  & relative humidity vs height, and time series for pressure

6. Results - Flights 1 & 2 Used kite
Rawinsonde dipped into water with no apparent effects on sensors

7. Results - Flights 1 & 2 (cont/…)
Evidence of contamination due to stack at heights between 10 to 20m
Drier RH
Warmer air temperatures
Not supported by weather conditions

8. Results Flights 3, 4, 5 & 6 Used balloon
Rawinsonde dipped into water with generally no apparent effects on sensors
Sonde held over side of ship

9. Results Flights 3, 4, 5 & 6 (cont/…)
Evidence of contamination due to stack and ship effects below 40m
Drier RH
Warmer air temperatures
Not supported by weather conditions

10. Summary
Kite
difficult to control at low levels
suffered contamination due to stack
Balloon
easy to control at low levels
suffered contamination from both stack and ship
It is recommended that balloons are not used in future experiments to sample the surface layer for evaporation duct height measurements.

11. Recommendations for Further Research
Lengthening string between balloon/kite and sonde may allow for less contaminated data
Maybe consider using a different ship for measurements
Avoid dangling sonde over the side of ship to obtain low-level measurements

12. Any Questions?