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

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

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

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

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

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

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

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

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

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.

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

Any Questions?