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SEAC4RS Balloon

SEAC4RS Balloon Platforms

CFH Instrument Description for SEAC4RS
Dr. Henry B. Selkirk

During the SEAC4RS campaign, our team will launch 20 cryogenic frost point hygrometer (CFH) instruments from Utapao, each as part of a payload also containing an ECC ozonesonde and an iMet-1-RSB-GPS radiosonde1. These combined water vapor/ozone payloads are a collaboration with the SEACIONS project led by Prof. Anne M. Thompson of Penn State Univeristy.

The total instrument package weighs ~1 kg is hand-launched on a small (1200-g) meteorological balloon that typically ascends at 5-7 m s-1. At the nominal data rate of close to 1 Hz, the data have a resolution of ~10 m. Balloon burst is typically above 30 km, at which point the entire package descends on a parachute; the package is often retrieved on the ground, and the CFH and ECC reused after reconditioning.

a. The Cryogenic Frost-point Hygrometer (CFH)

This instrument (Vömel et al., 2007), similar to the frost point hygrometer used by the Global Monitoring Division at NOAA ESRL in Boulder, CO, operates on the chilled mirror principle using a cryogenic liquid as cooling agent. The CFH is a microprocessor-controlled instrument which includes several improvements that allow it to measure water vapor continuously from the surface to about 28 km altitude. The accuracy in the troposphere is better than 5%, the stratospheric accuracy is better than 10%. The instrument has a large dynamic range from less than 1 ppmv to more than 30,000 ppmv H2O. The instrument thus can measure water vapor from the surface, through the tropopause,and into the middle stratosphere.

b. The ECC ozonesonde

Ozone is measured using electro-chemical concentration cell (ECC) ozonesondes. In these lightweight instruments the reaction of ozone with I2- in a weak aqueous solution of an electrochemical cell offsets the electrochemical equilibrium between the two parts of the cell, creating an electrical curren. This is directly proportional to the amount of ozone pumped through the cell [Komhyr et al., 1995] .The accuracy of the ozone mixing ratio is typically ~5% and slightly lower at low ozone mixing ratios. These instruments have been the mainstay for tropospheric and stratospheric ozone measurements, and the Southern Hemisphere Additional Ozonesonde (SHADOZ) network [Thompson et al., 2003] has vastly increased temporal and spatial coverage in the tropics.

Both the Cryogenic Frostpoint Hygrometer and ECC ozonesonde are manufactured by Droplet Measurement Technologies, Boulder, CO.