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Global radiosonde data are required by meteorological analysis
centers for initializing numerical prediction models for weather
forecasting, and represent an increasingly valuable resource for
studies of climate change and in the development, calibration
and validation of retrieval techniques for atmospheric temperature
and water vapor profiles from satellite. Unfortunately, the
usefulness of radiosonde data is limited by sensor accuracy,
by data reporting practices, and by the fact that sonde and
sensor types vary by location and with time. Numerous studies
and reports have called for a reference sonde to serve as a
transfer standard to compare and connect data from past,
present and future sonde systems. We are working on
developing a reference radiosonde system at the Atmospheric
Technology Division (ATD) at NCAR. The reference radiosonde
system will carry the best sensors, have a flexible infrastructure
to host multiple and different user-provided sensors and will be
recoverable to reduce costs. The first version of the reference
radiosonde system was deployed in the Oklahoma panhandle
and Dodge City, KS (NWS radiosonde site) during the
International H2O Project (IHOP_2002). A total of sixteen
reference sondes were launched during IHOP either with Vaisala
RS80 or Sippican (VIZ) radiosondes. The humidity data from
the reference humidity sensor (Snow White, SW) are compared
with Vaisala and VIZ data. The comparisons show that (a) VIZ
carbon hygristor fails to respond to humidity changes in the
upper troposphere, (b) the carbon hygristor inside the reference
sonde has slower response than that inside NWS VIZ sonde, (c)
Vaisala RS80-H agrees with SW very well in the middle and lower
troposphere, and (d) SW can detect cirrus clouds near the
tropopause and possibly estimate their ice water content (IWC).
The climate impacts of these results are also discussed.
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