After more then 60 years, in situ measurements made by radiosondes still provide the standard upper-atmospheric data set for numerical weather prediction, regional weather forecasting, climatology, research, and other applications. Radiosondes form the basis of inter-comparison, calibration and validation of most other atmospheric observing systems, and serve as the benchmark or ground-truth for satellite-derived estimates of temperature, moisture and other atmospheric constituents or properties. Because of the unique characteristics of radiosonde observations and the fact that many of the parameters measured by radiosondes are under-observed in time and space (e.g. moisture), verification of balloon soundings can be difficult under certain circumstances. The NOAA Forecast Systems Laboratory is collaborating with the Observing Systems Branch of the NWS Office of Operational Systems, and the Science Plans Branch of the NWS Office of Science and Technology, to evaluate an integrated atmospheric observing system strategy that uses ground-based Global Positioning System (GPS) water vapor measurements to quality control radiosonde moisture observations. Radiosondes, like all other observing systems, are subject to systematic and random errors. In recent years, sources of systematic errors in relative humidity and temperature measurements have been identified and mitigated with varying degrees of success. These efforts have resulted in superior sensor performance and data correction techniques that have measurably improved data quality and reliability. However, detection of random errors remains a difficult problem, primarily due to the lack of redundant or independent observations from measurement systems with comparable accuracy. The recent expansion of the Global Positioning System (GPS) network used to assess the utility of this technology for weather forecasting and climate monitoring has resulted in about 40 sites falling within 50 km of an NWS Upper-Air site. This fortuitous situation provides us with an opportunity to compare GPS IPW retrievals with operational rawinsondes on a regular basis. Results indicate that GPS can be used to verify the accuracy of radiosonde integrated moisture profiles with high probability of detection and low false alarm rate. We currently estimate that problematic moisture soundings occur in less than 5% of the launches; this is equivalent to 2-3 soundings per synoptic period in the U.S. Detection, elimination or application of adaptive quality control techniques will lead to immediate improvements in numerical weather forecasts over CONUS. In similar fashion, extending this technique to the 152 stations in the Global Climate Observing System (GCOS) Upper-Air Network, and approximately 600 stations that launch rawinsondes at 0Z and 12Z each day for weather forecasting, will have substantial impact on global weather forecasting, climate monitoring and satellite calibration and validation.
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