Monday, 20 June 2005: 2:30 PM
South Ballroom (Hilton DeSoto)
It has been always a challenge to assess the accuracy and precision of radiosonde instrumentation due to lack of transfer standards for comparisons. One of ways for such assessment is to compare data collected from neighboring stations. The U.S. National Weather Service radiosonde station at Norman, OK is 16 miles (25 km) away from a research station located at Purcell, OK and operated by Atmospheric Radiation Measurement (ARM) program. During 1996-2002, four types of radiosonde, VIZ-B, VIZ-B2, Vaisala RS80-H and Vaisala RS90, were launched at two stations. Total 490 pairs of soundings were launched within half hour and sampled the same air mass based on visual examinations. These co-incident soundings formed four types of inter-comparisons, VIZ-B vs. RS80-H, VIZ-B2 vs. RS80-H, RS80-H vs. RS80-H, and RS80-H vs. RS90. The comparisons between Vaisala and VIZ humidity data confirm the previous finding that the Sippican (VIZ) carbon hygristor used in 14% of global radiosonde stations fails to respond to humidity changes in the upper troposphere (UT), sometimes even in the middle troposphere. This lack of response has produced significant and artificial humidity changes in the UT when the transition occurred and resulted in incapability of carbon hygristor to measure vertical and seasonal variations of UT humidity. The comparisons between Vaisala RS80-H and RS90 data show unexplained significant and consistent drier (~5%) and warmer (~0.2-0.5°C) RS90 than RS80-H data in the middle and upper troposphere. The comparisons of RS80-H data collected at two stations show surprise warmer temperature (~0.5°C) in the middle and upper troposphere at ARM-B6 than at Norman although there are very good agreements in humidity. Random instrumentation error variances for four types of radiosondes, which are critical for the data assimilation, are estimated based on these pair soundings and will be presented.
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