Preliminary Correction of Vaisala Radiosonde Humidity Measurements for Slow Sensor Time-Response at Cold Temperatures

The goal of this study is to improve the accuracy of relative humidity (RH) measurements from Vaisala radiosondes, especially in the upper troposphere (UT), by correcting measurement error that results from slow time-response of the RH sensor at cold temperatures. Accurate water vapor profiles are important for such applications as input to radiative transfer algorithms, calibration, or evaluation of remote-sensor water vapor retrievals, initializing numerical models, and improving parameterizations of cloud processes. Inaccurate measurement of water vapor profiles has been shown by Atmospheric Radiation Measurement (ARM) Program studies to be the primary limitation to improving clear-sky radiative transfer models (e.g., Clough et al. 1999). Although water vapor concentrations are much less in the UT than at lower levels, atmospheric cooling rates in the UT due to water vapor exceed those in the mid troposphere due to the very strong contribution by the wave number range 250 cm to 350 cm (Clough et al. 1992). RH measurements from Vaisala RS80-H radiosondes are heavily relied upon by ARM to characterize the water vapor profile in the UT, because other means such as Raman Lidar or Differential Absorption Lidar have accuracy and/or vertical resolution limitations in the UT (see Turner et al. 2000).