Absolute accuracy of water vapor measurements from six operational radiosonde types launched during AWEX‐G and implications for AIRS validation

Abstract

[1] A detailed assessment of radiosonde water vapor measurement accuracy throughout the tropospheric column is needed for assessing the impact of observational error on applications that use the radiosonde data as input, such as forecast modeling, radiative transfer calculations, remote sensor retrieval validation, climate trend studies, and development of climatologies and cloud and radiation parameterizations. Six operational radiosonde types were flown together in various combinations with a reference-quality hygrometer during the Atmospheric Infrared Sounder (AIRS) Water Vapor ExperimentGround (AWEX-G), while simultaneous measurements were acquired from Raman lidar and microwave radiometers. This study determines the mean accuracy and variability of the radiosonde water vapor measurements relative to simultaneous measurements from the University of Colorado (CU) Cryogenic Frostpoint Hygrometer (CFH), a referencequality standard of known absolute accuracy. The accuracy and performance characteristics of the following radiosonde types are evaluated: Vaisala RS80-H, RS90, and RS92; Sippican Mark IIa; Modem GL98; and the Meteolabor Snow White hygrometer. A validated correction for sensor time lag error is found to improve the accuracy and reduce the variability of upper tropospheric water vapor measurements from the Vaisala radiosondes. The AWEX data set is also used to derive and validate a new empirical correction that improves the mean calibration accuracy of Vaisala measurements by an amount that depends on the temperature, relative humidity, and sensor type. Fully corrected Vaisala radiosonde measurements are found to be suitably accurate for AIRS validation throughout the troposphere, whereas the other radiosonde types are suitably accurate under only a subset of tropospheric conditions. Although this study focuses on the accuracy of nighttime radiosonde measurements, comparison of Vaisala RS90 measurements to water vapor retrievals from a microwave radiometer reveals a 6-8% dry bias in daytime RS90 measurements that is caused by solar heating of the sensor. An AWEX-like data set of daytime measurements is highly desirable to complete the accuracy assessment, ideally from a tropical location where the full range of tropospheric temperatures can be sampled.

Atmospheric Moisture and Cloud Cover Characteristics Forecast by AMPS*

“…Additionally, the RS92 radiosondes undergo a process called "regeneration," where the sensor is heated during launch preparations, effectively recovering the original calibration accuracy and removing any contaminations arising from the packaging (Hirvensalo et al 2003). Miloshevich et al (2006) show that relative humidity measurements from RS92 radiosondes not corrected for the time-lag error have close agreement (Ͻ10% difference) throughout the midlatitude troposphere, even at temperatures as cold as Ϫ70°C, compared to the University of Colorado Cryogenic Frostpoint Hygrometer (CFH), an instrument that has a known accuracy of 1%-3% throughout the troposphere. Further, their study demonstrates that applying the time-lag correction to the RS92 can lead to an overestimation of the relative humidity in the upper troposphere.…”

“…Radiosonde humidity measurements are subject to three main sources of error, but the magnitudes of these errors vary depending on the radiosonde type (Miloshevich et al 2001(Miloshevich et al , 2004(Miloshevich et al , 2006. During the validation period considered here, both McMurdo and South Pole station used the most recent version of Vaisala radiosondes, the RS92.…”

“…During the validation period considered here, both McMurdo and South Pole station used the most recent version of Vaisala radiosondes, the RS92. These radiosondes have faster sensor response times than their predecessors, the RS80-H and RS80-A , so temperaturedependent corrections have not been established for this equipment (Miloshevich et al 2004). Additionally, the RS92 radiosondes undergo a process called "regeneration," where the sensor is heated during launch preparations, effectively recovering the original calibration accuracy and removing any contaminations arising from the packaging (Hirvensalo et al 2003).…”

“…Further, their study demonstrates that applying the time-lag correction to the RS92 can lead to an overestimation of the relative humidity in the upper troposphere. Thus, timelag corrections are not done in this study, but the Atmospheric Infrared Sounder (AIRS) Water Vapor Experiment (AWEX) empirical calibration correction as discussed by Miloshevich et al (2006) is performed on all the soundings, leading to adjustments of ϳ3% in the measured relative humidity, with maximum changes up to 5%. The corrected measurements without the time-lag corrections are deemed accurate enough for the comparisons made here with modeled relative humidity values from AMPS.…”

Combining Meteosat-10 satellite image data with GPS tropospheric path delays to estimate regional integrated water vapor (IWV) distribution

“…The most common ones utilize radiosondes (Kley et al, 2000;Soden et al, 2004;Miloshevich et al, 2006), different techniques of GPS meteorology (Bevis et al, 1992(Bevis et al, , 1994Duan et al, 1996;Ware and Alber, 1997;Hagemann and Bengtsson, 2003;Vedel et al, 2004;Heise et al, 2009;Guerova et al, 2013;Hordyniec et al, 2015) or measurements from remote sensing satellites (Velden et al, 1997;Cresswell et al, 1999;Jiang et al, 2012). Radiosondes offer an essential component of the global observing system due to their extended lifetime and broad geographic coverage (Kley et al, 2000).…”