AMT paper Rosoldi et al. 2021 in review

Radiosounding profiles are essential for weather and climate applications, as well as for the calibration and validation of remote sensing measurements. Vaisala RS92 radiosondes have been widely used on a global scale until 2016, although in the fall of 2013 Vaisala introduced the RS41 model to progressively replace the RS92. To ensure homogeneity and the highest quality of data records following the transition from RS92 to RS41, intercomparisons of the two radiosonde models are needed. An intercomparison experiment has been performed where, for the first time and independently of the manufacturer, RS92 and RS41 radiosondes have been simultaneously tested and compared inside climatic chambers in order to characterize the noise, the calibration accuracy and the bias of their temperature measurements. A pair of RS41 and RS92 radiosondes has been tested at ambient pressure under very different temperature and humidity conditions. The results reveal that the temperature sensor of RS41 is less affected by noise and more accurate than that of RS92, with noise values less than 0.06 °C for RS41 and less than 0.1 °C for RS92. The error corrected by means of calibration, evaluated as the deviation from a reference value and referred as calibration error, is within ±0.1 °C for RS41 and the related uncertainty (hereafter with coverage factor k = 1) is less than 0.06 °C, while RS92 is affected by a cold bias in the calibration, which ranges from 0.1 °C up to a few tenths of a degree, with a calibration uncertainty less than 0.1 °C. Under conditions similar to those that radiosondes meet at the ground in nighttime radiosoundings, the temperature bias between RS41 and RS92 is within ±0.1 °C, while its uncertainty is less than 0.1 °C. The radiosondes have also been tested before and after fast (within ≈ 10 s) temperature changes of about ±20 °C, simulating a scenario similar to steep thermal changes that radiosondes may meet when passing from indoor to outdoor environment during the pre-launch phase. The results reveal that such thermal changes may increase the noise of temperature sensors during radiosoundings, up to 0.1 °C for the RS41 and up to 0.3 °C for the RS92, with a similar increase in the calibration uncertainty of temperature sensors, as well as an increase in the uncertainty of their bias up to 0.3 °C. However, the thermal changes do not appear to affect sensors’ calibration error and temperature bias.