Progress in managing the transition from the RS92 to the Vaisala RS41 as the operational radiosonde within the GCOS Reference Upper-Air Network

Abstract

Abstract. This paper describes the GRUAN-wide approach to manage the transition from the Vaisala RS92 to the Vaisala RS41 as the operational radiosonde. The goal of the GCOS Reference Upper-Air Network (GRUAN) is to provide long-term high-quality reference observations of upper air Essential Climate Variables (ECVs) such as temperature and water vapor. With GRUAN data being used for climate monitoring, it is vital that the change of measurement system does not introduce inhomogeneities in to the data record. The majority of the 27 GRUAN sites were launching the RS92 as their operational radiosonde, and following the end of production of the RS92 in the last quarter of 2017, most of these sites have now switched to the RS41. Such a large-scale change in instrumentation is unprecedented in the history of GRUAN and poses a challenge for the network. Several measurement programmes have been initiated to characterize differences in biases, uncertainties and noise between the two radiosonde types. These include laboratory characterization of measurement errors, extensive twin sounding studies with RS92 and RS41 on the same balloon, and comparison with ancillary data. This integrated approach is commensurate with the GRUAN principles of traceability and deliberate redundancy. A two-year period of regular twin soundings is recommended, and for sites that are not able to implement this burden sharing is employed, such that measurements at a certain site are considered representative of other sites with similar climatological characteristics. All data relevant to the RS92-RS41 transition are archived in a database that will be accessible to the scientific community for external scrutiny. Furthermore, the knowledge and experience gained about GRUAN's RS92-RS41 transition will be extensively documented to ensure traceability of the process. This documentation will benefit other networks in managing changes in their operational radiosonde systems. Preliminary analysis of the laboratory experiments indicates that the manufacturer's calibration of the RS41's temperature and humidity sensors is more accurate than for the RS92; with uncertainties of

Radiosounding HARMonization (RHARM): a new homogenized dataset of radiosounding temperature, humidity and wind profiles with uncertainty

“…In Ingleby et al (2017), operational radiosonde data are compared to ECMWF background values (12-hour forecast): mean and root-mean-square (rms) Observation-minus-Background (O-B) statistics show that RS92 NGP sondes have slightly poorer performance characteristics than the more common RS92 SGP, while there are indications that RS41 perform slightly better than the RS92. These indications are confirmed by the comparisons shown in Dirksen et al (2019) and Madonna et al (2020b). In Jensen et al 2018, a comparison is provided between RS41 and RS92 radiosondes on a limited dataset showing how RS41 does provide important improvements, particularly in cloudy conditions.…”

Characterising extratropical near‐tropopause analysis humidity biases and their radiative effects on temperature forecasts

“…Although the differences in measurements are small, the RS41 demonstrates a better precision and a reduced sensitivity to solar heating (Edwards et al 2014, Jensen et al 2016, Motl 2014. In terms of bias between the two instruments, it can be seen in intercomparison studies (Edwards et al 2014, Dirksen et al 2019, Jauhiainen et al 2014, Vaisala 2014) that the RS92 is < 1.5% RH drier than the RS41 in the upper troposphere and < 1% RH moister in the lower stratosphere, which is a very close agreement given the uncertainties of 4% RH and 5% RH for the two sonde types in these measurements.…”

Thermal metrology for climate: a review of projects, activities and open issues

“…Nevertheless the conditions met by radiosondes during the ascent in the troposphere and lower stratosphere are such that the uncertainty in their record is the main concern of the GRUAN scientists. Moreover, changes in technical features of the radiosondes and introduction of new models can introduce biases in record series [25] which may systemically alter the climate signal contained in the data with potential effects on every application using the radiosounding historical time series. Specific experiments are being made to evaluate the effect of instrument change in radiosondes use both as field tests, by launching couples of radiosonde and in laboratory.…”