Comparison of Vaisala radiosondes RS41 and RS92 at the ARM Southern Great Plains site

Abstract

Abstract. In the fall of 2013, the Vaisala RS41 (fourth generation) radiosonde was introduced as a replacement for the RS92-SGP radiosonde with improvements in measurement accuracy of profiles of atmospheric temperature, humidity, and pressure. In order to help characterize these improvements, an intercomparison campaign was undertaken at the US Department of Energy's Atmospheric Radiation Measurement (ARM) Climate Research Facility site in northcentral Oklahoma, USA. During 3-8 June 2014, a total of 20 twin-radiosonde flights were performed in a variety of atmospheric conditions representing typical midlatitude continental summertime conditions. The results show that for most of the observed conditions the RS92 and RS41 measurements agree much better than the manufacturer-specified combined uncertainties with notable exceptions when exiting liquid cloud layers where the "wet-bulbing" effect appears to be mitigated for several cases in the RS41 observations. The RS41 measurements of temperature and humidity, with applied correction algorithms, also appear to show less sensitivity to solar heating. These results suggest that the RS41 does provide important improvements, particularly in cloudy conditions. For many science applications -such as atmospheric process studies, retrieval development, and weather forecasting and climate modeling -the differences between the RS92 and RS41 measurements should have little impact. However, for long-term trend analysis and other climate applications, additional characterization of the RS41 measurements and their relation to the long-term observational records will be required.

Is it feasible to estimate radiosonde biases from interlaced measurements?

“…For a measurement network like GRUAN, it is essential to have more than one good-quality radiosonde type for operations. Instrument biases are also influenced by clouds as shown in Jensen et al (2016) who found systematic differences in temperature measurements greater than 2 K between the Vaisala RS92 and RS41 radiosonde when exiting cloud layers. This large difference in temperature measurements between the two radiosondes was attributed to the wetbulb effect, in which the temperature sensor gets wet while passing through a cloud layer and is subject to evaporative cooling after entering drier parts of the atmosphere.…”

“…Typically, inter-comparisons of measurements from dual or quadruple (two of each instrument type) radiosonde flights are used to robustly detect systematic differences between the instruments (e.g. Luers and Eskridge, 1998;Steinbrecht et al, 2008;Kobayashi et al, 2012;Jensen et al, 2016). Results presented in Steinbrecht et al (2008) indicated that temperature biases often increase significantly with increasing altitude, particularly in the lower stratosphere.…”

Is it feasible to estimate radiosonde biases from interlaced measurements?

“…Results presented in Steinbrecht et al (2008) indicated that temperature biases often increase significantly with increasing altitude, particularly in the lower stratosphere. Instrument biases are also influenced by clouds as shown in Jensen et al (2016) who found systematic differences in temperature measurements greater than 2K between the Vaisala RS92 and RS41 radiosonde when exiting cloud layers. This large difference in temperature measurements between the two radiosondes was attributed to the wet-bulb effect, where the 25 temperature sensor gets wet while passing through a cloud layer and is subject to evaporative cooling after entering dryer parts of the atmosphere.…”

“…Typically, intercomparisons of measurements from dual or quadruple (two of each instrument-type) radiosonde flights are used to robustly detect systematic differences between 20 the instruments (e.g. Luers and Eskridge, 1998;Steinbrecht et al, 2008;Jensen et al, 2016). Results presented in Steinbrecht et al (2008) indicated that temperature biases often increase significantly with increasing altitude, particularly in the lower stratosphere.…”

“…This large difference in temperature measurements between the two radiosondes was attributed to the wet-bulb effect, where the 25 temperature sensor gets wet while passing through a cloud layer and is subject to evaporative cooling after entering dryer parts of the atmosphere. Below 28km altitude, Jensen et al (2016) found a mean systematic difference between the temperature measurements of the two radiosondes of 0.13K. For radiosonde measurements performed at GRUAN sites, it is suggested that sites conduct dual sonde launches for at least 6 months when changing from one instrument type to another (GCOS-171, 2013).…”