The AquaVIT-1 intercomparison of atmospheric water vapor measurement techniques

Abstract

Abstract. The AquaVIT-1 intercomparison of atmospheric water vapor measurement techniques was conducted at the aerosol and cloud simulation chamber AIDA (Aerosol Interaction and Dynamics in the Atmosphere) at the Karlsruhe Institute of Technology, Germany, in October 2007. The overall objective was to intercompare state-of-the-art and prototype atmospheric hygrometers with each other and with independent humidity standards under controlled conditions. This activity was conducted as a blind intercomparison with coordination by selected referees. The effort was motivated by persistent discrepancies found in atmospheric measurements involving multiple instruments operating on research aircraft and balloon platforms, particularly in the upper troposphere and lower stratosphere, where water vapor reaches Published by Copernicus Publications on behalf of the European Geosciences Union. D. W. Fahey et al.: The AquaVIT-1 water vapor intercomparisonits lowest atmospheric values (less than 10 ppm). With the AIDA chamber volume of 84 m 3 , multiple instruments analyzed air with a common water vapor mixing ratio, by extracting air into instrument flow systems, by locating instruments inside the chamber, or by sampling the chamber volume optically. The intercomparison was successfully conducted over 10 days during which pressure, temperature, and mixing ratio were systematically varied (50 to 500 hPa, 185 to 243 K, and 0.3 to 152 ppm). In the absence of an accepted reference instrument, the absolute accuracy of the instruments was not established. To evaluate the intercomparison, the reference value was taken to be the ensemble mean of a core subset of the measurements. For these core instruments, the agreement between 10 and 150 ppm of water vapor is considered good with variation about the reference value of about ±10 % (±1σ ). In the region of most interest between 1 and 10 ppm, the core subset agreement is fair with variation about the reference value of ±20 % (±1σ ). The upper limit of precision was also derived for each instrument from the reported data. The implication for atmospheric measurements is that the substantially larger differences observed during in-flight intercomparisons stem from other factors associated with the moving platforms or the non-laboratory environment. The success of AquaVIT-1 provides a template for future intercomparison efforts with water vapor or other species that are focused on improving the analytical quality of atmospheric measurements on moving platforms.

Robust, spatially scanning, open-path TDLAS hygrometer using retro-reflective foils for fast tomographic 2-D water vapor concentration field measurements

“…2. The standard deviation is an indicator for precision, not for accuracy, which is expected to be in the order of magnitude of less than 5 % (Fahey et al, 2014). The concentration standard deviation in one channel ranges from about 380-750 ppmv, which corresponds to a relative standard deviation of 3 and 6 % of the average concentration.…”

Intercomparison of mid-latitude tropospheric and lower stratospheric water vapor measurements and comparison to ECMWF humidity data

“…Starting from a comparison 5 of the directly measured time series and profiles ( Figure 2) we further use the dataset from the entire ML-CIRRUS campaign, similar to previous approaches, e.g., by Rollins et al (2014), Fahey et al (2014) or Meyer et al (2015). This section describes the framework of the intercomparison and the methodology of the data evaluation including the determination of a water vapor reference value.…”

“…For that reason, we follow the approach of the AQUA-VIT campaign described in Fahey et al (2014) where the mean value of a set of core instruments was used as reference. This allows for a combined intercomparison of data in the lower stratosphere (AIMS, FISH) and in the upper troposphere in cirrus clouds (AIMS, SHARC) and clear sky (AIMS, FISH, SHARC, HAI).…”

An update on the uncertainties of water vapor measurements using cryogenic frost point hygrometers

“…Comparisons with the Fast In situ Stratospheric Hygrometer (FISH) during the AquaVIT-1 laboratory intercomparison (Fahey et al, 2014) indicate that the time response of the CFH at very low frost point temperatures is faster than 20 s. Here we use soundings with pronounced stratospheric features to study time lag in the CFH by comparing ascent and descent profiles. A profile at Lindenberg launched on 20 May 2014 showing two prominent features in the stratosphere at 22 and 23.5 km was sampled both on ascent and descent (Fig.…”

“…In 2007 an intensive laboratory campaign took place at the Aerosols Interaction and Dynamics in the Atmosphere (AIDA) test chamber at the Karlsruhe Institute of Technology (Fahey et al, 2014). During this campaign stratospheric and upper tropospheric water vapor concentrations were used to test a large number of water vapor instruments.…”