Critically Reassessing Tropospheric Temperature Trends from Radiosondes Using Realistic Validation Experiments

Abstract

Biases and uncertainties in large-scale radiosonde temperature trends in the troposphere are critically reassessed. Realistic validation experiments are performed on an automatic radiosonde homogenization system by applying it to climate model data with four distinct sets of simulated breakpoint profiles. Knowledge of the ''truth'' permits a critical assessment of the ability of the system to recover the large-scale trends and a reinterpretation of the results when applied to the real observations.The homogenization system consistently reduces the bias in the daytime tropical, global, and Northern Hemisphere (NH) extratropical trends but underestimates the full magnitude of the bias. Southern Hemisphere (SH) extratropical and all nighttime trends were less well adjusted owing to the sparsity of stations. The ability to recover the trends is dependent on the underlying error structure, and the true trend does not necessarily lie within the range of estimates. The implications are that tropical tropospheric trends in the unadjusted daytime radiosonde observations, and in many current upper-air datasets, are biased cold, but the degree of this bias cannot be robustly quantified. Therefore, remaining biases in the radiosonde temperature record may account for the apparent tropical lapse rate discrepancy between radiosonde data and climate models. Furthermore, the authors find that the unadjusted global and NH extratropical tropospheric trends are biased cold in the daytime radiosonde observations. Finally, observing system experiments show that, if the Global Climate Observing System (GCOS) Upper Air Network (GUAN) were to make climate quality observations adhering to the GCOS monitoring principles, then one would be able to constrain the uncertainties in trends at a more comprehensive set of stations. This reaffirms the importance of running GUAN under the GCOS monitoring principles.

Internal variability in simulated and observed tropical tropospheric temperature trends

“…We choose to use radiosonde observations, since they offer longer observational records and higher vertical resolution than satellite products, which is particularly relevant to investigating the warming maximum in the upper troposphere [Fu et al, 2004;Haimberger et al, 2012;Seidel et al, 2012;Sherwood and Nishant, 2015]. Care must be taken, however, because uncorrected radiosonde data suffer from biases toward insufficient tropospheric warming, and these biases are largest in the tropics [Lanzante et al, 2003;Sherwood et al, 2005Sherwood et al, , 2008Titchner et al, 2009;Thorne et al, 2011b]. These biases include step-like mechanisms that do not cancel over time, whereas the amplitude of internal variability diminishes with time scale.…”

Climate intercomparison of GPS radio occultation, RS90/92 radiosondes and GRUAN from 2002 to 2013

“…Radiosondes are known to suffer from radiation biases in temperature and humidity measurements, and there have been many attempts to quantify or correct these biases (e.g., Haimberger et al, 2008Haimberger et al, , 2012Ho et al, 2010;Titchner et al, 2009;Vömel et al, 2007;Miloshevich et al, 2006;Luers and Eskridge, 1998). Most sonde types include their own correction schemes which are applied at the ground station before the data are transmitted.…”

Comparisons of temperature, pressure and humidity measurements by balloon-borne radiosondes and frost point hygrometers during MOHAVE-2009

“…These measurements were predominantly made for weather forecasting and other short-term investigations, hence the collected data often lack the long-term stability and traceability necessary for climate research (Thorne et al, 2005;Titchner et al, 2009;Immler et al, 2010). Long-term measurement records from balloon-borne radiosondes are particularly questionable because of poorly documented instrument and procedural changes over the years (Titchner et al, 2009;Seidel et al, 2004).…”