Observation errors in early historical upper‐air observations

Abstract

[1] Upper-air observations are a fundamental data source for global atmospheric data products, but uncertainties, particularly in the early years, are not well known. Most of the early observations, which have now been digitized, are prone to a large variety of undocumented uncertainties (errors) that need to be quantified, e.g., for their assimilation in reanalysis projects. We apply a novel approach to estimate errors in upper-air temperature, geopotential height, and wind observations from the Comprehensive Historical Upper-Air Network for the time period from 1923 to 1966. We distinguish between random errors, biases, and a term that quantifies the representativity of the observations. The method is based on a comparison of neighboring observations and is hence independent of metadata, making it applicable to a wide scope of observational data sets. The estimated mean random errors for all observations within the study period are 1.5 K for air temperature, 1.3 hPa for pressure, 3.0 ms -1 for wind speed, and 21.4 ı for wind direction. The estimates are compared to results of previous studies and analyzed with respect to their spatial and temporal variability.

The potential value of early (1939–1967) upper‐air data in atmospheric climate reanalysis

“…Given the fact that the modern network is of (much) higher quality than the historical data (Wartenburger et al, ), the historical upper‐air data are probably assigned errors that are too small, and consequently given too much weight. Also, no bias corrections were applied to the observations, except for the CHUAN ‘c’ records that contain RAOBCORE v1.3 (Haimberger, ) bias adjustments.…”

ERA-CLIM: Historical Surface and Upper-Air Data for Future Reanalyses

“…The ERA-CLIM upper-air data provide an independent reference for the validation of other products such as 20CR (e.g., Brönnimann and Stickler 2013). Also, observation errors can be estimated directly from the observations (Wartenburger et al 2013). Additionally, a homogenization of the upper-air data is being undertaken at the University of Vienna, also a partner in ERA-CLIM, as far as this is possible with the often very short and irregular historical time series.…”

A global radiosonde and tracked balloon archive on 16 pressure levels (GRASP) back to 1905 – Part 1: Merging and interpolation to 00:00 and 12:00 GMT

“…In addition, the precision of the pressure measurements as well as of the interpolation procedure has to be taken into account. Thus it is not surprising that Wartenburger et al (2013) found much larger observation errors on the order of 1 K for soundings in the 1940s and 1950s. Only for the modern GPS-based sounding systems, the nominal precision is actually reached.…”

“…However, one can build on the results of earlier integration efforts. These are -the Comprehensive Historical Upper-Air Network (CHUAN) data set version 1.7 (Stickler et al, 2010;Wartenburger et al, 2013) and the ERA-CLIM Historical Upper-Air Data (Stickler et al, 2014). The ERA-CLIM historical upper-air data set (termed ECUD here) contains upper-air data collected and digitized within the EU 7th Framework Programme project ERA-CLIM.…”