Global Radiosonde Data for Climate Research




Global historic in situ upper air data for climate change research

 Long, homogeneous observed time series of climate state quantities are needed for climate monitoring not only at the Earth's surface but also in the free atmosphere, since climate anomalies and climate change have a three-dimensional spatial structure.

In situ upper air data, mostly radiosonde and tracked balloon data, are available over the northern hemisphere from the late 1930s onward and global coverage is given from the International Geophysical Year 1958 onward.

To exploit their full potential for climate research, it is essential

  • to remove spurious biases and shifts from the station records
  • to assimilate the data with proper dynamic data assimilation systems in the framework of so-called reanalyses.


The task of removing temporal changes in observation biases is referred to as homogenization.

The lack of homogenized upper air records back to the 1970s or even the 1920s has been identified by the Intergovernmental Panel on Climate Change (IPCC) 4th assessment report as a major source of uncertainty that causes serious limitations in our ability to diagnose climate change and to better understand how was the atmosphere state.

Apart from a few aircrafts, the radiosonde and tracked balloon (PILOT) network is practically the only global upper air observing system until 1972 and even in the satellite era (1979-) it remains an important component of the Global Climate Observing System (GCOS, WMO 2004).

The upper air data have been assimilated in global climate data assimilation (reanalysis) efforts (Uppala et al. 2005; Onogi et al. 2007; Kistler et al. 2001), which have been designed to make optimal use of the available digital climate data. Reanalyses have proven extremely fruitful for climate research and are essential input for studies in many disciplines.

Analysis quality and homogeneity is highly dependent on the available input data. Therefore any improvement of the available reanalysis input data will increase the accuracy of the estimated climate state and will be directly beneficial for future studies related to it.

The Project has two research aims directed towards lifting current limitations to diagnose climate change:

  1. Development of a unified automatic homogenization system that analyzes and adjusts upper air temperature, wind and humidity dataset together, using available reanalysis background departure data (Twenty century Reanalysis, ERA-Interim and ERA-40). It should yield homogenized datasets of these parameters back to 1958.
  2. Investigation and, as far as possible, homogenization of the 1900-1958 balloon/radiosonde dataset.


Aim (1) addresses the fact that radiosonde coverage is global from 1958 onward, but no homogenized global radiosonde humidity and wind data set comprehensive enough for use as input in climate data as- simulation yet exists.

Homogenized temperature data from University of Vienna and other sources between 1958-1978 exist but still contain substantial inconsistencies that must be removed, as recent research has shown (Randel et al. 2008).

Treating all these parameters together is a novel approach that should yield improved detection efficiency, since breaks in different parameters often occur synchronously, but are not detectable in all time series.

The homogenization of data from later periods may be further improved through optimization of the underlying statistical methods and through comparison with new datasets (e.g. re-calibrated satellite radiances).

Aim (2) should be feasible for the first time with the increasing number of digitized upper air data together with background departure time series from available surface observation only reanalyses (Twenty Century Reanalysis) and test assimilations of the early period.

In order to achieve these purposes the new RAOBCORE 2.0 (RAdiosone OBservation COrrection using REanalyses) is under developing.

Preliminary results are presented below.

A visualization utility for RAOBCORE 2.0 global radiosonde dataset  is now available, and it shows, on demand, the radiosonde and PILOT uncorrected timeserie for Temperature, Wind Speed and Direction, U and V components, relative and Specific Humidity (detailed Viewer).



  1. L. Ramella-Pralungo, Haimberger, L., 2012: Global historic in situ upper air data for climate change research. 4th WCRP International Conference on Reanalysis, 2012, Silver Spring, Maryland USA.
  2. Haimberger, L., L. Ramella-Pralungo, Christina Tavolato, Marco Milan, Stefan Sperka: Bias Adjustments for the Upper Air Temperature and Wind Dataset. 4th WCRP International Conference on Reanalysis,2012,Silver Spring, Maryland USA
  3. L. Ramella-Pralungo, Haimberger, L., 2012: Global historic in situ upper air data for climate change research. ERA-CLIM work package 4th Workshop on observation errors, 2012, Vienna.
  4. Haimberger, L., L. Ramella-Pralungo, J. Hadzimustafic, and C. Tavolato (2011): Homogenization of the global radiosonde temperature and wind data set. European Geosciences Union (EGU) 2011, Vienna, A.