RAdiosonde OBservation COrrection using REanalyses (RAOBCORE)

Version 1.4, 30 Jan 2007

Version 1.4 of RAOBCORE contains 2 major improvements compared to the versions 1.2, 1.3 described in Haimberger (2007) (J. Climate, in press). These improvements are:
1) The dataset is updated up to December 2006
2) The ERA-40 background modification described in Haimberger (2007) is only applied between Jan 1972 and Dec 1986. It has turned out that the ERA-40/ECMWF bg forecast time series are quite consistent with recent versions of the RSS and UAH satellite datasets, so that a modification of the ERA-40 bg is not necessary. Between 1972 and 1986, modifications of the bg are unavoidable. The bg is modified more strongly in the tropics in v1.4 compared to the modification applied in version 1.2. The differences between 1.2, 1.3 and 1.4 can be examined using the web visualization tool.

Cautionary note: The tropical mean trends 1958-1978 show warming at low levels but cooling at upper tropospheric levels, which seems unrealistic. This feature is related to a strong warming anomaly over the Eastern US which is spread to the Caribbean by the ERA-40 bg. Consequently the Carribean stations may be overcorrected at low levels during this period. Since most tropical stations are in the Caribbean during these early days, this problem strongly affects also the global tropical means. This issue, which affects all RAOBCORE versions, will be fixed in the next version.

The RAOBCORE radiosonde temperature dataset consists of 2881 records from radiosondes. The file merged_stations.t contains the IDs and coordinates of the stations used. The first 1536 WMO stationIDs in the file strictly correspond to the IGRA station list. The other 1355 stationIDs are from radiosonde data that have not been included in IGRA but have been used as input in the ERA-40 reanalysis project. Many of the latter records are very short. Homogeneity adjustments have been applied to temperature records with a minimum length of 180 days. 1184 stationIDs met this criterion.

The RAOBCORE web visualization allows to view homogeneity adjustments and other plots for individual stations as well as maps of trends and 12GMT-00GMT differences in a Web browser.

RAOBCORE v1.4 data are available as adjustments for single stations and as MSU-equivalent gridded anomalies. The data format is the same as the UAH satellite dataset, i.e. one file for each year 1958-2006 and with 2.5 degree horizontal resolution. In this format is should be useful for regionally detailed comparison with satellite datasets, reanalyses and climate models.

The file biascor-1.4.t.gz contains all necessary information for applying the homogeneity adjustments to temperature time series of radiosonde stations. It is a compressed ASCII file and a record looks like this:

101  4320    76.77   -18.67 Y  5
1957010100 0.13 -0.25 0.07 0.23 -0.48 -0.36 -0.69 -1.20 -0.24 -0.53 -0.35 -0.46 -0.56 0.05 0.00 0.00
1957010112 1.09 0.83 1.01 1.45 1.24 0.32 -0.43 -0.84 0.38 0.06 -0.10 -0.34 -0.57 -0.24 0.00 0.00
1961041600 0.13 -0.25 0.07 0.64 0.53 0.50 -0.05 -0.44 -0.20 0.10 0.33 0.23 0.15 0.13 0.00 0.00
1961041612 1.09 0.83 1.01 1.45 1.24 1.06 0.39 0.08 0.38 0.68 0.45 0.16 0.08 -0.01 0.00 0.00
1976060600 0.41 0.07 0.41 0.89 0.68 0.99 0.58 0.15 0.26 0.53 0.74 0.84 0.65 0.37 0.00 0.00
1976060612 0.75 0.33 1.00 1.56 1.32 1.41 0.81 0.43 0.54 0.68 0.57 0.50 0.53 0.32 0.00 0.00
1983101000 1.07 0.33 0.06 0.52 0.76 0.58 0.06 -0.17 -0.02 0.20 0.50 0.64 0.30 0.07 0.00 0.00
1983101012 0.90 0.09 -0.03 0.37 0.65 0.66 0.21 -0.14 -0.08 0.07 0.29 0.46 0.46 0.16 0.00 0.00
1992120200 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
1992120212 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

The headline contains the record number, the radiosonde stationID, station coordinates, a flag whether homogeneity adjustments are available (Y/N) and how many breakpoints have been adjusted (i.e. how many lines describing the adjustments will follow for this station). The following lines contain the adjustments for 16 pressure levels. These need to be subtracted from the original temperature data. There are two lines per breakpoint, one for 00GMT, one for 12GMT. The first column is the date of the first day for which the adjustments have to be applied. The other 16 columns are the adjustments to be applied, starting with the uppermost (10 hPa) pressure level. The adjustments specified in one line are valid until the date specified in the next two lines. The last lines of a records always contain adjustments with value zero. No adjustments have been applied after this date. In records where even the most recent part of the time series has been adjusted, last two lines contain the date 20081229. Then the next station headline follows. The Fortran90 program read_biascor.f90 can be used to convert this file into a more readible time series format.

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