THE NERC MST RADAR FACILITY AT ABERYSTWYTH
NOTE: the contents of this page have now be superseded by those of announcement for 2008-04-16.
Owing to a bug in the new MST radar control and data acquisition system, which began operations at 13:44 UT on 6th February 2007, there has been an error of approximately 1 km in the reported ranges and altitudes of data products. The quality of the data appears to be otherwise unaffected. A compensation for this error was introduced to the signal processing software, starting at 12:48 UT on 7th February 2008. A fix for the radar control and data acquisition software will need to be applied in the near future.
Which files are affected?
- spectral data from 2007-02-06 13:44 UT onwards
- radial data from 2007-02-06 13:44 UT until 2008-02-07 12:48 UT
- Cartesian data from 2007-02-06 13:44 UT until 2008-02-07 12:48 UT
- Met Office data from 2007-02-06 13:30 UT until 2008-02-07 11:00 UT
How to compensate for this error in affected data
- For spectral and radial data:
actual range gate number = recorded range gate number + 7
actual range (of range gates from radar) = recorded range + 1050.0 m - for Cartesian data:
actual range gate number = recorded range gate number + 7
actual altitude (of range gates above mean sea level) = recorded altitude + 1044.2 m
Evidence for the problem
As can be seen from the first of the two plots below, the problem is not necessarily immediately obvious in comparisons with wind-profile data from radiosondes (black lines) launched at Aberport, which is located 45 km to the SW of the radar site. This is why it took so long to identify the problem. It is typically only when there are sharp changes in wind vector with altitude, e.g. around the jet in the second plot below, that the altitude mismatch is clear.
The radar data correspond to 1 hour averages, starting at the time of the radiosonde launch. Wind directions are according to the meteorological convention, i.e. from which the wind is blowing. The red and yellow crosses show, respectively, the radar data without and with altitude compensation.
It was known, from monthly comparison statistics against the Met Office model, that the switch to the new radar control and data acquisition system had lead to the following changes:
- there was an increased bias in the differences between radar and model wind (northward and eastward) components
- the magnitude of this bias was a maximum around the tropopause level, i.e. where there is typically a sharp reduction in wind speed with increasing altitude
- the wind direction was largely unaffected
- there was a decrease in radar altitude coverage
