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Science Week 2016: Met Éireann regional reanalysis of the Irish climate
18 November 2016

Met Éireann researchers are close to completing a high resolution regional reanalysis of Ireland's climate called MÉRA (Met Éireann ReAnalysis). A reanalysis is produced by carrying out weather analyses and forecasts for a period of time using an invariant version of a weather forecast system. By assimilating available observations and using a modern weather forecast model, past weather and climate can be reconstructed extending the knowledge gained from observations alone.

The MÉRA project is using the shared ALADIN-HIRLAM system to assimilate observations and produce past forecasts for the period 1981-2015. MÉRA data are produced on a high resolution horizontal grid (2.5 km) providing more detail of surface and atmospheric parameters when compared with another dataset such as ECMWF's ERA-Interim (80 km). 

  
(left) MÉRA (2.5 km grid spacing) and (right) ERA-Interim (79 km grid spacing) orographies. By using a 2.5 km grid MÉRA data benefit from a more accurate orography and coastline definition.

Validation of MÉRA data has started. Initial results show that MÉRA data compare well with surface and upper-air observations providing a consistent dataset for the 35-year reanalysis period. MÉRA has also made it possible to look at how modern weather forecast models would have forecasted severe weather events in the past. MÉRA forecast data show how a heavy rainfall event over the August Bank Holiday weekend in 1997 would have been forecast. Rainfall accumulations of over 200 mm were recorded in the south of the country. MÉRA forecasted rainfall accumulations in excess of 180 mm for the same period. The benefits of using a higher resolution grid are clear when MÉRA data are compared with coarser ERA-Interim data.

    
(left) MÉRA and (right) ERA-Interim rainfall forecasts for 3rd August 1997. The rainfall accumulation detail and magnitude forecasted by MÉRA show the value of using higher resolution.

By looking to the past with MÉRA, Met Éireann researchers hope to be able to learn more about Ireland's climate.

Sample MÉRA output: monthly mean 2 m temperature for 1997.

 

For further information contact Eoin Whelan (Eoin dot Whelan AT met dot ie) or Emily Gleeson (Emily dot Gleeson AT met dot ie).

 
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