Page History

Creation of M-Climate

The M-Climate is derived from a set of medium range re-forecasts.  These are created using the same calendar start dates over several years for data times either side of the time of the ensemble run itself.  The re-forecast runs are at the same resolution as the medium range ensemble (currently 9km) and run over the 15-day medium range ensemble period.   

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• medium range forecast verification metrics are based on the re-forecasts
  
• re-forecasts allow computation of the M-climate.

Selection of medium range re-forecasts

The set of re-forecasts is made up from:

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• to present the 15-day ensemble meteograms with the medium range climate (M-climate)
• to deliver the extreme forecast index (EFI) and shift of tails (SOT) products 
• to highlight significant forecast departures of 2m temperature, wind speed, cloudiness and precipitation from the norm for a given location and time of year.  

Values evaluated in M-climate

• 2m temperature.
• soil temperature.
• sea-surface temperature.
• mean sea level pressure.
• precipitation.
• cloudiness. 

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• Day1 M-climate is used with T+12h to 36h forecasts from the 12UTC run and T+0h to 24h forecasts from the 00UTC run.
• Day2 M-climate is used with T+36h to 60h forecasts from the 12UTC run and T+24h to 48h forecasts from the 00UTC run.

Updates to M-climate

In Cy49 and later, re-forecasts are made every four days during each month on 1/5/9/13/17/21/25/29 (excluding 29 February).  There remain problems using each newly updated M-climate, particularly in spring and autumn when mean temperatures change most rapidly day by day. 

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Cy41r1 in spring 2015, the M-climate was constructed from only 500 re-forecasts was more prone to sampling errors and as a result.

Different reference periods for M-Climate and ER-M-Climate

ECMWF uses different reference periods but essentially the same re-forecast runs to build the M-Climate and the ER-M-Climate.   The key difference is that those runs are grouped and used in different ways:  

• For shorter ranges, the priority is the best possible capture of the climatological distribution of the tails (e.g. extreme forecast index (EFI) and shift of tails (SOT)).  This can be better achieved using a re-forecast span of 5 weeks (1980 re-forecast values).  
• For longer ranges, the priority is the correct representation of seasonal cycles.  This can be better achieved by using a span of 1 week (660 re-forecast values).  The tails should not be so prone to having a reduced sample size.

(FUG Associated with Cy49r1)