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ER-M-climateextended range

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

Creation of ER-M-Climate

The ER-M-Climate is derived from a set of extended range re-forecasts evaluated created using the same calendar start dates over several years for data times either side of the time of the extended ENS run itself.  The re-forecast runs are at the same resolution as the extended range run itself (currently ~18km up to day15 and ~36km thereafter) and run over the 46-day extended range ENS period.   

Extended range re-forecasts for verification

There is some merit in examining the real-time performance of a seasonal forecasting system.  But the sample sizes created for one system are far too small to conclude anything about the true performance levels of that system. Hence we use the re-forecasts.  

Re-forecasts are a fundamental component of all seasonal forecasting system; they have two applications:

• extended range forecast verification metrics are based on the re-forecasts
  
• re-forecasts allow computation of the ER-M-climate which allows actual forecasts to be converted into an anomaly format.   Forecasts in terms of anomalies relative to a model climate (rather than relative to the observed climatology) mean that some calibration for model bias and drift into the products is incorporated.

Selection of extended range re-forecasts

The set of re-forecasts is based on using the three consecutive dates surrounding the day and month of the extended ENS run in question.  Also further re Re-forecasts are created using the same calendar start dates for each of the last 20 years.  

Each re-forecast consists of an 11-member ensemble (1 control and 10 perturbed members).  Therefore altogether 20 years x 3 runs x 11 ENS members = 660 re-forecast values are available to define the ER-M-climate for a given location and each forecast parameter, forecast lead-time, calendar start date and location.  These are used to define the ER-M-climate.  

based on Mondays and Thursdays (is it still this with daily extended range forecasts?)

In fact it is essentially the same re-forecast runs that are utilised to build the M-Climate and the ER-M-Climate; the key difference is that those runs are grouped together in different ways.

ER-M-climate is updated twice a week, every Monday and Thursday, and based on 00UTC runs only (there are no 12UTC re-forecast sets). The new files start to be used from the 00UTC run that day.  So if one compares, for the same lead-time, the ER

Values evaluated in ER-M-climate

...

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

...

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

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