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First example:  You require initial data for a single start date, created from ERA5 reanalysis data.

• The field "Source for initial data" needs to display ERA5 reanalysis (which is the default value). 
• Ensure that both date fields "First start date" and "Last start date" are set to the same date. When both dates are the same, any value selected for "Time increment between forecasts" will be ignored.
• Note that ERA5 data may not yet be available for the most recent months. If in doubt, check the MARS Catalogue prior to submitting your request.
• Select the experiment start time (default is 00:00 UTC) and the forecast length. The forecast length value determines the number of days for boundary conditions data (e.g. SSTs) in the ICMCL*INIT file.
• Select the model cycle and the model grid parameters for your request.
• Press "Submit".

Second example:  You require initial data with multiple start dates, every 12 hours, created from historical operational archive data.

• The field "Source for initial data" should now be set to Operational archive. 
• Note that the default value for the start date is set to the most recent possible date for operational archive data (for a 24 hour forecast, i.e. forecast length set to 1 day).  
• Ensure that the "First start date" and "Last start date" are set to the appropriate range of dates for your request; they must not be the same value for multiple start dates.
• In this case the value for "Time increment between forecasts" will be evaluated. For instance, if you need 12-hourly gaps between forecast start dates you should set this to 12. 
• Complete all the other fields as in the first example.
• Press "Submit". 

Third example:  You require initial data for a forecast experiment with atmospheric composition.

• CAMS operational data for cycle 48r1 is only available since 28 June 2023, so no earlier start date can be selected.
• To obtain initial data for the tropospheric chemistry scheme TM5 (including initial data for the AER bulk aerosol scheme) select the appropriate option in the drop-down menu for the chemistry. If additionally initial data for the BASCOE stratospheric chemistry is required change the option accordingly.
• Note that currently no time-varying surface or aircraft emissions are provided.