Initial State Generation

Each month, the GMAO produces an ensemble of 12 (13 in November) real-time GEOS-5 coupled model forecasts. The ensemble is produced by initializing the model every five days prior to the start of the month, except for the date closest to the start of the month when additional GEOS-5 forecasts are generated by various perturbation methods. The perturbations are produced using a breeding approach (perturbing the atmosphere and/or ocean), and a simple scaled differencing approach involving nearby (in time) atmosphere and ocean states. We note that due to time constraints only 11 ensemble members are delivered to the NMME project (forecasts are due by the 8th of the month).

In addition to the forecasts, the GMAO produced a suite of hindcasts (1982-2012) used to calibrate/bias correct the forecasts and assess forecast skill. The ensemble members for the hindcasts are produced in the same way as for the forecasts and span the period 1982-2012.


Starting in 1993 there are 3 more ensembles from the A004 analysis (these are not delivered to NMME)

On the date closest to the start of the month we have:
  • before 1993:  6 perturbations (plus the unperturbed state) = 7
  • beginning in 1993:  8 perturbations (plus the 2 unperturbed states) = 10
add to that the 5 (6 in November) other initial dates each month to give for each month the following number of ensemble members:

  • before 1993:  5 + 7 = 12 (13 in Nov)
  • beginning in 1993:  5 + 10 = 15 (16 in Nov)