This set of retrospective experiments has been produced using the ECHAM4.5 AGCM (T42, L18), forced with Constructed Analogue (CA) SST (van den Dool, 1994) as boundary conditions over tropical oceans (30S-30N). Over the extra-tropical oceans, the observed SST anomalies are persisted and added to the climatological annual cycle.
The retrospective forecast covers the period 1957-2002, with 0-6 months as lead time. So far, 24 ensemble member forecasts are available; the initial conditions are obtained from large ensemble simulations of each corresponding member.
The lead time is defined as the difference between the month when the forecast is made, and the month being predicted (or target month). For example, a forecast made in August for the month of September, has a lead time of one month; the lead time for October is 2-month, and so on.
Li, S. and L Goddard 2005: Retrospective Forecasts with the ECHAM4.5 AGCM IRI Technical Report 05-02 December 2005.