Does it really make a difference if the SSTs contain information “from the future”? What would be the harm in using AMIP SSTs rather than the persisted values?
It makes a difference if the SSTs include information from the future because GLACE-2 is being looked at as a component of the “Task Force for Seasonal Prediction” effort, and one of their “prime directives” is that any forecast performed in the effort be a true forecast, using knowledge only of initial conditions and the historical statistics of the climate. And in a sense, we are trying to forecast the historical anomalies. If we initialize the model on June 1 of 1988, for example, we want to see if we can forecast the 1988 drought *without* benefit of knowing what the actual July 1988 sea surface temperatures were. Now we could argue that because the Series 1 and Series 2 forecasts use the same SSTs, and because we subtract the skill obtained in Series 2 from that obtained in Series 1, the effect of the SSTs “cancels out”, but that still doesn”t go over very well with the TFSP people.
