220: Start at

Upon successful opening of an input file, the dates of the first and last data in the dataset will be indicated. The first year in the X input file does not have to be the same as in the Y input file. You may start the analysis at a later year in either or both of the datasets, particularly if the first years in each dataset differ. If, for example, the X input data starts in 1950, and the Y input data starts in 1965, you will normally want CPT to ignore the first 15 years in the X input file. In this case, set the start-at date of the X training period to 1965. CPT will set what it considers to be sensible default values for the starting years on the basis of setting a lead-time that is less than one year, and using as long a training period as possible (although it will avoid resetting the Start-at date if a replacement file is selected). It will recognise whether the forecast lag spans the year-end, and will adjust the default starting dates accordingly. These defaults can be overridden by using the Edit ~ Start at menu items and by typing the desired dates in the respective boxes, or using the attached fly-wheels. Although CPT does permit the forecast lag to exceed one year or to be negative, this would not normally be advisable. The analysis of climate predictability with lags of one year or more would most likely have little physical basis. A warning is issued if the lag is larger than one year or is negative.

Select the appropriate menu to change the predictors (X), predictands (Y) or new predictors (Z) start-at date:

• Predictors (X)
• Predictands (Y)
• New Predictors (Z)