cause two out of three ain’t bad
Julienne Stroeve has responded to my query about yesterday afternoon’s three day shift between climatology and current year.
Steve, as Walt mentioned earlier, NSIDC was in the process of changing the way we do the 5-day average, switching from a 5-day centered mean to a new method that takes the average of the previous five days. As you know, we average in order to remove artificial ice from weather effects. Weather effects can result in noisy data that is not a real sea ice signal. The underlying data going into the averaging are unchanged.
Apparently, the new averaging was implemented yesterday. Note the ice has not been lowered, it has been shifted back two days. The climatology is a 9-day running mean rather than a 5-day, so the climatology will be shifted by more days.
If you have any further questions, feel free to contact me.
As Richard Muller might say, we don’t do that in science.
By switching to a five day trailing mean for current, and a nine day trailing mean for climatology, they created an artificial relative shift of two days. The center point of the current data is -2.5 days, and the center point of the climatology is now -4.5 days.
This accounts for two days error out of the three. The third day of error is because someone lobbed off the April 16 data.
The timing of this error looks very suspicious, because the data would have nearly touched the mean today – which hasn’t happened for for many years.