BLOGGER'S update, April 23rd (evening):

Hank Roberts was kind enough to post the explanation (although, looking at this evening's graph, I must admit, after viewing the 4 graphs, that I still have no idea what is going on with them -- only time will tell, it seems):

"The satellite data sources for these products, while generally providing complete coverage, are subject to gaps (shown in dark grey) in coverage because of satellite operations. In the daily extent time series, gaps are replaced with values interpolated from surrounding days, but temporary spurious results may occur. The current satellite source is aging and showing more frequent data gaps. NSIDC is investigating a reliable replacement data source. —Credit: National Snow and Ice Data Center"

Blogger's note -- update of April 23 (morning): This just gets weirder and weirder. April 20 shows one thing, April 21 another, and now April 23 looks more like April 20 again. Anyway, I guess the NSIDC are the only ones who can tell us how they update this graph.


ABOVE: Graph from April 20, 2008.

BELOW: Graph from April 21, 2008.



BELOW: Graph from the morning of April 23rd, 2008.
(Once again, thank you to Leon for pointing it out to me.)


BELOW: Graph from the evening of April 23rd, 2008.


BELOW: Graph from the evening of April 25th, 2008.

Link to updated graph: http://nsidc.org/data/seaice_index/images/daily_images/N_timeseries.png