On 22/01/2017 11:27, JohnD wrote:
"N_Cook" wrote in message news
Anyone know which version is corrct?
I suspect Wipneus is using a different data feed than the Charctic one,
area rather than extent perhaps, JAXA ?

TBH I'm not too bothered about this slight day-to-discrepancies,
irritating though they may be, because there are several possible
causes. It could be a slightly different algorithm in use, which is fine
in one sense - one wouldn't expect different sources to give _precisely_
the same value on any given day and indeed there may be some days when
the trend ticks up from one source and down on another. But as long as
the overall trend averaged over a few days is comparable on multiple
sources then I'd suggest that's actually powerful evidence supporting
the conclusion that we're watching major milestone events in global sea
ice.

But what is tricky for us amateur observers to assess is exactly how the
different sources are processing the data. For instance, I'm never quite
sure what the date on the charts actually means - is that the date of
the data or the date on which the chart was prepared (ie maybe using
yesterday's data). And sometimes the charts don't get updated every day
- maybe if the charts are coming from academic institutions then perhaps
they may not (always?) get updated at weekends? So, as I write, the
latest data on the NSIDC Charctic chart is 20th Jan and perhaps in 2-3
hours time this will update to 21st Jan. But the latest Wipneus charts
that I can see are still dated the 19th.

And then there's the issue of whether the data are single-day or 3- or
5-day means from different sources.

Wipneus does specifically mention that his/her data is sourced from
NSIDC, though I don't know whether that automatically means that it's
the same as Charctic or not.

Finally, I suspect that any serious questions would be welcome on the
arctic sea ice forum eg on the thread at:

https://forum.arctic-sea-ice.net/ind...c,1837.50.html

You never know, you might get an answer direct from Wipneus?

Reassuring to see
https://sites.google.com/site/arctis...t_byyear_b.png
has stopped on the 19th ( 20th day update)
It credits NSIDC in the filename and refers to extent
as does the Charctic source , obviously as NSIDC itself.
So if Wipneus does not credit NSIDC as the source , then perhaps the
file-naming in that sites.google plot is erroneous.
Perhaps there are 2 data feeds out of NSIDC , one automatic and one
human reviewed. Too many unknowns.
I'll stay with the Charctic source for data and take that as correxct
and consitent.
The forum.arctic site is moderated , so that is out

Just look at the top of the Wipneus charts - they say 'from NSIDC sea ice
concentration data'.

Re the sea ice forum being moderated, what's the problem? You just need a
standard forum registration, wait a day or two for approval and you should
be in. I don't have any sense that it's any more difficult to join than any
forum that puts the small hurdle of registration at the entrance. Provided
you don't abuse the forum and stick to the rules then it's as open as any
other forum.

On 22/01/2017 11:47, JohnD wrote:
Just look at the top of the Wipneus charts - they say 'from NSIDC sea
ice concentration data'.

Re the sea ice forum being moderated, what's the problem? You just need
a standard forum registration, wait a day or two for approval and you
should be in. I don't have any sense that it's any more difficult to
join than any forum that puts the small hurdle of registration at the
entrance. Provided you don't abuse the forum and stick to the rules then
it's as open as any other forum.

So not just sea-ice area and extent but also concentration
https://nsidc.org/cryosphere/seaice/...rminology.html
" Concentration
Concentration is a unitless term that describes the relative amount of
area covered by ice, compared to some reference area. Thus,
concentration describes how much of a 25.0 kilometer by 25.0 kilometer
(15.5 mile by 15.5 mile) box is covered by sea ice. Ice concentration
typically is reported as a percentage (0 to 100 percent ice), a fraction
from 0 to 1, or sometimes in tenths (0/10 to 10/10). Our Sea Ice Index
products show ice concentration as a percentage. A value of 0 means
there is no ice, while a value of 100 means the region is completely
covered by ice. "

Certainly not the y-axis of any Wipneus plots I've seen, despite marked
"from NSIDC sea ice concentration data"