"Martin Rowley" wrote ...
"comp.john" wrote in message
...
On 2009-12-07, John Hall wrote:

The GFS Ensemble 850mb temps for London are now looking decidedly
chilly:

http://91.121.93.17/pics/MT8_London_ens.png

What do the coloured P numbers mean down the left side of the
chart?

... tags identifying the individual perturbation outcome depicted on
the composite plume. P=0 is the first perturbation, P=1 is the
second and so on. The colours match the individual (thin) lines on
the chart. Useful if you're trying to identify clustering of the
members of the plume-set.

.... I should have added that for each main time-step of the ensemble
run, a set of 'postage stamps' will be available. They're called that
because they look like a sheet of stamps you might see in a post
office.

Usually (based on the EC output), for the main VT times, each 'postage
stamp' sheet will show the 'operational' run mslp pattern, the
'control' run mslp pattern, and for each perturbation, the model's
idea of what the mslp pattern would be that produced that individual
outcome.

So, the analyst would look as these data - and want, say to
investigate why P16 was markedly colder than the rest, and view the
mslp (and perhaps other diagnostics) that are attached to that
particular outcome.

We don't (AFAIK) see these on the open 'web', so in a sense the
coloured 'P' lines/numbers aren't of high relevance.

Martin.


--
Martin Rowley
West Moors, East Dorset (UK): 17m (56ft) amsl
Lat: 50.82N Long: 01.88W
NGR: SU 082 023