North Winter Polar Vortex Animations
This analysis uses the vortex edge selection developed by V.
Lynn Harvey, R. Bradley Pierce, and Duncan Fairlie (A climatology of
stratospheric polar vorticies
and anticyclones, JGR 107 No. D20, 4432, doi:1029/2001jd001471,2002 )
which picks streamline(s) where the integrated value of "Q" (see paper
for definition) changes
sign.
The stream function program was contributed by William Randel
(written/
modified by M. Fischer,1985 and Tom Blackshear,1990). The analysis
is performed on global potential-temperature-level U,V grids.
The data used are the daily stratospheric analyses from UK Met office
("UKMO", now "MetO") originally by way of the British Atmospheric Data
Centre (BADC), now from The Centre for Environmental Analysis, CEDA.
The more recent (after March 2006) high spatial resolution data are
reduced, by selection, to the original 96 longitudes x 72 latitudes
before analysis.
In the animations, cyclonic edges are solid, anti-cyclonic
dashed. The average speed for cyclonic streamlines are written over their
respective colours in the legend.
If there is more than one line selected at a particular level, usually
the speed label is for the larger ( but no guarantees). Sometimes there
are nested edges at the same level - this remains a puzzle - but
considering the noisiness of "Q", the integrated value is also sometimes
noisy about zero, so more than one line can be selected.
Vortex edge analysis details
Another vortex edge method is by scaled PV (Gloria Manney), innner and outer
edge defined by sPV levels, yellow filled:
Example:Q method vs sPV(Manney) ,
and one rare case in very disturbed conditions where edge definition
is a lost cause:Chaos
And just for pretty - here is a plot of streamlines with local speed
indicated by colour.
View Local Speeds
Unfortunately the MetO/UKMO stratospheric data we have been using are no longer
available. Consequently, for this year we had switched to NCEP reanalysis1,
which has an upper limit of 10 hPa (~30 Km, ~700K). But recently the GEM model
(Meteorological Service of Canada, documentation at
https://eccc-msc.github.io/open-data/readme_en/)
has gone from 20 hPa to a 1 hPa upper limit - much better for us.
So we will use it instead.
Most recent winter day
Finally, here is a workshop paper on
long term statistics
(Our go-to program for controlled viewing of the gif89a animations is
"gif movie gear")