.... interesting pattern in the low cloud sheet has developed downwind
of (I think) the highest spots on Dartmoor ...

http://www.sat24.com/frame.php?html=...try=gb&sat=vis

some sort of vortex shedding?

Martin.


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

On 25 Aug, 12:51, "Martin Rowley"
wrote:
... interesting pattern in the low cloud sheet has developed downwind
of (I think) the highest spots on Dartmoor ...

http://www.sat24.com/frame.php?html=...try=gb&sat=vis

some sort of vortex shedding?

Martin.

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

Also shows the sunny skies over Scilly & west Cornwall earlier. Now
clouding over.

Graham
Penzance

Mountain wave. Note the stationary nature of some of the clouds.

Stratocu sheets are often the cloud types that give glider pilots the
best wave conditions in Britain. "Classic" lenticulars frequently
disappoint pilots.

The midday Camborne sounding shows a very strong inversion at around
920 mbs, one of the most significant factors:

http://weather.uwyo.edu/cgi-bin/soun...512&STNM=03808

Jack

wrote in message
...
Mountain wave. Note the stationary nature of some of the clouds.



.... My fault - I know they're mountain waves!

In my haste, I didn't make it clear what had excited me: it was the
'bow-wave' nature of the pattern that appeared to be spawned downwind
[i.e. to the east] of the highest part of the moor around Yes Tor /
High Willhays. I assume it was due to some turbulent descent
along-flow clearing a lane in the Sc len. It's mostly gone now of
course, presumably with subtle changes in either the flow direction or
humidity content, though there are still some elements over east
Devon/west Dorset/south Somerset.

Martin.


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

"Martin Rowley" wrote in message
...
wrote in message
...
Mountain wave. Note the stationary nature of some of the clouds.



... My fault - I know they're mountain waves!

In my haste, I didn't make it clear what had excited me: it was the
'bow-wave' nature of the pattern that appeared to be spawned downwind
[i.e. to the east] of the highest part of the moor around Yes Tor / High
Willhays. I assume it was due to some turbulent descent along-flow
clearing a lane in the Sc len. It's mostly gone now of course, presumably
with subtle changes in either the flow direction or humidity content,
though there are still some elements over east Devon/west Dorset/south
Somerset.

Martin.


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


If it's any help Martin at 1100 local this morning the Sc cloud base was at
circa 480m asl looking west (just covering the Hameldown ridge) and it was
drizzling very slightly. Ties in I think with the inversion higher up. Sc
elements slooked very thin with blue sky visible at times.

Will (Haytor, Devon, 1017 feet asl)
--

"Will Hand" wrote...
If it's any help Martin at 1100 local this morning the Sc cloud base
was at circa 480m asl looking west (just covering the Hameldown
ridge) and it was drizzling very slightly. Ties in I think with the
inversion higher up. Sc elements slooked very thin with blue sky
visible at times.

Will (Haytor, Devon, 1017 feet asl)

.... thanks Will - yes I thought of you when I looked at the imagery -
tramping about the Moor :-)

The mechanics involved must have been quite interesting; I only have
access to low-res imagery, so couldn't accurately pinpoint the
'origin' of the divergence seen on the course-res imagery, but it was
quite dramatic; it looked for all the world as if Dartmoor was
steaming *westward* through a bank of Sc leaving a clear wake. The
mesoscale (even microscale) circulations must have been quite
interesting. Had a look through 'Images in Weather Forecasting' but
couldn't find anything similar.

Martin.


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

"Martin Rowley" wrote in message
...
"Will Hand" wrote...
If it's any help Martin at 1100 local this morning the Sc cloud base was
at circa 480m asl looking west (just covering the Hameldown ridge) and it
was drizzling very slightly. Ties in I think with the inversion higher
up. Sc elements slooked very thin with blue sky visible at times.

Will (Haytor, Devon, 1017 feet asl)

... thanks Will - yes I thought of you when I looked at the imagery -
tramping about the Moor :-)

The mechanics involved must have been quite interesting; I only have
access to low-res imagery, so couldn't accurately pinpoint the 'origin' of
the divergence seen on the course-res imagery, but it was quite dramatic;
it looked for all the world as if Dartmoor was steaming *westward* through
a bank of Sc leaving a clear wake. The mesoscale (even microscale)
circulations must have been quite interesting. Had a look through 'Images
in Weather Forecasting' but couldn't find anything similar.

Martin.



Hi Martin, another thought, do you remember Von Karman vortices? They are
sometimes seen where the Azores interrupts a stable flow.

Will
--

"Will Hand" wrote...
snip


Hi Martin, another thought, do you remember Von Karman vortices?
They are sometimes seen where the Azores interrupts a stable flow.


.... thanks for that Will - yes, that was something that did cross my
mind, but without more data can't really say: must dig out more info
on same to see if I can pin it down - I'm sure that the mechanism must
be of that ilk: what impressed me was that 'effect' as of a ship
ploughing a wake through a calm ocean - or perhaps a submarine's
conning tower doing the same thing to keep the scale correct. It must
have made a dramatic difference to those folk downwind as between OVC
SC (ST) & -DZ and bright sunshine.

I'm sure we had a small element of it here - we stayed resolutely OVC
until 15Z, with morning drizzle, but not too far away in north Dorset,
there seemed to be better breaks between the elements of the Sc len.

Martin.

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

Martin Rowley wrote:

"Will Hand" wrote...
snip


Hi Martin, another thought, do you remember Von Karman vortices?
They are sometimes seen where the Azores interrupts a stable flow.


... thanks for that Will - yes, that was something that did cross my
mind, but without more data can't really say: must dig out more info
on same to see if I can pin it down - I'm sure that the mechanism
must be of that ilk: what impressed me was that 'effect' as of a ship
ploughing a wake through a calm ocean - or perhaps a submarine's
conning tower doing the same thing to keep the scale correct. It must
have made a dramatic difference to those folk downwind as between OVC
SC (ST) & -DZ and bright sunshine.

I'm sure we had a small element of it here - we stayed resolutely OVC
until 15Z, with morning drizzle, but not too far away in north
Dorset, there seemed to be better breaks between the elements of the
Sc len.

Martin.

The following is an impressive satpic showing what you are describing,
Martin. It shows the Crozet Islands in the Indian Ocean under a layer
of Sc. The island on the left does not penetrate through the top of the
Sc and is producing a ship-type wake. The island on the right is
protruding above the top of the Sc and is producing von Karman vortices
downstream.

http://www.weather-consultancy.com/s...rozet-ship.jpe


Quite striking.


Norman
--
Norman Lynagh
Chalfont St Giles, Buckinghamshire
85m a.s.l.
(remove "thisbit" twice to e-mail)

"Norman" wrote...

snip
The following is an impressive satpic showing what you are
describing,
Martin. It shows the Crozet Islands in the Indian Ocean under a
layer
of Sc. The island on the left does not penetrate through the top of
the
Sc and is producing a ship-type wake. The island on the right is
protruding above the top of the Sc and is producing von Karman
vortices
downstream.

http://www.weather-consultancy.com/s...rozet-ship.jpe

.... that's interesting: what I saw yesterday was the left-hand
structure (though with near-clear skies between the perturbed cloud
rolls), and could not detect the classic VKVs as on the right -
however, they may have been there just not visible in the course-res.
stuff I was looking at. However, as it was unlikely that the highest
part of the ground did not penetrate the Sc sheet, it's perhaps not
surprising.

Martin.


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