"Mike Tullett" wrote :

I agree about the low, Jon. Warmer air was sucked in to it when it was
near Iceland. I recall, many years ago, there was a debate on just
important baroclinic factors were in the development of polar lows. But
it's a long time since I read the literature on the subject.

I think I remember the same literature, Mike. There were a lot
of mesoscale features in the 1960s which were lumped together
under the generic title "polar low", and they spawned a lot of
papers in the meteorological journals. Browning and Harrold
in QJ rings in about 1967 rings a bell (when I could actually
understand most [well, some] of the papers in QJ!)

Some of these features could be traced to lee vortices
south of Iceland (in a N-ly), some to vortex-shedding
from the Norwegian lee trough (in a NE-ly), and some
to shallow quasi-baroclinic disturbances developing in Denmark
Strait marking the boundary between Greenland air and
peripheral Atlantic air (which these days would be recognised
by contrasting theta-w characteristics). My memory is that
pseudo-frontal boundaries were often evident at the 700 mbar
level, but rarely at 500mbar, and that the pseudo-cold front
was almost invariably much more clearly defined than the
pseudo-warm front.

Philip

"Mike Tullett" wrote :

I agree about the low, Jon. Warmer air was sucked in to it when it was
near Iceland. I recall, many years ago, there was a debate on just
important baroclinic factors were in the development of polar lows. But
it's a long time since I read the literature on the subject.

"just important baroclinic factors" should read
"just how important baroclinic factors were in the development of polar
lows"

Found it .... "The Polar Low as a Baroclinic Disturbance",
TW Harrold and KA Browning, QJRMetS, 95, 1969, pp710-723.

The intro reads:
"This paper describes the 3-dimensional airflow and precipitation within
small 'polar' depressions which sometimes cross Britain during N-ly
outbreaks and which in winter can be responsible for heavy snowfalls.
The data used in the study consist of Doppler and conventional radar
information, together with routine synoptic data and sequential radiosonde
ascents from the radar station. 3-dimensional airflow was derived from
the radisonde data assuming that wet bulb potential temperature was
conserved. Horizontal and vertical air velocities were also derived from
the Doppler radar measurements.
Previous knowledge of polar lows is meagre; they are generally thought
to be shallow features resulting from enhanced convection within cold air
flowing over a warm sea. However, the well-developed polar low
which is the main subject of this paper is shown to have been an essentially
baroclinic disturbance. Although enhanced small-scale convection occurred in
one sector, the main area of widespread precipitation associated with the
polar low was produced not be smallscale convective overturning but rather
by slantwise convection within a narrow tongue of air ascending steadily
at about 10cm sec-1.
The speed of travel and short wavelength (9ookm) of the polar low in
this study are consistent with its having formed in a region of enhanced
baroclinicity within the polar air below 850mbar rather than in the major
baroclinic zone bounding the polar air mass. Considerable low-level
baroclinicity within the polar air is also shown to have been present during
the formation of other intense polar lows."

pe

On Wed, 6 Jan 2010 23:58:34 -0000, Philip Eden wrote in


"Mike Tullett" wrote :

I agree about the low, Jon. Warmer air was sucked in to it when it was
near Iceland. I recall, many years ago, there was a debate on just
important baroclinic factors were in the development of polar lows. But
it's a long time since I read the literature on the subject.

I think I remember the same literature, Mike. There were a lot
of mesoscale features in the 1960s which were lumped together
under the generic title "polar low", and they spawned a lot of
papers in the meteorological journals. Browning and Harrold
in QJ rings in about 1967 rings a bell (when I could actually
understand most [well, some] of the papers in QJ!)

Some of these features could be traced to lee vortices
south of Iceland (in a N-ly), some to vortex-shedding
from the Norwegian lee trough (in a NE-ly), and some
to shallow quasi-baroclinic disturbances developing in Denmark
Strait marking the boundary between Greenland air and
peripheral Atlantic air (which these days would be recognised
by contrasting theta-w characteristics). My memory is that
pseudo-frontal boundaries were often evident at the 700 mbar
level, but rarely at 500mbar, and that the pseudo-cold front
was almost invariably much more clearly defined than the
pseudo-warm front.

Thanks so much Philip for refreshing my memory. It was indeed in the last
60s and into the 70s I recall reading this stuff. I guess you have an
advantage being younger than me with more grey cells working properly
still:-)
PS agreed about QJRMS - it was possible in those days to understand the
occasional paper.

--
Mike Tullett - Coleraine 55.13°N 6.69°W posted 07/01/2010 12:34:39 GMT

On Thu, 7 Jan 2010 12:23:54 -0000, Philip Eden wrote in


Found it .... "The Polar Low as a Baroclinic Disturbance",
TW Harrold and KA Browning, QJRMetS, 95, 1969, pp710-723.

The intro reads:
"This paper describes the 3-dimensional airflow and precipitation within
small 'polar' depressions which sometimes cross Britain during N-ly
outbreaks and which in winter can be responsible for heavy snowfalls.
The data used in the study consist of Doppler and conventional radar
information, together with routine synoptic data and sequential radiosonde
ascents from the radar station. 3-dimensional airflow was derived from
the radisonde data assuming that wet bulb potential temperature was
conserved. Horizontal and vertical air velocities were also derived from
the Doppler radar measurements.
Previous knowledge of polar lows is meagre; they are generally thought
to be shallow features resulting from enhanced convection within cold air
flowing over a warm sea. However, the well-developed polar low
which is the main subject of this paper is shown to have been an essentially
baroclinic disturbance. Although enhanced small-scale convection occurred in
one sector, the main area of widespread precipitation associated with the
polar low was produced not be smallscale convective overturning but rather
by slantwise convection within a narrow tongue of air ascending steadily
at about 10cm sec-1.
The speed of travel and short wavelength (9ookm) of the polar low in
this study are consistent with its having formed in a region of enhanced
baroclinicity within the polar air below 850mbar rather than in the major
baroclinic zone bounding the polar air mass. Considerable low-level
baroclinicity within the polar air is also shown to have been present during
the formation of other intense polar lows."

Many thanks again for that. That is certainly one of the papers I had
tucked away in my head.

--
Mike Tullett - Coleraine 55.13°N 6.69°W posted 07/01/2010 15:00:31 GMT