This is a little bedtime reading for Dawlish (Paul Garvey).

Author(s): Riemer M (Riemer, Michael)1,2, Jones SC (Jones, Sarah C.)1,2,
Davis CA (Davis, Christopher A.)3
Source: QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY Volume: 134
Issue: 630 Pages: 69-91 Part: Part A Published: JAN 2008

Abstract: The interaction of a tropical cyclone undergoing extratropical
transition (ET) with the midlatitude synoptic-scale flow is investigated
using full-physics numerical experiments with idealized initial conditions.
The emphasis is on the impact on the midlatitude flow downstream of the ET
event. The midlatitude flow is represented by a balanced straight jet
stream. As the tropical cyclone approaches the jet, a ridge-trough couplet
and a distinct jet streak form in the upper-level flow. A midlatitude
cyclone develops rapidly downstream of the ET system and the further
evolution is characterized by downstream baroclinic development.

Based on Hovmoller diagrams, the upper-level development is interpreted as
the excitation and subsequent dispersion of a Rossby wave train on the
potential vorticity gradient associated with the jet. The characteristics of
this wave train are sensitive to the structure of the jet and to moist
processes in the midlatitudes. The tropical cyclone undergoing ET acts as a
sustained forcing for the wave train and the structure of the ET system
impacts the development most significantly one to two wavelengths downstream
of ET.

Piecewise inversion of potential vorticity, complemented by the partitioning
of the flow into its rotational and divergent parts, is applied to assess
the impact of the ET system quantitatively. Both the cyclonic circulation
and the outflow of the tropical cyclone are important contributors to the
formation and amplification of the ridge-trough couplet. The outflow anomaly
reduces the eastward motion of the ridge-trough couplet significantly and
thus promotes phase-locking between the tropical cyclone and the upper-level
pattern. Copyright (c) 2008 Royal Meteorological Society.
====

Note the words "sustained forcing".

As I kept on saying ertel potential vorticity is important!

Will
--

On 6 Sep, 21:52, "Will Hand" wrote:

Note the words "sustained forcing".

As I kept on saying ertel potential vorticity is important!

Will
--

Title: "The impact of extratropical transition on the downstream flow:
An idealized modelling study with a straight jet"

But it's only an idealised experiment, Will - not real outcomes.
Outcomes, Will, outcomes... :-)

I've often wanted to re-run a simulation of the October storm without
the mass of tropical air to its south just to see what impact the
lower latent heat release would have had on its development.

Mid-September to late October always interests me with its potential
for rapid deepeners spiced up with air of tropical origin. Bonnie,
Lili, Charlie...etc. - given the rain in Dublin in the last 24-hours
(and that's with the Wicklow mountains rain-shadow, too) I'm sure that
the tropics have something to do with it.

Richard

Thanks for finding the time to dig out that reference for me Will. Much
appreciated.

Paul
--

"Will Hand" wrote in message
...
This is a little bedtime reading for Dawlish (Paul Garvey).

Author(s): Riemer M (Riemer, Michael)1,2, Jones SC (Jones, Sarah C.)1,2,
Davis CA (Davis, Christopher A.)3
Source: QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY Volume:
134 Issue: 630 Pages: 69-91 Part: Part A Published: JAN 2008

Abstract: The interaction of a tropical cyclone undergoing extratropical
transition (ET) with the midlatitude synoptic-scale flow is investigated
using full-physics numerical experiments with idealized initial
conditions. The emphasis is on the impact on the midlatitude flow
downstream of the ET event. The midlatitude flow is represented by a
balanced straight jet stream. As the tropical cyclone approaches the jet,
a ridge-trough couplet and a distinct jet streak form in the upper-level
flow. A midlatitude cyclone develops rapidly downstream of the ET system
and the further evolution is characterized by downstream baroclinic
development.

Based on Hovmoller diagrams, the upper-level development is interpreted as
the excitation and subsequent dispersion of a Rossby wave train on the
potential vorticity gradient associated with the jet. The characteristics
of this wave train are sensitive to the structure of the jet and to moist
processes in the midlatitudes. The tropical cyclone undergoing ET acts as
a sustained forcing for the wave train and the structure of the ET system
impacts the development most significantly one to two wavelengths
downstream of ET.

Piecewise inversion of potential vorticity, complemented by the
partitioning of the flow into its rotational and divergent parts, is
applied to assess the impact of the ET system quantitatively. Both the
cyclonic circulation and the outflow of the tropical cyclone are important
contributors to the formation and amplification of the ridge-trough
couplet. The outflow anomaly reduces the eastward motion of the
ridge-trough couplet significantly and thus promotes phase-locking between
the tropical cyclone and the upper-level pattern. Copyright (c) 2008 Royal
Meteorological Society.
====

Note the words "sustained forcing".

As I kept on saying ertel potential vorticity is important!

Will
--

"Richard Dixon" wrote in message
...
On 6 Sep, 21:52, "Will Hand" wrote:

Note the words "sustained forcing".

As I kept on saying ertel potential vorticity is important!

Will
--

Title: "The impact of extratropical transition on the downstream flow:
An idealized modelling study with a straight jet"

But it's only an idealised experiment, Will - not real outcomes.
Outcomes, Will, outcomes... :-)


Don't wind me up today Richard, I'm in a foul mood :-)

I've often wanted to re-run a simulation of the October storm without
the mass of tropical air to its south just to see what impact the
lower latent heat release would have had on its development.


According to theory, I think above paper relates to it, it would not have
deepened as much.
But yes it would be fascinating. Maybe one day!

Mid-September to late October always interests me with its potential
for rapid deepeners spiced up with air of tropical origin. Bonnie,
Lili, Charlie...etc. - given the rain in Dublin in the last 24-hours
(and that's with the Wicklow mountains rain-shadow, too) I'm sure that
the tropics have something to do with it.


Indeed.

Will
--

On 7 Sep, 17:26, "Will Hand" wrote:

But it's only an idealised experiment, Will - not real outcomes.
Outcomes, Will, outcomes... :-)

Don't wind me up today Richard, I'm in a foul mood :-)

Some nicked your raingauge?!

I've often wanted to re-run a simulation of the October storm without
the mass of tropical air to its south just to see what impact the
lower latent heat release would have had on its development.

According to theory, I think above paper relates to it, it would not have
deepened as much.
But yes it would be fascinating. Maybe one day!

I've already tried to resimulate - it's a sod with both the NCEP
reanalysis and ERA-Interim analysis kicking off the WRF. File under
"difficult".

Richard

On Sep 6, 9:52*pm, "Will Hand" wrote:
This is a little bedtime reading for Dawlish (Paul Garvey).

Author(s): Riemer M (Riemer, Michael)1,2, Jones SC (Jones, Sarah C.)1,2,
Davis CA (Davis, Christopher A.)3
Source: QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY * *Volume: 134
Issue: 630 * *Pages: 69-91 * *Part: Part A * *Published: JAN 2008

*Abstract: The interaction of a tropical cyclone undergoing extratropical
transition (ET) with the midlatitude synoptic-scale flow is investigated
using full-physics numerical experiments with idealized initial conditions.
The emphasis is on the impact on the midlatitude flow downstream of the ET
event. The midlatitude flow is represented by a balanced straight jet
stream. As the tropical cyclone approaches the jet, a ridge-trough couplet
and a distinct jet streak form in the upper-level flow. A midlatitude
cyclone develops rapidly downstream of the ET system and the further
evolution is characterized by downstream baroclinic development.

Based on Hovmoller diagrams, the upper-level development is interpreted as
the excitation and subsequent dispersion of a Rossby wave train on the
potential vorticity gradient associated with the jet. The characteristics of
this wave train are sensitive to the structure of the jet and to moist
processes in the midlatitudes. The tropical cyclone undergoing ET acts as a
sustained forcing for the wave train and the structure of the ET system
impacts the development most significantly one to two wavelengths downstream
of ET.

Piecewise inversion of potential vorticity, complemented by the partitioning
of the flow into its rotational and divergent parts, is applied to assess
the impact of the ET system quantitatively. Both the cyclonic circulation
and the outflow of the tropical cyclone are important contributors to the
formation and amplification of the ridge-trough couplet. The outflow anomaly
reduces the eastward motion of the ridge-trough couplet significantly and
thus promotes phase-locking between the tropical cyclone and the upper-level
pattern. Copyright (c) 2008 Royal Meteorological Society.
====

Note the words "sustained forcing".

As I kept on saying ertel potential vorticity is important!

Will
--

Yes, thanks Will. The modelling shows promise, but this paper a year
earlier is a little more relevant to prediction and it appears to pour
cold water on the forecastability of such ET events, saying this; "The
extratropical transition (ET) of tropical cyclones often has a
*negative* impact on the predictability of the atmospheric situation
both around the ET event and farther downstream."

There's no doubt about the increase in energy and humidity that these
extra tropical events bring to our latitudes and the theories you've
proposed are cogent, but how that can actually be used in forecasting
is a long way from being determined. Did Danielle influence out
weather to the extent that you'd forecasted? No. Do we know whether it
did? No. Outcomes Will! Where's the forecasting outcomes? (a la
Richard!) *))



http://journals.ametsoc.org/doi/abs/.../2008MWR2249.1

"Dawlish" wrote in message
...
On Sep 6, 9:52 pm, "Will Hand" wrote:
This is a little bedtime reading for Dawlish (Paul Garvey).

Author(s): Riemer M (Riemer, Michael)1,2, Jones SC (Jones, Sarah C.)1,2,
Davis CA (Davis, Christopher A.)3
Source: QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY Volume: 134
Issue: 630 Pages: 69-91 Part: Part A Published: JAN 2008

Abstract: The interaction of a tropical cyclone undergoing extratropical
transition (ET) with the midlatitude synoptic-scale flow is investigated
using full-physics numerical experiments with idealized initial
conditions.
The emphasis is on the impact on the midlatitude flow downstream of the ET
event. The midlatitude flow is represented by a balanced straight jet
stream. As the tropical cyclone approaches the jet, a ridge-trough couplet
and a distinct jet streak form in the upper-level flow. A midlatitude
cyclone develops rapidly downstream of the ET system and the further
evolution is characterized by downstream baroclinic development.

Based on Hovmoller diagrams, the upper-level development is interpreted as
the excitation and subsequent dispersion of a Rossby wave train on the
potential vorticity gradient associated with the jet. The characteristics
of
this wave train are sensitive to the structure of the jet and to moist
processes in the midlatitudes. The tropical cyclone undergoing ET acts as
a
sustained forcing for the wave train and the structure of the ET system
impacts the development most significantly one to two wavelengths
downstream
of ET.

Piecewise inversion of potential vorticity, complemented by the
partitioning
of the flow into its rotational and divergent parts, is applied to assess
the impact of the ET system quantitatively. Both the cyclonic circulation
and the outflow of the tropical cyclone are important contributors to the
formation and amplification of the ridge-trough couplet. The outflow
anomaly
reduces the eastward motion of the ridge-trough couplet significantly and
thus promotes phase-locking between the tropical cyclone and the
upper-level
pattern. Copyright (c) 2008 Royal Meteorological Society.
====

Note the words "sustained forcing".

As I kept on saying ertel potential vorticity is important!

Will
--

Yes, thanks Will. The modelling shows promise, but this paper a year
earlier is a little more relevant to prediction and it appears to pour
cold water on the forecastability of such ET events, saying this; "The
extratropical transition (ET) of tropical cyclones often has a
*negative* impact on the predictability of the atmospheric situation
both around the ET event and farther downstream."

There's no doubt about the increase in energy and humidity that these
extra tropical events bring to our latitudes and the theories you've
proposed are cogent, but how that can actually be used in forecasting
is a long way from being determined. Did Danielle influence out
weather to the extent that you'd forecasted? No. Do we know whether it
did? No. Outcomes Will! Where's the forecasting outcomes? (a la
Richard!) *))



http://journals.ametsoc.org/doi/abs/.../2008MWR2249.1
=================

Ah! Thanks Paul. I have actually read that paper in full last year.
That paper DOES NOT pour cold water over links between hurricanes and the
jet, what it does say is that the predictability in the ocean basins goes
down when ET depressions are around. Every forecaster knows that but this
paper is trying to quantify it better using the ECMWF ensemble system.
It is perfectly possible, as more recent theoretical modelling studies show,
for the ET to affect the jet but in subtlely different ways producing a
myriad of outcomes.
According to advanced theory, it is highly likely that Danielle influenced
our weather, predictability is another question.

Will
--

On 7 Sep, 21:32, Dawlish wrote:

There's no doubt about the increase in energy and humidity that these
extra tropical events bring to our latitudes and the theories you've
proposed are cogent, but how that can actually be used in forecasting
is a long way from being determined. Did Danielle influence out
weather to the extent that you'd forecasted? No. Do we know whether it
did? No. Outcomes Will! Where's the forecasting outcomes? (a la
Richard!) *))

Thank heavens you're not a PhD supervisor - all this interesting
research you'd pour cold water over it just because there's no blessed
"outcome". Sigh. I was lucky enough to do some research for my PhD
where I produced some interesting results - not conclusive - which in
the years following someone else linked to a potential process that
can aid our understanding of weather systems and what the possible
causes of damaging winds are in the likes of the 1987 storm. Not all
research is obsessed with outcomes like you are.

Richard

On Sep 7, 10:26*pm, Richard Dixon wrote:
On 7 Sep, 21:32, Dawlish wrote:

There's no doubt about the increase in energy and humidity that these
extra tropical events bring to our latitudes and the theories you've
proposed are cogent, but how that can actually be used in forecasting
is a long way from being determined. Did Danielle influence out
weather to the extent that you'd forecasted? No. Do we know whether it
did? No. Outcomes Will! Where's the forecasting outcomes? (a la
Richard!) *))

Thank heavens you're not a PhD supervisor - all this interesting
research you'd pour cold water over it just because there's no blessed
"outcome". Sigh. I was lucky enough to do some research for my PhD
where I produced some interesting results - not conclusive - which in
the years following someone else linked to a potential process that
can aid our understanding of weather systems and what the possible
causes of damaging winds are in the likes of the 1987 storm. Not all
research is obsessed with outcomes like you are.

Richard

In forecasting, it's always outcomes for me Richard. I've never said
research should be "obsessed with outcomes" that's a strawman and to
accuse me of not supporting research if the results are not tied to
outcomes is disingenouos and would be wrong. Science usually
progresses in very small steps and I'm glad your research helped
someone else. However, when anyone reasons for the probability of
particular weather occurring, which are presented as likely, but which
are actually not based in research and are not producing accurate
forecasting, it needs to be addressed.

It happens all the time in Internet UK winter forecasts where all
sorts of reasons whh it will get cold are trotted out every year,
hardly any of which have any basis in reality, but appear to the
readers to back the writer's (always cold) forecast with scientific
reasoning. most of it is BS. Some of it is interesting and well
presented BS and there are some people with real knowledge (Will and
the MetO would be a good examples) who are prepared to have a go and
use what research knowledge is available to the best extent. The
outcome success, or not is there to see. The MetO have abandoned
public seasonal forecasting because of the lack of accuracy and the
highly negative public perception of that. Such a shame in many ways,
but an exercise in how hubris can produce dreadful public relations.

I wish forecasting was better at 7-10 days and also seasonally, but
the outcomes show that is simply not the case, thus the reasoning must
be presented with a pinch of salt. I think it is highly possible that
Danielle has had an effect on our weather over this last week, but
there have been other factors as well. As yet, no-one can sort the
wood for thetrees on that one, or we'd have accurate forecasts at 7-10
days and we haven't - by anyone.