This question is primarily for sci.geo.meteorology; I'm x-posting to
soc.history.ancient and .medieval because the answer is for their sake.

It's a common meme among us Late Antiquity fans that there was a vast global
chill in 535 CE, which threw at least Europe into the Dark Age. This was
popularised by David Keys in "Catastrophe" in 2000, and its claims are still
cited in scholarly journals; for instance Hirschfeld in "THE CRISIS OF THE
SIXTH CENTURY" (pdf:
http://www.rhodes.aegean.gr/maa_journal/Issues/Current%20Issue/Current_Issue_Papers/HIRSCHFELD_s06.pdf)
and several post-2000 articles cited therein (esp. McCormick). I'm concerned
with Europe right now, primarily Lombardy and Merovingian France, so I'll
restrict this post to that region.

Hirschfeld tells me that the Po River flooded in 540 CE. David Keys did not
employ particularly deep meteorological expertise in "Catastrophe"; from the
book, I got the impression that if it was anomalous then it could be blamed
on the global chill. To his credit, Keys did not list the Po flood among the
calamities stemming from the 535 CE sunless year.

What causes the floods, to my limited understanding, is humid air running
into the basin of the Po; specifically, into the southern Alps. Presumably
that air would come in from the southwest. So what we are looking for is a
large low-pressure system far off in the Atlantic to the northwest of the
Alps. (Cyclones of this sort, up here in the Northern Hemisphere, spin
anticlockwise around the "eye".)

The seemingly obvious culprit would be the famed North Atlantic Oscillation,
"NAO". Meteorologists measure, in winter, the relative barometric pressure
between the Azores (west of Europe) and Iceland (northwest). When the index
is "positive", it follows that there is lower pressure in Iceland than in
the Azores. When it is VERY positive then there is a cyclone in the north
Atlantic, pulling moist and warmer air off the Canary Islands and into
southern France. When this stuff hits the Alps, depending on how cold it was
there before it hits, it precipitates out and floods the Po. (Do I have this
right so far?)

The NAO index oscillates between positive and negative. Some say it does
this over a span of slightly less than 10 years. In general, over the last
32 years it has been positive 25 times and negative 7. Either way, the NAO
is not caused by, e.g., the sunspot cycle.

The next step would be to ascertain what creates cyclones in Iceland, of all
places. But since I am on the subject of the late 530s, which as mentioned
above Keys blames on a vast global cooling...

1. What happens when Iceland suffers an anomalous downturn in its
temperature? I seem to remember from high school that cold fluids, water
excepted, are less dense than hot ones. Could a deep chill in Iceland
suffice to lower its air pressure, to the extent of creating a low pressure
system / high NAO index?

2. Perhaps Krakatoa could erupt; perhaps Santorini or Vesuvius. Iceland has
enough volcanoes of its own. Any of these could increase "cloud" cover
locally; or, some other factor might boost actual clouds over Iceland.
However it happens: does cloud cover over Iceland affect its air pressure,
directly or through chilling it? What happens when the whole Northern
Hemisphere is clouded?

Thank you in advance

This question is primarily for sci.geo.meteorology; I'm x-posting to
soc.history.ancient and .medieval because the answer is for their sake.

It's a common meme among us Late Antiquity fans that there was a vast global
chill in 535 CE, which threw at least Europe into the Dark Age. This was
popularised by David Keys in "Catastrophe" in 2000, and its claims are still
cited in scholarly journals; for instance Hirschfeld in "THE CRISIS OF THE
SIXTH CENTURY" (pdf:
http://www.rhodes.aegean.gr/maa_journal/Issues/Current%20Issue/Current_Issue_Papers/HIRSCHFELD_s06.pdf)
and several post-2000 articles cited therein (esp. McCormick). I'm concerned
with Europe right now, primarily Lombardy and Merovingian France, so I'll
restrict this post to that region.

Hirschfeld tells me that the Po River flooded in 540 CE. David Keys did not
employ particularly deep meteorological expertise in "Catastrophe"; from the
book, I got the impression that if it was anomalous then it could be blamed
on the global chill. To his credit, Keys did not list the Po flood among the
calamities stemming from the 535 CE sunless year.

What causes the floods, to my limited understanding, is humid air running
into the basin of the Po; specifically, into the southern Alps. Presumably
that air would come in from the southwest. So what we are looking for is a
large low-pressure system far off in the Atlantic to the northwest of the
Alps. (Cyclones of this sort, up here in the Northern Hemisphere, spin
anticlockwise around the "eye".)

The seemingly obvious culprit would be the famed North Atlantic Oscillation,
"NAO". Meteorologists measure, in winter, the relative barometric pressure
between the Azores (west of Europe) and Iceland (northwest). When the index
is "positive", it follows that there is lower pressure in Iceland than in
the Azores. When it is VERY positive then there is a cyclone in the north
Atlantic, pulling moist and warmer air off the Canary Islands and into
southern France. When this stuff hits the Alps, depending on how cold it was
there before it hits, it precipitates out and floods the Po. (Do I have this
right so far?)

The NAO index oscillates between positive and negative. Some say it does
this over a span of slightly less than 10 years. In general, over the last
32 years it has been positive 25 times and negative 7. Either way, the NAO
is not caused by, e.g., the sunspot cycle.

The next step would be to ascertain what creates cyclones in Iceland, of all
places. But since I am on the subject of the late 530s, which as mentioned
above Keys blames on a vast global cooling...

1. What happens when Iceland suffers an anomalous downturn in its
temperature? I seem to remember from high school that cold fluids, water
excepted, are less dense than hot ones. Could a deep chill in Iceland
suffice to lower its air pressure, to the extent of creating a low pressure
system / high NAO index?

2. Perhaps Krakatoa could erupt; perhaps Santorini or Vesuvius. Iceland has
enough volcanoes of its own. Any of these could increase "cloud" cover
locally; or, some other factor might boost actual clouds over Iceland.
However it happens: does cloud cover over Iceland affect its air pressure,
directly or through chilling it? What happens when the whole Northern
Hemisphere is clouded?

I suggest you follow up some of the leads in http://tinyurl.com/2qqsux

There may be an altogether different explanaton.

Try a minus instead of a plus in your search to find the

In soc.history.medieval Zimri <zimriel@sbcspammlesforglobal.net

But if you want to investigate world-wide temperatures I'd
think that tree ring data is one way to go.

Paul J Gans wrote:
In soc.history.medieval Zimri <zimriel@sbcspammlesforglobal.net

But if you want to investigate world-wide temperatures I'd
think that tree ring data is one way to go.


You'll need world wide tree ring samples going back enough.

Good luck with the project.

It is needed for historical and archaeological reasons as well

Paul J Gans wrote:
In soc.history.medieval Zimri <zimriel@sbcspammlesforglobal.net

But if you want to investigate world-wide temperatures I'd
think that tree ring data is one way to go.

You'll need world wide tree ring samples going back enough.

Good luck with the project.

It is needed for historical and archaeological reasons as well

Eric Stevens wrote:
snip

I suggest you follow up some of the leads in http://tinyurl.com/2qqsux

There may be an altogether different explanaton.

Try a minus instead of a plus in your search to find the
probably real explanation, for example in
http://www.pnas.org/cgi/content/full/101/51/17837
"Note Added in Proof: Independent amplification of Y.
pestis-specific DNA from Justinian's plague has now been reported
(39). Y. pestis-specific DNA from Justinian's plague and the Black
Death has been shown to most closely resemble biovar Orientalis (40)."

Eric Stevens wrote:
snip

I suggest you follow up some of the leads in http://tinyurl.com/2qqsux

There may be an altogether different explanaton.

Try a minus instead of a plus in your search to find the probably real
explanation, for example in
http://www.pnas.org/cgi/content/full/101/51/17837
"Note Added in Proof: Independent amplification of Y. pestis-specific DNA
from Justinian's plague has now been reported (39). Y. pestis-specific DNA
from Justinian's plague and the Black Death has been shown to most closely
resemble biovar Orientalis (40)."

1. What happens when Iceland suffers an anomalous downturn in its
temperature? I seem to remember from high school that cold fluids, water
excepted, are less dense than hot ones. Could a deep chill in Iceland
suffice to lower its air pressure, to the extent of creating a low
pressure
system / high NAO index?

You've got it backwards. Cool air is *more* dense than warm air.

2. Perhaps Krakatoa could erupt; perhaps Santorini or Vesuvius. Iceland
has
enough volcanoes of its own. Any of these could increase "cloud" cover
locally; or, some other factor might boost actual clouds over Iceland.
However it happens: does cloud cover over Iceland affect its air pressure,
directly or through chilling it? What happens when the whole Northern
Hemisphere is clouded?

That depends. Clouds reflect sunlight back to outer space.
Thus widespread clouding over a period of time is cooling.

On the other hand, clouds also reflect heat from the earth
back to the earth, which means that at night clouds keep
the surface of the earth warmer.

But if you want to investigate world-wide temperatures I'd
think that tree ring data is one way to go.

"Erik Hammerstad" <egeha.is.all.you.need@start.no> wrote in message
news:51pg3kF1k75v7U1@mid.individual.net...
Eric Stevens wrote:
snip

I suggest you follow up some of the leads in http://tinyurl.com/2qqsux

There may be an altogether different explanaton.

Try a minus instead of a plus in your search to find the probably real
explanation, for example in
http://www.pnas.org/cgi/content/full/101/51/17837
"Note Added in Proof: Independent amplification of Y. pestis-specific DNA
from Justinian's plague has now been reported (39). Y. pestis-specific DNA
from Justinian's plague and the Black Death has been shown to most closely
resemble biovar Orientalis (40)."


That was pretty much what I was hoping to do; to fill in the gaps which Keys
leaped over. As I see it, there are a number of steps in order to get to his
conclusion (or Baillie's):

1. Provide evidence that Justinian's plague is Y pestis. This was based on
description before; now we know that the Orientalis strain of Y pestis was
extant in that time and place.

2. Provide evidence of harbour / ship rat migration in affected cities. This
step hasn't been done yet; Keys and Baillie assume this for their theses.

3. Where did the rats come from - Black Sea or Suez? The plague's most
direct route would appear to be the Black Sea, thus casting doubt upon a
minor lemma of Keys; but other routes are possible. e.g.: Through the Khyber
into the Indus, and thence to Alexandria etc; or following the Persian army,
into some Syrian port and thence to Alexandria; or through the Black Sea,
kept out of Constantinople but finding safe port in Alexandria.
4a. Provide evidence of climate change conducive to plague rat migration
(not necessarily harbour) in the homeland of the harbour rats.
4b. Provide other evidence of climate change in 535 CE. This has been shown
to be cooling.

5. Provide models (plural) of the effects of widespread cooling patches
535-546 CE. Chills have been found for numerous individual places; but Keys
and Baillie have not drawn the full climatological picture of 535 CE versus
the "control year" of, say, 525 CE.

This same work should be carried out in
Central Asia and in East Africa. Which models of localised or global cooling
are consistent with the rat migration?

6. Would cloud cover cause this cooling? Show what kind of cloud cover would
affect the weather ascertained in step #5, and how it would do it.
7. Provide evidence of this sort of cloud cover. Here we are stuck with what
people reported at the time; and they do report a "year without a sun" as it
were.
8. What caused the cloud cover?

Most historians have hit upon #4b. They've done an admirable job over the
Mediterranean; it's a little more questionable elsewhere. As a
non-plague-historian, #4b is where I start from.

Keys and Baillie agree on steps #1-4a. IMO, historians of the plague have a
lot more work to do on those steps. Further work on #1 should be focused on
finding out answers to those questions. But that's not relevant to my
original post.

Keys and Baillie are arguing over step #8. I admire their confidence in
steps #4b-7, but from #5 on I don't share it. This *is* relevant to my
original post.

I am working with other second-order effects of the cooling: a corollary of
step #5. What model would fit the weather experienced in year 540?
(Although, once the plague historians get as far as #4a, findings on
Lombardy floods will be a nice corrective or else vindication of whatever
they find.)

In soc.history.medieval Zimri <zimriel@sbcspammlesforglobal.net> wrote:
This question is primarily for sci.geo.meteorology; I'm x-posting to
soc.history.ancient and .medieval because the answer is for their sake.

It's a common meme among us Late Antiquity fans that there was a vast global
chill in 535 CE, which threw at least Europe into the Dark Age. This was
popularised by David Keys in "Catastrophe" in 2000, and its claims are still
cited in scholarly journals; for instance Hirschfeld in "THE CRISIS OF THE
SIXTH CENTURY" (pdf:
http://www.rhodes.aegean.gr/maa_journal/Issues/Current%20Issue/Current_Issue_Papers/HIRSCHFELD_s06.pdf)
and several post-2000 articles cited therein (esp. McCormick). I'm concerned
with Europe right now, primarily Lombardy and Merovingian France, so I'll
restrict this post to that region.

Hirschfeld tells me that the Po River flooded in 540 CE. David Keys did not
employ particularly deep meteorological expertise in "Catastrophe"; from the
book, I got the impression that if it was anomalous then it could be blamed
on the global chill. To his credit, Keys did not list the Po flood among the
calamities stemming from the 535 CE sunless year.

What causes the floods, to my limited understanding, is humid air running
into the basin of the Po; specifically, into the southern Alps. Presumably
that air would come in from the southwest. So what we are looking for is a
large low-pressure system far off in the Atlantic to the northwest of the
Alps. (Cyclones of this sort, up here in the Northern Hemisphere, spin
anticlockwise around the "eye".)

The seemingly obvious culprit would be the famed North Atlantic Oscillation,
"NAO". Meteorologists measure, in winter, the relative barometric pressure
between the Azores (west of Europe) and Iceland (northwest). When the index
is "positive", it follows that there is lower pressure in Iceland than in
the Azores. When it is VERY positive then there is a cyclone in the north
Atlantic, pulling moist and warmer air off the Canary Islands and into
southern France. When this stuff hits the Alps, depending on how cold it was
there before it hits, it precipitates out and floods the Po. (Do I have this
right so far?)

The NAO index oscillates between positive and negative. Some say it does
this over a span of slightly less than 10 years. In general, over the last
32 years it has been positive 25 times and negative 7. Either way, the NAO
is not caused by, e.g., the sunspot cycle.

The next step would be to ascertain what creates cyclones in Iceland, of all
places. But since I am on the subject of the late 530s, which as mentioned
above Keys blames on a vast global cooling...

1. What happens when Iceland suffers an anomalous downturn in its
temperature? I seem to remember from high school that cold fluids, water
excepted, are less dense than hot ones. Could a deep chill in Iceland
suffice to lower its air pressure, to the extent of creating a low pressure
system / high NAO index?

You've got it backwards. Cool air is *more* dense than warm air.

2. Perhaps Krakatoa could erupt; perhaps Santorini or Vesuvius. Iceland has
enough volcanoes of its own. Any of these could increase "cloud" cover
locally; or, some other factor might boost actual clouds over Iceland.
However it happens: does cloud cover over Iceland affect its air pressure,
directly or through chilling it? What happens when the whole Northern
Hemisphere is clouded?

That depends. Clouds reflect sunlight back to outer space.
Thus widespread clouding over a period of time is cooling.

On the other hand, clouds also reflect heat from the earth
back to the earth, which means that at night clouds keep
the surface of the earth warmer.

But if you want to investigate world-wide temperatures I'd
think that tree ring data is one way to go.

--
--- Paul J. Gans

This question is primarily for sci.geo.meteorology; I'm x-posting to
soc.history.ancient and .medieval because the answer is for their sake.

It's a common meme among us Late Antiquity fans that there was a vast
global chill in 535 CE, which threw at least Europe into the Dark Age.
This was popularised by David Keys in "Catastrophe" in 2000, and its
claims are still cited in scholarly journals; for instance Hirschfeld in
"THE CRISIS OF THE SIXTH CENTURY" (pdf:
http://www.rhodes.aegean.gr/maa_journal/Issues/Current%20Issue/Current_Issue_Papers/HIRSCHFELD_s06.pdf)
and several post-2000 articles cited therein (esp. McCormick). I'm
concerned with Europe right now, primarily Lombardy and Merovingian
France, so I'll restrict this post to that region.

Hirschfeld tells me that the Po River flooded in 540 CE. David Keys did
not employ particularly deep meteorological expertise in "Catastrophe";
from the book, I got the impression that if it was anomalous then it could
be blamed on the global chill. To his credit, Keys did not list the Po
flood among the calamities stemming from the 535 CE sunless year.

What causes the floods, to my limited understanding, is humid air running
into the basin of the Po; specifically, into the southern Alps. Presumably
that air would come in from the southwest. So what we are looking for is a
large low-pressure system far off in the Atlantic to the northwest of the
Alps. (Cyclones of this sort, up here in the Northern Hemisphere, spin
anticlockwise around the "eye".)

The seemingly obvious culprit would be the famed North Atlantic
Oscillation, "NAO". Meteorologists measure, in winter, the relative
barometric pressure between the Azores (west of Europe) and Iceland
(northwest). When the index is "positive", it follows that there is lower
pressure in Iceland than in the Azores. When it is VERY positive then
there is a cyclone in the north Atlantic, pulling moist and warmer air off
the Canary Islands and into southern France. When this stuff hits the
Alps, depending on how cold it was there before it hits, it precipitates
out and floods the Po. (Do I have this right so far?)

The NAO index oscillates between positive and negative. Some say it does
this over a span of slightly less than 10 years. In general, over the last
32 years it has been positive 25 times and negative 7. Either way, the NAO
is not caused by, e.g., the sunspot cycle.

The next step would be to ascertain what creates cyclones in Iceland, of
all places. But since I am on the subject of the late 530s, which as
mentioned above Keys blames on a vast global cooling...

1. What happens when Iceland suffers an anomalous downturn in its
temperature? I seem to remember from high school that cold fluids, water
excepted, are less dense than hot ones. Could a deep chill in Iceland
suffice to lower its air pressure, to the extent of creating a low
pressure system / high NAO index?

2. Perhaps Krakatoa could erupt; perhaps Santorini or Vesuvius. Iceland
has enough volcanoes of its own. Any of these could increase "cloud" cover
locally; or, some other factor might boost actual clouds over Iceland.
However it happens: does cloud cover over Iceland affect its air pressure,
directly or through chilling it? What happens when the whole Northern
Hemisphere is clouded?

Thank you in advance
--
zimriel sbc dot
at global net
.
http://pages.sbcglobal.net/zimriel/
*new improved shorter .sig*

1. What happens when Iceland suffers an anomalous downturn in its
temperature? I seem to remember from high school that cold fluids, water
excepted, are less dense than hot ones. Could a deep chill in Iceland
suffice to lower its air pressure, to the extent of creating a low
pressure system / high NAO index?

Air is a gas

Cold air is denser that warm air. That gets you a high cool air high
pressure zone. A low is warm air or at least warmer than the high.

Water is fuild/liquid but nothing else acts exactly like it does.

Cooling warm water causes it to contract until near the freezing point at
which time it starts to expand. Salt concentration will change both the
density and freezing point so you need to do some serious reading.



2. Perhaps Krakatoa could erupt; perhaps Santorini or Vesuvius. Iceland
has enough volcanoes of its own. Any of these could increase "cloud" cover
locally; or, some other factor might boost actual clouds over Iceland.
However it happens: does cloud cover over Iceland affect its air pressure,
directly or through chilling it? What happens when the whole Northern
Hemisphere is clouded?

Depends but usually cloud cover cools the surface.

It's a common meme among us Late Antiquity fans that there was a vast
global chill in 535 CE, which threw at least Europe into the Dark Age.
This was popularised by David Keys in "Catastrophe" in 2000, and its
claims are still cited in scholarly journals; for instance Hirschfeld in
"THE CRISIS OF THE SIXTH CENTURY" (pdf:
http://www.rhodes.aegean.gr/maa_journal/Issues/Current%20Issue/Current_Issue_Papers/HIRSCHFELD_s06.pdf)
and several post-2000 articles cited therein (esp. McCormick). I'm
concerned with Europe right now, primarily Lombardy and Merovingian
France, so I'll restrict this post to that region.

Hirschfeld tells me that the Po River flooded in 540 CE.
....
1. What happens when Iceland suffers an anomalous downturn in its
temperature? I seem to remember from high school that cold fluids, water
excepted, are less dense than hot ones. Could a deep chill in Iceland
suffice to lower its air pressure, to the extent of creating a low
pressure system / high NAO index?

Air is a gas

Cold air is denser that warm air. That gets you a high cool air high
pressure zone. A low is warm air or at least warmer than the high.

Water is fuild/liquid but nothing else acts exactly like it does.

Cooling warm water causes it to contract until near the freezing point at
which time it starts to expand. Salt concentration will change both the
density and freezing point

so you need to do some serious reading.