Meteorology in the Middle Ages PART I Thermally driven Coastal Flows

1
Meteorology in the Middle AgesPART IThermally
driven Coastal Flows
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Modern texts on thermally driven coastal winds
Sea breeze Land breeze
(met.no)
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Wikipedia
NB Sloping land
A Sea breeze, B Land breeze
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Land breeze (Wikipedia)
Land breezes At night, the land cools off quicker
than the ocean due to differences in their
specific heat values, which forces the dying of
the daytime sea breeze. If the land cools below
that of the adjacent sea surface temperature, the
pressure over the water will be lower than that
of the land, setting up a land breeze as long as
the environmental surface wind pattern is not
strong enough to oppose it. If there is
sufficient moisture and instability available,
the land breeze can cause showers or even
thunderstorms, over the water. Overnight
thunderstorm development offshore can be a good
predictor for the activity on land the following
day, as long as there are no expected changes to
the weather pattern over the following 12-24
hours. The land breeze will die once the land
warms up again the next morning.
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Egils saga Snorri Sturluson(?) A.D. 1220 (?)
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Snorri Sturluson A wealthy politician and an
outstanding scholar in Iceland. Assassinated at
his home in Iceland upon request from Håkon the
foul, king of Norway on the 23rd of September
1241
Ólafur, Haraldur, Eiríkur, Hákon, Hálfdán,
kings of Norway
Family relations
Magnus with naked legs, king of Norway Þóra
Magnúsdóttir Jón Loftsson
Egill Skallagrímsson
6 generations
Snorri Sturluson
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Egill Skallagrímsson (10th Century) A very good
poet, mercenary in England and Continental
Europe, greedy, strong and clever Egils father
and grandfather fled from Norway to Iceland
around 880 AD. Egill claimed an inheritance in
Norway on behalf of his wife
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Eirik bloodaxe, king of Norway (10th
century) Greedy, strong, ill-tempered and
maybe not excessively clever Prevents Egill
from collecting the money
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Egils saga (English transl. W. C. Green, 1893 )
The weather was calm, a fell-wind blew by night,
a sea breeze by day. One evening Egil sailed out
to sea, but the fishermen were then rowing in to
land, those, to wit, who had been set as spies on
Egil's movements. They had this to tell, that
Egil had put out and sailed to sea, and was gone.
This news they carried to Bergonund. And when he
knew these tidings, then he sent away all those
men that he had had before for protection.
Thereafter he rowed in to Alrekstead, and bade
Frodi to his house, for he had a great
ale-drinking there. Frodi went with him, taking
some men. They were feasted well there, and they
made merry, with no fear of danger. There too
was no lack of drink.
fell-wind fjallvindr katabatic wind
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There are in fact two forces at stake
Katabatic flow
Pressure gradient force
H
L
Gravity force
Land breeze
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Who is right, Snorri and Egill or the spirit of
the modern textbooks?
We simulate the thermally driven winds Model
MM5, Dx3km, starting from rest with clear skies
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Ágústsson Ólafsson, 2008
N-Iceland Surface winds late summer night
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Flat Iceland Surface winds late summer night
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Surface winds in December
True topography
Flat
Ágústsson Ólafsson, 2008
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A mountainous region in N-Iceland. Strong flow
to the sea
How did Snorri know that the land breeze was
katabatic flow?
South-Iceland Lowlands No winds from land
Snorri grew up here
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Egils saga (English transl. W. C. Green, 1893 )
The weather was calm, a fell-wind blew by night,
a sea breeze by day. One evening Egil sailed out
to sea, but the fishermen were then rowing in to
land, those, to wit, who had been set as spies on
Egil's movements. They had this to tell, that
Egil had put out and sailed to sea, and was gone.
This news they carried to Bergonund. And when he
knew these tidings, then he sent away all those
men that he had had before for protection.
Thereafter he rowed in to Alrekstead, and bade
Frodi to his house, for he had a great
ale-drinking there. Frodi went with him, taking
some men. They were feasted well there, and they
made merry, with no fear of danger. There too
was no lack of drink.
Where is the katabatic flow going to bring Egill?
17
They thought that the katabatic wind would bring
Egill far away to England or Iceland!
18
Egil sailed out to sea for the night, as was
written above. And when morning came the wind
fell and there was a calm. They then lay
drifting, letting the ship ride free for some
nights. But when a sea-breeze came on, Egil said
to his shipmen, We will now sail to land,
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Egill returned and killed all the kings men,
Egill raises a curse-pole and sets the curse that
Eirikur blood-axe will lose his kingdom. He did
very soon thereafter
20
First conclusions These men knew about
thermally driven coastal winds, their knowledge
was solid on nighttime flows, more solid than
some modern textbooks The alleged land-breeze in
Iceland (and most likely Norway too) is not
land-breeze, but katabatic wind Do not rely on
people that are ignorent in meteorology if you
want to keep your kingdom
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Meteorology in the Middle AgesPART IIA
downslope windstorm
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Laxdæla saga Ólafur Þórðarson (?) A.D. 1255 (?)
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A ship sinks
24
The drowning of Þorsteinn Surtur Höskuldur
buys Hrappsstaðir farm
Kings of Scotland and the Hebrides
Egill Skallagrímsson
Gunnhildur, wife of Eirik Bloðöx, king of Norway
Mýrkjartan, king of Ireland
Hrútur
Höskuldur Dala-Kollsson
Ólafur Tryggvason, king of Norway
Ingibjörg, sister of Ólafur Tryggvason, king of
Norway
Ólafur Pá Höskuldsson
Kjartan Ólafsson
Snorri Sturluson
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Myrkjartan, king of Ireland (around 970
AD) Melkorka, doughter of Myrkjartan Ólafur
Pá Höskuldsson
Ólafur
Melkorka
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Myrkjartan, king of Ireland Melkorka Mýrkjartansdóttir. (910)    Höskuldur Dala-Kollsson (910)   
        
Ólafur "pá" Höskuldsson 0930
Þorbjörg "digra" Ólafsdóttir 0960
Kjartan Ásgeirsson 1000
Þorvaldur Kjartansson 1055
Þórður Þorvaldsson 1075 - 1143
Snorri Þórðarson 1125 - 1194
Þorvaldur Snorrason 1160 - 1228
Einar Þorvaldsson 1227 - 1286
Ónefnd Einarsdóttir 1250
Eiríkur Sveinbjarnarson 1277 - 1342
Einar Eiríksson 1320 - 1382
Björn "Jórsalafari" Einarsson 1350 - 1415
Kristín Björnsdóttir 1374 - 1468
Björn "ríki" Þorleifsson 1408 - 1467
Þorleifur Björnsson 1430 - 1486
Helga Þorleifsdóttir 1470













Kristín Eyjólfsdóttir 1515
Vilborg Gísladóttir 1555
Erlendur Þorvarðsson 1585
Þorvarður Erlendsson 1620 - 1690
Einar Þorvarðarson 1650 - 1703
Þorvarður Einarsson 1691 - 1769
Agatha Þorvarðardóttir 1762 - 1788
Kristrún Guðmundsdóttir 1787 - 1870
Gísli Guðmundsson 1817 - 1899
Kristrún Gísladóttir 1854 - 1942
Ólafur Einarsson 1888 - 1980
Ólafur Einar Ólafsson 1928 - 1974
Haraldur Ólafsson Eydís Lilja Haraldsdóttir 1965 1999 -
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Eydís Lilja Haraldsdóttir (b.1999)
Melkorka Myrkjartansdóttir (910)
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Thorstein's daughter, and Hild, her daughter, who
was three years old, went with them too.
Thorstein fell in with a high south-westerly
gale, and they sailed up towards the roosts, and
into that roost which is called
Coal-chest-Roost,which is the biggest of the
currents in Broadfirth. They made little way
sailing, chiefly because the tide was ebbing, and
the wind was not favourable, the weather being
squally, with high wind when the squalls broke
over, but with little wind between whiles. 1880,
English transl. Muriel A. C. Press,
29

• the ebbing of the sea, but the breeze was not
  friendly to them for the weather was showery and
  the wind was strong when it grew clear, but blew
  little between-whiles.
• 1903, English v.2 transl. Robert Proctor

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Two versions/possibilities

• Convective precipitation associated with a
  temporary increase in wind speed
• Strong winds during a clearing A downslope
  windstorm associated with a (weak) front in
  stably stratified southerly flow

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Laxdæla Ch.18
Icelandic (Old Norse) Þorsteinn tók útsynning
hvassan. Sigla þeir inn að straumum í þann straum
er hét Kolkistustraumur. Sá er í mesta lagi
þeirra strauma er á Breiðafirði eru. Þeim tekst
siglingin ógreitt. Heldur það mest til þess að þá
var komið útfall sjávar en byrinn ekki vinveittur
því að skúraveður var á og var hvasst veðrið þá
er rauf en vindlítið þess í milli. Þórarinn
stýrði og hafði aktaumana um herðar sér því að
þröngt var á skipinu. New-Norwegian
(Nynorsk) Osk Torsteinsdotter og Hild
Helgesdotter, som var berre 3 vintrar gamall. Dei
fekk ein kvass sudvest og siglde etter straumom
inn i Kolkistestraumen, ein av dei sterkaste
straumom i Breidafjorden. Der vart det ugreidt
med siglingi deira, av di at sjøen fall og vinden
ikkje var god for det var skurver, kvast naar
det reiv i, men mest stilt dessimillom. Torarin
styrde og hadde brasen um akslerne sine, av di
det var trongt paa skipe
32
Two possibilities

• Convective precipitation associated with a
  temporary increase in wind speed
• Strong winds during a clearing A downslope
  windstorm associated with a (weak) front in
  stably stratified southerly flow

And the MM5 is restarted
33
Wind speed forecast, valid 6 June 2008 at 15 UTC
dx3km
Strong downslope flow
Mountain crest
www.belgingur.is
34
MS Edda sank in a downslope windstorm at the
South Coast of Breidafjörður in 1953
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Meteorology in the Middle AgesPART IllThe
early discoveries of the Bergen Cyclone Model and
America
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From Laxdæla. Ólafur Pá is on his way to his
grandfather, the king of Ireland
Then the king and Gunnhild bade Olaf farewell.
Then Olaf and his men got on board, and sailed
out to sea. They came in for unfavourable weather
through the summer, had fogs plentiful, and
little wind, and what there was was unfavourable
and wide about the main they drifted, and on most
on board fell "sea- bewilderment." But at last
the fog lifted over head and the wind rose, and
they put up sail. Then they began to discuss in
which direction Ireland was to be sought and
they did not agree on that. Orn said one thing,
and most of the men went against him, and said
that Orn was all bewildered they should rule who
were the greater in number. Then Olaf was asked
to decide. He said, "I think we should follow the
counsel of the wisest for the counsels of
foolish men I think will be of all the worse
service for us in the greater number they gather
together."
Where did Örn get his knowledge from? What was
there to do when you were lost at sea? Is
democracy useless?
37
The Kings Mirror (Konungsskuggsjá)
Written around 1240
The Kings mirror has a chapter on
meteorology Rain is associated with
southeasterly winds Fog is associated with
southerly winds Rainshowers are associated
with southwesterly winds
This is the Bergen Cyclone Model!
See Páll Bergþórsson The Wineland Millenium, 2000
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Can we use the wisdom of the Kings Mirror to
navigate? The navigators could - tell the time
of the day - estimate the latitude (if not
overcast) (- determine the wind direction from
the clouds)
39
Using the rules of the Kings Mirror, it becomes
apparently quite easy to navigate across the ocean
Experiment 4 ships depart from Norway towards
Iceland on 4 different days in June - they all
arrive safely in less than 5 days
40
2
3
4
2
1
3
1
?
41
FLOW OVER MOUNTAINS
Nh/U gt Nh/U C
Nh/U C (mountain shape,?/? z (U,N),...)
1.5
gt Blocked flows
FAST
WAKE
SLOW
Dense Air
SLOW
L
H
L
BLOCKING
N Brunt-Vaisala frequency (stability), U
Wind speed h Mountain height
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Greenland in easterly flow
Surface winds almost perpendicular to the isobars
Ólafsson Ágústsson, Meteorol. Atm. Phys., 2009
43
Ólafsson, 2004
44
Bjarni Herjólfsson set off for Greenland. His
ship sailed into fog and barrier winds blowing
from the NE to the southeast of Greenland.
Bjarni turned too far to the south, missed
Greenland and ended up in Wineland (America).
The first European settlements in N-America were
a direct result of Bjarni Herjólfssons lack of
knowledge of mountain meteorology
45
Bottom lineThey knew more than we think they
did
46
Laxdæla The king answered, "This is clearly
seen in this Olaf, that he is a highborn man,
whether he be a kinsman of mine or not, as well
as this, that of all men he speaks the best of
Irish. Bottom line II Wise and highborn men
speak Irish
47
Thank you
48
Then they rode so near to the ship, that each
could hear what the other said. The king asked
who was the master of the ship. Olaf told his
name, and asked who was the valiant-looking
knight with whom he then was talking. He
answered, "I am called Myrkjartan." Olaf asked,
"Are you then a king of the Irish?" He said he
was.
The king answered, "This is clearly seen in this
Olaf, that he is a highborn man, whether he be a
kinsman of mine or not, as well as this, that of
all men he speaks the best of Irish."
49
Egils saga (1893, English transl. W. C. Green )
The weather was calm, a fell-wind blew by night,
a sea breeze by day. One evening Egil sailed out
to sea, but the fishermen were then rowing in to
land, those, to wit, who had been set as spies on
Egil's movements. They had this to tell, that
Egil had put out and sailed to sea, and was gone.
This news they carried to Bergonund. And when he
knew these tidings, then he sent away all those
men that he had had before for protection.
Thereafter he rowed in to Alrekstead, and bade
Frodi to his house, for he had a great
ale-drinking there. Frodi went with him, taking
some men. They were feasted well there, and they
made merry, with no fear of danger. Rognvald, the
king's son, had a pinnace, rowed by six men on
either side, painted all above the sea line. He
had with him ten or twelve who constantly
followed him and when Frodi had left home, then
Rognvald took the pinnace and they rowed out to
Herdla twelve in number. A large farm of the
king's was there, whereof the manager was named
Skegg-Thorir. Rognvald in his childhood had been
fostered there. Thorir received the king's son
joyfully. There too was no lack of drink.
50
Sea and land breezes occur along the coastal
regions of oceans or large lakes in the absence
of a strong large-scale wind system during
periods of strong daytime heating or nighttime
cooling. Those who live within 10 to 20 km (6 to
12 miles) of the coastline often experience the
cooler 19- to 37-km-per-hour (12- to
23-mile-per-hour) winds of the sea breeze on a
sunny afternoon only to find it turn into a
sultry land breeze late at night. One of the
features of the sea and land breeze is a region
of low-level air convergence in the termination
region of the surface flow. Such convergence
often induces local upward motions and cloud
formations. Thus, in sea and land breeze regions,
it is not uncommon to see clouds lying off the
coast at night these clouds are then dissipated
by the daytime sea breeze, which forms new
clouds, perhaps with showers occurring over land
in the afternoon.
http//www.britannica.com/EBchecked/topic/121560/c
limate/53291/Local-windsref293131
51
(No Transcript)
52
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53
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54
The drowning of Þorsteinn Surtur Höskuldur
buys Hrappsstaðir farm
Gunnhildur, wife of Eirik Bloðöx, king of Norway
Mýrkjartan, king of Ireland
Hrútur
Höskuldur Dala-Kollsson
Ólafur Tryggvason, king of Norway
Ingibjörg, sister of Ólafur Tryggvason, king of
Norway
Ólafur Pá Höskuldsson
Kjartan Ólafsson
Snorri Sturluson
55
These men knew about katabatic winds, sea
breeze, downslope windstorms and the Bergen
School Cyclone Model
56
Solgangsbris (land- og sjøbris) På varme
sommerdager med mye sol blir landjorda varmet
opp. Det dannes lavtrykk over land. Lufta stiger
og brer seg mot sidene i høyere luftlag, mens
luft siger inn fra sjøen i lavere luftlag
(sjøbris). Om natta skjer det motsatte I klarvær
avkjøles landjorda mye og det dannes et svakt
høytrykk over land med tilhørende lavtrykk over
sjøen (landbris).  Monsun er et annet fenomen med
samme årsak som solgangsbris. Men monsunen
skifter retning bare 2 ganger i året. Mer om
monsun. SjøbrisSjøluft blir dratt inn mot
lavtrykket, dvs. inn mot land. Effekten kan
merkes fra tidlig formiddag, men er som regel
sterkest et stykke ut på ettermiddagen. Langs det
meste av Norskekysten kan vindstyrken komme opp i
ca frisk bris 8-10m/s. I tillegg kan det være
andre årsaker til at vindstyrken blir høyere
eller lavere. Sjøbrisen kan av og til merkes
flere mil inn over land, men med mindre styrke
enn på kysten. Vindretningen dreier etter hvert
som sola passerer over horisonten, derav navnet
solgangsbris. Først blåser det rett på kysten,
senere parallelt med kysten. Retningen bestemmes
i hovedsak av trykk-kraften (lavtrykksplasseringen
) og Coriolis-kraften, og varierer langs kysten.
Lurer du på hvilken retning det er i ditt
nærområde? Se oppgaven nederst på
siden.    "Havgula" er et annet navn på sjøbris
som særlig er brukt på Vestlandet. Landbris Om
natta ligger lavtrykket over sjøen og lufta siver
ut fra land. Landbrisen er som regel svak, men
det kan blåse friskt enkelte steder. Et stykke
fra land kan man også om natta merke at
Coriolis-krafta dreier vinden mot høyre.
http//retro.met.no/met/met_lex/q_u/solgangsbris.
html
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Laxdæla Ch.18
Þorsteinn tók útsynning hvassan. Sigla þeir inn
að straumum í þann straum er hét
Kolkistustraumur. Sá er í mesta lagi þeirra
strauma er á Breiðafirði eru. Þeim tekst
siglingin ógreitt. Heldur það mest til þess að þá
var komið útfall sjávar en byrinn ekki vinveittur
því að skúraveður var á og var hvasst veðrið þá
er rauf en vindlítið þess í milli. Þórarinn
stýrði og hafði aktaumana um herðar sér því að
þröngt var á skipinu. Osk Torsteinsdotter og
Hild Helgesdotter, som var berre 3 vintrar
gamall. Dei fekk ein kvass sudvest og siglde
etter straumom inn i Kolkistestraumen, ein av dei
sterkaste straumom i Breidafjorden. Der vart det
ugreidt med siglingi deira, av di at sjøen fall
og vinden ikkje var god for det var skurver,
kvast naar det reiv i, men mest stilt
dessimillom. Torarin styrde og hadde brasen um
akslerne sine, av di det var trongt paa skipe
58
Egils saga Ch.59
Veður voru vindlítil, fjallvindur um nætur, en
hafgola um daga. Eitt kveld sigldu þeir Egill út
á haf, en fiskimenn reru þá inn til lands, þeir
er til njósnar höfðu settir verið um farar þeirra
Egils. Kunnu þeir það að segja, að Egill hafði út
látið og á haf siglt og hann var á brottu létu
þessa njósn koma til Berg-Önundar. Og er hann
vissi þessi tíðindi, hann sendi þá frá sér menn
þá er hann hafði áður haft þar til varúðar. Reri
hann þá inn til Álreksstaða og bauð Fróða til
sín, því að Berg-Önundur átti öl mikið heima að
sín Fróði fór með honum og hafði með sér nokkura
menn tóku þeir þar veislu góða og höfðu gleði
mikla var þar þá allt óttalaust. Rögnvaldur
konungsson átti karfa einn, reru sex menn á borð
hann var steindur allur fyrir ofan sjó hann
hafði með sér menn tíu eða tólf, þá er honum
fylgdu einart. Og er Fróði var heiman farinn, þá
tók Rögnvaldur karfann, og reru þeir út til
Herðlu tólf saman þar var konungsbú mikið, og
réð sá maður fyrir, er hét Skegg-Þórir þar hafði
Rögnvaldur verið á fóstri í barnæsku. Tók Þórir
feginsamlega við konungssyni skorti þar og eigi
drykk mikinn.
59
Then they rode so near to the ship, that each
could hear what the other said. The king asked
who was the master of the ship. Olaf told his
name, and asked who was the valiant-looking
knight with whom he then was talking. He
answered, "I am called Myrkjartan." Olaf asked,
"Are you then a king of the Irish?" He said he
was.
The king answered, "This is clearly seen in this
Olaf, that he is a highborn man, whether he be a
kinsman of mine or not, as well as this, that of
all men he speaks the best of Irish."
60
(No Transcript)
61
The king answered, "This is clearly seen in this
Olaf, that he is a highborn man, whether he be a
kinsman of mine or not, as well as this, that of
all men he speaks the best of Irish." He began
his speech thus "You all know that last autumn
there came hither a man who is the son of my
daughter, and highborn also on his father's side
and it seems to me that Olaf is a man of such
prowess and courage that here such men are not to
be found. Now I offer him my kingdom after my day
is done, for Olaf is much more suitable for a
ruler than my own sons. Olaf thanked him for
this offer with many graceful and fair words, and
said he would not run the risk as to how his sons
might behave when Myrkjartan was no more said it
was better to gain swift honour than lasting
shame and added that he wished to go to Norway
when ships could safely journey from land to
land, and that his mother would have little
delight in life if he did not return to her.