Meteorology in the Middle Ages
PART I
Thermally driven Coastal Flows
Modern texts on thermally driven coastal winds
Sea breeze
(met.no)
Land breeze
Wikipedia:
NB: Sloping land
A: Sea breeze, B: Land breeze
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.
Egils saga
Snorri Sturluson(?)
A.D. 1220 (?)
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
Family
relations
Ólafur, Haraldur, Eiríkur,
Hákon, Hálfdán, kings
of Norway
Magnus with naked legs,
king of Norway
Egill Skallagrímsson Þóra Magnúsdóttir
6 generations
Jón Loftsson
Snorri Sturluson
Egill Skallagrímsson
(10th Century)
A very good poet, mercenary in
England and Continental Europe,
greedy, strong and clever
Egil´s father and grandfather fled from
Norway to Iceland around 880 AD.
Egill claimed an inheritance in Norway
on behalf of his wife
Eirik bloodaxe, king of Norway
(10th century)
Greedy, strong, ill-tempered and
maybe not excessively clever
Prevents Egill from collecting the money
Egil´s 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
There are in fact two forces at stake
Katabatic flow
Pressure gradient force
L
H
Land breeze
Gravity force
Who is right, Snorri and Egill or the spirit of the
modern textbooks?
We simulate the thermally driven winds
Model: MM5, Dx=3km, starting from rest with clear skies
Ágústsson & Ólafsson, 2008
N-Iceland
Surface winds late summer night
Flat Iceland
Surface winds late summer night
Surface winds in December
”True” topography
Flat
Ágústsson & Ólafsson, 2008
A
mountainous
region in NIceland.
Strong flow
to the sea
How did Snorri know
that the land breeze
was katabatic flow?
SouthIceland
Lowlands:
No winds
from land
Snorri grew up here
Egil´s 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 aledrinking 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?
They thought that the
katabatic wind would
bring Egill far away –
to England or Iceland!
”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,…”
Egill returned and killed all the
king´s men, Egill raises a cursepole and sets the curse that
Eirikur blood-axe will lose his
kingdom.
He did very soon thereafter
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 landbreeze, but katabatic wind
Do not rely on people that are
ignorent in meteorology if you
want to keep your kingdom
Meteorology in the Middle Ages
PART II
A downslope windstorm
Laxdæla saga
Ólafur Þórðarson (?)
A.D. 1255 (?)
A ship sinks
The drowning of Þorsteinn Surtur –
Höskuldur buys Hrappsstaðir farm
Egill Skallagrímsson
Mýrkjartan, king
of Ireland
Ingibjörg, sister of Ólafur
Tryggvason, king of
Norway
Kings of Scotland
and the Hebrides
Gunnhildur, wife of
Eirik Bloðöx, king of
Norway
Hrútur
Höskuldur Dala-Kollsson
Ólafur Pá Höskuldsson
Ólafur Tryggvason,
king of Norway
Kjartan Ólafsson
Snorri Sturluson
Myrkjartan, king of Ireland
(around 970 AD)
Melkorka, doughter of Myrkjartan
Ólafur
Ólafur ”Pá” Höskuldsson
Melkorka
Myrkjartan, king of Ireland
Melkorka Mýrkjartansdóttir. (910)
Ólafur "pá"
Höskuldsson
Höskuldur Dala-Kollsson (910)
0930
Kristín Eyjólfsdóttir
1515
0960
Vilborg Gísladóttir
1555
Kjartan Ásgeirsson
1000
Erlendur Þorvarðsson
1585
Þorvaldur
Kjartansson
Þorvarður Erlendsson
1620 - 1690
1055
Einar Þorvarðarson
1650 - 1703
Þórður Þorvaldsson
1075 - 1143
Þorvarður Einarsson
1691 - 1769
Snorri Þórðarson
1125 - 1194
1762 - 1788
Þorvaldur Snorrason
1160 - 1228
Agatha
Þorvarðardóttir
Einar Þorvaldsson
1227 - 1286
Kristrún
Guðmundsdóttir
1787 - 1870
Ónefnd Einarsdóttir
1250
Gísli Guðmundsson
1817 - 1899
Eiríkur
Sveinbjarnarson
1277 - 1342
Kristrún Gísladóttir
1854 - 1942
Einar Eiríksson
1320 - 1382
Ólafur Einarsson
1888 - 1980
Björn "Jórsalafari"
Einarsson
Ólafur Einar Ólafsson
1928 - 1974
1350 - 1415
Kristín Björnsdóttir
1374 - 1468
Björn "ríki"
Þorleifsson
1408 - 1467
Þorleifur Björnsson
1430 - 1486
Helga Þorleifsdóttir
1470
Þorbjörg "digra"
Ólafsdóttir
Haraldur Ólafsson
1965
Eydís Lilja
Haraldsdóttir
1999 -
Eydís Lilja Haraldsdóttir (b.1999)
Melkorka Myrkjartansdóttir (~910)
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-chestRoost,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,
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
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
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
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:
Wind speed forecast, valid 6 June 2008 at 15 UTC dx=3km
Strong downslope flow
Mountain crest
www.belgingur.is
MS Edda sank in a downslope windstorm at the
South Coast of Breidafjörður in 1953
Meteorology in the Middle Ages
PART Ill
The early discoveries of the
Bergen Cyclone Model and
America
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 "seabewilderment." 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?
The King’s Mirror (Konungsskuggsjá)
Written around 1240
The King’s 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
Can we use the wisdom of the King´s 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)
Using the rules of the King’s 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
4
3
3
2
2
1
1
4
3
?
3
2
2
1
1
FLOW OVER MOUNTAINS
{ Nh/U } > { Nh/U } C
{ Nh/U } C = (mountain shape,∂/∂ z (U,N),...) ≈ 1.5
=> Blocked flows
FAST
Dense
Air
SLOW
H
BLOCKING
SLOW
L
WAKE
L
N = Brunt-Vaisala frequency (stability), U = Wind speed; h = Mountain height
Greenland in easterly flow
Surface winds almost
perpendicular to the isobars
Ólafsson & Ágústsson, Meteorol. Atm. Phys., 2009
The mountain wind forecasting diagram
Red=speed up Green=slow down
T
10
Ro=U/fL
1
0.1
0.1
1
Nh/U
Ólafsson, 2004
10
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).
4
3
3
2
2
1
1
FOG
Bjarni Herjólfsson
approx. 999 A.D.
The first European settlements in N-America were a direct result of
Bjarni Herjólfsson’s lack of knowledge of mountain meteorology
Bottom line:
They knew more
than we think they
did
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
Thank you
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."
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.
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/climate/53291/Localwinds#ref293131
The drowning of Þorsteinn Surtur –
Höskuldur buys Hrappsstaðir farm
Gunnhildur, wife of
Eirik Bloðöx, king of
Norway
Mýrkjartan, king
of Ireland
Ingibjörg, sister of Ólafur
Tryggvason, king of
Norway
Hrútur
Höskuldur Dala-Kollsson
Ólafur Pá Höskuldsson
Ólafur Tryggvason,
king of Norway
Kjartan Ólafsson
Snorri Sturluson
These men knew
about
katabatic winds,
sea breeze,
downslope
windstorms –
and the
Bergen School
Cyclone Model
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.
Sjøbris:
Sjøluft 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
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
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 SkeggÞórir; þar hafði Rögnvaldur verið á fóstri í barnæsku. Tók Þórir feginsamlega við
konungssyni; skorti þar og eigi drykk mikinn.
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."
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.