Meteorology in the Middle Ages PART I Thermally driven Coastal Flows

1. Meteorology in the Middle AgesPART IThermally driven Coastal Flows

2. Modern texts on thermally driven coastal winds Sea breeze Land breeze (met.no)

3. Wikipedia: NB: Sloping land A: Sea breeze, B: Land breeze

4. 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.

5. Egils saga Snorri Sturluson(?) A.D. 1220 (?)

6. 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

7. 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

8. Eirik bloodaxe, king of Norway (10th century) Greedy, strong, ill-tempered and maybe not excessively clever Prevents Egill from collecting the money

9. 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

10. There are in fact two forces at stake Katabatic flow Pressure gradient force L H Gravity force Land breeze

11. 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

12. Ágústsson & Ólafsson, 2008 N-Iceland Surface winds late summer night

13. Flat Iceland Surface winds late summer night

14. Surface winds in December ”True” topography Flat Ágústsson & Ólafsson, 2008

15. 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

16. 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. 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,…”

19. Egill returned and killed all the king´s 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

21. Meteorology in the Middle AgesPART IIA downslope windstorm

22. Laxdæla saga Ólafur Þórðarson (?) A.D. 1255 (?)

23. 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

25. Myrkjartan, king of Ireland (around 970 AD) Melkorka, doughter of Myrkjartan Ólafur ”Pá” Höskuldsson Ólafur Melkorka

27. Eydís Lilja Haraldsdóttir (b.1999) Melkorka Myrkjartansdóttir (~910)

28. 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

30. 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

31. 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 dx=3km Strong downslope flow Mountain crest www.belgingur.is

34. MS Edda sank in a downslope windstorm at the South Coast of Breidafjörður in 1953

35. Meteorology in the Middle AgesPART IllThe early discoveries of the Bergen Cyclone Model and America

36. 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 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

38. 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)

39. 2 3 4 2 1 3 1 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

40. 2 3 4 2 1 3 1 ?

41. FLOW OVER MOUNTAINS { Nh/U } > { Nh/U } C { Nh/U } C = (mountain shape,∂/∂ z (U,N),...) ≈ 1.5 => Blocked flows FAST Dense Air SLOW WAKE SLOW L H L BLOCKING N = Brunt-Vaisala frequency (stability), U = Wind speed; h = Mountain height

42. Greenland in easterly flow Surface winds almost perpendicular to the isobars Ólafsson & Ágústsson, Meteorol. Atm. Phys., 2009

43. The mountain wind forecasting diagram Red=speed upGreen=slow down T 10 Ro=U/fL 1 0.1 0.1 1 10 Nh/U Ólafsson, 2004

44. 2 3 4 2 1 3 1 FOG Bjarni Herjólfsson approx. 999 A.D. 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 Herjólfsson’s lack of knowledge of mountain meteorology

45. Bottom line:They 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/climate/53291/Local-winds#ref293131