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181
w Tilfældet (Pl. XIX). Under (i()° Br. ved Wyville
Thomson-Ryggen er Maximum af Tryk og et Temperaturmaxinmm paa
over 5°. Ved Spidsen vestenfor Stad er kun 2°, i
Indbugtnin-gen udenfor Romsdalen med det høje Tryk er 5°, under 06°—
07° Br. er kun 3°, men udenfor Lofoten og Vesteraalen,
hvor Trykket i Indbugtningen er hojt, er mellem 5° og 4°.
I Indbugtningen Syd for Beeren Eiland, hvor Trykket har
et Minimum, er et Temperaturminimum af under 1°. Langs
Spidsbergbanken, hvor den horizontale Bevægelse maatte
foregaa tildels mod stigende Tryk, sker den i Virkeligheden
langs Isobarerne med Nedstigning over Banken og højere
Temperatur. Man sammenligne med Profilet PI. XXVI,
der viser disse Isothermernes op- og nedgaaende Bøjninger
ved 300 Favnes Dybde.
Wyville Thomson-Ryggens Dybde er omkring 300
Favne. Over denne Ryg strømmer det varme og salte
atlantiske Vand ind i Nordhavet, drevet af Tryk, der
repræsenteres, som vi have seet, ved Vindfladen, mod
Nordost indover Færø-Shetland Renden. Men denne er 600
Favne dyb. Det varme Vand drives hovedsagelig henimod
Rendens sydøstlige Bred. Dets Underflade slæber en Del
Vand med sig fra de dybere Lag. Dette erstattes derved,
at der i de underste Lag strømmer Vand ind langs
Rendens Bund fra Nordhavsbækkenet, og langs Rendens
nordvestre Bred — Færøbanken — imod det statiske Tryk.
Virkningen heraf se vi i Temperaturens Fordeling. Iskoldt
Vand dækker Rendens Bund helt op til 300 Favnes Dyb,
og iskoldt Vand løfter sig langs Færøbanken til et endnu
højere Niveau. (Profil VI, Pl. IX). Endvidere: Vandets
Bevægelse langs den sydøstre Bred mod aftagende Tryk
løfter det op, og Isothermen for —1" i dette Profil bøjer
sig op mod begge Sider, sænker sig ned i Midten. Hertil
kan ogsaa den Omstændighed bidrage, at Vandets
Bevægelse i de højere Lag foregaar med en større Hastighed
end i de dybere. Det hurtigere løbende Vand river det
langsommere med sig, og dette maa erstattes — tomme
Rum kunne ikke existere — fra neden. De her forklarede
Principer for denne Art Reactionsvirkning, der oprindelig
ere fremsatte af Professor Ekman i Stockholm, finde jevnlig
Anvendelse i den følgende Redegjørelse. En Bevægelse
mod mindre Tryk, altsaa under en Vinkel med Gradienten,
der er mindre end én ret, vil have tilfølge — under
uforandret Friction — en større Hastighed, og en raskere
Bevægelse opad. Den større horizontale Hastighed fremkalder
ogsaa en raskere Sugning af de dybere Lag opad.
Det Vand, som Polarstrømmen ikke sender ud gjennem
Danmarkstrædet, faar sit Afløb gjennem Jan
Mayen-Ren-den, langs Islandsbanken, Island-Færø-Ryggeu og
Færøbanken. I 300 Favnes Dyb kan dette Vand bevæge sig
temmelig nær paa normal cyclonisk Maade. Efter sin Op-
increase, a downward tendency, with an increase of
temperature. And such we see is actually the case (Pl. XIX).
In lat. 60° N, at the Wyville-Thomson Ridge, occurs a
maximum of pressure and a temperature-maximum of more than 5°.
At the salient point west of Stad, there is only 2°; in the
recess off Romsdalen, with the high pressure, the
temperature reaches 5°; in lat. 66° to 67° N, it is only 3°; but off
Lofoten and Vesteraalen, where the pressure in the
recess is considerable, it reaches between 5° and 4°.
In the recess south of Beeren Eiland, where the
pressure has a minimum, there is a temperature-minimum
of less than 1°. Along the Spitzbergen Bank, where the
horizontal motion should in part proceed against the
pressure, it really follows the isobars, with a descent across
the bank and a higher temperature. Compare with the
profile Pl. XXVI, that shows these upward and downward
bends of the isotherms in a depth of 300 fathoms.
The depth of the Wyville-Thomson Ridge reaches
about 300 fathoms. Over this ridge, flows into the North
Ocean the warm and salt water of the Atlantic, impelled
by pressure — which, as we have seen, is represented by
the wind-surface — towards the north-east, along the
Færoe-Shetland Channel. But this channel is 600 fathoms deep.
The warm water is carried chiefly towards the
southeasterly border of the channel. Its under surface carries
along with it water from the lower depths. This is
compensated by water pouring along the bottom of the
channel in the deepest strata from the basin of the North
Ocean, and also along the north-western border of the
channel — the Færoe Bank — against the static pressure.
The effect of this is seen in the distribution of temperature.
Ice-cold water covers the bottom ol the channel as high
up as 300 fathoms, and ice-cold water rises along the
Færoe Bank to a still higher level (Profile VI, Pl. IX).
Moreover, the motion along the south-eastern margin with
diminishing pressure raises the water, and the isotherm
for —1° in this profile rises towards either side and sinks
in the middle. Possibly this is brought about in part by
the motion of the water in the higher strata having a
greater velocity than in the deeper. The water running with
greater velocity carries along with it that flowing at a slower
rate, and this has to be compensated — a vacuum cannot
exist — from below. The principles, expounded here, on
which I base this kind of reaction (they were originally
set forth by Professor Ekman in Stockholm) meet with
frequent application in the following explanatory statement.
A motion with decreasing pressure, or at an angle with the
gradient less than a right angle, will be attended with the
result — friction unchanged — of greater velocity and a
more rapid upward motion. The greater horizontal velocity
will also occasion more rapid suction upwards of the
deeper strata.
The water which the Polar current does not
discharge by way of Denmark Strait, it sends through the
Jan-Mayen Channel, along the Iceland Bank, the Iceland-Færoe
Ridge, and the Færoe Bank. At a depth of 300 fathoms, this
water can move very nearly in a normal cyclonic manner.
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