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III.
Havets Strønminger.
in.
Ocean Circulation.
I. Lufttrykket.
At Strømningerne i Havets Overflade for en meget
væsentlig Del fremkaldes ved Vinden, tor man efter de
senere Tiders Undersøgelser anse for tilstrækkelig godtgjort.
Ligeledes er det bevistat Vindens Virkning paa Havets
Overflade forplanter sig til Dybet, og at det or Resultanten
af de paa Overfladen virkende Vinde, der er bestemmende
for Havets gjennemsnitlige stadige Bevægelse.
For at studere denne Bevægelse i dens Forhold til de
virkende Kræfter er det saaledes nødvendigt at kjende den
gjennemsnitlige Retning og Hastighed af Vinden, dens
Resultant for Aaret, paa den Strækning af Havet, hvis
almindelige, gjennemsnitlige Bevægelse man vil" undersøge.
Paa de fleste Steder vexle de herskende Vinde i Aarets
Løb baade i Retning og StyHiO. Virkningen af en saadan
Vexling forplanter sig dog ikke langt ned under Overfladen,
og den aldeles overvejende Del af Havets Vandmasse faar
sin Bevægelse reguleret efter de periodisk vexlende
Kræfters Resultant for lange Tidsrum.
Idet vi gaa ud fra, at Havvandets regelmæssige,
stadige Bevægelse har opnaaet at blive constant med Hensyn
til Tiden, som en Virkning af Aarsagernes scculære
Arbejde, gjælder det at finde et Udtryk for Vindens midlere
Retning og Hastighed for det tilsvarende Tidsrum. 1.
Betragtning af den korte Tid, der er hengaaet, siden man først
begyndte at udføre og sande meteorologiske Iagttagelser,
maa den Fremstilling, jeg kan give af Viudens Retning og
Hastighed for det normale Aar.-blive foreløbig og. for
vigtige Egnes Vedkommende, hvorfra Iagttagelser ere yderst
sjeldne eller endog ganske mangle, endnu beheftet med stor
Usikkerhed. Imidlertid vil den, støttet som den er af den
Kundskab, Meteorologien har erhvervet om den Indflydelse,
Fordelingen af Land og Hav har paa de herskende Vinde,
kunne afgive et godt Udgangspunkt for videre Studium, og
1 Zöppritz. Wiedemann» Annalen der Physik und Chemie,
X. F. III, s. ns•_>.
I. Atmospheric Pressure.
That the currents of the surface of the sea are
occasioned very materially by wind, we may regard as a fact to
which researches of recent date have given full confirmation.
It has likewise been shown,1 that the effect of the wind on
the surface of the sea becomes propagated to the deep;
and moreover, that it is the resultant of the winds acting
on the surface which determines the average steady motion
of the sea.
Hence, for studying this motion in its relation to the
operative forces, it is manifestly imperative to know the
general direction and velocity of the wind, i. e. its annual
resultant throughout the tract of ocean where the general
average motion is sought to be determined.
In most localities, the prevailing winds are found to
vary in the course of the year, alike as to direction and force.
The effect of such variation, however, does not become
propagated far beneath the surface; and by far the greater
part of the water of the sea has its motion regulated by
the resultant of the periodically varying forces for long
spaces of time.
Now, starting from the fact of the regular and steady
motion of the sea having become constant in regard
to time, as an effect of the secular agency of its causes,
we must seek an expression for the wind’s mean
direction and velocity for the corresponding period.
Considering the short period that has elapsed since anv attempt
was first made to carry out and collect meteorological
observations, the representation I can give of the wind’s
direction and velocity for the normal year must needs be
preliminary, and in regard to important tracts, where
observations are exceedingly scarce, nay wanting altogether,
as vet be clogged with great uncertainty. Meanwhile, it.
cannot fail, supported as it is by the knowledge
meteorology has acquired of the influence which the distribution
of land and water exerts on the prevailing winds, to
’ Ziippritz. Wiedemann« Annalen der Physik und Chemie.
X. F. TII. p. :»fcJ.
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