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PENGANTAR OSEANOGRAFI IV
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Densitas dirumuskan:
Sangat penting akan mempengaruhi sirkulasitermohaline dan gerak vertikal perairan (verticalmixing)
Densitas tidak bisa diukur langsung ditentukan daridata suhu, salinitas dan tekanan
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Densitas bertambah jika
Salintas meningkat
Suhu menurun
Tekanan meningkat
Lapisan permukaan dan gradienkecil (1,020 – 1,030 gr/cm3)
Lapisan dalam. ex: 0 = 1,028
5000 = 1,151 gr/cm3
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Vertical profile
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Horizontal distribution
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Vertical) circulation driven by density Thermohaline Circulation
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Kalkulasi densitas Densitas air laut > 1000 kg/m3, tetapi tidak pernah >
1100 kg/m3 (perubahan bersifat puluhan kg/m3)
Untuk kemudahkan penulisan, densitas dinyatakandengan sigma ( )
Densitas (sigma) Insitu ( S,t,p)
S,t,p = ( S,t,p –1) x 103
Contoh : S,t,p = 1.027,54
S,t,p = (1.027,54 – 1) x 103
= 27,54
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sigma-nol ( o)
o = ( s,0,0 - 1) x 103
o Hanya didapat dari nilai salintas melalui
Sigma t ( t )
t = ( s,t,0 – 1) x 103
Hubungan t dan o adalah :
t = o –D
Dimana: D faktor koreksi (diberikan dalam Tables
of Seawater Density )
o = 0,069 + 1,4708 S –0,001570 S2 + 0,0000348 S3
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Untuk menghitung , Fofonof dan Tabata (1958) membuat persamaan
Dimana T adalah suhu
A0 = 67,26 A10 = 1,0 A20 = 0
A1 = 4,53168 A11 = - 4,7867 E-3 A21 = 1,8030 E-5
A2 = -0,5459 A12 = 9,8185 E-5 A22 = - 8,164 E-7
A3 = -1,9825E-3 A13 = -1,0843 E-6 A23 = 1,667 E-8
A4 = - 1,438E-7
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Ekman (1908) menghitung pengaruh tek (p)pada berbagai t dan s s,t,p, sehingga t dapat
dikoreksi s,t,p ( densitas insitu).
Bjerkness and Sandstron (1910) membuat tabel:
t,s,p sampai 10.000db.
Hesselberg and Svendrup menyederhanakan tabel
t,s,p lebih mudah dihitung dari t
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Water Masses
Oceanic Surface Current
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The Approximate boundaries of the main upper water masses in the ocean
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T-S Diagrams Karena adanya
perbedaan T-S pada setiap massamassa perairanidentifikasi massaair
t
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Depth (pressure), Salinity and Temperature Tekanan ditentukan dari pers hidrostatik
P = - gz
P = gr/cm3.cm/det2.cm = gr cm/det2.1/cm2
= dyne/cm2 = 1/105 dbar
1 dbar = 1/10 bar = 105 dyne/cm2
CONSOL
Berapa tekanan air pada kedalaman 1 m??
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P = - gz
= 1,035 gr/cm3
g = 980 cm/det2
z = -100 cm
P = - (1,035 gr/cm3 ) x 980 cm/det2 x (-100 cm)
= 101430 gr cm/cm2 det2
= 101430 dyne/cm2.
= 1,01430 dbar 1 dbar
1000 meter tekanan air 1000 dbar.
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Mixing Processes in The Ocean
Laminar Flow
Turbulent Flow
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Horizontal mixing >> vertical mixing
Density <
Density >
Density >
Density <
More stable more energy
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Water base on stability
Cool/Salty
Warm/Less Salty
Warm/Less Salty
Cool/Salty
Cool/Less Salty
Warm/Salty
Warm/Salty
Cool/Less Salty
Always Stable Always InstableInstable
Salt Finger
InstableDifusion Convection
E = 0 NeutralE < 0 InstableE > 0 Stable
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Salt Finger Process
Effect only a few cm
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Internal Wave
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Effect of internal wave
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Front
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Eddies
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