Bahan Kuliah Oseper

1. 1

2. IMPACT OF AIR-SEA INTERACTION
ON THE OCEAN AND ATMOSPHERE

3. Air mass source regions and their paths

4. ITCZ dan Front ITCZ merupakan singkatan dari Inter-Tropical Convergence
Zones merupakan tempat bertemunya dua masssa udara yang
memiliki sifat dan kekuatan yang sama.
 Lokasi yang identik dengan terjadinya konvergensi (naiknya
massa udara) lalu tekanan udara menjadi rendah dikenal dengan
istilah siklon, pada akhirnya menjadi wilayah tempat semua
angin akan bergerak.
 Dampak yang terjadi adalah wilayah ITCZ menjadi wilayah yang
bercuaca buruk akan terbentuk awan besar yang berkembang
vertikal (Cumulonimbos, Cb).
 Sehingga terjadi hujan badai besar dengan angin dan petir.

5. ITCZ
Posisi ITCZ bulan Januari dan Juli

7. FRONT
 Front didefinisikan sebagai wilayah transisi tempat
bertemunya dua massa udara yang berbeda sifat fisik
dan kekuatannya.
 Lokasi kejadian lintang tinggi sekitar 66.5o lintang
utara atau selatan.
 Awal pembentukan, perkembangan hingga penguatan
front dikenal dengan istilah FRONTOGENESIS

8. What is an atmospheric front?
 A front is a transition zone between two air masses of different
densities.
 The density contrast results from:
 Difference in temperature;
 Difference in humidity.
 The frontal zone (surface) is the
upward extension of the front.
 Sometimes the frontal zones can be very sharp.
 The intensity of the weather along the front depends on the contrast of
the air mass properties.
 The type of front depends on both the direction in which the air mass is
moving and the characteristics of the air mass.

9. FRONT
Pada kondisi normal (a) dan tingkat pembentukan front (b)

10. FRONT
 Sedangkan fase akhir pelenyapan atau penghancuran
front dikenal sebagai FRONTOLISIS.
 Front sama halnya dengan ITCZ merupakan siklon
(pusat tekanan rendah) sehingga cuaca buruk.
 Gambar sebaran suhu ke arah tegak di dalam daerah
front dapat dilihat pada Gambar merupakan
indikator front adanya perbedaan suhu yang
tajam sepanjang front.

11. FRONT
Distribusi suhu pada penampang melintang front

12. JENIS-JENIS FRONTBerdasarkan hasil akhir dari pertempuran dua massa udara, mana
yang menjadi dominan akan dijadikan nama dari front tersebut:
(1). Front dingin: massa udara dingin menggilas massa udara
panas
(2). Front panas: massa udara panas mendesak massa udara
dingin
(3). Front campuran: front dingin dan front panas bertemu
sehingga front dingin akan lebih cepat mengambil alih lokasi
front panas.
(4). Front quasi stasioner: apabila dua massa udara baik dingin
mapun panas masing-masing tidak cukup kuat untuk saling
mendesak, sehingga tidak jelas mana yang mendominasi.
(5). Siklon frontal: adalah siklon ekstratropis yang mengandung
sistem frontal.

16. Cold Fronts
 Associated with low pressure centers (low pressure troughs): follow the
dashed line
 The pressure is minimum as the front passes (first decreases as the front
approaches and then increases behind the front)
 Steep leading edge: the vertical slope of a cold front surface is 1:50 - 1:100
(ratio of vertical rise to horizontal distance). For comparison: warm fronts
have ratios 1:200 – 1:300.
 The steeper the edge, the faster the front (the effect of surface friction).
 Cold fronts tend to move faster than all other types of fronts.
 Cold fronts tend to be associated with the most violent weather among all
types of fronts.
 Cold fronts tend to move the farthest while maintaining their intensity.
 Cirrus clouds well ahead of the front
 Strong thunderstorms with heavy showers and gusty winds along and ahead
of the front: squall lines
 Broad area of cumulus clouds immediately behind the front (although fast
moving fronts may be mostly clear behind the front).

20. Characteristics of a Warm Front
 The slope of a typical warm front is 1:200 (more gentle than cold
fronts) -> warm fronts tend to advance more slowly.
 Warm fronts are typically less violent than cold fronts.
 Overrunning: warmer, less-dense air rides up and over the colder,
more-dense surface air.
 Frontal inversion: temperature inversion at the front -> stable
atmosphere

21. Warm Fronts: cloud and precipitation patterns
 Although they can trigger thunderstorms, warm fronts
are more likely to be associated with large regions of
stratus clouds and light to moderate continuous rain.
 Warm fronts are usually preceded by cirrus first, then
altostratus or altocumulus, then stratus and possibly
fog.
 At the warm front, gradual transition.
 Behind the warm front, skies are relatively clear.

22. 1. The weather during a WARM FRONT starts with
cirrus clouds about 24-48 hours before the rain
begins
2. As more warm air is pushed upward, more moisture
condenses forming cirrostratus clouds
3. Warm front: rain or snow is steady over several
hours or days

24. Occluded fronts.
 Cold fronts move faster than warm fronts.
They can catch up and overtake their related
warm front. When they do, an occluded
front is formed.
 Cold occlusion: very cold air behind, not so
cold air ahead of, the warm front
 The upper warm front follows the surface
occluded front
Cold occlusion

25. Warm Occlusion
 Very cold air ahead of, not so cold air
behind, the warm front
 The cooler air from the cold front cannot
lift the very cold air ahead, rides
“piggyback”
 The warm front aloft precedes the surface
occluded front

27. Stationary Front
 Stationary front- a front which does not move or barely moves.
 Stationary fronts behave like warm fronts, but are more quiescent.
 Many times the winds on both sides of a stationary front are parallel to the
front and have opposite direction.
 Typically stationary fronts form when polar air masses are modified
significantly so as to lose their character (e.g., cold fronts which stall).
 Typically there is no strong precipitation associated with stationary fronts
(why? – no big contrast in the air mass properties, no air uplifting and
condensation).

29. Weakening/Strengthening of the Front
 Frontogenesis:
 The front intensifies.
 Why? – The temperature
(humidity) contrast across the
front is increasing.
 Example: cP air mass moves
over warm ocean water.
• Frontolysis:
♦ The front weakens and dissipates
♦ Why?-the air masses start losing
their identities.
♦ The temperature (humidity)
contrast across the front is
decreasing.
♦ Typical for slow moving fronts

30. Clouds and Fronts - Example

31. Perbedaan Siklon & Antisiklon
ANTI SIKLON SIKLON
Pusat tekanan udara tinggi semi
permanen, simbol HTerbentuk di suatu
wilayah yang sedang berlangsung musim
winter. Pola angin divergen (massa udara
turun). Cuaca cerah, sulit terbentuk awan
sehingga jarang hujan
Pusat tekanan udara rendah semi
permanen, simbol LTerbentuk di suatu
wilayah yang sedang berlangsung musim
summerPola angin konvergen (massa udara
naik)Cuaca berkabut, Terbentuk awan-
awan berpotensi sebagai hujan
Bila terjadi polusi udara akan
terperangkap di dekat permukaan contoh
kejadian di Kota London Desember
1952, sebanyak 5.000 penduduk tewas
karena polutan.
Akibat gaya coriolis badai tropis dengan
angin 60 km/jam, siklon trpois > 120
km/jam (Hurricane, Typhoon), dilaut
kecepatan angin > 250 km/jam. Contoh di
Banglades Nop 1970, sebanyak 20.000
penduduk tewas diterjang siklon tropis.
Pusat antisiklon tetap:
-23.5oLU/LS di darat pada wilayah
gurun dan di laut pada lintang kuda
-90oKU/KS dingin dan kering
Pusat siklon tetap:-di equator 0o: ITCZ
-di 66.5oLU/LS

32. 32
Katrina, 2005 Dean, 2007 Felix, 2007

33. In the back part of the cyclone
propagating over the GS front, cold
and dry Arctic air masses are
advected over the relatively warm
water (cold-air outbreak). In this case
the largest sea-air temperature
differences are observed exactly over
the SST front due to much smoother
spatial temperature gradients in the
atmosphere in comparison to the
ocean. South of the SST front
thermodynamic adjustment works to
decrease the air-sea temperature and
humidity differences. In the forward
part of cyclone the advection of the
moist and warm air to the north (warm
air outbreak) results in the local
decrease of surface fluxes, associated
with the advective fogs and strong
vertical motions in the lower 100-200
m layer of the atmosphere.
SST
Tair
cold
warm

34. SMMR

35.  Generating electric power from wind energy at sea
(floating wind farms)
 Avoid hazard conditions in shipping
 Ocean-atmosphere exchanges, in heat, water, and
greenhouse gases
Distribution of Wind Speed

36. Center of cyclonic currents

37. Center of cyclonic currents

38. Center of cyclonic currents

39. Center of cyclonic currents

40. Center of cyclonic currents

41. E-P
Flux Divergence

42. E-P
Subtropical
South Pacific
CC=0.856
CC=0.913

43. Equatorial
western Pacific
CC=0.81
CC=0.764

44. Global Water Balance - JASON

45. Global Water Balance-GRACE

46. Global Water Balance-GRACE

47. Water Balance over Global Ocean

48. Ocean’s Influence on Water Balance of South America
The approximate balance of dM/dt with ∫-R bolsters not
only the credibity of the spacebased measurements, but
supports the characterization of ocean’s influence on
continental water balance.
Liu et al., GRL 2006

50. Filtered ENW (color) and SST (contour)
Collocation of ENW magnitude with SST is inherent in
the definition of ENW and turbulent mixing theory.

51. Filtered precipitation (color) and SST (contour)
Precipitation is in quadrature with SST and in phase
with surface wind convergence.

53. Major currents, gyres, rings, and eddies
(basin scale)
 Winds and wind-driven basin circulation
 Meanders, rings, eddies and gyres
 The thermohaline circulation

54. Winds
Unevenly heating
by the sun
Spinning sphere
Winds and wind-driven basin circulation

55. Subtropical
gyre
Strong and narrow
western boundary
current
Subtropical
gyre
Subpolar gyre

56. 1. The Coriolis force causes the moving water to be deflected
to the right of the right of the wind (in NH). The net effect
of winds in the upper ocean is a flow perpendicular to the
wind (i.e. Ekman transport).
2. The strong western boundary currents are formed due to the
variation of the Coriolis parameter with latitude.

57. Meanders, rings, eddies and gyres
gyre

58. •Meanders: Jet stream develop large oscillations caused by
its unstable.
•Rings: Eddy pinched off from meander as it become too
large.
Anticlockwise and clockwise rotating rings are cold and
warm rings, respectively.
They contain water from the opposite side of the stream
having the other side’s physical, chemical and biological
properties.
The interaction of meander and rings create significant
vertical transports of nutrient and plankton which enhance
biological activity

59. •Eddies: The closed circulation with horizontal scale of
10-100km and time scale of 10-30 days. The upward
and downward vertical velocities in cyclonic and
anticyclonic will enhance biological productivity,
respectively.

61. High surface Chl-a

62. •Gyres: A circular current that is confined by or
associated with bathymetric features and covers a wide
range of spatial scales.

63. The Thermohaline Circulation (north-south vertical
circulation
Sinking of
dense water
due to
cooling in mid
to high
latitude.

66. •The global conveyor belt thermohaline circulation
is driven primarily by the formation and sinking of
deep water (from around 1500m to the Antarctic
bottom water overlying the bottom of the ocean) in
the Norwegian Sea.

67. •This circulation is thought to be responsible for
the large flow of upper ocean water from the
tropical Pacific to the Indian Ocean through the
Indonesian Archipelogo.

68. •The two counteracting forcings operating in the
North Atlantic control the conveyor belt circulation:
(1) the thermal forcing (high-latitude cooling and the
low-latitude heating) which drives a polar southward
flow; and (2) haline forcing (net high-latitude
freshwater gain and low-latitude evaporation) which
moves in the opposite direction. In today's Atlantic
the thermal forcing dominates, hence, the flow of
upper current from south to north.

69. What is an Eddy?
Turbulent rings that trap cold or
warm water in their centers and
then separate from the main
flow
Eddies or "rings "can be
detected from satellite infrared
sensors
69

70. How are they formed?
Cold-core Warm-core
 Forms from cold water
trapped within the
warmer Gulf Stream
water
 Cyclonic , Rotate
counterclockwise
 (N. Hemisphere)
 Forms from warm Gulf
Stream water
meandering and causes
a warm ring to break
off
 Anticyclonic ,Rotate
clockwise
 (N. Hemisphere)
70

71. Where Eddies are formed?
 You can find eddies in all parts of the ocean
but highly energetic rings and eddies are
commonly associated with faster flowing
currents, western boundary currents (Gulf
Stream, Kuroshio)
 Eddy formation from water flowing around
seamounts
 Areas of convergent or divergent water
masses
71

72. Sargasso Sea
15-25 deg C
“Slope water” Colder
more nutrient-rich
< 10 deg C
72

73. Warm-core
Core-core
73
Pictures from
www.jochemnet.de/fiu/Gulfstream.gif

74. 74

75. Mesoscale Eddies
 Diameter of an eddy can range from 10 to 1oos of
kilometers
 Formation time from the start of a meander and the
separation of the eddy is on the order of 40 days
 Eddies can last a month and up to a year- Average
lifetime of a few months ex. Cold-core eddies can be
tracked up to 2 yrs before it fully dissipates into the
Sargasso Sea, Warm-core eddies can last up to 1 yr
 They are maintained b/c of the strong density
difference between the eddy and the surrounding
water
75

76. Why are Eddies Important?
 Physical-They are an important mechanism for
mixing in the surface ocean and transporting
energy (ex. heat)
 Chemical- Cold-core eddies bring nutrients (N,
P, O) up to the surface for biological use
 Biological- Cold-core eddies can fertilize the
upper ocean to support phytoplankton blooms,
Warm-core can trap and transport a variety of
organisms (ecological importance ex. Larval
dispersal)
76

77. Research on Eddies
 Biological- Ecological
Perspective
 Entrainment of Antarctic
euphausiids across the
Antarctic Polar Front by a
cold eddy(2007)Bernard et al.
 Cold eddies transporting
Antarctic euphausiid (krill)
species equatorward,
contributing to the spatial
diversity of the zooplankton
community within the region
 Chemical-Biogeochemical
Perspective
 On the role of eddies for
coastal productivity and
carbon export to the open-
ocean (2007) Gruber et al.
 Model study of the California
Current that resulted in
weakening coastal upwelling,
reducing biological
productivity and carbon
export from the warm-core
nutrient depleted eddies
brought to the shore
77

78. Role of Eddies
Eddies are important to all aspects of
oceanography (Biological, Chemical
and Physical) and often involve the
overlap of research areas (ex.
Biogeochemical, Biophysical)
78

79. Western
Boundaries
Loder, Boicourt
and Simpson,
Vol. 11, THE SEA

80. Lohrenz and Castro
Vol. 14A, THE SEA

81. Western Ocean Boundaries
• Complex circulation patterns, typified by eddies and current instabilities, are
key to enhanced nutrient entrainment and high biological productivity.
• Exchanges between offshore and coastal waters create a dynamic
environment, in many cases stimulating high primary productivity.
• Role of intrusions of subsurface waters in enhancing nutrient supply is
important for extensive areas of continental shelves.
• Linkages are evident within regions, and important linkages exist between
western boundary current systems and other regions. Consequences and
importance for ecosystem processes have only begun to be explored.
• Lack of observations limits understanding of physics and associated ecosystem
processes. Examples: linkages between primary production and higher trophic
levels, and impact on recruitment of key fisheries species; biogeochemical
rates critical for carbon and nitrogen budgets; microbial processing of
terrigeneous organic matter; denitrification; and, nitrogen fixation.

82. Eastern Boundaries
Hill, Hickey, Shillington,
Strub, Brink, Barton,
Thomas,

83. Mackas, Strub,
Thomas,
Montecino,

84. Eastern Ocean Boundaries
• Mechanisms and rates of nutrient supply, and differences in these between
macronutrients (N, P, Si) vs. micronutrients (Fe, Cu, . . .)
• Within-region zonation of habitat utilization – ‘hotspots’ of high productivity
and abundance, spawning centers, nursery grounds.
• Strong variability at interannual to decadal time scales. Important between-
and within-region contrasts in seasonal and event-scale timing and
sequencing of key processes, especially relative phasing of nutrient supply,
advection, mixing, and somatic and reproductive growth of biota.
• Role of topographic complexity: islands, capes, canyons and shelf-edge
irregularities produce important and recurrent perturbations of distribution
fields.
Important research issues and oceanographic mechanisms are
important in all or most regions, including:

85. Polar Boundaries
Ingram, Carmack,
McLaughlin,
Nicol
Vol. 14A, THE

86. Ingram, Carmack,
McLaughlin,
Nicol
Vol. 14A, THE

87. Ingram, Carmack,
McLaughlin,
Nicol
Vol. 14A, THE

88. Three types:
i) nearly-enclosed with limited
exchanges with the open ocean (e.g.
Sea of Okhotsk, Bohai Sea, Japan
Sea)
ii) Partially-enclosed with moderate
exchanges along 1 or 2 boundaries
(e.g. Yellow Sea)
iii) Peripheral seas extending along
continental margins and having
strong interactions (e.g. Outer SE
China Sea, shelf seas around
Australia)
Semi-Enclosed Seas and Islands
Church, Bethoux, Theocharis, Vol. 11, THE SEA; Oguz and Su, Vol. 14, THE SEA

89. The effective management and protection of coastal ecosystems must
be science-based. With this general purpose in mind, the COASTS
Programme, sponsored by the Intergovernmental Oceanographic
Commission of UNESCO and the Scientific Committee on Oceanic
Research, was established to promote and facilitate research and
applications in interdisciplinary coastal and shelf ocean
sciences and technology on a global basis to increase scientific
understanding of coastal ocean processes.

90. Literature Sited
 Bernard, A.T.F, Ansorger, I.J., Froneman,P.W., Lutjeharms, J.R.E. and Swart, N.C. 2007.
Entrainment of Antarctic euphausiids across the Antarctic Polar Front by a cold eddy.
Deep Sea Research Part I. 54.10.1841-1851
 Gruber, N., Frenzel, H., Marchesiello, P., McWilliams, J.C., Nagai, T and Platter, G, -K.
(2007). On the role of eddies for coastal productivity and carbon export to the open
ocean. Geophysical Research Abstracts. 9.
 Garrison, T. Oceanography An Invitation to Marine Science 4th Edition
 Knass, J.A. Introduction to Physical Oceanography 2nd Edition
 Pickart, G.L. and Emery, W.J. An Introduction: Descriptive Physical Oceanography 5th
Edition
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