Oceanography
CRN # 10053
Lecture 2a
Debbie Reynolds Lecture Certification:
1
Lectures 1
a)
b)
Properties of sea water, ocean physics, ocean basins, explorers
Meteorology, heat balance, geostrophic circulation
Lectures 2
a)
b)
Surface ocean winds, currents, temperature and salinity
Deep circulation, instruments
Lectures 3
a)
b)
El Niño
Climate change on the oceans, including sea level rise
Lectures 4
a)
b)
Wind waves, rogue waves and tsunami
Tides
Lectures 5
a)
b)
Sea-floor spreading, continental drift − Plate Tectonics
Ocean basins, ocean sediments, coasts and estuaries
Lectures 6
a)
b)
Food web, plankton, invertebrate animals
Vertebrate animals, communities tidal to abyssal
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Introduction
•
Surface Currents driven by Surface Winds
•
•
•
5 Large Surface Circulation Patterns Formed:
Gyres
•
•
•
•
•
Currents are turned to the right of the winds in the
Northern Hemisphere
Currents are turned to the left of the winds in the
Southern Hemisphere
Clockwise rotation in Northern Hemisphere
Counter Clockwise rotation in Southern Hemisphere
West Wind Drift drives the Antarctic Circumpolar
Current around Antarctica
Sea Surface Temperatures are warmest in tropics
Sea Surface Salinities are highest in middle
latitudes (30°N and 30°S)
3
Unequal Partnership
Between 2 Fluids
← Atmosphere
Ocean →
•
•
Air Density ~ 0.0012 g/cc
Ocean Water Density ~ 1.025 g/cc
4
Temperature vs. Depth
• Temperature decreases
with increasing depth
• cline is a thin horizontal
layer
 where a property
changes greatly over
depth
• Thermocline is where the
temperature changes
greatly with depth
 Thermocline is the region
of maximum
temperature change
with depth
39°F
54°F
68°F
1640 ft
3300 ft
9800 ft
13,000 ft
5
Heat Budget & Transport
Deficit
Surplus
Heat
Transfer
Deficit
Heat
Transfer
Average annual Average annual
solar heat
infrared radiation
absorbed
emitted
Heat Transfer from
Equator to Poles
6
Global Air Circulation
Coriolis effect
produces
3 circulation
cells:
 Polar easterlies
 Mid-latitude
westerlies
 Easterly trades
ITCZ – Intertropical Convergence Zone
7
ITCZ – Intertropical Convergence Zone
•
•
ITCZ indicated by east/west band of clouds
ITCZ is north of the equator
8
North Atlantic Gyre
Surface Currents
1. Gulf Stream –
Western
Boundary Current
2. North Atlantic
Current –
Transverse
Current
3. Canary Current –
Eastern
Boundary Current
4. North Equatorial
Current –
Transverse
Current
Surface Winds
9
Ekman Current Spiral: Northern Hemisphere
• Surface currents 45° to the right of the wind
• Currents spiral to the right with depth and weaken
Vagn
Walfrid
Ekman
1874 –1954
Transport
is
Average
Current
10
Ekman
Transport:
Northern
Hemisphere
H
A
B
• Transport is
90° to the
right of the
wind
• Continuity of
flow leads to
upwelling
11
Ekman Transport: Southern Hemisphere
Transport is 90° to the left of the wind
12
North Atlantic Gyre
Surface Currents
1. Gulf Stream –
Western
Boundary Current
2. North Atlantic
Current –
Transverse
Current
3. Canary Current –
Eastern
Boundary Current
4. North Equatorial
Current –
Transverse
Current
Surface Winds
13
Ekman Transport Dome
Surface transports around gyre in North Atlantic are to the
right of the wind and lead to dome of water (Sargasso Sea) in
center of gyre (2 m high)
14
Ocean Gyres and Coriolis Impact
• Hill at center of Gyre is displaced to the west by Coriolis
Effect
• Height of hill at center of Gyre is ~ 2 m (6.5 ft)
15
Cross-section of North Atlantic Currents
• Gulf Stream – Narrow, deep (450 m, 1500 ft), warm, strong, 2 m/sec
(5 mi/hr)
• Canary Current – Broad, shallow, cold, weak: 0.9 m/s (2 mi/hr)
• Hill is displaced to west; Height of hill is ~ 2 m (6.5 ft)
16
January Satellite Scatterometer Winds
10 m/s = 19 knots = 22 mi/hr
8 years of data
17
July Satellite Scatterometer Winds
10 m/s = 19 knots = 22 mi/hr
8 years of data
18
Thermal Equator
• Position of ITCZ (Intertropical Convergence Zone) marks the
thermal equator of earth in January and July
• Note large changes in Indian Ocean
 July ITCZ in Red
 January ITCZ in Cyan
19
Satellite Scatterometer Climate Winds
10 m/s = 19 knots = 22 mi/hr
8 years of data
20
5 Main Gyres in World Ocean
21
Surface Currents
Warm Currents →
Cold Currents →
22
Currents
• A – Agulhas
• WW – West
Wind Drift
• WA – West
Australia
• SE – South
Equatorial
Seasonal Monsoons: Indian Ocean
Winter (Nov-Mar) Northeast
Summer (May-Sep) Southwest
• NE – North
Equatorial
• S – Somali
• EC –
Equatorial
Counter
• SM –
Southwest
Monsoon
L – Leeuwin
?
23
Climate Sea Surface Temperature (SST)
Contour Intervals:
0, 5, 10, 15, 20, 25, 28
°C
32°F
50°F
68°F
86°F
24
Climate Sea Surface Temperature (SST)
Contour Intervals:
0, 5, 10, 15, 20, 25, 28
°C
32°F
50°F
68°F
86°F
25
North Atlantic Gyre
Surface Currents
1. Gulf Stream –
Western
Boundary Current
2. North Atlantic
Current –
Transverse
Current
3. Canary Current –
Eastern
Boundary Current
4. North Equatorial
Current –
Transverse
Current
Surface Winds
26
Gulf Stream Transport
Current Averaged over Depth
1 Sverdrup (sv) is a
flow of 1 cubic
meter per second
• Largest flow is
Gulf Stream
which reaches
55 sv
• All freshwater
rivers have flow
of ~1 sv
• Center of
circulation
displaced to the
west
27
Gulf Stream Eddies
• Cold water from
the north is due
to the Labrador
Current
• Eddies form
between cold and
warm currents
• W – warm eddies
which spin
clockwise
• C – cold eddies
which spin
counter
clockwise
28
Gulf Stream Sea Surface Temperature
From the satellite
advanced very
high resolution
radiometer
(AVHRR)
instrument
Data available
from September
1981 to present
View must be
cloud free
29
Surface Salinity - Satellite
psu
• Atlantic Ocean is saltier than Pacific Ocean
• Middle latitudes saltier than tropics or poles
30
Evaporation minus Precipitation
psu
• Precipitation greater than Evaporation Blue colors
• Evaporation greater than Precipitation Red colors
31
Surface Salinity - Satellite
psu
• Atlantic Ocean is saltier than Pacific Ocean
• Middle latitudes saltier than tropics or poles
32
Surface Currents
Warm Currents →
Cold Currents →
33
34
Surface Currents in North Pacific
35
Model Forecast of Debris
from Japan Tsunami
36
Debris from Japan Tsunami
37
21 Containers Lost in May 1990 Storm
5 Held 80,000 Nike Shoes
38
Summary
•
Surface Currents driven by Surface Winds
•
•
•
5 Large Surface Circulation Patterns Formed:
Gyres
•
•
•
•
•
Currents are turned to the right of the winds in the
Northern Hemisphere
Currents are turned to the left of the wind in the
Southern Hemisphere
Clockwise rotation in Northern Hemisphere
Counter Clockwise rotation in Southern Hemisphere
West Wind Drift drives the Antarctic Circumpolar
Current around Antarctica
Sea Surface Temperatures are warmest in tropics
Sea Surface Salinities are highest in middle
latitudes (30°N and 30°S)
39
James Balog
40