clear concept of oceanic temperature
TRANSCRIPT
Pressure
• The SI unit for pressure is the K Pa = 10 3 pascals. Previous unit was the Bar. 1 bar = 1 standard atmospheric pressure (sea-level) Standard Atmospheric pressure = 101.32 Kpa = 1.01325 bars = 1013.25 mb = 760 mm Hg.
• Important to note: 1 decibar = 10 Kpa = pressure due to 1 metre depth of seawater. Why is this useful?
Temperature
1. Main source is Sun The Ocean can transfer large amounts of heat with little
temperature change due to water’s high specific heat capacity and high latent heats
2. Gas vents at the ocean bottomThree layers exist in the ocean1.The surface layer2. Thermocline3. The deep ocean
Water molecules in different states of matter
Fig. 5.5
The surface layer
1. Variation mainly with latitude2. Average temperature is 17o C3. Polar seas -20 C and Persian Gulf (Low latitude) 36o
C4. Ocean water freezes at -1.94o C when salinity is 35
ppt 5. In summer surface temp is higher and the mixed
layer is shallower in winter surface temp is lower and mixed layer deeper
Thermocline
Rapid or sudden change in temperature in vertical direction.
Mainly between 50 m to 500 m1. Permanent in the tropics2. Seasonal at temperate latitudes i.e. present in
summer and missing in winter3. Absent in the polar waters
The deep ocean
1. 90 % water belong to this layer2. Is not well mixed ,mainly made up of
horizontal layer of equal density.3. Temperature ranges from 0-3o C
Average temperature of the ocean is 3.8o C
Wind
Temperature degree C
Most of the ocean is cold
Thermocline
permanent in the tropics;
seasonal at temperate latitudes, i.e., present in summer, missing in winter; and
absent in the polar waters.
Therefore, thermocline (i.e., the inflection point in
temperature-depth graph) is ...
Dep
thTemperature
Tropical all year round, in summer at temperate latitudes.
Polar latitudes all year round, in winter at temperate latitudes
Temperature- Bay Of Bengal
Indian Ocean-Temperature Profile
Annual cycle of SSTin the Indian Ocean-South Asia region
Surface Temperature-World Ocean
24
Effect of Ocean Heat Transport
Pattern of currents flow impacts sea surface temperatures and, as a result, air temperatures over land.
25
Equatorial Pacific: Sea Surface Temperature (SST)
Wind-driven upwelling keeps the SST low at eastern boundaries
Equatorial Ekman upwelling keeps the SST low right along the equator
Ocean temperature -August
Ocean temperature-February
Fig. 5.6
Latent heat serves as a thermostat
• water has higher latent heat of fusion and latent heat ofvaporization than almost any other substance
• ice melting consumes heat in summer and freezing releasesheat in winter--reduces seasonality
• vaporization/evaporation consumes heat in the tropics andcondensation releases heat at higher latitudes--polewardheat transport
• Earth’s surf. temp (-90 to 58°C, -2 to 32 over ocean) isnear 0 to 100°C
Heat (calories)0 200 400 600 800
This is the temperature
range for liquid water
0
150
50
100
-50
Heat is the energy needed to change the temperature of a body or material (e.g., 1 calorie is the heat needed to change the temperature of 1 gram of water by 1°C)
Tem
pera
ture
(°C
)Te
mpe
ratu
re m
easu
res
the
ther
mal
st
ate
of m
atte
r
Heat versus Temperature• Heat, the energy needed to change the temperature of a body, can be specific (i.e.,
temperature change at constant phase or state) or latent (i.e., state or phase change at constant temperature).
A
1. Start with 1 g of ice at -50°C
B
2. 25 cal of heat will change it to 1 g of ice at 0°C = ½ 50°C1g (Specific Heat)
calg°C
C
3. 80 cal of heat will change it from 1 g ice at 0°C to 1 g water at 0°C, i.e., 80 1g (Latent Heat)cal
g
D
4. 100 cal of heat will change 1 g water at 0°C to 1 g water at 100°C
= 1 100°C1g (Specific Heat)
calg°C
E
5. 540 cal of heat will change 1 g water at 100°C to 1 g water vapor at 100°C = 540 1g (Latent Heat)cal
g
F
6. 25 cal of heat will change 1 g water vapor at 100°C to 1 g water vapor at 150°C
= ½ 50°C1g (Specific Heat)calg°C
• This example shows how much heat is needed to change the temperature of 1 g ice at -50°C to 1 gWater vapor at 150°C.
• The following changes occur in this process− ice from -50°C to 0°C (this
involves specific heat)− ice to water at 0°C (this involves
latent heat)− water from 0°C to 100°C (this
involves specific heat)− water to water vapor at 100°C (this
involves latent heat)− water vapor from 100°C to 150°C
(this involves specific heat)
Let us use the following constants:Specific Heat = 1 for water and
½ for ice/vaporLatent Heat = 80 cal/g to melt ice
540 cal/g to boil water
calg°C
calg°C
Total heat needed = (25+80+100+540+25) or 770 calories
http://pubs.usgs.gov/gip/deserts/what/world.html
Deserts tend to cluster about 30º North and South latitudes, towards the western margins of land.
Tropical cyclones develop in the hot, humid air over a sea surface exceeding 26°C in temperature.