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

Thermocline

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.