2. TEMPORAL & SPATIALTEMPORAL & SPATIAL
VARIATION OFVARIATION OF
TEMPERATURE &TEMPERATURE &
PRESSURE ON EARTHPRESSURE ON EARTH
3. Temperature BasicsTemperature Basics
Temperature : Measure of average kinetic energy
(motion) of individual molecules in matter
Three temperature scales (units): Kelvin (K), Celsius (C),
Fahrenheit (F)
– All scales are relative
– degrees F = 9
⁄5 degrees C + 32
– degrees K = degrees C + 273.15
4. Vertical Variation of
Temperature
The rate of decrease in temperature
of air with increase in height as it
moves upward due to adiabatic
cooling is termed as adiabatic lapse
rate.
The average lapse rate upto
tropopause is 6.5degrees/km.
A positive lapse rate means decrease
in temperature with height whereas a
negative lapse rate is called
inversioninversion in which temperature
increases with height.
5. Atmosphere and Temperature
Due to
surface
heating
(Longwave,
Latent heat,
Sensible
heat)
Due to
ozone
absorption
of sunlight
Due to
Solar
winds,
Cosmic
rays
Decreasing
rate w/
height
(Lapse
rate):
6.5 o
C/km
6. Spatial variation of
Temperature
temperature across the latitude i.e change in
temperature with horizontal distance is known
as Temperature gradientTemperature gradient..
The isothermsisotherms joins the places of equal
temperature and thus exhibit the horizontal
distribution of temperature.
7. Factors affecting
Temperature on Earth
Latitude
Altitude
Land and water mass
Oceanic currents
Topography of land
Forest and vegetation
Clouds and rainfall
10. Temporal VariaTion of
TemperaTure
Diurnal variation:-
Minimum temperature at sunrise.
Continuous rise in temperature upto noon.
Difference between the max. and min. temp.
attained is referred to as the daily range.
Diurnal temp. range is the greatest at low
latitudes and continental locations.
Least at high latitudes and at maritime
locations.
12. ANNUAL PATTERN OF
TEMPERATURE
Difference between highest and
lowest temperature attained during
the year is annual range(diff. between
average temperature of the warmest
& coldest month).
2 temperature maxima and 2 minima
in the tropics.
Smallest range occurs near equator &
largest in high latitudes.
14. Pressure Essentials
Pressure – force exerted/unit area.
units - Pascals (Pa) ormillibars (mb) (1 mb =
100 Pa)
Average surface pressure overglobe: 1013.2 mb.
Atmosphere is mixture of gases -> partial
pressure.
Dalton’s Law: sum of partial pressures equals
total pressure
Pressure gradient (pressure difference between
two locations/distance) gives rise to a force
(pressure gradient force), which sets the air in
15. IDEAL GAS LAW
Describes relationships between pressure,
temperature, and density (Start w/ molecular
movement in sealed container Pressure
proportional to rate of collisions between
molecules and walls).
At constant temperatures, an increase in
air density will cause a pressure
increase (Add more molecules
increase density increase rate of
collisions raise pressure)
Under constant density, an increase in
temperature will lead to an increase in
pressure (Raise temperature increase
speed of molecules increase rate of
collisions raise pressure)
Pressure = density x temperature x 287 J kg-1
K-1
[ p = ρTR]
16. Pressure decreases with height
Because downward gravity force is
balanced by vertical pressure
gradient force (called hydrostatic
equilibrium)
ΔΔp/p/ΔΔz =z = ρρgg
Pressure decreases non-linearly
with height (Because air is
compressible, so denser near the
surface)
Vertical pressure distribution: Hydrostatic
equilibrium
ρρgg
ΔΔp/p/ΔΔzz
17. Spatial distribution of Pressure
Pressure maps depict isobars, lines of equal pressure
Through analysis of isobaric charts, pressure gradients are
apparent
Steep pressure gradients are indicated by closely spaced
isobars
Typically only small gradients
exist across large spatial scales
(4% variation at continental
scale), smaller than
vertical gradients.
18. Causes of Horizontal
Variation of Pressure
• Differential heating producing density
contrasts and atmospheric circulation.
• Gravitational pull of moon causing
atmospheric tides.
• Effect of latitude forming symmetrical
pattern of pressure zones on the earth.
19. Global Pressure
Belts
• Along the equator, doldrums or equatorial lowsdoldrums or equatorial lows are
found.
• Sub tropic highsSub tropic highs are found at 25degree-30degree
north and south.
• Sub polar lowsSub polar lows are found at 60-70degree north and
south latitude.
• Polar highsPolar highs at poles.at poles.
