Daily Temperature Variations Diurnal temperature range the difference between the daily maximum and minimum temperature 2 Daily Temperature Variations Factors that control how warm it can get during the day include ID: 929973
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Slide1
Thermodynamics
Chapter 3
Slide2Daily Temperature Variations
Diurnal temperature range = the difference between the daily maximum and minimum temperature.2
Slide3Daily Temperature Variations
Factors that control how warm it can get during the day include:Season – warmer in summer than winterPresence of clouds or haze will reduce warmingType of soil and soil moisture content –
less warming with moist soil
Presence or absence of vegetation
–
more warming without vegetation
Snow cover
–
will reduce temperature
3
Slide4Daily Temperature Variations
Coldest nighttime temperatures and strongest nocturnal inversions occur with:Winter – long night and long period of radiative coolingClear skies – allows LW radiative loss from ground with little downwelling LW from the atmosphere
Light winds
–
reduce depth of atmosphere that cools by turbulent heat fluxes so this thin layer can become very cold
Snow cover
–
insulates the atmosphere from warmer ground below and is an effective emitter of LW radiation
4
Slide5The Earth’s Annual Energy Budget
On an annual basis, the earth and atmosphere have a balance between energy gained and lost.5
Each part of the atmosphere (top, atmosphere, and ground) must be in energy balance.
Slide6Regional Temperature Variations
Factors controlling temperature variability across Earth:Latitude – T decreases with increasing latitudeLand/water distribution
–
larger temperature variation over continents than over oceans
Ocean currents
–
warm currents like Gulf Stream or cold currents like along the west coast of North America
Elevation
–
T decreases with elevation (removed from figures)
6
Average January Temperature (
)
Average July Temperature (
)
Slide7Regional Temperature Variations
Temperature gradient is larger between the tropics and the pole in the winter hemisphere.The warmest air occurs in the sub-tropics of the summer hemisphere (NH in July, SH in January).The main reason ocean temperatures varies less than continental temperatures is that water has a larger heat capacity than land so oceans warm and cool less than land for the same radiative input.Ocean currents transport heat to reduce the amount of warming and cooling locally.
7
Slide8Apparent Temperature Indices
How hot or cold we feel depends on more than just the air temperature.The human body transfers energy from/to its environment by:Radiation – LW loss by humans and LW & SW gain from environment
Conduction and turbulent transfer
Evaporation
–
latent heat
The wind chill and heat indices attempt to account for how exposed skin “feels” under windy or humid conditions compared to reference conditions.
8
Slide9Apparent Temperature Indices
Wind Chill IndexTemperature and wind impact how cold we feelWater on the skin will evaporate and cool a personFrostbite = freezing of the skinHypothermia = a lowering of the body’s core temperature below its normal range
9
Slide10Apparent Temperature Indices
The heat index accounts for the role of humidity in making you feel warmer (or cooler) than the actual air temperature.In the summer, high humidity limits how much sweat can evaporate and thus limits how effectively the human body can cool itself.
10
Slide11Review + Exercices
11
Slide12Lapse Rate (
)
Process (parcel) lapse rate = the lapse rate of an air parcel experiencing a specific process (such as moving vertically through the atmosphere):
Theoretical lapse rate
C
an be determined using the First
L
aw of
T
hermo
!
Environmental lapse rate = the lapse rate of the air surrounding an air parcel:
Observational lapse rate
Can be determined by launching a radiosonde!
12
Slide13Exercise 1
Calculate the environmental lapse of the troposphere for the standard atmosphere temperature profile shown here.
11 km
-56.5
1
5
13
Slide14Exercise 1
Troposphere:At z1 = 0 km, T
1
= 15
At z
2
= 11 km, T
2
= -56.5
→ T decreases 6.5 K for every 1 km increase in altitude in the troposphere.
11 km
-56.5
1
5
14
Slide15Dry Adiabatic Lapse Rate (
)
DALR = an air parcel lapse rate when no heat (energy) enters or leaves the air parcel (
).
DALR is larger than the average lapse rate in the troposphere (
) calculated before.
The standard atmosphere is not completely dry (contains water).
Water has a high heat capacity, which acts to decrease the lapse rate.
15
Slide16Exercise 2
Suppose you hike down in the Grand Canyon on a dry day (
). On the rim, the temperature is 95
(35
). In the canyon, 1500m below, how hot is it?
Don’t forget to convert T in K!!
16
Slide17Exercise 2
What do we know?
What
are
we
looking
for?
17
Slide18Potential Temperature (
)
The potential temperature can be calculated using:
Potential temperature will not change as the parcel rises or sinks for a dry adiabatic process because no heat is added or removed from the air parcel.
Potential temperature is conserved (constant) for a dry adiabatic process but the temperature of the air parcel will change.
Always use SI units!! (temperature in K and pressure in Pa)
Poisson’s Equation
18
Slide19Exercise 3
What is the potential temperature
at NCAR’s Mesa Lab? (you can assume dry air)
19
Slide20Exercise 3
1st method:
2
nd
method:
20
Need to know T and z!
Need to know T and p!
Slide21Exercise 4
If a parcel is lifted dry adiabatically, what happens to pressure, temperature, and potential temperature q?
Pressure increases, temperature decreases,
q
increases
Pressure increases, temperature increases,
q
decreases
Pressure decreases, temperature stays the same,
q
decreases
Pressure decreases, temperature decreases,
q
stays the same
Pressure decreases, temperature increases,
q
stays the same
21
Slide22Exercise 4
If a parcel is lifted dry adiabatically, what happens to pressure, temperature, and potential temperature q?Pressure increases, temperature decreases,
q
increases
Pressure increases, temperature increases,
q
decreases
Pressure decreases, temperature stays the same,
q
decreases
Pressure decreases, temperature decreases,
q
stays the same
Pressure decreases, temperature increases,
q
stays the same
22
Slide23Thermodynamic Diagram
Pressure
Temperature
isobars = lines
of constant pressure
isotherms = lines of
constant temperature
dry
adiabats
= lines of constant potential temperature
23
Slide24Thermodynamic Diagram
Dry adiabats:
Relate temperature and pressure at different levels in the atmosphere for a dry adiabatic process on a thermodynamic diagram.
Represent the process lapse rate for a dry adiabatic process (a process in which no heat is exchanged with the parcel and no phase change of water occur).
24
Slide25Exercise 5
25
Air parcel:
p = 750
mb
T = 15
What happens when the air parcel is:
brought down isothermally to p = 1000
mb
?
cooled
isobarically
to T = -10
?
raised adiabatically to p = 500
mb
?