Lecture Atmospheric Temperature

ATMOSPHERICATMOSPHERIC
TEMPERATURETEMPERATURE

WHAT IS TEMPERATURE?
Temperature is a measure of the average heat or
thermal energy of the particles in a substance. Since
it is an average measurement, it does not depend on
the number of particles in an object. In that sense it
does not depend on the size of it. For example, the
temperature of a small cup of boiling water is the
same as the temperature of a large pot of boiling
water. Even if the large pot is much bigger than the
cup and has millions and millions more water
molecules.

It is expressed according to a comparative scale and
shown by a thermometer or perceived by touch.

DIFFERENCE BETWEEN HEAT &
TEMPERATURE!
•Heat is the amount of thermal energy in an object
because of its moving molecules. Thermal (heat)
energy is the total energy of the particles that make
up an object
•Temperature is a measure of thermal energy or how
fast molecules are moving in an object. The more
you
heat something, the faster the molecules move. This
is what causes temperature to rise. Temperature is a
measure of the average kinetic energy of each
particle within an object.

The Tool used for measuring
temperature is called a
Thermometer

What is a Thermometer?
An instrument for measuring and indicating temperature,
typically one consisting of a narrow, hermetically sealed
glass tube marked with graduations and having at one end
a bulb containing mercury or alcohol that expands and
contracts in the tube with heating and cooling.
An analog thermometer consists of a sealed tube with
markings on it. These markings are increasing
temperatures in Celsius or Fahrenheit or Kelvin. The
markings on a clinical and weather thermometer are
different, but they work in the same way. The name is
made up of two smaller words: "Thermo" means heat and
"meter" means to measure.

HOW TO MEASURE
TEMPERATURE?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

How does a Thermometer work?
The glass tube of a thermometer usually contains
mercury. Mercury is perfect to test temperature
because it changes from a solid to liquid very easily.
When the metal tip of the thermometer comes into
contact with the material it is testing, it conducts heat
energy to the mercury. The mercury turns into liquid
and so it expands. It begins to rise up the tube. Where
it stops, is where you can take the temperature reading
on the scale.

Lecture Atmospheric Temperature

How does a Digital Thermometer
work?
Digital thermometers are different because they use a
computer chip to tell the temperature instead of mercury.
You would normally have to wait three whole minutes for
the mercury to heat up and give you a reading.
It takes only 30 seconds for a digital thermometer to give
you a reading because the heat-sensitive tip is able to
accurately tell the computer chip inside what the
temperature is.
Your normal body temperature would be 98.6 °F on the
Fahrenheit scale. On the Celsius scale, it would be 37 C.
The Celsius scale is used in most countries, aside from the
USA, because it is a part of a metric system.

FAHRENHEIT SCALE
This scale is mostly understood and used in the US.
Weather reports and the news media usually state
temperatures in degrees Fahrenheit. It is named after
the German physicist Gabriel Fahrenheit. Reference
points on this scale include sea level freezing and
boiling points of pure water – which are 32 F & 212 F.
For converting Celsius to Fahrenheit :
F = (C X 1.8) + 32 OR (C X 9/5) +32

CELSIUS SCALE
In most countries the Celsius scale is used – which is
named after the Swedish astronomer Andres Celsius.
It is a component of the International system of
measurement (S.I) because it is a decimal scale with
100 units (degrees) between the freezing and boiling
points of water at sea level.
For converting Fahrenheit to Celsius :
C = (F-32) X 5/9 OR (F-32) / 1.8

KELVIN SCALE
For scientific purposes – the Kelvin scale named after
the British physicist Lord Kelvin – has long been used
because it measures what are called absolute
temperatures – which means that the scale begins at
absolute zero O K – the lowest possible temperature.
The scale maintains a 100 unit range between the
freezing and boiling points of water. There are no
negative values. Because the scale is usually used by
the scientific community – we only use it for
comparison to the Fahrenheit and Celsius scale.
C = K - 273.15

THERMOMETERS USED
FOR WEATHER
OBSERVATIONS

Energy Transfer as Heat
Three mechanisms of energy transfer as heat are
conduction, convection, and radiation.
Conduction is the transfer of heat through matter by
molecular activity.
Convection is the transfer of heat by mass movement
or circulation within a substance.
Radiation is the transfer of energy (heat) through
space by electromagnetic waves that travel out in all
directions.

Radiation
All objects, at any temperature, emit radiant
energy.
Hotter objects radiate more total energy per unit
area than colder objects do.
The hottest radiating bodies produce the shortest
wavelengths of maximum radiation.
Objects that are good absorbers of radiation are
good emitters as well.

Advection
When the dominant direction of energy transfer in a
moving fluid is horizontal (sideways) – the term
advection is used. In the atmosphere the wind may
transfer warm or cool air horizontally from one place
to another through the process of advection. Some
wind systems develop as part of a large atmospheric
convection cells – the horizontal component of air
movement within such a convection cell is properly
called advection.

THE VERTICAL DISTRIBUTION
OF TEMPERATURE

PRINCIPAL TEMPERATURE
CONTROLS
1. Latitude – Insolation is the single most important
influence on temperature variations. The intensity
of
insolation decreases as one moves away from the
equator. In addition day length and sun angle
change through out the year – increasing seasonal
effect with increasing latitude. From equator to poles
- earth ranges from continually warm to seasonally
variable to continually cold

2. Altitude/Elevation – In the troposphere
temperature decreases with increase in
altitude.
At high elevations, air temperatures are
generally cooler and show a greater day-to-
night range. The sun would be cold in space,
because there is no air for it to heat. As the air
is thinner the higher up a mountain you go,
the temperature drops. The higher
the air pressure, the higher the temperature
and vice versa. As the air pressure is so much
thinner, the temperature is therefore lower.

Adiabatic Temperature Changes
As air is heated it expands becoming less dense,
and as a result, lighter. Because it is lighter, it
rises upwards above the cooler air. As it does so,
this air continues to expand. This is because
there is less pressure higher in the atmosphere,
allowing the air molecules to spread out more.
In order to spread out, these molecules require
energy. As they do so, they become less agitated
and vibrate slower. As a result, the temperature
of these air molecules drops, despite the fact that
no heat has been removed from them.

This process is referred to as adiabatic cooling.
As the air cools down, it again begins to fall
towards the surface of the Earth. As it sinks
deeper into the atmosphere, the pressure from
the weight of the air above it pushes air
molecules closer together, causing them to
become more agitated and heating them up
again. As a result, their temperature rises, even
though no heat has been added. This process is
referred to as adiabatic warming.

Dry air is air that contains no water.
Moist air is air that contains water in
vapor form.
The moisture in the air is usually
referred to as humidity.

The stability of dry air - dry convection.
The stability of air under vertical displacement is
determined by the outcome of a small change in an air
parcels elevation:
If the environment (the surrounding atmosphere) is
such that vertically displaced parcels continue to rise
on their own, even when the lifting exerted on them
stops, the environment is referred to as unstable.
If vertically displaced parcels sink back to their initial
elevation after the lifting ceases, the environment
is stable.
If vertically displaced parcels remain where they are
after being lifted, the environment is neutral.

Three Categories of Stability:
Stable: Returns to its original position
after displacement
Neutral: Remains in new position after
being displaced
Unstable: Moves further away from its original
position after being displaced

What are Lapse Rates
Parcel lapse rate – the rate at whichParcel lapse rate – the rate at which
temperature changes as the parcel is liftedtemperature changes as the parcel is lifted
to a higher altitudeto a higher altitude
Environmental lapse rate – the rate atEnvironmental lapse rate – the rate at
which the air surrounding the parcelwhich the air surrounding the parcel
changes as altitude increaseschanges as altitude increases

The three fundamental stability conditions of the
atmosphere are:
(1) Absolute stability - when the
environmental lapse rate is less than the
wet adiabatic rate
(2) Absolute instability - when the
environmental lapse rate is greater than
the dry adiabatic rate
(3) Conditional instability - when moist air
has an environmental lapse rate between
the dry and wet adiabatic rates.
Stability Conditions

What is the difference between stable
and unstable air
If a rising parcel of air is cooler than the
surrounding atmosphere it will tend to sink back
to its original position. This is because cool air is
more dense or heavier than warmer air. This is
referred to as stable air. If a rising parcel of air is
warmer than the surrounding atmosphere it will
continue to rise. This is because warm air is less
dense or lighter than cool air. This is referred to
as unstable air.

In general, when stable air is forced aloft, the
associated clouds have little vertical thickness,
and precipitation, if any, is light.
In contrast, clouds associated with unstable air
are towering and frequently accompanied by
heavy rain.
Any factor that causes air near the surface to
become warmed in relation to the air aloft
increases the air's instability.
The opposite is also true; any factor that causes
the surface air to be chilled results in the air
becoming more stable.

Most processes that alter stability result from
temperature changes caused by horizontal or
vertical air movement, although daily
temperature changes are important too.
Changes in stability occur as air moves
horizontally over a surface having markedly
different temperatures.
On a smaller scale, the loss of heat from cloud
tops during evening hours adds to their
instability and growth.
Furthermore, in general, subsidence ( a general
downward airflow) generally stabilizes the air,
while upward air movement enhances

Two ways to saturate the air (or raise
the relative humidity)
1. Add more water vapor to it
2. Decrease the temperature
This is because warm air is capable of “holding”
more water vapor molecules than cold air.
(Remember the water vapor molecules are
moving faster in warm air and less likely to stick
and condense)

DALR
Air in parcel must be unsaturated
(RH < 100%)
Rate of adiabatic heating or cooling =
9.8°C for every 1000 meter (1 kilometer)
change in elevation
Parcel temperature decreases by about 10°
if parcel is raised by 1km, and increases
about 10° if it is lowered by 1km

SALR/MALR
As rising air cools, its RH increases
because the temperature approaches the
dew point temperature, Td
If T = Td at some elevation, the air in the
parcel will be saturated (RH = 100%)
If parcel is raised further, condensation will
occur and the temperature of the parcel will
cool at the rate of about 6°C per 1km in the
mid-latitudes

DALR VS MALR
The MALR is less than the DALR because of
latent heating
As water vapor condenses into liquid water
for a saturated parcel, LH is released,
lessening the adiabatic cooling

The higher the
air
temperature,
the more water
vapor will be
present in the
air at
saturation

Saturation is when evaporation = condensation

Dew Point = the temperature to
which air must be cooled in order to
become saturated
When air temperature
=
Dew point temperature
RH = 100%

Temperature Inversion
Under normal circumstances, the air near the surface
of the Earth is warmer than the air above it. Typically
air is hottest at the ground. Air is fairly transparent to
sunlight, most of which passes straight through it
without heating it. When the sunlight reaches the
ground it is almost entirely absorbed, heating the land.
Some of this energy is then re-radiated as black body,
and due to the average temperatures involved, much of
this is in the infrared. Unlike the original sunlight,
infrared light interacts more strongly with air, which is
then heated from below.
Hot air, however, rises. This leads to constant

convection which draws the warmer air up, to be
replaced with cooler air which is then heated. It is this
process that leads to cloud building, thermals, and
other convection related atmospheric behavior.
However, it is sometimes possible to find situations
where the gradient is inverted, so that the air gets
actually colder as you approach the surface of the
Earth. This is called a temperature inversion. It is most
commonly created by the movement of air masses of
different temperature moving over each other. A warm
air mass moving over a colder one can "shut off" the
convection effects, keeping the cooler air mass
trapped below.

The weather plays an important role in the formation
and disappearance of air pollution. During winters, air
quality has been observed to decline very quickly after
long clear nights with weak winds. Then pollutants
from different sources are emitted into the air, but
because of poor mixing circumstances near the
ground, pollutants released into the atmosphere's
lowest layer are trapped at breathing level and can
reach unhealthy levels in a few hours. Winters are
characterized by short days and low solar activity. The
snow-covered ground is cold and its white colour
reflects almost all heat coming in. When the sun goes
down, the ground loses heat very quickly and this
cools the air above the

ground. Nights in the summertime are much shorter
than nights during the wintertime when cooling of the
ground can continue over a longer period of time.
Weak winds prevent air mixing near the surface and
clear skies increase the rate of cooling at the Earth's
surface. Stable conditions inhibit vertical and
horizontal mixing near the ground and consequently,
favour the development of a strong surface
temperature inversion or radiation inversion (see
picture above). The condition like this is called an
inversion because it is the reverse of a normal air
pattern (i.e., warmer air below and cooler air above).

How do inversions impact air
quality?
Winter temperature inversions play a significant role
in the winter pollution episodes in Nordic urban sites.
An inversion can prevent the rise and dispersal of
pollutants from the lower layers of the atmosphere,
because warm air above cooler air acts like a lid,
preventing vertical mixing and trapping the pollution
material e.g. at the breathing level. Traffic emissions
especially have a great impact on air quality at the
breathing level, because they are released near the
ground.
The strength and duration of the inversion and

elevation of the release compared to the inversion
elevation has a large influence on the air quality. Air
pollution will continue to accumulate until inversion
disappears. Traffic particularly and other sources add
more pollutants to the air. A strong and low height
inversion will lead to high pollutant levels, while a
weak inversion will lead to lower levels. In other
words, the smaller is the mixing volume; the higher is
the pollution concentration. Inversions are also
stronger and more common during the winter months.
In summer, inversions are less frequent and weaker.

3. CLOUD COVER
At any one time – 50% of the earth is covered with
clouds. This causes a moderation of temperature and
this varies with cloud type – height and density. The
moisture in the clouds reflects – absorbs and liberates
large amounts of energy released upon condensation
and cloud formation. At night clouds act as insulation
and radiate LW energy – preventing rapid energy loss.
During the day – clouds reflect insolation due to their
high albedo value. In general they lower daily
maximum temperature and raise nighttime minimum
temperature. Clouds are the most variable factor
influencing the earth’s radiation budget.

Land-Water Heating Difference
The continents heat up faster than the oceans, and they
cool down faster too. There are a few reasons for the
land-ocean cooling differences, and they all have to do
with how heat is absorbed and transported.
(1) Specific Heat Capacity. Water has a higher heat
capacity than land. So it takes more heat to raise the
temperature of one gram of water by one degree than
it does to raise the temperature of land. 1 calorie of
solar energy (any type of energy really) will warm one
gram of water by 1 degree Celcius, while the same
calorie would raise the temperature of a gram of
granite by more than 5 degrees C.

(2) Transparency. The heat absorbed by the ocean is
spread out over a greater volume because the oceans
are transparent (to some degree). Since light can
penetrate the surface of the water the heat from the sun
is dispersed over a greater depth.
(3) Evaporation. The oceans loose a lot of heat from
evaporation. While there is some evaporation from
wet soils and transpiration by plants, the land does not
have anywhere near as much available moisture to
cool it down.
(4) Currents. Not only do the oceans absorb heat over
a greater depth, but they can also move that energy
around with their currents. The solar energy absorbed
at the equator gets transported towards the poles,

the colder polar water gets transported the other way.
Currents help average out ocean temperatures. Gulf
stream being an example.
(5) Movement – Land is rigid and solid – whereas
water is fluid and capable of movement. Differing
temperatures and currents result in mixing of cooler
and warmer waters and that mixing spreads the
available energy over an even greater volume than if
the water were still. Surface and deeper waters mix
and redistribute energy. Both land and oceans radiate
LW radiation at night but land loses its energy more
rapidly than does the moving oceanic energy
reservoir.

World air temperature patterns forWorld air temperature patterns for
JanuaryJanuary

World air temperature patterns for
July

Summary – Marine effects Vs
Continental effects
High ocean temperatures produce higher evaporation
rates and more energy is lost from the oceans as latent
heat. As the water vapor content of the overlying air
mass increases - the ability of the air to absorb LW
radiation also increases. Therefore the air mass
becomes warmer – the warmer the air and the ocean
become – the more evaporation that occurs –
increasing the amount of water vapor entering the air
mass. More water vapor leads to cloud formation –
which reflects insolation and produces lower
temperatures.

The interior landmass, will cool and heat much more
rapidly then the ocean. This effect leads to a wider
annual range of temperature for the landmass then that
of the ocean. The more moderate temperature range
(due to the longer cooling and warming periods) found
in the ocean does influence the mainland landmasses.
While all land cools and warms quicker then water,
the mainland temperature is moderated by the water
air temperature that moves from the ocean the land.
This means that to locations on land, with the same
latitude, can have vastly different temperatures.

DAILY AND YEARLY CYCLES
OF TEMPERATURE
Daily Cycle of Air Temperature/Diurnal Cycle
At the Earth's surface quantities of insolation and net
radiation undergo daily cycles of change because the
planet rotates on its polar axis once every 24 hours.
Insolation is usually the main positive component
making up net radiation. Variations in net radiation are
primarily responsible for the particular patterns of
rising and falling air temperature over a 24 hour
period. The following three graphs show hypothetical
average curves of insolation, net radiation, and air
temperature for a typical land based location at 45°

of latitude on the equinoxes and solstices.
INSOLATION
Hourly variations in insolation received for a location
at 45° North latitude over a 24 hour period.
In the diurnal cycle – there is one maximum and one
minimum daily

NET RADIATION
Hourly variations in net radiation for a location at 45°
North latitude over a 24 hour period.

TEMPERATURE
Hourly variations in surface temperature for a location
at 45° North latitude over a 24 hour period.

The relative placement of the temperature profiles for
the various dates correlates to the amount of net
radiation available for daily surface absorption and
heat generation. The more energy available, the higher
up the Y-Axis the profile is on the graph. September
Equinox is warmer than the March Equinox because
of the heating that occurred in the previous summer
months. For all dates, minimum temperature occurs
at sunrise. Temperature drops throughout the night
because of two processes. First, the Earth's radiation
balance at the surface becomes negative after sunset.
Thus, the surface of the Earth stops heating up as solar
radiation is not being absorbed.
Secondly, conduction and convection transport heat

energy up into the atmosphere and the warm air that
was at the surface is replaced by cooler air from above
because of atmospheric mixing. Temperature begins
rising as soon as the net radiation budget of the
surface becomes positive. Temperature continues to
rise from sunrise until sometime after solar noon.
After this time, mixing of the Earth's surface by
convection causes the surface to cool despite the
positive addition of radiation and heat energy.

Annual Cycle of Air Temperature
As the Earth revolves around the Sun, locations on the
surface may under go seasonal changes in air
temperature because of annual variations in the
intensity of net radiation. Variations in net radiation
are primarily controlled by changes in the intensity
and duration of received solar insolation which are
driven by variations in day length and angle of
incidence. Now we examine how changes in net
radiation can effect mean monthly temperatures for
the following five locations: Manaus – Brazil,
Bulawayo – Zimbawe, Albuquerque – USA, London –
England & Fairbanks - USA

Manaus, Brazil - 3°South, 60°West
Monthly variations in net radiation and average
monthly temperature for Manaus, Brazil.

At Manaus, values of monthly net radiation average
about 135 Watts per square meter. Monthly variation
in net radiation is only about 35 Watts over the entire
year. Two peaks in net radiation are visible on the
graph. Both of these peaks occur during
the equinoxes when the height of the Sun above
the horizon is at its maximum (90° above the horizon).
Minimum values of net radiation correspond to the
time of the year when the Sun reaches its minimum
height of only 66.5° above the horizon at solar noon.
Because of the consistent nature of net radiation, mean
monthly air temperature only varies by 2° Celsius over
the entire year.

Bulawayo, Zimbabwe - 20° South, 29° East
monthly temperature for Bulawayo, Zimbabwe.

Net radiation at Bulawayo has a single peak and
trough over the one year period graphed. This pattern
is primarily controlled by variations in the intensity
and duration of incoming solar insolation. During
the December solstice, the Sun reaches its highest
altitude above the horizon and day length is at a
maximum (13 hours and 12 minutes). The lowest
values of net radiation occur around the June
solstice when the Sun reaches its lowest altitude above
the horizon and day length is at a minimum (10 hours
and 48 minutes) in the Southern Hemisphere. Monthly
temperature variations follow the monthly change in
net radiation. When received at the Earth's surface
much of this energy is used to create sensible heat.

Albuquerque, USA - 35° North, 107° West
monthly temperature for Albuquerque, USA.

At Albuquerque, maximum net radiation occurs in
May. The timing of this peak roughly coincides with
the June solstice when day lengths are at their longest
and solar heights are their greatest. However, monthly
temperature variations do not mirror the changes in
net radiation exactly. Peak monthly temperatures
occur about two months after the net radiation
maximum. This lag is probably caused by the delayed
movement of stored heat energy in the ground into the
atmosphere. Minimum monthly temperatures do
coincide with the lowest values of net radiation which
occur during the December solstice.

London, England - 52° North, 1° East
monthly temperature for London, England.

The annual patterns of net radiation and mean monthly
temperature for London are quite similar to those
already described for Albuquerque. London does,
however, experience a greater annual variation in net
radiation. This greater variation can be explained by
the effect increasing latitude has on annual variations
of insolation. During the winter months outgoing
LW radiation actually exceeds incoming insolation
producing negative net radiation values. This was not
seen in Albuquerque. The variation in monthly mean
temperature is also less extreme in London when
compared to Albuquerque. Intuitively, one would
expect London to have a greater annual change in

radiation over the year. However, London's climate is
moderated by the frequent addition of latent
heat energy from seasonal precipitation.

Fairbanks, USA - 65° North, 148° West
monthly temperature for Fairbanks, USA.

Of the five locations examined, Fairbanks has the
greatest variations in mean monthly temperature.
Fairbanks is also the coldest of the climates examined.
This is primarily due to the fact that during six months
of the year net radiation is negative because
outgoing long wave exceeds incoming insolation.
Fairbanks also receives the least cumulative amount of
net radiation over the entire year. Mean month
temperature is at its maximum in July which is one
month ahead of the peak in net radiation.

WHAT ARE ISO-THERMS?
Isotherms are lines on a weather map that connect
points where the temperature is the same.
Isotherms generally trend east and west and show a
decrease in temperatures from the tropics toward the
poles.
Isotherm: is a iso line that connects points of equal
temperature.
Isotherm maps allows Geographers to study the spatial
analysis of temperatures.

Measurement of airMeasurement of air
temperaturetemperature
Air temperatures are now automatically
recorded by thermometers at a uniform
height above the ground.

The daily cycle of airThe daily cycle of air
◆ Because the earth rotates on its axis, incoming
solar energy at a location can vary widely
throughout the 24-hour period.
◆ Insolation is greatest in the middle of the
daylight period, when the sun is at its highest
position in the sky, and falls to zero at night.

Daily insolation and netDaily insolation and net
radiationradiation
◆ The daily cycle of temperature is
controlled by the daily cycle of net
radiation.
◆ At the equinox, insolation begins at
about sunrise (6 a.m.),rises to a peak
value at noon, and declines to zero at
sunset (6 p.m.).

◆ At the June solstice, insolation begins
about two hours earlier (4 a.m.) and
ends about two hours later (8 p.m.).
◆ At the December solstice, insolation
begins about two hours later than the
equinox curve (8 a.m.) and ends about
two hours earlier (4 p.m.).

◆ When net radiation is positive, the
surface gains heat, and when negative, it
loses heat.
◆ Net radiation begins the 24-hour day as
a negative value-a deficit-at midnight.
The deficit continues into the early
morning hours. Net radiation shows a
positive value- a surplus-shortly after
sunrise and rises sharply to a peak at
noon.

Daily temperatureDaily temperature
The minimum daily temperature usually
occurs about a half hour after sunrise. Air
temperature rises sharply in the morning
hours and continues to rise long after the
noon peak of net radiation. Air temperature
rises as long as net radiation is positive.
Temperatures are lowest just after sunrise
and highest in midafternoon.

Urban and rural temperatureUrban and rural temperature
contrastscontrasts
◆ Urban surfaces lack moisture and so
are warmer than rural surfaces during
the day. At night, urban materials
conduct stored heat to the surface, also
keeping temperatures warmer.

The urban heat islandThe urban heat island
◆ As a result of the above effects, air
temperatures in the central region of a
city are typically several degrees
warmer than those of the surrounding
suburbs and countryside. This is called
a heat island.

◆ The heat island persists through the
night because of the availability of a
heat stored in the ground during the
daytime hours.
◆ Another important factor in warming
the city is fuel consumption. In
summer, city temperatures are raised
through the use of air conditioning.

Temperature Inversion andTemperature Inversion and
FrostFrost
◆ In a temperature inversion, air
temperature increases with altitude.
◆ Low-level temperature inversions
often occur over snow-covered
surfaces in winter.

◆ Inversions can also result when a
warm air layer overlies a colder one.
This type of inversion is often found
along the west coasts of major
continents.

Frost
◆ If the temperature of the lowermost air
falls below the freezing point, for
sensitive plants during the growing
season, this temperature condition is
called a killing frost.

The annual cycle of airThe annual cycle of air
The annual cycle of net radiation,
which results from the variation of
insolation with the seasons, drives the
annual cycle of air temperatures.

Land and water contrastsLand and water contrasts
◆ Land-water contrasts keep air temperatures
at coastal locations more constant than at
interior continental locations.
◆ Oceans heat and cool more slowly than
continents.

◆ The surface of any extensive, deep
body of water heats more slowly and
cools more slowly than the surface of a
large body of land when both are
subjected to the same intensity of
insolation.

The average daily cycle of air
temperature for four different months
shows the effect of continental and
maritime location. Daily and seasonal
ranges are great at El Paso, a station in
the continental interior, but only
weakly developed at North Head,
Washington, which is on the Pacific
coast. The seasonal effect on overall
temperatures is stronger at El Paso.

Annual temperature cycleAnnual temperature cycle
P63 figure 3.16 Annual cycles of insolation
(a) and monthly mean air temperature (b)
for two stations at lat. 50°N: Winnipeg,
Canada, and Scilly Islands, England.

Insolation is identical for the two stations.
Winnipeg temperatures clearly show the
large annual range and earlier maximum
and minimum that are characteristic of its
continental location. Scilly Islands
temperatures show its maritime location in
the small annual range and delayed
maximum and minimum.

World Patterns of airWorld Patterns of air
◆ Isotherms: Lines drawn to connect
locations having the same temperature.
◆ Maps of isotherms show centers of
high and low temperatures as well as
temperature gradients.

Factors controlling airFactors controlling air
temperature patternstemperature patterns
◆ Global air temperature patterns are
controlled primarily by latitude,
coastal-interior location, and elevation.

◆ Temperatures decrease from the
equator to the poles.
◆ Large landmasses located in the
subarctic and arctic zones develop
centers of extremely low temperatures
in winter.
◆ Temperatures in equatorial regions
change little from January to July.

◆ Isotherms make a large north-south
shift from January to July over
continents in the midlatitude and
subarctic zones.
◆ Highlands are always colder than
surrounding lowlands.
◆ Areas of perpetual ice and snow are
always intensely cold.

The annual range of airThe annual range of air
temperaturestemperatures
◆ The annual range increases with
latitude, especially over northern
hemisphere continents.
◆ The greatest ranges occur in the
subarctic and arctic zones of Asia and
North America.

◆ The annual range is moderately large
on land areas in the tropical zone, near
the tropics of cancer and Capricorn.
◆ The annual range over oceans is less
than that over land at the same latitude.
◆ The annual range is very small over oceans
in the tropical zone.

Lecture Atmospheric Temperature

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Lecture Atmospheric Temperature