Transcript Document

Outline for Lesson 6
World Distributions of Temperature
Cycles of Air Temperature
Temperature Measurements
2/13/03
World Temperature Distributions
Isotherms trend east to west
Q. Why ?
(Temperature)
North
Large change
in temperature.
north to south
A. Heating of
the Earth’s
surface and
atmosphere is
in large part a
function of
latitude.
Little change
in temperature.
east to west
World mean sea level temperature in January in °C.
South
World Temperature Distributions
Decreasing temperature toward the Poles
(Temperature)
Q. Why ?
A. Heating of
the Earth’s
surface and
atmosphere is
in large part a
function of
latitude.
North
Cold
Hot
Cold
World mean sea level temperature in January in °C.
South
World
Temperature
Distributions
Hot and Cool
“spots” continuously
migrate south
from June 21-22
until Dec 22-23
them migrate north
from Dec 22-23 until
June 21-22.
World mean sea level temperature in January in °C.
Q. Why ?
World mean sea level temperature in July in °C.
Migration of position where sun’s rays are 90° overhead
Summer
Spring
The “hot spots”on the temperature
plot migrate with latitude, as does
the position where the
Summer
Sun’s rays are 90°
overhead.
23.5° N
Tropic of Cancer
Equator
Tropic of Capricorn
23.5° S
Fall
Winter
Winter
The higher the angle of the sun the more solar radiation to heat
the Earth and atmosphere.
Most intense
Intense
Least Intense
World
Temperature
Distributions
The hottest and
coldest places are
over land.
Warm ocean
currents moving to
the Poles warm the
air. Equatorial
bound currents
Help cool the air.
-40 °C
Equatorial
temperatures
do not fluctuate
significantly
(there are no
seasons).
25 °C
World mean sea level temperature in January in °C.
Middle and
higher latitudes
have much
stronger seasonal
signals.
10 °C
25 °C
World mean sea level temperature in July in °C.
Another way to
think about the
effect of latitude
on temperature
data
Comparison of
solar noon sun
angles for for the
summer and
winter solstice.
Cycles of Air temperatures
“Its hot in the day and cold in the night!!….” –Public Enemy
Rate of
outgoing
exceeds
the rate
Of incoming.
The daily cycle of incoming solar radiation, earth’s radiation
And the resulting temperature cycle. Midday, Equinox.
Rate of
incoming
exceeds
the rate
of outgoing.
Annual Temperature Variations
The months of the year with the highest and lowest temperatures
do not coincide with the months receiving the most or lowest
radiation.
The other processes
which also control
temperature (i.e. winds
and surface ocean
currents do not happen
instantaneously. There
is a “lag time”.
Urban heat islands have been created over time
here in the United States and around the world.
In these cities, the temperature on
the hottest summer day is rising by
up to 1°F each decade.
In Baltimore, Phoenix,
Tucson, Washington,
Shanghai, and Tokyo,
for example, scientific
data show that July's
maximum temperatures
during the last 30 to 80 years
have been steadily increasing
at a rate of one-half to one
degree Fahrenheit every
ten years.
Data from these cities indicate increases in urban
temperatures ranging from 0.2°F to 0.8°F per decade.
The Heat Island Effect (Washington DC)
Changes in the earth’s
surface when vegetated
areas are transformed
to asphalt .
Tall buildings and
Concrete have a higher
specific heat than
vegetation and soil
Average Minimum Temperatures (Dec-Feb)
Heat that would have gone to convert
liquid water to water vapor is goes toward
increasing the surface temperature.
Rapid runoff of
rainwater reduces the
amount of energy
consumed by
evaporative cooling.
Average Temperatures For Suburban Philadelphia
Airport and Downtown Philadelphia
Temperature (deg C)
30
25
20
15
Suburban
Downtown
10
5
0
-5
Annual Mean
Mean June max
Mean
Mean June min
-Mean
December max
December min
Data from table 3-D on page 74
Higher temperatures in urban heat islands results in
increased energy use, mostly due to a greater demand for
air conditioning. As power plants burn more fossil fuels,
they increase both the pollution level and energy costs.
As temperature rises, so does the likelihood that
ozone (and smog) will exceed the national standard.
Bimetal strips are often used to construct
thermographs.
A type of thermometer
with two metal strips connected
together. The two metals expand
at drastically different rates when
heated which causes the stripe to
bend. The bending moves the pen
up and down the roll of graph paper
Maximum Temperature in the afternoon
Cooling trend..
Perhaps a “cold front”
- Maximum temperatures observed.
- Minimum temperatures observed.
Thermograph plot of temperatures for Peoria Illinois, during a seven-day span
in May 1992. Temperature typically reaches a maximum in the afternoon,
however, a weather event results in a cooling trend that results in the maximum
being observed near midnight.
Temperature Measurements
Mechanical Thermometers
Temperature rises, molecules in the fluid
grow more expansive and rise in the column.
Have to account for optical distortions created
by the meniscus….calibrate it with a known
standard
Special thermometers have been developed to record the
maximum and minimum temperatures.
Electrical Thermometers
-thermistor (thermal resistor) is a stripe of metal which varies its
resistance to a current flow with temperature. As temperature goes
down the resistance decreases temperature goes up and the
resistance increases.
various thermistors
Temperature Scales
•Fahrenheit
•Celsius
•Kelvin
All temperature scales need
reference points.
The freezing and boiling point of
water are convenient.
How to convert between the different scales.
The interval between the boiling and freezing point is 100
degrees on the Celsius scale and 180 between on Fahrenheit
scale.
180/100 = 1.8
F to C:
°F = (1.8 x °C) + 32
or
C to F:
°C = (°F-32)/1.8
Kelvin Scale
Degrees Kelvin are called Kelvins.
The divisions are exactly the same
as Celsius. The reference points are
different however, 373 K is the boiling
point and 273 is the freezing point. The
unique reference point for Kelvin is
point at which all molecular motion
is presumed to stop.
Chapter 4 Moisture and Atmospheric Stability
•Movement of Water through the Atmosphere
•Waters Changes of State
atmosphere
Movement of Water
through the Atmosphere
land
oceans
It is the Atmosphere which links the Oceans to the Land.
Even though the amount of water in the atmosphere at
any time is only a fraction if the total Earth’s total
hydrosphere, it is the rapid exchange taking place that
creates what we call weather.
How fast is the exchange?
It is estimated that over North America, almost six times
as much water is carried within the atmospheric currents
than is transported in all the rivers in the continent.
Energy is absorbed or released from the atmosphere
during the exchange. The energy that is liberated
helps to drive the “weather machine”