Week 02

Heat and Air Temperature

BS-281
Dr. Kareem Tonbol
Meteorology & Hydrographic Survey Program
ktonbol@aast.edu
 Energy, Temperature, and Heat
• Energy: is a property of objects which can be
transferred to other objects or converted into
different forms. (power derived from the
utilization of physical or chemical resources,
especially to provide light and heat or to work
machines).
 Energy, Temperature, and Heat
• Temperature: is a measure of the average
speed of the atoms and molecules, where
higher temperatures correspond to faster
average speeds.

• Heat: is the energy transferred into or out of

an object because of temperature differences
between that object and its surroundings.

• Sensible Heat - Latent heat.

 Temperature Units
• Degrees Celsius (C) : usually used to quote
temperature in general use – more readily
understood and values in convenient range.
• Degrees Fahrenheit (F) : widely used in America.
(°F) = (9/5) (°C) + 32

(°C) = (°F – 32)(5/9)

• Each Celsius degree (°C) is 180/100 or 1.8 times
bigger than a Fahrenheit degree (°F). In another
way, an increase in temperature of 1°C equals an
increase of 1.8°F.
Mechanisms of Heat Transfer
 Mechanisms of Heat Transfer
• Conduction: is the transfer
of heat through matter by
electron and molecular
collisions between
molecules. Because air is a
poor conductor, conduction
is significant only between
Earth’s surface and the air
immediately in contact with
the surface.
 Mechanisms of Heat Transfer
• Convection: Convection is
heat transfer that involves
the actual movement or
circulation of a substance.
Convection is an important
mechanism of heat transfer
in the atmosphere, where
warm air rises and cooler air
descends.
 Mechanisms of Heat Transfer
• Radiation: consists of a
large array of energy that
includes X-rays, visible
light, heat waves, and
radio waves that travel as
waves of various sizes.
Shorter wavelengths of
radiation have greater
energy.
 Mechanisms of Heat Transfer
• These are four basic laws of radiation:

1. All objects emit radiant energy;

2. Hotter objects radiate more total energy per unit area

than colder objects;

3. The hotter the radiating body, the shorter is the

wavelength of maximum radiation;

4. Objects that are good absorbers of radiation are also

good emitters.
 Solar Constant - Insolation
• Solar Constant: the rate at which energy reaches the earth's
atmosphere from the sun, usually taken to be 1,388 watts per
square meter.

• Insolation (Incoming Solar Radiation): is the solar radiation

that reaches the earth's surface. It is measured by the amount
of solar energy received per square centimeter per minute.

• Insolation is main source of energy for the Earth's

atmosphere.

• The amount of Insolation varies with latitude, time of day,

and season of the year.
 Factors affect the amount of
Insolation received by the Earth
1. Angle of insolation:
i. the more direct
(vertical) the rays,
the warmer the
temperature,
ii. highest angle at
equator; lowest
angle at the poles.
 Factors affect the amount of
Insolation received by the Earth
2. Duration of insolation:
i. the more hours of
the day the sun
shines, the warmer
the temperature,
ii. always 12 hours
day & 12 hours
night at the
equator.
 Factors affect the amount of
Insolation received by the Earth
3. Reflection, refraction, or
absorption of insolation:
i. during the day, clouds
block insolation, therefore
cooler temperature.
ii. during the night, clouds
insulate, therefore warmer
temperature.
iii. dark and rough surfaces
tend to absorb insolation
iv. light and smooth surfaces
tend to reflect insolation.
 Earth’s Heat Budget
Approximately 50 percent of the solar radiation that strikes the atmosphere
reaches Earth’s surface. About 30 percent is reflected back to space. The
remaining 20 percent of the energy is absorbed by clouds and the atmosphere’s
gases.
 Earth’s Heat Budget

• Because Earth has a much lower surface

temperature than the Sun, its radiation is in the
form of longwave infrared radiation. Because
the atmospheric gases, primarily water vapor
and carbon dioxide, are more efficient
absorbers of terrestrial (longwave) radiation,
the atmosphere is heated from the ground up.
 Earth’s Heat Budget

• The selective absorption of Earth radiation by

atmospheric gases, mainly water vapor and
carbon dioxide, that results in Earth’s average
temperature being warmer than it would be
otherwise is referred to as the greenhouse
effect.
 Earth’s Heat Budget
• The greenhouse effect is a natural
phenomenon that makes Earth habitable.
Human activities that release greenhouse
gases (primarily carbon dioxide) are the
“villains” of global warming—not the
“greenhouse effect” as it is often, but
inaccurately, portrayed.
 Temperature
• The Controls of Temperature:

1.Latitude,

2.Differential heating of land and water,

3.Ocean currents,

4.Altitude,

5.Geographic position,

6.Cloud cover.
 Temperature
• Isotherm is a line that connects points on a
map that have the same temperature (iso =
equal, therm = temperature).
 Temperature
• Isothermal Layer: layer through which
temperature remains constant with elevation.

• Temperature Inversion: A layer in which

temperature increases with altitude. It is a reversal
of the normal behavior of temperature in the
troposphere, where, under normal conditions,
temperature usually decreases with height.
Types of Temperature Inversion
 Lack of heavy cloud cover
Signs of a surface
inversion in the
early morning Windless or light
variable wind

Ground Fog

Frost (or dew)

 Temperature
• Ideal Conditions For Temperature Inversion:

1.Long nights, so that the outgoing radiation is

greater than the incoming radiation.

2.Clear skies, which allow unobstructed escape of

radiation.

3.Calm and stable air, so that there is no vertical

mixing at lower levels.
 Temperature

• Warm air holds more moisture than colder air.

• Warm, moist, humid air has less air pressure

than cold, dry air.

• Warm air is less dense than cold air.

Diurnal Variation of Air
Temperature
 Adiabatic Process
Adiabatic Process: is the process whereby the temperature of
air changes without the addition or subtraction of heat.
 Adiabatic Process
• Lapse Rate: is the rate of decrease of air temperature per unit
height in the atmosphere.

• Dry Adiabatic Lapse Rate (DALR): is the rate of decrease of air

temperature with height for unsaturated air rising under adiabatic
conditions. (10⁰C/1KM).

• Saturated Adiabatic Lapse Rate (SALR): is the rate of decrease

of air temperature with height for saturated air rising under adiabatic
conditions. (5⁰C/1KM).

• Environmental Lapse Rate (ELR): is the rate at which the air

temperature decrease with height in the atmosphere surrounding a
cloud or a rising parcel of air.
 Measuring Air Temperature
Thermometers were developed to measure air temperature.

Thermograph