L.4: Energy, Temperature, and Atmospheric Heat Transfer

Large, tall clouds (called "cumulonimbus clouds") are created partly as a result of which process of heat transfer in the atmosphere?

convection

Specific Heat

*** the heat required to raise the temperature of the unit mass of a given substance by a given amount (usually one degree). The specific heat of a substance is heat capacity of the substance per unit mass: cp=Cp / M The heat capacity from one object to another varies. Some substances show a larger rise in temperature than others, given a certain amount of heat input. This is because the specific heat capacity from one object to another also varies. Basically, certain substances (such as water) require more energy to demonstrate the same rise in temperature as another substance (such as air). High specific heat equates to slow warming, while low specific heat equates to fast warming. The table below lists the specific heat for several common substances. Key Points: (1) The specific heat of a substance is the amount of heat required to increase the temperature of 1 gram of that substance by 1° C. The unit for specific heat is cal/g/°C or J/kg/°C. (2) 1 calorie (cal) is the energy needed to raise the temperature of 1 gram of water by 1° C. 1 cal = 4.186 Joules of energy (or, 1 Joule = 0.2389 cal). Just as it requires 1 cal to raise 1 gram of water by 1° C. Note that the specific heat for water is 1 cal/g/°C, while specific heat for dry air is 0.24, only a quarter of that of water. As a result, it is easier to heat (or cool) air than to heat (or cool) water. This is explains why in the air over the Great Lake surfaces is cooler in the summer than is the air over land; the reverse is true in winter. As you will learn later, this is the basic reason behind lake-effect snow.

The sun emits a maximum amount of radiation at wavelengths near __________, while the earth emits maximum radiation near wavelengths of __________.

0.5 micrometers; 10 micrometers

At which temperature would the earth be radiating energy at the greatest rate or intensity?

105 F (the highest one)

Temperature

A measure of heat (or lack of heat). A measure of the avg. kinetic energy of molecules of a substance. Air is a mixture of billions of atoms and molecules, all moving in different directions. However, some of are moving faster than others, and some are moving slower than others. The energy that this movement creates is called kinetic energy. Because temperature is measuring kinetic energy, it is actually measuring the average speed (motion) of the atoms and molecules. High temperatures correspond to faster average molecule speed, and lower temperatures correspond to slower average speeds.

Selective absorbers

All gases in earth's atmosphere are selective absorbers that selectively absorb and emit radiation. For example, water vapor and carbon dioxide are strong absorbers (and emitters) of infrared radiation. As you may know, these are two of the greenhouse gases that keep the lower atmosphere warm enough for life to exist.

Go back to converting degrees Kelvin to degrees Celsius and Fahrenheit. What is 255 degrees K in each of these temperature measurements?

Answer: -18 degrees Celsius, and 0 degrees Fahrenheit.

Blackbody

Any object that ABSORBS ALL OF THE RADIATION it encounters and emits all of the radiation that it receives is called a blackbody. Both the Sun and the Earth are blackbodies.

IDK pg 33

At this temperature, the earth is absorbing radiation from the Sun and emitting radiation at the same rate; therefore, its average temperature does not change. This temperature is approximately 255 K This is a very cold temperature, right? Yet, the average surface temperature felt on the Earth is approximately 59 degrees Fahrenheit, so what causes such a large difference in temperature? The answer: the earth's atmosphere. The atmosphere is also absorbing and emitting infrared radiation. All gases in earth's atmosphere are selective absorbers that selectively absorb and emit radiation. For example, water vapor and carbon dioxide are strong absorbers (and emitters) of infrared radiation. As you may know, these are two of the greenhouse gases that keep the lower atmosphere warm enough for life to exist. On the other hand, ozone and molecular oxygen are good absorbers of ultraviolet (UV) radiation, so they can keep us from getting sunburned. Because UV wavelengths are much shorter than those of visible light, UV radiation carries more energy. They have the potential to produce sunburns and penetrate skin tissue, which could cause skin cancer. This is one of the reasons why the loss of the ozone layer (sometimes called the earth's sunscreen) in the atmosphere is of significant concern--it could potentially have left us much more vulnerable to sunburns and skin cancer.

Convection

COOL air SINKS WARM air RISES DEPENDENT ON THE MOVEMENT OF AIR Heat is transferred by the mass movement of a fluid (which can be water or air). As air moves from one place to another, it carries its heat energy with it - therefore, convection ALWAYS REQUIRES MOTION. In meteorology, convection is usually associated with the vertical movement of air because this is the most efficient way for the atmosphere to transport heat from one place to another. Surfaces heated by the Sun transfer heat energy to the air molecules touching the heated surface, and gain heat energy through conduction. The warmed air (being lighter than the surrounding air) rises, and cooler, heavier air sinks back toward the surface to replace this warm air. That cooler air is then warmed and the process repeats itself. The rate of energy transferred by convection depends on the temperature of the rising air parcel compared to the temperature of the surrounding atmosphere. Convection is strong in summer and weak in winter, strong on sunny days and weak on cloudy days, and strong over the tropics and weak in polar regions (as the temperature of the surrounding atmosphere is so much colder).

Kelvin

Despite the common use of these scales, neither Fahrenheit nor Celsius is used in scientific calculations. Instead, another scale, Kelvin (K), named for William Thompson (also known as "Lord Kelvin") is commonly used in scientific calculations. The Kelvin scale is the same as Celsius, except that it is 273 degrees higher than Celsius. In other words, 0 K is equal to -273 degrees Celsius or K = 273 + C.

Fahrenheit

Developed by German physicist Gabriel Daniel Fahrenheit in the early 18th century. 32° F being freezing point 212° F being boiling point Used in the United States Q: If there is 100 degrees between freezing and boiling water temperatures in Celsius, and 180 degrees (212-32) between freezing and boiling water temperatures in Fahrenheit, what is a 1 degree difference in temperature equivalent to in Fahrenheit? 1.8 Q: Given that information, how do you convert a Celsius temperature to a Fahrenheit temperature measure? (1) Take the temperature in degrees Celsius and multiply by 1.8 (as there are 1.8 degrees Fahrenheit for every degree of Celsius). (2) Next, add 32 degrees (because Fahrenheit "starts" at 32, while Celsius starts at 0). (3) The result is degrees Fahrenheit.

Heat and temperature are two ways of saying the same thing.

False

Krichoff's Law

Finally, objects that are good absorbers of radiation are also good emitters of radiation. This can be described with Krichhoff's Law, which equates the absorptivity of matter to emissivity at the same wavelength. We will go into more of this in a moment when we discuss how different gases in the earth's atmosphere absorb energy in different ways.

Conduction

Heat Transfer. Occurs as warmer molecules transmit heat to adjacent cooler molecules. Flows warmer to ---> colder Heat is transferred within a substance from one molecule to another when they come into contact with one another. Ex: The ground warms the air through conduction. The amount of heat transferred by conduction depends on two factors: temperature difference between the two objects and their thermal conductivity (ability of a substance to conduct heat by molecular motion) Conduction is an inefficient process for heat transfer in the atmosphere.

Calorie

Heat is the energy transferred between objects as a result of temperature difference between those objects. Heat is measured in calories (cal). The temperature change of an object depends on three factors: how much heat is being added, the amount of matter in the object, the heat capacity of the substance.

Factors for radiating heat

How an object radiates and absorbs energy is strongly dependent on its surface characteristics. These characteristics can include its color, texture, and moisture. If you have ever worn a black shirt on a hot, sunny day, you have experienced this firsthand. Wearing black, you are likely to feel warmer (and more uncomfortable) than you would had you worn a lighter colored shirt. This happens because dark colors, like black, absorb more energy than lighter colors, such as white.

In the Celsius temperature scale, what is the significance of the temperature increment of 1 degree C?

It is 1/100 of the interval between the freezing point and the boiling point of water.

Which of the following is NOT a reason why water warms and cools much more slowly than land?

It takes more heat to raise the temperature of soil 1 degree C than it does to raise the temperature of water 1 degree C.

Stevenson Shelter

Meteorologists use a wooden box called a Stevenson shelter to observe temperature at a location. The Stevenson shelter consists of a 30 inch by 20 inch wooden box. It is painted white, contains slats, and the door opens to the north. The shelter is placed in an open area, about four to six feet above ground surface. Thermometers and other meteorological equipment are located inside the shelter, protected from the sun's direct rays, precipitation, wind, and other meteorological phenomena that may damage the sensors or cause false readings.

Celsius

Most other countries around the world use celsius. Swedish scientist Andres Celsius developed this scale later in the 18th century. The Celsius Scale is also referred to as Centigrade. Freezing point (of water) is 0°C Boiling point is 100°C

Latent Heat

One of two basic forms of heat energy. ***Latent heat energy is an important source of atmosphere energy. Heat REQUIRED to CHANGE A SUBSTANCE (such as water from one state to another). Ex: When water freezes to ice it releases heat to the environment and thus heats the environment. Equations: L = ± 2.5 x 106 J/kg condensation (heat released) or evaporation (heat taken in) L = ± 0.334 x 106 J/kg freezing (heat released) or melting (heat taken in) L = ± 2.83 x 106 J/kg deposition (heat released) or sublimation (heat taken in)

Sensible Heat

One of two basic forms of heat energy. Heat we FEEL or SENSE Measured with a thermometer

Radiation

Radiant energy travels in the form of waves (electromagnetic waves) and these waves release energy when an object absorbs them. ** Does not require molecules of air to transfer the heat. Does not require contact between two substances to transfer heat. Does not require motion to transfer heat. Electromagnetic waves do not need molecules to move them, therefore, radiation can occur in nothing. It is important to note that while all things on earth are constantly radiating energy, they are also absorbing energy as well. Question: Question: What do you think happens if an object radiates more energy than it absorbs? Answer: It gets colder. And vice versa - if an object absorbs more energy than it radiates, it gets warmer.

Wein's law

Radiation depends on the object's temperature. This can be measured with Wien's Law, which describes the relationship between temperature and the wavelengths of emitted radiation (see the difference in wavelength emitted by the Sun and Earth in the figure below). Key: As the temperature of an object increases, it will emit shorter wavelengths of radiation.

Kinetic Energy

Some air molecules are moving faster than others. The energy that this movement creates is called kinetic energy. Because temperature is measuring kinetic energy, it is actually measuring the average speed (motion) of the atoms and molecules.

Albedo

Some of the sun's radiation (about 30%) is scattered and reflected by the atmosphere, clouds, and the earth's surface. This reflection of radiation is known as the earth's albedo. Albedo refers to the percent radiation that returns (bounces back) from a surface compared to the amount of radiation that originally struck a surface. Essentially, albedo is a measure of reflectivity. A roof painted bright white will have a higher albedo than one with black shingles, as more radiation will reflect off the white roof. In turn, that radiation will not enter the house, making it cooler in the summer. 30% albedo, 19% absorbed by atmosphere and clouds, 51% absorbed by Earth's surface

Stefan-Boltzman law (pg 32)

Temperature can also affect the intensity of emitted radiation. This can be described using the Stefan-Boltzman law. This law states that the amount of energy per square meter per second that is emitted by a blackbody is related to the 4th power of its Kelvin temperature.

Heat Capacity

The heat capacity of a substance is the ratio of the amount of heat absorbed by the substance to its corresponding rise in temperature. Cp= heat input / temperature rise

Radiative Equilibrium temperature

The temperature at which this perfect absorption and emission occurs is called the radiative equilibrium temperature

High specific heat equates to slow warming, while low specific heat equates to fast warming.

True

Deposition is the change of state of water from:

Vapor to Ice.

Greenhouse gases

Water vapor, carbon dioxide, ozone Strong absorbers of infrared radiation. The greenhouse effect allows the Earth's atmosphere to absorb and emit infrared radiation back to the surface which helps keep the atmosphere warm (15°C and 50°F instead of -18°C, 0°F)

Clouds __________ infrared radiation and ___________ visible radiation.

absorb; reflect

If the amount of energy lost by the earth to space each year were NOT approximately equal to that received, the:

atmosphere's average temperature would change.

Which process below is most efficient for transferring heat in the atmosphere?

convection

A change of one degree on the Celsius scale is ________________ a change of one degree on the Kelvin scale.

equal

If the sun suddenly began emitting more energy, the earth's radiative equilibrium temperature would:

increase.

According to Wein's displacement law, the wavelength at which maximum radiation occurs is:

inversely proportional to the pressure.

Which of the following is known primarily as a selective absorber of ultraviolet radiation?

ozone

Which of these substances has the lowest specific heat?

rock

The change of state of ice into water vapor is known as:

sublimation.

Electromagnetic Spectrum

the range of wavelengths or frequencies over which electromagnetic radiation extends.

Condensation of water vapor to cloud droplets _________ its surroundings because _____________________________.

warms; latent heat is released during phase change

Which of these substances has the highest specific heat?

water