Chapter 2 -- Heating Earth's Surface and Atmosphere

Earth has two principal motions—rotation and revolution. Rotation is the spinning of Earth about its axis. Revolution refers to the movement of Earth in its orbit around the Sun.

The two most important reasons for the variation in solar energy reaching a particular location are:

1. The seasonal changes in the angle at which the Sun's rays strike the surface

2. The length of daylight.

The seasonal variation in the angle of the Sun affects where on Earth the solar rays are most concentrated and the thickness of atmosphere the rays must penetrate.
Important pages and Smart figures Pages 30-35, Figures: 2.2, 2.5, 2.6, 2.8

The four days each year given special significance based on the annual migration of the direct rays of the Sun and its importance to the yearly cycle of weather are (1) June 20/21, the summer solstice for people living in the Northern Hemisphere, when the vertical rays of the Sun are striking 23.5° north latitude (Tropic of Cancer), (2) December 21/22, the winter solstice for people living in the Northern Hemisphere, when the vertical rays of the Sun are striking 23.5° south latitude (Tropic of Capricorn), (3) September 22/23, the autumnal equinox in the Northern Hemisphere, when the vertical rays of the Sun strike the equator, and (4) March 20/21, the spring or vernal, equinox in the Northern Hemisphere, when the vertical rays of the Sun also strike the equator.

Convection and Conduction

Convection and Conduction

Convection and Conduction

Convection and Conduction

Convection and Conduction

Hint: Cancer comes before Capricorn

Figure 1 direct rays on the earth Figure 2

Know latittude lines.

Seasons of 2017:
SPRING EQUINOX March 20, 6:29 A.M. EDT
FALL EQUINOX September 22, 4:02 P.M. EDT
WINTER SOLSTICE December 21, 11:28 A.M. EST

Monthly Almanacs

Daily climatological data can be analyzed to produce averages and records. This information is included in our monthly almanacs.
The almanacs also contain times of sunrise and sunset times and daily records of precipitation and snowfall.


Seasons of 2018:
SPRING EQUINOX March 20, 12:15 P.M. EDT
FALL EQUINOX September 22, 9:54 P.M. EDT
WINTER SOLSTICE December 21, 5:23 P.M. EST


Why Do the Seasons Change?

The four seasons are determined by shifting sunlight (not heat!)—which is determined by how our planet orbits the Sun and the tilt of its axis.


Figure 1

C: March 20-21 Spring or Vernal Equinox

D: Summer Solstice June 20-21, About 15 hours of daylight

B: Autumnal Equinox September 22-23

A: Winter Solstice December 21-22, About 9 hours of daylight

Figure 2

C: 66 1/2 Degrees North: Arctic Cirle

E: 23 1/2 Degrees North: Tropic of Cancer

B: 0 Degrees: Equator

A: 23 1/2 Degrees South: Tropic of Capricorn

D: 66 1/2 Degrees South: Antarctic Circle

Energy is the ability to do work. The two major categories of energy are (1) kinetic energy, which can be thought of as energy of motion, and (2) potential energy, energy that has the capability to do work.

Heat is the transfer of energy into or out of an object because of temperature differences between that object and its surroundings. (Page 38)

Convection and Conduction
The three mechanisms of heat transfer are ( Smart Figure 2.11 Page 39) (1) conduction, the transfer of heat through matter by molecular activity, (2) convection, the transfer of heat by mass movement or circulation within a substance, and (3) radiation, the transfer mechanism by which solar energy reaches our planet.

Radiation or electromagnetic radiation, whether X-rays, visible light, heat waves, or radio, travels as various size waves through the vacuum of space at 300,000 kilometers per second. Shorter wavelengths of radiation are associated with greater energy. The wavelength of visible light ranges from 0.4 micrometer (violet) to 0.7 micrometer (red). Although the Sun emits many forms of radiation, most of the energy is concentrated in the visible and near visible (infrared and ultraviolet) parts of the spectrum. The basic laws of radiation are (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, and (4) objects that are good absorbers of radiation are also good emitters.

Satellite Views: Visible and Infrared
Smart Figure 2.13 Page 41

wavelength picture

incoming energy

wavelength picture

wavelength picture

wavelength picture

wavelength picture

Important pages and Smart figures Pages 44-47, Figures: 2.15, 2.16, 2.17, 2.18

Approximately 50 percent of the solar energy that strikes the top of the atmosphere reaches Earth's surface. About 30 percent is reflected back to space by the atmosphere. The remaining 20 percent of the energy is absorbed by clouds and the atmosphere's gases. The wavelength of the energy being transmitted, as well as the size and nature of the absorbing or reflecting substance, determine whether solar radiation will be scattered, reflected back to space, or absorbed. The fraction of radiation reflected by a surface is called its albedo. Fresh Snow has the highest Albedo.

wavelength picture

Radiant energy that is absorbed heats Earth and eventually is reradiated skyward. 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. The general drop in temperature with increased altitude in the troposphere (about 6.5°C/kilometer, a figure called the normal lapse rate) supports the fact that the atmosphere is heated from below. The transmission of shortwave solar radiation by the atmosphere, coupled with the selective absorption of terrestrial radiation by atmospheric gases that results in the warming of the atmosphere, is referred to as the greenhouse effect.

Because of the annual balance that exists between incoming and outgoing radiation, called Earth's heat budget, (Smartfigure 2.23, 2.24, Page 51,52) Earth's average temperature remains relatively constant, despite seasonal cold spells and heat waves.

Although the balance of incoming and outgoing radiation holds for the entire planet, it is not maintained at each latitude. Averaged over the entire year, a zone around Earth between 38°N and 38°S receives more solar radiation than is lost to space. The opposite is true for higher latitudes, where more heat is lost through longwave terrestrial radiation than is received. It is this energy imbalance between the low and high latitudes that drives the global winds and ocean currents, which in turn transfer surplus heat from the tropics poleward. Furthermore, the radiation balance of a given place fluctuates with changes in cloud cover, atmospheric composition, and most important, Sun angle and length of daylight. Thus, areas of radiation surplus and deficit migrate seasonally as the Sun angle and length of daylight change.

Don't forget you MUST read the chapters in the Book!!!!

Know levels of the atmosphere. What is important about each level, what makes one different from the next. Air, Temperature, Gases and Location. Climate and weather - They are different. Why and How.
Seasons - why and why do we have sesasons. Where do they sun's rays hit the Earth. How much radiation do we receive?
Three heat transfers.
Why is the sunsets red and sky blue?

Some of the main topics on Test 1 --email me if you have any questions -

TEST 1 - Chapter 1 / Chapter 2