Earth & Environment
 








 

The Atmosphere – Chapters 26 – 28 Notes & Review Questions

Directions: First read Chapters 26 – 28 in your Earth Science textbook.

  Our atmosphere is made of layers of air of decreasing density as you go higher. The first layer, the troposphere, contains most of the air and all the weather. The second layer, the stratosphere, contains the ozone (O₃) that protects us from ultraviolet (UV) radiation from the sun. The next layer, the mesosphere, is the coldest layer of the atmosphere, and the last layer, the thermosphere, is the hottest.

  Heat is transferred through the atmosphere (and through everything else, for that matter) through either conduction, convection, or radiation. Conduction is the transfer through a solid by touch. Convection is the transfer through a liquid or gas by circulation by a current of some sort. Radiation is the transfer through a gas or vacuum with wave energy.

  There are several reasons for temperature variations. Some are caused by changes in altitude or depth. The atmosphere typically gets colder as you go up, and the ocean gets colder as you go down. Cloud cover causes sunlight to be reflected instead of absorbed, so it can keep the earth cooler during daylight hours. It traps heat in like a blanket, so clouds keep the Earth warmer at night. Our seasons are not caused by the distance to the sun, but by the angle the sunlight hits the Earth at. During the summer the sun’s rays hit the earth from directly overhead, and it gets hotter, during winter the sun is coming in at a low angle, so it does not heat the ground as well.

  This is the only planet on which water naturally occurs in all three states at the same time. In order for water or any substance to melt, and change from a solid to a liquid, you must heat it up. The molecules must move farther apart and vibrate more rapidly, colliding into each other more frequently. In order for the liquid to vaporize into a gas, more heat must be added. Evaporation is slow vaporization, and boiling is rapid vaporization. In order for a solid to sublimate into a gas, a lot of heat must he added very quickly, and only certain substance, like frozen CO₂ will do this. In order for a gas to condense into a liquid, heat must be given off. In order for the liquid to freeze into a solid, more heat must be given off. These changes of state or phase all require the addition or removal of heat to occur.

  Our air can only hold a certain amount of water vapor in it before it begins to condense and fall as precipitation, and it can hold more when it is warmer than when it is cooler. That is why our summers are so humid and our winters are so dry. When cool, dry air warms up during the day, it can hold more humidity. When warm, moist air cools off at night, it may get so saturated that it can’t hold any more and dew forms. The specific humidity is the actual amount of water vapor in the air, and it is always less than a percent or two. The relative humidity is how much water vapor is in the air compared to how much there could be at that temperature, so it is a measure of how saturated the air is, and the number can be anywhere from 0-100%.

  Clouds form when air cools off and can no longer hold all the moisture, so tiny particles clump together into larger particles of water. When they are large enough to be visible, but not large enough to be heavy enough fall to the earth, clouds (or fog) form. As the particles keep condensing, the particles get large enough (and heavy enough) to start falling through the air. They will become precipitation, either rain, snow, sleet or hail, depending on the temperature of the air they fall through. It almost always starts out as snow, up high in the clouds, which is frozen water vapor (not frozen rain) and if it is cold enough on the way down, it will stay snow. If it melts on the way down, it will be rain. If it re-freezes, it will be sleet (which is frozen rain.). If it gets caught in an updraft, and stays in the clouds for a while, freezing layer upon layer, getting larger and larger, it will be hail.

  Clouds are named by their altitude and shape. The prefix cirro- means a high cloud. The prefix alto- means a medium altitude cloud. The prefix strato- means a low cloud. Clouds that are thin and wispy are called cirrus clouds. If they are puffy, they are cumulus. If they stretch across the sky like a blanket, they are called stratus. If they produce precipitation, they are called nimbo- or nimbus, as in nimbostratus or cumulonimbus.

  Air pressure is the weight of the air above you, so it is greater at sea level than here, and greater here than on a mountain top (where there is less air above you!) We use a barometer to measure air pressure, be familiar with the several types in your chapter. When the air pressure is low in one area, perhaps because hot air is rising, and it is high in another area, perhaps because a cold mass is sinking, the air will move from the area of high pressure to the area of low pressure, causing wind. It would flow in a straight line, but is forced to turn by the Coriolis force. Read about this in Chapter 28, it greatly affects our wind zones. Your teacher will explain this further on the board on a “B” day. Be familiar with “local” winds, like sea breezes, land breezes, jet streams and seasonal winds like the Santa Anna winds in CA and the monsoons in Asia.