Introduction

 

 

• The atmosphere is a cloud of gas and suspended solids extending from the Earth's surface out many thousands of miles, becoming increasingly thinner with distance but always held by the Earth's gravitational pull.

 

• The atmosphere is made up of layers surrounding the earth that holds the air we breath, protects us from outer space, and holds moisture (clouds), gases, and tiny particles. In short, the atmosphere is the protective bubble we live in.

 

• This protective bubble consists of several gases with the top four making up 99.998% of all gases. By far, the most common, nitrogen (78%), dilutes oxygen (21%) and prevents rapid burning at the earth's surface. Living things need it to make proteins. Oxygen is used by all living things and is essential for respiration.  It is also necessary for combustion or burning. Argon (.90%) is used in light bulbs. Plants use carbon dioxide (.03%) to make oxygen. Carbon dioxide also acts as a blanket and prevents the escape of heat into outer space.

 

Click here to learn more about:

Layers of Earth's Atmosphere

 

 

The Earth-Atmosphere Energy Balance:

 

The earth-atmosphere energy balance is the balance between:

1. incoming energy from the Sun and
2. outgoing energy from the Earth.

 

Energy released from the Sun is emitted as light energy. When it reaches the Earth, some is reflected back to space by clouds, some is absorbed by the atmosphere, and some is absorbed at the Earth's surface.  The type of medium (soil, rock, sand, water) covering an area has an effect on how much radiation is absorbed or reflected and how much energy it takes to warm the area up.  The type of medium helps determine the climate of an area.

 

Since the Earth is much cooler than the Sun, when it reradiates the energy it is much weaker (long wavelength) infrared energy. We can indirectly see this energy radiation into the atmosphere as heat, rising from a hot road, creating shimmers on hot sunny days. The earth-atmosphere energy balance is achieved as the energy received from the Sun balances the energy lost by the Earth back into space. In this way, the Earth maintains a stable average temperature and therefore a stable climate.

 

 

The absorption of infrared radiation trying to escape from the Earth back to space is particularly important to the global energy balance. The average surface temperature of the moon, which has no atmosphere, is 0°F (-18°C). By contrast, the average surface temperature of the Earth is 59°F (15°C). This heating effect is called the greenhouse effect.

 

Greenhouse warming is enhanced during nights when the sky is overcast. Heat energy from the earth can be trapped by clouds leading to higher temperatures as compared to nights with clear skies. The air is not allowed to cool as much with overcast skies. Under partly cloudy skies, some heat is allowed to escape and some remains trapped. Clear skies allow for the most cooling to take place.

 

The Coldest Nights In the Winter Are Clear Dark Nights

 

 

Lab: Insulating Properties of Sand, Soil, Water, Rock, and Snow

 

Relating the Lab to Climate

 

 

Air Pressure

 

The atoms and molecules that make up the various layers in the atmosphere are always moving in random directions. Despite their tiny size, when they strike a surface they exert pressure.  Each molecule is too small to feel and only exerts a tiny bit of pressure. However, when we add up the all the pressures from the large number of molecules that strike a surface each moment, then the total pressure is considerable. This is air pressure. As the density of the air increases, then the number of strikes per unit of time and area also increases.

 

Since molecules move in all directions, they can even exert air pressure upwards as they smash into objects from underneath. Air pressure can be exerted in all directions.  In the International Space Station, the density of the air is maintained so that it is similar to the density at the earth's surface. Therefore, the air pressure is the same in the space station as the earth's surface (14.7 pounds per square inch).

Back on Earth, as elevation increases, the number of molecules decreases and the density of air therefore is less, meaning a decrease in air pressure. In fact, while the atmosphere extends more than 15 miles (24 km) up, one half of the air molecules in the atmosphere are contained within the first 18,000 feet (5.6 km).

Because of this decrease in pressure with height, it makes it very hard to compare the air pressure at one location to another, especially when the elevations of each site differ. Therefore, to give meaning to the pressure values observed at each station, we need to convert the station air pressures reading to a value with a common dominator.

The common dominator we use is the sea-level. At observation stations around the world, through a series of calculations, the air pressure reading, regardless of the station elevation, is converted a value that would be observed if that instrument were located at sea level.

 

Units:

The two most common units in the United States to measure the pressure are "Inches of Mercury" and "Millibars". Inches of mercury refers to the height of a column of mercury measured in hundredths of inches. This is what you will usually hear from the NOAA Weather Radio or from your favorite weather or news source. At sea level, standard air pressure in inches of mercury is 29.92.

 

Millibars comes from the original term for pressure "bar". Bar is from the Greek "báros" meaning weight. A millibar is 1/1000th of a bar and is the amount of force it takes to move an object weighing a gram, one centimeter, in one second. Millibar values used in meteorology range from about 100 to 1050. At sea level, standard air pressure in millibars is 1013.2. Weather maps showing the pressure at the surface are drawn using millibars.

 

Although the changes are usually too slow to observe directly, air pressure is almost always changing. This change in pressure is caused by changes in air density, and air density is related to temperature.  Warm air is less dense than cooler air because the gas molecules in warm air have a greater velocity and are farther apart than in cooler air. So, while the average altitude of the 500 millibar level is around 18,000 feet (5,600 meters) the actual elevation will be higher in warm air than in cold air.

 

The most basic change in pressure is the twice daily rise and fall in due to the heating from the sun. Each day, around 4 a.m./p.m. the pressure is at its lowest and near its peak around 10 a.m./p.m. The magnitude of the daily cycle are greatest near the equator decreasing toward the poles.

 

On top of the daily fluctuations are the larger pressure changes as a result of the migrating weather systems. These weather systems are identified by the blue H's and red L's seen on weather maps. The H's represent the location of the area of highest pressure. The L's represent the position of the lowest pressure.

 

How do changes in weather related to changes in pressure?

The FALL of the barometer (decreasing pressure) denotes BAD WEATHER

The RISE of the barometer (increasing pressure) CLEAR WEATHER

 

 

 

Bernoulli's Principle states that as the speed of a moving fluid increases, the pressure within the fluid decreases.

 

To understand how and why Bernoulli's Principle works, we can consider the following:

1. Take a room full of children, and ask each child to start running in a classroom at top speed. Children will start bouncing off each other, and the walls.
2. Now take those same children out of the room, and ask them to run down the hall at top speed. Now they are all running together, and all collisions between children are much more gentle than before since they are all running in the same direction.

The children in both cases represent the atoms in the fluid, and the force of the collisions represents the pressure between those atoms. In the first case, when the speed of the group as a whole was zero, the jostling (or pressure) was high. In the second case, when the speed of the group as a whole was large, the jostling (or pressure) was low.

 

Check out this Youtube video and the ping pong example video below:

 

Why doesn't the ping pong ball fly out of the stream of air?

 

Collapsing Can Experiment

 

 

 

 

The Hydrologic (Water) Cycle:

 

 ess05_int_hydrocycle.swf

 

 

 

1. Evaporation is the change of state of water (a liquid) to water vapor (a gas). On average, about 47 inches (120 cm) is evaporated into the atmosphere from the ocean each year.
2. Transpiration is evaporation of liquid water from plants and trees into the atmosphere. About 90% of all water that enters the roots transpires into the atmosphere.
3. Sublimation is the process where ice and snow (a solid) changes into water vapor (a gas) without moving through the liquid phase.
4. Condensation is the process where water vapor (a gas) changes back into a water droplets (a liquid). This is when we begin to see clouds.
5. Transportation is the movement of solid, liquid and gaseous water through the atmosphere. Without this movement, the water evaporated over the ocean would not precipitate over land.
6. Precipitation is water that falls to the earth. Most precipitation falls as rain but includes snow, sleet, drizzle, and hail. Around 313,000 mi³ (515,000 km³) of water falls each year, mainly over the ocean.
7. Runoff is the variety of ways of which water moves over the earth's surface. This comes from melting snow or rain.
8. Infiltration is the movement of water into the ground from the surface.
9. Groundwater flow is the flow of water underground in aquifers. The water may return to the surface in springs or eventually seep into the oceans.
10. Plant uptake is water taken from the groundwater flow and soil moisture.