What is air pressure?
How does air pressure change with altitude?
Why aren’t we crushed by all this pressure on our bodies?
Because we have an equal amount of pressure inside our bodies!
The fluids and gases inside our body cells have their own pressure.
internal body pressure pushing outward = air pressure pushing inward
Imploding train car – demonstrating the massive effect of air pressure. This large container has has had the air inside of it removed.
– – – – –
The Earth’s Atmopshere
Earth Science, Tarbuck and Lutgens
Chapter 17.1 Atmosphere characteristics
Earth’s atmosphere is unique. No other planet in our solar system has an atmosphere with the exact mixture of gases or the moisture conditions and heat needed to sustain life as we know it. The gases that make up Earth’s atmosphere and the controls to which they are subject are vital to our existence. In this chapter, you will begin to examine the ocean of air in which we live.
Composition of the atmosphere
The composition of air varies from time to time and from place to place. However, if the water vapor, dust, and other variable components were removed from the atmosphere, its makeup would be very stable worldwide up to an altitude of about 80 kilometers.
Two gases—nitrogen and oxygen—make up 99 percent of the volume of clean, dry air.
The remaining 1 percent of dry air is mostly the inert gas argon (0.93 percent) plus tiny quantities of a number of other gases.
CO2 (Carbon dioxide) is present in only small amounts (approximately 0.039 percent)
It is an active absorber of energy given off by Earth. Therefore, it plays a significant role in heating the atmosphere.
Important materials that vary in the air from time to time and place to place include water vapor, dust particles, and ozone. These components also can have significant effects on weather and climate.
The amount of water vapor varies from almost none to about 4 percent by volume.
Human influence: Primary pollutants – what they are, and where they come from.
Air pollutants are airborne particles and gases that occur in concentrations large enough to endanger the health of organisms. Primary pollutants are emitted directly from identifiable sources. Emissions from transportation vehicles account for nearly half the primary pollutants by weight.
Emission of air pollution
Atmospheric pressure versus altitude
Changes in atmospheric pressure with height.
Atmospheric pressure is the weight of the air above.
At sea level, average air pressure =
1000 millibars = 1 kilogram / cm^2 = 14.7 pounds / in^2
One half of the atmosphere lies below an altitude of 5.6 kilometers.
Above 100 km = 0.00003 percent of the atmosphere
Note the axes!
2 different Y-axes: Both are for altitude, but one is in km while the other is in miles.
2 different X-axes: Both are for temperature, but one is in degrees C while the other is in degrees F.
Purpose of graph? Learn how air temperature changes with altitude
At what altitude do air molecules have the warmest temperature?
Why would it nonetheless feel cold if you were in this region of the atmosphere?
Troposphere – bottom layer – temperature decreases with an increase in altitude. This is where our weather occurs.
temperature drops, to a height of about 12 kilometers
Stratosphere – here temperature remains constant to about 20 kilometers. Temp then gradually increases until the stratopause, at 50 km
Temp increase here because ozone is concentrated here: ozone absorbs ultraviolet radiation from the sun.
Mesosphere – temp decreases with altitude, until 80 km. Air temperatures approach −90°C.
Thermosphere – contains only a tiny fraction of the atmosphere’s mass.
Temp increases here because O2 and N2 gas molecules absorb short-wave, high-energy solar radiation.
Yet it would feel cold if you exposed yourself to these hot air molecules! Why?
Because although the air molecules are vibrating faster (‘hotter’) there are far fewer of them.
What would keep you warmer? Having only one huge fireplace, for a very large apartment building? Or having small fireplaces in every single apartment?
Heat = ( temp of air molecules ) x ( # air molecules )
It is colder in the winter than in the summer. But why? Length of day and a gradual change in the angle of the noon sun above the horizon affect the amount of energy Earth receives.
Earth’s axis is not perpendicular to the plane of its orbit around the sun. Instead it is tilted 23.5 degrees from the perpendicular, as shown in Figure 7. Because the axis remains pointed toward the North Star as Earth moves around the sun, the position of Earth’s axis to the sun’s rays is constantly changing. If the axis were not tilted, we would not have seasonal changes.
Orientation of Earth relative to the sun and the constant movement of Earth cause the angle of the noon sun to vary by up to 47 degrees (−23.5 degrees to −23.5 degrees) for many locations during the year.
For example, a midlatitude city like New York, located about 40 degrees north latitude, has a maximum noon sun angle of 73.5 degrees when the sun’s vertical rays reach their farthest northward location in June.
Six months later, New York has a minimum noon sun angle of 26.5 degrees.
Why do we have seasons? Due to the tilt of the Earth’s axis
The earth actually rotates, around an imaginary axis
As the Earth moves around the Sun, the axis keeps pointing in the same direction.
On June 21 or 22 each year the axis is such that the Northern Hemisphere is “leaning” 23.5 degrees toward the sun. This date, shown on the left side of Figure 8, is known as the summer solstice, or the first day of summer.
Six months later, in December, when Earth has moved to the opposite side of its orbit, the Northern Hemisphere “leans” 23.5 degrees away from the sun.
December 21 or 22 is the winter solstice, the first day of winter.
On days between these extremes, Earth’s axis is leaning at amounts less than 23.5 degrees to the rays of the sun.
The equinoxes occur midway between the solstices.
September 22 or 23 is the date of the autumnal equinox in the Northern Hemisphere.
March 21 or 22 is the date of the spring equinox for the Northern Hemisphere.
On these dates, the vertical rays of the sun strike the equator (0 degrees latitude) because Earth is in a position in its orbit so that the axis is tilted neither toward nor away from the sun.
Layers of the atmosphere
The ionosphere can reflect radio waves