Layers of the Atmosphere Weather and Climate

Pressure Pressure is a force that acts over a certain area. Liquids and gases are fluids. Fluids are any material that is able to flow. Fluids exert pressure because of the motion of their particles. Pressure will always move from a high pressure to a low pressure area. The pressure will always try to equalize. You see this when you get a hole in your bicycle tire.

Inflating example Air inside a ball pushes against the sides. The more air we put in a ball, the more the molecules push. So the pressure increases as we add air. Remember this

Air Pressure Air pressure is the result of the column of air that is above you. There is so much air above you that at sea level you have 14.7 lbs/in2 pushing on you. Gravity causes most of the air to be pulled down to the surface.

Why are we not crushed by air pressure? Air pressure is equal in all directions. So air pushes equally in all sides of us. The forces are balanced!

Diagram on page 5 Analogy for air pressure

Units of Air Pressure TV weather stations and aviation use inches of mercury. Meteorologists (and the NWS) use millibars, an SI unit.

Altitude and Density Shows density of air As the air pressure decreases, the density of the air decreases. The air particles are not squashed together as tightly the higher one goes. This is caused by gravity! The air at sea level and at 6km has the same 21% oxygen, but at 6km there are fewer molecules, so you take in less oxygen with each breath. Shows density of air

Layers in a different diagram

Temperature and the Troposphere Troposphere: temperature at surface is warmed by the earth absorbing energy from the sun. Air cools as it rises (air molecules lose energy) The air cools by about 6.5°C for every 1-km above the ground. In 10 KM air will cool 6.5*10=65

Temperature and the Stratosphere Ozone absorbs ultraviolet radiation from the sun, causing the temperature to increase.

Temperature and the Mesosphere This layer does not absorb energy from the sun, so it starts to cool again. Without greenhouse gases, energy pretty much passes straight through!

Temperature and the Thermosphere Solar radiation first hits this layer, so the few particles that are here can gain lots of energy. They move rapidly, so they have a very high temperature. But the air is so thin here that it takes special instruments to measure the temperature accurately. So even though it is very hot (over 1000°C), it would feel cold because there are so few particles to transfer heat to you.

The Troposphere Lowest (inner) layer weather occurs here we live in it. “tropo” means turning or changing conditions depth varies from 9km above the poles to 16km at the equator shallowest (least thick) layer, but contains most of the mass (90%).

The Stratosphere “strato” means layer or spreading out Contains the ozone layer which absorbs energy and causes the temperature to rise The ozone layer protects the surface from dangerous UV rays

The Mesosphere Drop in temperature marks beginning of mesosphere “Meso” means middle Most meteors burn up here

The Thermosphere Very top layer Air is very, very thin, about 1/1000th as dense as the air at sea level “Thermo” means heat Extends from 80km to space No definite outer edge Very hot (over 1000°C), but since air is so thin it would not feel warm at all. Divided into two parts, the ionosphere and the exosphere

The Ionosphere Energy from sun strips the electrons from the gas molecules creating charged particles called ions. Radio waves can bounce off of ions, allowing radio waves to travel great distances. The aurora borealis (Northern Lights) occur here

The Exosphere “Exo” means outer Extends for 1000’s of miles Satellites orbit here No definite edge Molecules gradually escape out into space