Altitude and Air Pressure
As altitude increases, air pressure  decreases. As altitude decreases, air  pressure increases.

Take a deep breath. As you inhale, your lungs fill with a mixture of molecules and a small number of single atoms.

 

Air is composed of many different molecules and atoms in a gaseous state. On average, nitrogen molecules make up about 78 percent of the gases in air. Oxygen molecules account for another 21 percent of air. Carbon dioxide, argon, and other rare gases make up the remaining one percent. The amount of water vapor in the atmosphere varies. Depending on the weather, water vapor can make up from zero to four percent of the gases in air.

 

Although you can’t see it, you live at the bottom of an ocean of air. Every molecule and atom of air is pulled down by gravity. At Earth’s surface, the accumulated weight of all of this air produces a pressure of one atmosphere. Meteorologists, however, usually use other units to measure air pressure. Scientists more often use the unit millibar (mb) or the unit hectopascal (hPa) to measure air pressure. We experience a standard air pressure of 1013.25 mb = 1 atmosphere at sea level. Converting this value to hectopascals is easy. One millibar is equal to one hectopascal, so Earth’s standard air pressure in hectopascals is 1013.25 hPa.

 

Unlike solids and liquids, gases are easily compressed. The weight of the air above compresses, or squeezes together, air closer to the Earth’s surface. Because more molecules and atoms are in a smaller space, collisions occur more frequently. Every time a molecule or an atom of air strikes something, it exerts a force. When atoms and molecules are squeezed closer together, more collisions occur and the force is greater. The greater force produces a higher air pressure, which is the force exerted on an area of surface in contact with the air.

 

When air pressure changes, the weather usually changes. An increase in air pressure typically indicates clear skies, more sun, less wind, and drier weather ahead. If the air pressure begins to decrease, just the opposite is probably ahead—clouds, less sun, more wind, and possibly precipitation of some kind.

 

Anthony Guillory’s team uses Aerosonde to collect air pressure data in the atmosphere. These measurements recorded along the flight path can help researchers understand a storm and predict its behavior. Is the storm intensifying? Is it weakening? The low air pressure measurements collected by Aerosonde typically occur in strong tropical storms and hurricanes.