The 3 main factors that affect barometric (air) pressure are:
- Temperature of air.
- Altitude or Elevation.
- Moisture.
Temperature of air
| Temperature of air has an inverse relationship to air pressure.
Warm air = lighter and rises = less density = lower barometric pressure. |
However, the relationship between local temperature and barometric pressure is more complicated, whereby the change in air pressure in a given location may be affected by a moving weather system rather than the change in local temperature. For example:
City A
Air temperature falls from 30C to 20C
Apparent Answer: Temperature falls and barometer shows barometric pressure rise.
Actual answer: Air pressure rise was actually due to an atmospheric region of high pressure passing over the location that brought in cooler temperatures and not directly due to temperature change.
City B
Air temperature rises from 20C to 30C
Apparent Answer: Temperature rises and barometer shows barometric pressure fall.
Actual answer: Air pressure fall was actually due to a storm with an atmospheric region of low pressure passing over the location and not directly due to temperature change.
Altitude or Elevation
| Altitude has an inverse relationship to air pressure.
Higher altitude = less air pressing down = lower barometric pressure. |
Moisture
| Air moisture has an inverse relationship to air pressure.
Even though it seems counterintuitive to many people, actually, dry air has a higher density than moist air. Therefore, Moist air = reduced air density = lower barometric pressure. |
How does this relate to real world examples?
Warm air and associated high moisture = less air density = lower barometric pressure (such as produced at the equator)
Cold air and associated low moisture = higher air density = higher barometric pressure (such as produced at the polar regions)