If your ears have ever popped while driving through the high elevations of mountains or riding an airplane, it was likely due to a change in atmospheric pressure. The popping balances the difference in pressure between the inside and outside of the ear. However, this phenomenon is not just limited to changes in altitude. In fact, a few different things can contribute to changes in atmospheric pressure.
Atmospheric pressure is essentially the weight of air molecules on a given point. Air molecules take up space, but generally but generally have a comparatively large amount of empty space between them. Because of the empty space, air can compress and expand, and it’s the number of air molecules in a space that dictates the weight and thus determines the measurement of air pressure at the given point.
Realizing changes in atmospheric pressure accounts for a large portion of weather study and weather predictions. Meteorologists use barometers to measure atmospheric pressure. A barometer allows a normal or average pressure to be determined for an area under study. Barometers also show any changes as the pressure increases and decreases. Many factors contribute to weather conditions, but in most cases barometers are pretty accurate indicators of what is to come. An increase in pressure usually predicts cooler temperatures and clear skies to come. On the other hand, a decrease in pressure predicts warmer temperatures and possible storms and/or rain. Predictions with barometers become most accurate when considering the air density and the direction the air flows.
Differences in densities and air movement play big roles in the overall pressure of the atmosphere, in much the same way different aspects contribute to the weight of more common objects. Imagine standing on a scale to check how much you weigh. Then, hold a loose handful of feathers (not dense) and note only a slight weight change, if any. Exchanging the feathers for a dense substance of the same general size, such as a handful of lead, causes a dramatic increase in weight. After that, no matter what’s in your hand, if another person tries lifting you off the scale, you’ll notice a decrease in the measured weight. These concepts become useful when studying different properties of the atmosphere.
Temperature and humidity may affect air density more than anything. Warmth and/or moisture decreases air density. At the same time, lack of heat and/or moisture increases air density.
Air currents and other things that cause air to move in especially vertical directions also cause changes in atmospheric pressures. Much like when someone lifts while you’re on the scale to reduce your weight, upward wind currents reduce pressure; just as downward currents can increase air pressure. In addition to directly causing changes in air pressure, differences in temperature provide a driving force for air currents in both vertical and horizontal directions. Even geological features, such as mountains or plains, can move air in important ways.
Understanding changes in atmospheric pressure to a greater extent requires a more detailed understanding of the different weather systems and conditions present in a given area and the entire planet system, as a whole. Though factors of density, air flow, and temperature all produce tangible outcomes with atmospheric pressure, all it takes is a tiny, unperceivable motion to bring about huge and powerful weather forces, on the entirely opposite side of the world. Edward Lorenz may have popularized perhaps this most unattainable and flighty ruler of weather in general; with the Butterfly Effect. A massive hurricane and low pressure system in Florida may form unpredictably, spawning innocently from a butterfly flapping its wings, somewhere in Peru.