As you rise in the atmosphere, air pressure decreases because fewer and fewer air molecules are above you. However, you do not have to change altitude to encounter a change in air pressure. The concentration of gas particles, and therefore the air pressure, can differ in neighboring air masses. Air will move from a region with higher pressure to a region with lower pressure. This movement produces wind.

How are high and low air pressure regions created? Air pressure differences result from the uneven heating of Earth and the atmosphere. As air gains heat energy, its molecules and atoms move faster and spread out. This produces an air mass having low pressure. If an air mass cools, its particles slow down and become more concentrated, producing an air mass with high pressure. The pressure difference between different air masses causes wind to blow from regions of higher pressure to regions of lower pressure. The wind’s speed depends on the pressure difference, and is influenced as well by Earth's rotation. The greater the pressure difference is, the faster the wind blows.

Using Aerosonde, NASA and NOAA can measure hurricane strength wind speeds without putting a flight crew and research scientists in danger. Having the capability of flying lower than any piloted aircraft, Aerosonde can collect data at altitudes that are much closer to where we live. These measurements provide better information about how the storm is behaving.