During geomagnetic storms, energetic electrons enter the upper mesosphere around 70 kilometers above the Earth's surface. These energetic electrons enhance the chemical reactions that produce nitrogen oxides (NOx), which can destroy ozone. If the nitrogen oxides are transported downward to lower altitudes in the stratosphere (below about 40 kilometers in altitude), they can destroy ozone in the ozone layer that protects life on Earth's surface from harmful ultraviolet radiation. Large solar energetic particle events have been shown to cause decreases in stratospheric ozone, but those large events are uncommon. The extent to which more common moderate-sized geomagnetic storms affect middle atmosphere chemistry has been uncertain.