The stratosphere is the layer of Earth's atmosphere at altitudes between 8 and 30 mi (13 and 50 km). It is a stable region with few clouds and no storms. While the stratosphere is important for the environment at the Earth's surface (it contains the ozone layer that protects us from harmful ultraviolet radiation), it has been thought to have little influence on weather and climate near the ground. The density of air decreases rapidly with altitude, so in order to conserve their total energy, disturbances must strengthen when they propagate upward through the atmosphere and weaken when they propagate downward. Upward influences, therefore, are stronger than downward ones. While there has been sporadic interest in the idea that winds and temperatures in the stratosphere might influence weather and climate, only in the past few years has this idea found enough observational support to merit serious attention from meteorologists.