Aspects of Weather and Space Weather in the Earth's Upper Atmosphere: The Role of Internal Atmospheric Waves
INTRODUCTION
Much of what we call the “weather” near the surface of the Earth involves patterns of winds that propagate like waves across the planet. In fact, the high- and low-pressure areas we see displayed in the newspapers or on television are the crests and troughs of what are called planetary waves by atmospheric scientists. Weather in the upper atmosphere and in space has many wavelike characteristics as well. These waves are of interest in their own right, and most of this lecture will revolve in one way or another around the topic of internal waves in the atmosphere and their effects on the near-space regions of the Earth and on space weather in the Earth's ionosphere.
Space weather is distinct from space science just as meteorology is distinct from atmospheric science. Weather deals more with the aspects of atmospheric phenomena that have a direct impact on humanity. Of course, detailed knowledge of the associated science is of great importance to understanding and predicting the behavior of these complex systems. In the field of space weather we are just beginning to see how our knowledge can be used in this manner.
There are two fundamental drivers in space weather, only one of which is treated here. One is the searingly hot, tenuous outer layer of the Sun's surface, which sweeps over and by the Earth's protective magnetic field. The second is the cool, dense, but extremely dynamic atmosphere of the Earth itself. The latter is of most interest here.
Wave phenomena play a very important role in human and animal behavior, chiefly through the sensory apparatus we use to sample our environment. Our eyes detect electromagnetic waves with a response more or less equivalent to the spectrum of light emitted from our Sun. Our ears detect sound waves propagating through our planet's atmosphere. As technology developed, we extended the reach of our perceptions using instruments capable of detecting signals our eyes and ears cannot perceive. As the phenomena we study range higher and higher in the atmosphere where the human eye is less useful, remote sensing using such tools is of greater importance. As a crucial tool for the study of space weather, remote sensing becomes the second topic of this treatise.
Humans are by and large oblivious to many other wave phenomena supported by the atmosphere or part of the electromagnetic spectrum. Other species, however, have specialized sensory organs with which they extract information from these waves. Bees use the ultraviolet (UV) portion of the electromagnetic spectrum. Large animals such as elephants and whales use infrasound (low-frequency sound waves) to communicate. Studying remarkable feats of animal navigation has revealed how little we actually know about sensory techniques in the animal kingdom. Clearly,
