Winds and Electric Fields in the Upper Atmosphere

Abstract

Winds and electric fields are in fact some of the oldest problems in the field of atmospheric physics. In 1882 Balfour Stewart suggested that an electrically conducting region may exist in the atmosphere which is moved (winds !) relative to the geomagnetic field of the Earth. In this moving conductor electromotive forces (electric fields !) will be induced which in turn will produce electric currents. Stewart introduced this hypothesis in order to explain observed variations in the geomagnetic field, although in those days nothing was known about the existence of an ionosphere nor of any motion there. Meanwhile these suggestions have been confirmed and we know that, indeed, neutral air motions, i.e., winds, and electric fields exist in the upper atmosphere. Some of their features and some theoretical aspects will be discussed now. We shall restrict ourselves to large scale phenomena, i.e., on effects that appear more or less on a global scale. Section 2 will deal with winds, where the term wind stands for movements of neutral air. First, the air circulation in the mesosphere is considered in the altitude range from about 40 to 90 km. Next, tidal oscillations of the atmosphere will be discussed. Since the atmosphere oscillates as a whole, emphasis will be placed upon the altitude range of 90 to 150 km, which is the so-called ‘dynamo region’. Finally global wind systems are described that are present above 150 km up to several hundreds of kilometers height. Section 3 deals with the mechanisms that produce electric fields in the ionosphere and some of the observational evidence we have for them. In Section 4, finally, the effects of electric fields and winds on the ionospheric F layer will be briefly illustrated.