ABSTRACT
The subject of atmospheric electricity had its origins in the eighteenth century. The concept of the global atmospheric electric circuit in the early twentieth century by C. T. R. Wilson and matured considerably in the first decade of the twenty-first century [1-4]. Atmospheric electrical coupling occurs from near the Earth’s surface up to the ionosphere at ~80 km altitude. This coupling takes place rapidly close to the speed of light (c), contrary to coupling mechanisms involving mechanical waves which propagate at speeds much lower than c [5]. The Earth’s atmosphere is a layer of gases surrounding the Earth and is retained by Earth’s gravity. On the basis of temperature distribution, the atmosphere can be classified into four layers consisting of the troposphere, stratosphere, mesosphere, and thermosphere. The temperature in the thermosphere remains nearly constant. The stratosphere and mesosphere regions are counted as the middle atmosphere above which the atmosphere is marked as the upper atmosphere. At the upper atmosphere the solar radiation and other sources ionize the neutral constituents producing plasma of ions and electrons. The region extending from the mesosphere to the thermosphere is known as the ionosphere where plasma dynamics is controlled by the collisions between the ionized particles and neutrals and also between the ionized particles themselves [6,7]. The region above the ionosphere is called the magnetosphere wherein the dynamics of charged particles is controlled largely by the Earth’s magnetic field, as the density collision frequency is very low in this region. There is no sharp boundary between the upper ionosphere and the lower magnetosphere region. The study of electrical coupling between the troposphere and the ionosphere is an important assignment related to atmospheric electrodynamics [8]. Observations in mesosphere support strong electric fields of up to 10 V/m [9,10], indicating that the mesosphere should be treated as an active element in the atmospheric circuit. The formation of transient optical emissions in the mesosphere and lower ionosphere are named as sprites, which further supports the concept of strong mesospheric electric fields [11]. All this phenomena demand a critical searching of mechanisms related to electrodynamics caused by the effects of disturbances of tropospheric conductivity on lower ionosphere [12,13]. It is the purpose of this chapter to examine the present understanding of the link between the processes operative in the lower atmosphere and their electrodynamical coupling with the ionosphere. In spite of the existence of aerosol, ions, polar molecules, and convection, it has become difficult to apply the terrestrial model of a global circuit to outer planets of the solar system mainly because of the probable absence of a conducting surface. A different electrical model for the gas giant planetary atmospheres
may be attempted but further theoretical work is necessary to enhance our understanding first. The same or at least similar atmospheric electrical processes may act across the solar system but a clear concept is initially essential to implement it successfully. Lightning has been detected on many other planets but without their elaborate knowledge of electrical and physical properties we are only able to approach so far as quasi-terrestrial global circuits. Ion-mediated nucleation has been noted on Earth but no successful attempt has yet been made to identify it in other planetary atmospheres. A comparative approach with all the available future information may provide new insight for successful development of electrical global circuits for other planets where the earth’s electrical global circuit may be taken as a ready reference.
