Middle atmospheric electrodynamics at low lattitude over India. Published by Elsevier Science Ltd. These special features play a vital role in governing the electrodynamics of the global middle atmosphere. In India, a well coordinated multi- institutional campaign was organised under MAP Middle Atmosphere Programme to carry out balloon and rocket borne experiments to measure electrical parameters of the middle atmosphere. The experiments were carried out during different seasons and solar activity epochs.
The results obtained from these investigations are discussed and compared with similar measurements over the middle latitude stations to assess the integrated effect of the global atmospheric electrodynamic phenomenon. In recent times there has been a revival of research interests in the field particularly related to the electrodynamics of the middle atmosphere and its possible linkages with the near earth environment as well as with the ionospheric electric, fields and current system Holzworth, , The main purpose of this paper is to review the results of various campaign experiments to measure middle atmospheric ionisation and conductivity parameters over low latitude stations of India using balloon and rocketborne sensors and compare them with those obtained over middle latitude stations.
Chakravarty et al. Special high altitude balloons capable of reaching altitudes of about 35 - 36 km were only used for the purpose. A series of 78 M rockets for D- region ionisation measurements were launched during grouped in high and low sunspot periods outside the scope of IMAP. Paltridge, ; Hale, Small symbols show the data over low latitude station, Hyderabad and large symbols for Melbourne, Wallops Island and Fort minimum, sunspot maximum and Churchill. PCA conditions respectively. Apex valve was used to have long period measurements at two different balloon float altitudes.
It may be noted that the positive and negative ion conductivities are comparable except during morning hours. Small period wave structures are observed in the conductivity values indicating the effect due to propagating atmospheric gravity waves.
The figure in the lower panel taken from Holtzworth , shows two series of simultaneous measurements of the vertical electric field and conductivity at 26 km altitude by two balloons horizontally separated by over km during March, Temporal variation of stratospheric conductivities and electric fields over Hyderabad and middle latitude station at balloon float altitudes. Bottom diagram after Holtzworth et at, Chakravarty er al.
T, Hr the mesospheric region. Vertical profile of electric field over Hyderabad Stratospheric electric fields over Hyderabad are found to be higher than those over the middle latitude stations. Ion densities are modelled by using these standard q values.
The integrated ratio is found to be around 2. Model calculations with lighter complex ions e. This model result shows that the conductivity of the stratosphere may be subjected to large variations due to changes in temperature, water vapour and aerosol concentrations. The resultant effects on the conductivity would be reflected in variable electric fields of the region.
Handbook Of Atmospheric Electrodynamics, Volume I by Volland, Hans
Global enhancements in stratospheric volcanic aerosols should reduce stratospheric conductivities resulting in enhancement of global electric field in the region. The average profiles of the two sunspot epochs are shown in Figure 6 with the error bars. The channel of a R stroke can be considered as a thin isolated wire of length L and diameter d in which negative electric charge has been stored.
In terms of electric circuit theory, one can adopt a simple transmission line model with a capacitor , where the charge is stored, a resistance of the channel, and an inductance simulating the electric properties of the channel. In order to fulfill the boundary conditions at the top of the wire zero electric current and at the ground zero electric voltage , only standing resonant waves modes can exit.
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In the case of the K stroke, the lower boundary is the same as the upper boundary. Sferics can be simulated approximately by the electromagnetic radiation field of a vertical Hertzian dipole antenna. The effect of the real ground is to attenuate the higher frequencies more strongly than the lower frequencies Sommerfeld 's ground wave.
Reflection and attenuation on the ground depends on frequency, distance, and orography. In the case of the ionospheric D-layer, it depends, in addition, on time of day, season, latitude, and the geomagnetic field in a complicated manner.
VLF propagation within the Earth—ionosphere waveguide can be described by ray theory and by wave theory. The ground wave and the first hop or sky wave reflected at the ionospheric D layer interfere with each other. Therefore, mode theory is here more appropriate. The Earth—ionosphere waveguide is dispersive.
Therefore, the Earth—ionosphere waveguide behaves like a bandpass filter, selecting this band out of a broadband signal. Here, the zeroth mode begins to dominate and is responsible for the second window at greater distances. Resonant waves of this zeroth mode can be excited in the Earth—ionosphere waveguide cavity, mainly by the continuing current components of lightning flowing between two return strokes. About lightning strokes per second are generated all over the world excited by thunderstorms located mainly in the continental areas at low and middle latitudes.
Atmospheric Electrodynamics (Physics & Chemistry in Space)
Measurements of Schumann resonances at only a few stations around the world can monitor the global lightning activity fairly well. Certainly there are sources of variability in the conductivity which actively modify the expected signal from external generators. The many-fold increase in available electric parameter data from within the middle atmosphere has been a great stimulus to recent research. However, this review will conclude that these measurements have tended to raise more questions than answers.