Abstract
The dynamic state of the ionosphere at low latitudes is largely controlled by electric fields originating from dynamo actions by atmospheric waves propagating from below and the solar wind-magnetosphere interaction from above. These electric fields cause structuring of the ionosphere in wide ranging spatial and temporal scales that impact on space-based communication and navigation systems constituting an important segment of our technology-based day-to-day lives. The largest of the ionosphere structures, the equatorial ionization anomaly, with global maximum of plasma densities can cause propagation delays on the GNSS signals. The sunset electrodynamics is responsible for the generation of plasma bubble wide spectrum irregularities that can cause scintillation or even disruptions of satellite communication/navigation signals. Driven basically by upward propagating tides, these electric fields can suffer significant modulations from perturbation winds due to gravity waves, planetary/Kelvin waves, and non-migrating tides, as recent observational and modeling results have demonstrated. The changing state of the plasma distribution arising from these highly variable electric fields constitutes an important component of the ionospheric weather disturbances. Another, often dominating, component arises from solar disturbances when coronal mass ejection (CME) interaction with the earth’s magnetosphere results in energy transport to low latitudes in the form of storm time prompt penetration electric fields and thermospheric disturbance winds. As a result, drastic modifications can occur in the form of layer restructuring (Es-, F3 layers etc.), large total electron content (TEC) enhancements, equatorial ionization anomaly (EIA) latitudinal expansion/contraction, anomalous polarization electric fields/vertical drifts, enhanced growth/suppression of plasma structuring, etc. A brief review of our current understanding of the ionospheric weather variations and the electrodynamic processes underlying them and some outstanding questions will be presented in this paper.
Highlights
Ionosphere is an important domain of the earth’s space environment and has been the subject of intensive studies since its discovery in the early years of the 20th century
The elements controlling the ionospheric weather can be represented by: electric fields, currents, plasma drifts, instabilities, and plasma structuring. They suffer variability due to (1) upward propagating waves from their sources in the lower atmosphere, which include: planetary waves, Kelvin waves, their interactions with tidal modes resulting in electric field generation by E- and F- layer dynamo, and gravity waves; (2) solar and magnetospheric disturbances that cause penetration electric fields, disturbance winds, and disturbance dynamo electric field that prevail over low latitudes
The situation is less than satisfactory regarding the predictive capability for short-term and day-to-day variabilities, which is to be expected because the nature of the corresponding driving sources originating from above and below are not tractable
Summary
Ionosphere is an important domain of the earth’s space environment and has been the subject of intensive studies since its discovery in the early years of the 20th century. While the largescale structures are symmetric at the conjugate regions the smaller structures (of decameter sizes) as observed by Digisonde do not map along the entire field lines as can be noted from the corresponding asymmetric spread F traces in ionograms shown Fig. 3b These irregularities embedded in the large density background plasma of the EIA as pictured in the TIMED/GUVI map in Fig. 3c can cause strong scintillation, and loss of lock, of the satellite communication and navigation signals. Oscillations in varying degrees have been observed due to 2, 3–5, 10, and 16-days periods in the key ionospheric parameters: the EEJ intensity, post-sunset/night-time F layer heights, evening prereversal enhancement in the F region vertical drift/zonal electric field (PRE), equatorial bubble/ spread F irregularities, etc.
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