Multi-scale 3D modeling of mesospheric electric fields and thunderstorm electrodynamics
Abstract/Contents
- Abstract
- Thunderstorms are an important component of the Earth electrical system responsible for maintaining the fair weather potential difference between the Earth and its ionosphere. The electric fields created by thundercloud charges and lightning discharges create upward coupling between the tropospheric storms and the mesospheric regions at altitudes of $\sim$50--90~km. The strong and slowly changing electric fields of lightning discharges referred to as quasi-electrostatic fields are capable of electron heating, ionization breakdown and excitation of optical emissions at mesospheric altitudes, resulting in high altitude gas discharges collectively known as transient luminous events. The thundercloud fields also keep the ionospheric electrons at a sustained heating level. The modification of the thunderstorm charges by a lightning discharge results in a transient change in the electron heating level which can be observed as the so-called Early/Fast VLF events: an amplitude and/or phase perturbation in subionospherically propagating VLF waves transmitted by naval submarine and long-range communications systems. Over the last two decades, experimental observations have created a large data set and have vastly improved our understanding of thunderstorm upward coupling. However, theoretical and numerical models of the physics of the various processes involved are required to help understand the underlying physics of the observed features and to quantify their effects on ionospheric dynamics. With an improved understanding of the physics of these phenomena, we can use them as a remote sensing tool of the Earth's upper atmosphere, especially these altitude regions not easily accessible by satellites. In this dissertation, we have developed the first three-dimensional model of thunderstorms electrodynamics and the resultant upward coupling between thundercloud systems and the overlying mesosphere and ionosphere. The model can accommodate any realistic background neutral and electron densities and thunderstorm charge distributions. Effects of the Earth's geomagnetic field on atmospheric electrical currents induced by the thundercloud charges and lightning discharges are also investigated. By including a realistic geomagnetic field, we demonstrate that the electrostatic fields of the thundercloud charges mapped to the mesosphere altitudes have been substantially underestimated by previously used 2D models. The larger electric fields result in a stronger coupling of the thunderstorms and the Earth's upper atmosphere. These fields can map to much farther altitudes in the magnetosphere and create large scale electron irregularities known as whistler ducts that can trap and guide lightning generated whistler waves. This stronger coupling further leads to a more significant sustained heating of the ionospheric electrons which in turn more noticeably interact with the subionospheric propagating VLF signals. Using a 2D subionospheric propagation model of VLF waves, we estimate these perturbations and show that they are in good agreement with experimental observations. The sustained heating of the ionospheric electrons by thunderstorms is thus reintroduced as the most likely mechanism responsible for many of the Early/Fast VLF events. The developed 3D model can also be used to simulate thunderstorm electrodynamics and lightning evolution. Combined with a physics-based lightning discharge model, we simulated long-time evolution of a thunderstorm electrical environment and the associated lightning activity. Important aspects of experimentally measured thunderstorm electrical features are reproduced. In particular, the model results indicate various phases of thunderstorm lightning activity and the transition of intracloud (IC) to cloud-to-ground (CG) lightning discharges which are consistent with observations of lightning discharges in a typical electrically active thunderstorm. The new model of thunderstorm electrodynamic evolution reveals many interesting and new insights about lightning physics. Based on these results we propose a new mechanism for cloud-to-ground lightning discharge generation. The new mechanism is capable of producing cloud-to-ground discharges from a dipolar charge distribution inside the thundercloud. The model results also support previously proposed mechanisms of creation of the lower positive charge layers in thunderstorm charge distributions.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2015 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Kabirzadeh, Rasoul |
|---|---|
| Associated with | Stanford University, Department of Electrical Engineering. |
| Primary advisor | Inan, Umran S |
| Primary advisor | Zebker, Howard A |
| Thesis advisor | Inan, Umran S |
| Thesis advisor | Zebker, Howard A |
| Thesis advisor | Lehtinen, Nikolai G |
| Advisor | Lehtinen, Nikolai G |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Rasoul Kabirzadeh. |
|---|---|
| Note | Submitted to the Department of Electrical Engineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2015. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2015 by Rasoul Kabirzadeh
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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