Date of Award:

8-2020

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Physics

Committee Chair(s)

Bela G. Fejer

Committee

Bela G. Fejer

Committee

Ludger Scherliess

Committee

Michael J. Taylor

Committee

Anthony R. Lowry

Committee

David Peak

Abstract

We present the first complete study of the dynamics of the equatorial upper atmosphere (180-350 km) during periods of strong magnetic activity driven by the Sun, which are generally referred as geomagnetic storms. These storms have the potential to considerably affect satellite-based communications and navigation systems among other severe technological challenges. We used large databases of two of the most important parameters at these altitudes, which are the velocities of the neutral and ionized gas (plasma) referred to as neutral winds and plasma drifts. These measurements were acquired in the Peruvian equatorial region by the Jicamarca radar and by a network of optical instruments nearby. In the first part, we derived average patterns of the neutral winds under weak geomagnetic activity conditions, or quiet times, for different seasons and compared them with predictions from current upper-atmospheric models. Then, we present, for the first time, the seasonal patterns of the night-time perturbations in the neutral winds at equatorial latitudes, and their variations for different solar-driven geomagnetic storms. These wind perturbations are strongest in the east-west direction and around midnight. They are strongest and longer lasting during and after extended periods of geomagnetic activity. We present a simple empirical model that significantly improves the prediction of the perturbations in the neutral winds compared with current models. In the second part, we derive the velocity perturbations in the plasma drifts along the vertical direction following 3 to 9 hours of geomagnetic activity. We show in detail that these vertical velocity perturbations are small and down-ward during the day and upward and stronger at night, and vary throughout the year and for different solar conditions. They are strongest near sunrise and sunset and during the equinoxes. In the last part of the thesis, we show the close relationship of the neutral wind and plasma drift velocities along the east-west direction during both geomagnetic quiet and disturbed conditions. Finally, we summarize our main results and make suggestions to improve the understanding of this important topic.

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