THE PROPERTIES AND 3D STRUCTURE OF MEDIUM SCALE TRAVELING IONOSPHERIC DISTURBANCES

Open Access
Author:
Seker, Ilgin
Graduate Program:
Electrical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
May 12, 2009
Committee Members:
  • John David Mathews, Dissertation Advisor
  • John David Mathews, Committee Chair
  • C Russell Philbrick, Committee Member
  • Julio Urbina, Committee Member
  • Eugene Edmund Clothiaux, Committee Member
Keywords:
  • F-region
  • ionosphere
  • instabilities
  • irregularities
  • plasma depletion
  • mid-latitude
  • allsky imager
  • radar
  • ISR
  • MSTID
  • model
  • Arecibo Observatory
Abstract:
Perhaps the most persistent and prominent of the mid-latitude ionospheric phenomena are the Medium-Scale Traveling Ionospheric Disturbances (MSTIDs) in the F-region that are usually observed when geomagnetic activity is low. These MSTIDs have been identified and associated with various other phenomena such as plasma depletion bands, plasma bubbles, ionospheric slabs, and thermospheric waves. Using a combination of instruments to simultaneously observe these MSTIDs proves to be useful. In particular, allsky images provide the horizontal information complement to the narrow-beam Incoherent Scatter Radar (ISR) vertical and (nearly vertical) azimuth-scanned profiles. A new description of the 3D geometry of these structures is presented. This model-based description results from using a specific observational technique that is based on combined or fused ISR and allsky imager observations that define the horizontal and vertical features of night-time F-region MSTID structures over the Arecibo Observatory (AO) in Puerto Rico. This is the first application of the azimuth-scanning radar data combined with the imager data to develop the picture of the electrodynamic structures in the ionosphere. In particular, by using the azimuth-scanning ISR data and allsky images together, this research has shown for the first time that the southern part of an MSTID band reaches higher altitudes than its northern part implying that the MSTID bands are vertically tilted towards but not aligned with the orientation of the geomagnetic field lines. To confirm and further investigate these findings on the 3D structure of MSTID bands, a simple empirical 3D model of night-time MSTID bands is constructed. This empirical model is intended to show the bubble shape of MSTID bands in 3D and to replicate both the azimuth-scanning ISR and the allsky imager observations. Furthermore, the model is especially useful in explaining how these complex structures appear in azimuth-scanning ISR data. In particular, the causes of various complex features seen in the azimuth-scanning ISR data, such as the packets of thinner spikes, mirror-spikes, and high-altitude striations, are easily explained using the model. For example, it was found that MSTID bands are both uplifts and depletions and that the high-altitude striations seen in the azimuth-scanning ISR data can be caused either by the MSTIDs or the midnight collapse. Also, ISR and allsky imager results derived from the model are compared with the actual observations to confirm that the model is valid and to better understand various properties of MSTIDs. The results of the empirical model provide clues on what to expect from the theoretical models of geomagnetically quiet, nighttime, mid-latitude, F-region electrodynamics. Finally, the technique described here is not limited to F-region or mid-latitudes only. It can be applied to any other ionospheric phenomenon which can be observed by both radar and imager.