Boston University Libraries OpenBU
    JavaScript is disabled for your browser. Some features of this site may not work without it.
    View Item 
    •   OpenBU
    • Theses & Dissertations
    • Boston University Theses & Dissertations
    • View Item
    •   OpenBU
    • Theses & Dissertations
    • Boston University Theses & Dissertations
    • View Item

    Beam-plasma interactions and Langmuir turbulence in the auroral ionosphere

    Thumbnail
    License
    Attribution 4.0 International
    Date Issued
    2015
    Author(s)
    Akbari, Hassanali
    Share to FacebookShare to TwitterShare by Email
    Export Citation
    Download to BibTex
    Download to EndNote/RefMan (RIS)
    Metadata
    Show full item record
    Permanent Link
    https://hdl.handle.net/2144/16310
    Abstract
    Incoherent scatter radar (ISR) measurements were used in conjunction with plasma simulations to study two micro-scale plasma processes that commonly occur in the auroral ionosphere. These are 1) ion acoustic turbulence and 2) Langmuir turbulence. Through an ISR experiment we investigated the dependence of ion acoustic turbulence on magnetic aspect angle. The results showed a very strong aspect angle sensitivity which could be utilized to classify the turbulence according to allowable generation mechanisms and sources of free energy. In addition, this work presents results that led to the discovery of a new type of ISR echo, explained as a signature of cavitating Langmuir turbulence. A number of incoherent scatter radar experiments, exploiting a variety of beam and pulse patterns, were designed or revisited to investigate the Langmuir turbulence underlying the radar echoes. The experimental results revealed that Langmuir turbulence is a common feature of the auroral ionosphere. The experimental efforts also led to uncovering a relationship between Langmuir turbulence and one type of natural electromagnetic emission that is sometimes detected on the ground, so-called “medium frequency burst”, providing an explanation for the generation mechanism of these emissions. In an attempt to gain insights into the source mechanism underlying Langmuir turbulence, 1-dimensional Zakharov simulations were employed to study the interactions of ionospheric electron beams with a broad range of parameters with the background plasma at the F region peak. A variety of processes were observed, ranging from a cascade of parametric decays, to formation of stationary wave packets and density cavities in the condensate region, and to direct nucleation and collapse at the initial stage of the turbulence. The simulation results were then compared with the ISR measurements where inconsistencies were found in the spectral details and intensity of the simulated and measured Langmuir turbulence echoes, suggesting the possibility that the direct energy for the turbulence was provided by unstable low-energy (5 − 20 eV) electron populations produced locally in the F region of the ionosphere rather than by electron beams originating from the magnetosphere.
    Rights
    Attribution 4.0 International
    Collections
    • Boston University Theses & Dissertations [6746]


    Boston University
    Contact Us | Send Feedback | Help
     

     

    Browse

    All of OpenBUCommunities & CollectionsIssue DateAuthorsTitlesSubjectsThis CollectionIssue DateAuthorsTitlesSubjects

    Deposit Materials

    LoginNon-BU Registration

    Statistics

    Most Popular ItemsStatistics by CountryMost Popular Authors

    Boston University
    Contact Us | Send Feedback | Help