Geometric aspects of HF driven Langmuir turbulence in the ionosphere

Mjølhus, E.; Helmersen, E.; DuBois, D. F.

doi:10.5194/npg-10-151-2003

Cited by 27 publications

(35 citation statements)

References 59 publications

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“…Mjølhus 1990) arcsin sin where . Ray-tracing results for EISCAT parameters (Mjølhus et al 2003) show very similar features as here. Inside the Spitze range, the polarization of the electric field tend to be along the magnetic field as the wave reaches the critical layer, while outside the Spitze, the polarization instead approaches vertical (Mjølhus et al 2003).…”

Section: Full-wave Modeling Of Strong Langmuir Turbulencesupporting

confidence: 77%

Incidence angle dependence of Langmuir turbulence and artificial ionospheric layers driven by high-power HF-heating

et al. 2014

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Abstract:We have numerically investigated the development of strong Langmuir turbulence (SLT) and associated electron acceleration at different angles of incidence of ordinary (O) mode pump waves. For angles of incidence within the Spitze cone, the turbulence initially develops within the first maximum of the Airy pattern near the plasma resonance altitude. After a few milliseconds, the turbulent layer shifts downwards by about one kilometer. For injections outside the Spitze region, the turning point of the pump wave is at lower altitudes. Yet, an Airy-like pattern forms here, and the turbulence development is quite similar to that for injections within the Spitze. SLT leads to the acceleration of 10-20 eV electrons that ionize the neutral gas thereby creating artificial ionospheric layers. Our numerical modeling shows that most efficient electron acceleration and ionization occur at angles between the magnetic and geographic zenith, where SLT dominates over weak turbulence. Possible effects of the focusing of the electromagnetic beam on magnetic field-aligned density irregularities and the finite heating beam width at the magnetic zenith are also discussed. The results have relevance to ionospheric heating experiments using ground-based, high-power radio transmitters to heat the overhead plasma, where recent observations of artificial ionization layers have been made.

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Section: Full-wave Modeling Of Strong Langmuir Turbulencesupporting

confidence: 77%

Incidence angle dependence of Langmuir turbulence and artificial ionospheric layers driven by high-power HF-heating

et al. 2014

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show abstract

“…These calculations suggest that the maximum turbulence seen by the UHF radar ought to lie at the critical height between the Spitze angle and the vertical, yet the maximum occurs outside the Spitze, at an angle where the pump wave does not reach critical, and, perhaps even more puzzling, at an altitude several km below the maximum height reached by the pump. Mjølhus et al (2003) consider this problem and are unable to suggest an explanation. At positions beyond the Spitze to the south, conditions for strong polarization of the pump electric field along the geomagnetic field are present when the pump wave is propagating downward after reflection.…”

Section: Discussionmentioning

confidence: 99%

“…Stubbe and Hagfors (1997) comment: "One of the shortcomings in the theoretical work appears to be an inappropriate treatment of the low frequency turbulence which depends very sensitively on the direction with respect to the magnetic field, implying that the full angular spectrum rather than a prescribed fixed angular component should be considered." Although Mjølhus et al (2003) have recently addressed this criticism for the theoretical interpretation of incoherent scatter observations of Langmuir turbulence, much remains to be done. Furthermore, this comment applies equally well to experimental results.…”

Section: Discussionmentioning

confidence: 99%

An interferometer experiment to explore the aspect angle dependence of stimulated electromagnetic emission spectra

Isham¹,

Hagfors

Khudukon

et al. 2005

Ann. Geophys.

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Abstract. When the Earth's ionosphere is irradiated by a radiofrequency (RF) electromagnetic wave of sufficiently high power density and tuned to match a natural E-or F-region plasma frequency, ionospheric magnetoionic wave modes may be excited and may generate RF electromagnetic sideband waves via nonlinear interactions. These secondary emissions, which may then escape from the ionosphere, have been termed stimulated electromagnetic emission or SEE. The frequency spectra of this radiation has been studied extensively, and a number of characteristic spectral features have been identified and in some cases related to particular plasma processes. The separation in frequency between the RF pump and the harmonics of the local electron gyrofrequency is critical in determining the amount of anomalous absorption suffered by the pump wave and the spectral properties of the stimulated sidebands. The pump can excite electrostatic waves which do not propagate away but can in some cases be observed via radio-wave scattering from the electron density fluctuations associated with them. These enhanced density fluctuations are created by processes commonly referred to as upper-hybrid and Langmuir turbulence. Langmuir turbulence has been the subject of 930-MHz scattering observations with antenna scanning through several pre-selected angles between the geographic and geomagnetic zenith directions, and a preference for pointing angles between the Spitze angle and geomagnetic field-aligned was identified. Other phenomena, such as the generation of enhanced electron temperatures and artificial aurora, have more recently been shown to have special behavior at similar angles, near but apparently not quite at field-aligned. In view of this evidence for angular structureCorrespondence to: B. Isham (bisham@bc.inter.edu) in several pump-induced effects, in light of the rich variety of SEE phenomena strongly dependent on the geomagnetic field via the frequency interval between the pump and the gyrofrequency harmonics, and in view of the not yet understood but complex relationship between electrostatic fluctuations and SEE, it is of interest to investigate experimentally whether a similar angular structure is present in the various spectral features of the SEE signals and to compare the results with radar and other observations of RF-pump-induced effects. To this end we describe a simple two-element radio interferometer designed to search for aspect angle dependence of SEE features. We present an example of the initial data produced by this system, and draw preliminary conclusions based on the example data.

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“…The SSA dynamics as a whole conforms to theoretical calculations in the weak-turbulence approximation [59], while the SEE generation process at this stage of pumping has not been given adequate interpretation. Large progress has been achieved in the numerical simulation of the nonlinear stage of SPI within the framework of Zakharov's equation with allowance for the isothermal nature and regular inhomogeneity of the ionospheric plasma, as well as for the geomagnetic field [60]. At the same time, this modeling was performed for a time-constant amplitude of the PW, which disagrees with the experiment data.…”

Section: Initial Stage Of the Action: Striction Parametric Instabilitymentioning

confidence: 99%

The “Sura” facility: Study of the atmosphere and space (a review)

Belikovich¹,

Грач

Karashtin³

et al. 2007

Radiophys Quantum El

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Geometric aspects of HF driven Langmuir turbulence in the ionosphere

Cited by 27 publications

References 59 publications

Incidence angle dependence of Langmuir turbulence and artificial ionospheric layers driven by high-power HF-heating

Incidence angle dependence of Langmuir turbulence and artificial ionospheric layers driven by high-power HF-heating

An interferometer experiment to explore the aspect angle dependence of stimulated electromagnetic emission spectra

The “Sura” facility: Study of the atmosphere and space (a review)

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