A new scenario applying traffic flow analogy to poleward expansion of auroras

Mapping Intimacies ◽

10.5194/angeo-2018-89 ◽

2018 ◽

Author(s):

Osuke Saka

Keyword(s):

Acoustic Wave ◽

Electric Fields ◽

Electrostatic Potential ◽

Ion Acoustic Wave ◽

F Region ◽

Electrons And Ions ◽

Ion Acoustic ◽

E Region ◽

Field Lines ◽

Poleward Expansion

Abstract. An auroral ionosphere is generally incompressive and non-uniform medium with anisotropic conductivities. Compressibility may occur, however, following the onset of field line dipolarization. This behavior can happen when; (1) Westward directing electric fields transmitted from the dipolarization region accumulate both electrons and ions in equatorward latitudes in F region. (2) The mobility difference of electrons and ions in E region produces electrostatic potential in a quasi-neutral condition, positive in higher latitudes and negative in lower latitudes. (3) Density modulation in F region excites ion acoustic wave propagating along the field lines towards the magnetosphere. (4) The ion acoustic wave stops in the ionosphere for about 4 min because of a low phase velocity (~ 1.6 km/s). During this compressive interval, density accumulation in equatorward latitudes expands upstream to form a poleward expansion of auroras analogous to upstream propagation of a shock in traffic flow on crowded roads. Electrostatic potential produced in the E region generates field-aligned currents and closing Pedersen currents to retain electrostatic potential in a quasi-neutral ionosphere. The ion acoustic wave produces upward electric fields along the field lines in accordance with the Boltzmann relation which contributed to the ion upflow at topside ionosphere.

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Effects of solar eclipse on the electrodynamical processes of the equatorial ionosphere: a case study during 11 August 1999 dusk time total solar eclipse over India

Annales Geophysicae ◽

10.5194/angeo-20-1977-2002 ◽

2002 ◽

Vol 20 (12) ◽

pp. 1977-1985 ◽

Cited By ~ 26

Author(s):

R. Sridharan ◽

C. V. Devasia ◽

N. Jyoti ◽

Diwakar Tiwari ◽

K. S. Viswanathan ◽

...

Keyword(s):

Electric Fields ◽

Solar Eclipse ◽

Equatorial Ionosphere ◽

Hf Radar ◽

F Region ◽

Large Enhancement ◽

Temporal Structures ◽

E Region ◽

Field Lines ◽

Electric Fields And Currents

Abstract. The effects on the electrodynamics of the equatorial E- and F-regions of the ionosphere, due to the occurrence of the solar eclipse during sunset hours on 11 August 1999, were investigated in a unique observational campaign involving ground based ionosondes, VHF and HF radars from the equatorial location of Trivandrum (8.5° N; 77° E; dip lat. 0.5° N), India. The study revealed the nature of changes brought about by the eclipse in the evening time E- and F-regions in terms of (i) the sudden intensification of a weak blanketing ES-layer and the associated large enhancement of the VHF backscattered returns, (ii) significant increase in h' F immediately following the eclipse and (iii) distinctly different spatial and temporal structures in the spread-F irregularity drift velocities as observed by the HF radar. The significantly large enhancement of the backscattered returns from the E-region coincident with the onset of the eclipse is attributed to the generation of steep electron density gradients associated with the blanketing ES , possibly triggered by the eclipse phenomena. The increase in F-region base height immediately after the eclipse is explained as due to the reduction in the conductivity of the conjugate E-region in the path of totality connected to the F-region over the equator along the magnetic field lines, and this, with the peculiar local and regional conditions, seems to have reduced the E-region loading of the F-region dynamo, resulting in a larger post sunset F-region height (h' F) rise. These aspects of E-and F-region behaviour on the eclipse day are discussed in relation to those observed on the control day.Key words. Ionosphere (electric fields and currents; equatorial ionosphere; ionospheric irregularities)

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Determination of the electron temperature in the modified ionosphere over HAARP using the HF pumped Stimulated Brillouin Scatter (SBS) emission lines

Annales Geophysicae ◽

10.5194/angeo-27-4409-2009 ◽

2009 ◽

Vol 27 (12) ◽

pp. 4409-4427 ◽

Cited By ~ 36

Author(s):

P. A. Bernhardt ◽

C. A. Selcher ◽

R. H. Lehmberg ◽

S. Rodriguez ◽

J. Thomason ◽

...

Keyword(s):

Electromagnetic Wave ◽

Acoustic Wave ◽

Electric Fields ◽

Pump Wave ◽

Scattered Wave ◽

Matching Condition ◽

Ion Acoustic Wave ◽

Matching Conditions ◽

Ion Acoustic ◽

Stimulated Brillouin

Abstract. An ordinary mode electromagnetic wave can decay into an ion acoustic wave and a scattered electromagnetic wave by a process called stimulated Brillouin scatter (SBS). The first detection of this process during ionospheric modification with high power radio waves was reported by Norin et al. (2009) using the HAARP transmitter in Alaska. Subsequent experiments have provided additional verification of this process and quantitative interpretation of the scattered wave frequency offsets to yield measurements of the electron temperatures in the heated ionosphere. Using the SBS technique, electron temperatures between 3000 and 4000 K were measured over the HAARP facility. The matching conditions for decay of the high frequency pump wave show that in addition to the production of an ion-acoustic wave, an electrostatic ion cyclotron wave may also be produced by the generalized SBS processes. Based on the matching condition theory, the first profiles of the scattered wave amplitude are produced using the stimulated Brillouin scatter (SBS) matching conditions. These profiles are consistent with maximum ionospheric interactions at the upper-hybrid resonance height and at a region just below the plasma resonance altitude where the pump wave electric fields reach their maximum values.

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