A theoretical framework for the changing spectral properties of meter‐scale Farley‐Buneman waves between 90 and 125 km altitudes

Stimulated by recent observations described in a companion paper, we have revisited existing theories of the Farley‐Buneman instability throughout the altitude range 90 to 125 km. We have assumed that the irregularities detected by radars at a given altitude are dominated by structures moving at the...

Full description

Saved in:
Bibliographic Details
Published in:Journal of geophysical research. Space physics 2016-10, Vol.121 (10), p.10,341-10,366
Main Authors: St.‐Maurice, Jean‐Pierre, Chau, Jorge L.
Format: Article
Language:English
Subjects:
Altitude
Asymmetry
aurora radar
aurora spectra
Doppler effect
E region
Echoes
Electric fields
Electrons
Farley‐Buneman
Geophysics
Instability
ionospheric irregularities
Ions
Mathematical models
Spectra
Thresholds
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Stimulated by recent observations described in a companion paper, we have revisited existing theories of the Farley‐Buneman instability throughout the altitude range 90 to 125 km. We have assumed that the irregularities detected by radars at a given altitude are dominated by structures moving at the threshold speed in a direction associated with maximum linear growth rate conditions. We included recent nonisothermal electron and ion theories, which can modify threshold speeds by considerable amounts. We included altitude‐dependent models of ion and electron temperature and of the ion motion in the phase velocity calculations. Our treatment of the instability explains why some spectra are slow (Doppler shifts typically 200 m/s) and narrow, while others are fast (1500 m/s or close to the E × B) and narrow. These narrow spectra have all the characteristics of what has been labeled as “Type III” and “Type IV” in the past. Our calculations also offer an explanation for the observation of a strong asymmetry in the number of events with positive Doppler shifts near the nominal ion‐acoustic speed and those with negative Doppler shifts of the same magnitude. Key Points Slow‐narrow Farley‐Buneman echoes are explained after taking into account nonisothermal electron theories below 100 km altitude Fast‐narrow Farley‐Buneman echoes are from near 115 km, where the waves must grow slowly and move at nearly the electron drift Nonisothermal ions and the ion drift velocity introduce pronounced east‐west asymmetries in strong northward electric field situations
ISSN:2169-9380
2169-9402
DOI:10.1002/2016JA023105