Open AccessOutstanding issues in the theory of radar aurora: Evidence from the frequency dependence of spectral characteristics
Author(s) -
Moorcroft D. R.
Publication year - 2002
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2001ja009218
Subject(s) - backscatter (email) , radar , physics , ultra high frequency , computational physics , spectral line , range (aeronautics) , focus (optics) , perspective (graphical) , frequency dependence , geophysics , optics , geology , geometry , nuclear magnetic resonance , astronomy , materials science , computer science , telecommunications , mathematics , composite material , wireless
A review of the spectral characteristics of radar aurora with a focus on the behavior over a wide range of frequencies gives a different perspective on several issues concerning auroral backscatter. Some of the conclusions from this study are as follows: (1) It appears most likely (but has certainly not been proven) that auroral backscatter at large geometric magnetic aspect angles has the same general characteristics at all frequencies; VHF observations showing other characteristics are most likely refracted to small aspect angle by sporadic E . (2) The broadest spectra are observed at neither HF or UHF, but at VHF frequencies, but it is unclear whether this is a topic for theoreticians to consider, or if it is an observational effect. (3) The flow angle dependence of sub‐ion‐acoustic UHF echoes and large aspect angle echoes both present theoretical challenges which remain unaddressed. (4) In spite of several attempts, there appears to be no satisfactory theory of either type 3 or type 4 echoes, especially when the frequency dependence of these echoes is considered.