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A new type of Doppler velocity fluctuations in HF ground scatter from the polar cap
Author(s) -
Scoular G.,
Ponomarenko P. V.,
St.Maurice J.P.
Publication year - 2013
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/grl.50960
Subject(s) - doppler effect , ionosphere , physics , polar , noon , geophysics , line of sight , computational physics , geology , astrophysics , atmospheric sciences , astronomy
We report a new type of variations in Doppler velocity of HF ground scatter echoes from the polar cap at f ∼10 mHz. Similar fluctuations from lower latitudes are usually associated with large‐scale dayside Pc3‐4 ULF waves. However, the polar cap oscillations exhibit a puzzling anisotropy in spatial coherence along and across the radar's line of sight. Furthermore, in contrast to Pc3‐4 waves, these fluctuations show no ground magnetic signatures and display a pronounced gap in power/occurrence around local noon. We hypothesize that localized, ≤100 km, auroral particle precipitations near the radar site can modulate Doppler shift of the radio waves entering the ionosphere. In the ground scatter returns, due to the geometrical spread of the rays propagating through the ionosphere to the ground, these variations would appear to have a much larger line‐of‐sight scale.