Open AccessVariance of the vertical ion speed measured with the European Incoherent Scatter (EISCAT) UHF radar in the polar lower ionosphere at Tromsø, Norway
Author(s) -
Oyama S.,
Brekke A.,
Tsuda T. T.,
Kurihara J.,
Watkins B. J.
Publication year - 2011
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 - 10.1029/2010ja016129
Subject(s) - incoherent scatter , ionosphere , earth's magnetic field , electric field , polar , f region , atmospheric sciences , physics , radar , oscillation (cell signaling) , geodesy , computational physics , geology , geophysics , magnetic field , telecommunications , quantum mechanics , astronomy , biology , computer science , genetics
The vertical component of the ion velocity measured with the European Incoherent Scatter (EISCAT) Tromsø UHF radar (69.6°N, 19.2°E) in the lower ionosphere (from 95 to 130 km) was found to be characterized by notably large variances at oscillation periods of 2–8 min. Of particular interest was the geomagnetic activity dependence above ∼106 km, which showed larger variances (100–500 m 2 s −2 ) during periods of geomagnetic disturbance than during quiet periods. Below 106 km, the variance was less sensitive to the geomagnetic activity. Height profiles of the variance during the disturbed period showed steep increases with heights above 106 km, then reaching a peak at 120 km, where the ion gyrofrequency is equal to the modeled ion‐neutral collision frequency. A theoretical prediction well reproduced the height profile for the geomagnetically disturbed period by assuming oscillations in the meridional component of the electric field. The theoretical study suggested that the electric field oscillation is a possible cause of large variances of the vertical ion speed in the polar lower ionosphere. However, below 106 km, other mechanisms were necessary.