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f o F 2 long‐term trend linked to Earth's magnetic field secular variation at a station under the northern crest of the equatorial ionization anomaly
Author(s) -
Pham Thi Thu Hong,
AmoryMazaudier Christine,
Le Huy Minh,
Elias Ana G.
Publication year - 2016
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2015ja021890
Subject(s) - secular variation , earth's magnetic field , crest , ionosphere , magnetic dip , equator , anomaly (physics) , atmospheric sciences , latitude , geology , geodesy , physics , magnetic field , geophysics , condensed matter physics , quantum mechanics
Long‐term trend of the critical frequency of the F 2 ionospheric region, f o F 2 , at Phu Thuy station (21.03°N, 105.96°E), Vietnam, located under the northern crest of the equatorial ionization anomaly, EIA, is studied. Annual mean data are analyzed at 04 LT and 12 LT for the period 1962–2002 using monthly median values and monthly mean values during magnetically quiet days ( am < 20). In both cases we obtain similar trends at 4 LT and 12 LT, which we interpret as an absence of geomagnetic activity effect over trends. The positive trends obtained are not consistent with the negative values expected from greenhouse gases effect at this layer of the upper atmosphere. The increasing trend observed at 12 LT is qualitatively in agreement with the expected effect of the secular displacement of the dip equator over the EIA latitudinal profile. At 04 LT, when the EIA is absent, the positive trend is in qualitative agreement with the secular variation of the Earth's magnetic field inclination, I , and the consequent increase of the sin( I )cos( I ) factor at the corresponding location.