A World-Wide Annual Variation in Sq
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The amplitude of the annual variation in the horizontal component of <I>Sq</I> is larger in the southern hemisphere than the northern hemisphere. This asymmetry may be represented as the superposition of a world-wide annual variation with its maximum at or near perihelion and summer-winter annual variations of equal amplitudes in the two hemispheres and maxima at the local summer solstice. The amplitude of the world-wide annual variation, as a fraction of the yearly mean value of <I>Sq</I>, is about 0.07 ± 0.02. The variation in ionospheric conductivity associated with the earth's orbital eccentricity is inadequate alone to account for this annual variation in <I>Sq</I>. If joule heating by the <I>Sq</I> currents is appreciable, its annual and semi-annual variations could account for the similar variations in the temperature of the thermosphere.
- Earth, Planets and Space
Earth, Planets and Space 47(10), 1029-1031, 1995-10
Society of Geomagnetism and Earth, Planetary and Space Sciences