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Ann. Geophys., 26, 1269-1273, 2008
www.ann-geophys.net/26/1269/2008/
© European Geosciences Union 2008
Latitudinal variation of foF2 hysteresis of solar cycles 20, 21 and 22 and its application to the analysis of long-term trends
N. Ortiz de Adler1 and A. G. Elias1,2
1Laboratorio de Física de la Atmósfera, Departamento de Física, Facultad de Ciencias Exactas y Tecnología, Universidad Nacional de Tucumán, Av. Independencia 1800, 4000 Tucuman, Argentina
2Consejo Nacional de Investigaciones Científicas y Técnicas, CONICET, Argentina
Abstract. Noon foF2 monthly median values for equinoctial months of solar cycles 20,
21 and 22, were analyzed for 37 worldwide stations. For each solar cycle and
for a given Rz, the difference between foF2 in the falling branch of the
cycle and the corresponding value of the rising branch is evaluated. The
maximum difference, considered as the hysteresis magnitude, varies
systematically with geomagnetic latitude. The pattern is similar for every
cycle, with greater hysteresis magnitudes for stronger solar cycles. It is
positive between 45° S and 45° N, with minimum values at equatorial
latitudes and maximum at around 25°–30° on either side of the
equator. For latitudes greater than 50° negative values are observed.
At around 25°–30° and at high latitudes the hysteresis magnitude
reaches 2 MHz for solar cycle with high activity levels, which represents
around 20% of foF2. The effects of foF2 hysteresis on the analysis of
long-term data sequences is analyzed. In the case of long-term trend
analysis, the hysteresis behavior may induce spurious trends as a
consequence of the filtering processes applied to foF2 time series previous
to trend values estimation. This problem may be solved by considering time
series covering several solar cycles.
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