Index Geophysics

Equatorial ionospheric response to the 10.7 cm radio flux over two sunspot cycles (1969−1991)

It is evident that fluctuations in a standard ionospheric parameter, the minimum (virtual) height (<i>h</i>^´<i>F</i>) of the equatorial F-region in the African (Ouagadougou), Asian (Manila) and American (Huancayo) longitudinal sectors, closely resemble changes in solar activity as deduced from the 10.7 cm solar flux index (<i>S</i>), over two solar cycles (1969–91). The monthly median hourly value of <i>h</i>^´<i>F</i>, particularly in the post-sunset period (18–20 LT), are positively correlated with the monthly average <i>S</i>. The value of <i>h</i>^´<i>F</i> can be deduced from an empirical formula: <i>h</i>^´<i>F</i>=0.68<i>S</i>+218.3, with the correlation coefficient (<i>r</i>) between <i>h</i>^´<i>F</i> and <i>S</i> being 0.78. The diurnal distribution of <i>r</i> during daytime (06–14 LT) was radically different for the African and Asian longitudinal sectors during 1980-1991, with the most pronounced difference in the post-noon period (12–14 LT) when the correlation coefficients <i>r</i> for the Asian and African sectors are 0.8 and 0.2, respectively. Thus, the daytime F-region in the African sector responded far less to changes in solar activity than the Asian F-region during this cycle. This longitudinal anomaly was however absent in the preceding cycle (1969–1979) when the African and Asian sectors were both characterised by low daytime and pronounced post-sunset correlation coefficient <i>r</i>. The American sector appears to have a high correlation coefficient <i>r</i> in daytime increasing to a small maximum in the post-sunset interval. The post-sunset enhancement in <i>r</i> is a characteristic feature for equatorial stations only (corrected geomagnetic latitude &lt;10^°).

Hajkowicz, L. A.

2018-09-27

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10.1007/s00585-996-0725-z

https://angeo.copernicus.org/articles/14/725/1996/

eISSN: 1432-0576

eng