Abstract
The afternoon maximum (AMX) observed in 40 kHz signal strength, propagated over a distance of 5100 km in the low latitudes of the Northern Hemisphere, exhibits an appreciable asymmetric decrease in its time of occurrence about June-July. The time of occurrence of the AMX of this low-latitude E-W propagation follows the sunset lime equation at the centre of the propagation path. A significant test shows a high correlation of the absence of the AMX with geomagnetic storms. The extra-ionizations in the ionospheric D region during geomagnetic storms may lead to the absence of the afternoon maximum.
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De, B.K., Sarkar, S.K. Seasonal Behaviour of the Afternoon Maximum of a Long-Distance 40 kHz Signal. Studia Geophysica et Geodaetica 41, 382–390 (1997). https://doi.org/10.1023/A:1023311517946
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DOI: https://doi.org/10.1023/A:1023311517946