The lunar geomagnetic tide at night

Abstract

Hourly values from 1964-65 of the three geomagnetic elements from a large number of stations have been analysed for the various lunar components. These were combined to examine in detail the seasonal and diurnal variations of the lunar geomagnetic tide at night.Comparison of the values for the oceanic component calculated in a similar way to Malin (1973) showed good agreement between sunspot maximum and minimum years.When seasonal changes were included, the D and Z elements gave evidence of a lunar modulation of magnetic field aligned currents entering the ionosphere in auroral regions. The effects of these currents appeared to extend as far away as the equator. Changes in their amplitude during the night also suggest a relation to auroral processes.There is a just-resolved nighttime equatorial electrojet H component and a quite large lunar H component in the auroral regions.

Daily geomagnetic variations on the Iberian Peninsula

“…In fact the separation described above is imperfect because L I is not identically zero at local midnight. Stening & Winch (1987) checked the method of separation by comparing the L O value at several observatories. If L O has a significant ionospheric contribution then its value will be expected to be higher when the sunspot number is maximum.…”

Lunar daily geomagnetic variations in New Zealand

“…The separation is imperfect because L , is not identically zero at local midnight. Stening & Winch (1987) tested the method of separation by comparing Lo at each of a number of observatories for times of sunspot maximum and sunspot minimum. If Lo contains a significant ionospheric contribution then it might be expected to be greater at sunspot maximum than at sunspot minimum.…”

A lunar tide in the Dst index.

“…It should also be noted that there is a significant lunar geomagnetic tide of oceanic origin at Honolulu, and this will also be present in Dst (MALIN, 1973;STENING and WINCH, 1987).…”