Diurnal phase shift
The diurnal phase shift (uncommon German translation: diurnal phase shift) is in the Telecommunications a phenomenon in electromagnetic signals in a 24-hour rhythm (lat diurnal.) To a phase shift resulting from electromagnetic signals. This phase shift is related to the daily changes in the structure of the ionosphere . The reflective properties of the ionosphere change at night. Roughly simplified, the reflection occurs at a greater height at night and is stronger. During the day the lower limit of the ionosphere is 80 km high and at night it rises to 100 km.
Irrespective of this, the propagation of radio waves can be disrupted by deep ionization of the earth's atmosphere (e.g. after solar flares ).
The phase shift is of practical importance for long wave broadcasting because of its large range of the sky waves occurring at night . The omega navigation method, which works with longitudinal waves (now switched off), was also influenced by this phase shift. Since long waves and long waves exceed the day-night limit due to their large range and the ionosphere has a different height and reflection properties during the day than at night than at night, it is precisely here that a phase shift that is difficult to calculate occurs.
The greatest changes usually occur during sunrise or sunset at critical points along the path of propagation of electromagnetic rays.
In communication cables, there can be significant phase shifts due to the daily rhythm of the daily temperature fluctuations, but these have nothing to do with the ionosphere.