Sudden ionospheric disturbance
A sudden ionospheric disturbance disrupts radio communications via enhanced D-region absorption.
A sudden ionospheric disturbance (SID) is a type of ionospheric disruption marked by an abnormal increase in ionization or plasma density within the D region of the ionosphere. This is triggered by a solar flare or a solar particle event. The disturbance causes a rapid rise in radio-wave absorption, particularly affecting the upper medium frequency and lower high frequency bands, which often disrupts or interferes with telecommunications.
The phenomenon is also known as the Dellinger effect, or the Mögel–Dellinger effect. It was identified by John Howard Dellinger around 1935, and earlier described by German physicist Hans Mögel in 1930. These fadeouts begin suddenly and can take minutes or hours to recover.
When a solar flare occurs, a burst of intense ultraviolet, X-ray, and sometimes gamma-ray radiation reaches Earth’s dayside in about eight minutes. This high-energy radiation is absorbed by atmospheric particles, exciting them and freeing electrons through photoionization. The lower ionospheric layers—the D and E regions—immediately become denser across the entire dayside. This disturbance enhances very low frequency (VLF) radio propagation. Scientists detect solar flares by monitoring the signal strength of a distant VLF transmitter; such recordings indicate when a flare has occurred. A small geomagnetic effect in the lower ionosphere appears as a hook-shaped mark on magnetic records, called the geomagnetic crochet effect or sudden field effect.
Shortwave radio signals in the high frequency range are absorbed by the increased particle density in the D region, causing a complete blackout of radio communications known as a short wave fadeout (SWF). These fadeouts last from a few minutes to a few hours and are most severe in equatorial regions where the Sun is directly overhead. While high frequency signals fade, the disturbance enhances longwave (VLF) propagation. SIDs are observed by monitoring the signal strength of a distant VLF transmitter. Solar flares can also cause short-term changes in the upper atmosphere’s temperature structure and circulation patterns, linking sudden D-region ionization to broader space-weather effects on atmospheric dynamics.
- Discoverer
- John Howard Dellinger (around 1935) and Hans Mögel (1930)
- Other name
- Dellinger effect or Mögel–Dellinger effect
- Cause
- Solar flare emitting intense ultraviolet, x-ray, and sometimes gamma ray radiation
- Propagation time
- About 8 minutes from Sun to Earth
- Affected frequencies
- Upper medium frequency and lower high frequency ranges
- Duration
- Minutes to hours
Lore & Background
The Dellinger effect, also called the Mögel–Dellinger effect, was discovered by John Howard Dellinger around 1935 and described earlier by German physicist Hans Mögel in 1930. These fadeouts are characterized by sudden onset and a recovery that takes minutes or hours. When a solar flare occurs, a blast of intense ultraviolet and x-ray radiation hits the dayside of Earth after about 8 minutes. This high-energy radiation is absorbed by atmospheric particles, raising them to excited states and knocking electrons free through photoionization. The low-altitude D and E regions of the ionosphere immediately increase in density over the entire dayside.
The ionospheric disturbance enhances very low frequency (VLF) radio propagation, which scientists use to detect solar flares by monitoring the signal strength of a distant VLF transmitter. A small geomagnetic effect in the lower ionosphere appears as a small hook on magnetic records, called the geomagnetic crochet effect or sudden field effect. Short wave radio waves in the HF range are absorbed by the increased particles in the D-region, causing a complete blackout of radio communications known as a short wave fadeout (SWF). These fadeouts last from a few minutes to a few hours and are most severe in equatorial regions where the Sun is most directly overhead.
Reader's Guide
The sudden ionospheric disturbance has significant and lasting implications for radio communications and space weather monitoring. Its most notable effect is the short wave fadeout, which can completely blackout high frequency radio communications for minutes to hours, particularly in equatorial regions. This phenomenon has been critical for understanding how solar activity directly impacts terrestrial systems. The disturbance also enhances VLF propagation, providing a practical method for detecting solar flares from the ground. Scientists monitor the signal strength of distant VLF transmitters to record SIDs, which indicate when solar flares have taken place. A whole array of sub-classes of SIDs exist, detectable by different techniques at various wavelengths, including the short-wave fadeout, sudden phase anomaly, sudden frequency deviation, sudden cosmic noise absorption, and sudden enhancement of atmospherics. The link between sudden ionization events in the D-region and broader space-weather effects on atmospheric dynamics has been established, showing that solar flares can contribute to short-term disturbances in the upper atmosphere that influence its temperature structure and circulation patterns. This makes SIDs a key element in understanding the coupling between solar activity and Earth's upper atmosphere.
Did You Know?
- A sudden ionospheric disturbance is also called the Dellinger effect or Mögel–Dellinger effect.
- The radiation from a solar flare reaches Earth in about 8 minutes.
- SIDs enhance VLF radio propagation while causing blackouts in HF communications.
- The geomagnetic crochet effect is a small hook on magnetic records caused by the disturbance.
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