Dellinger effect: when the Sun presses the 'mute' button on short waves

In the world of amateur radio, phenomena occur that act as moody fluctuations of the cosmic orchestra. The most prominent of these is Dellingerov efekt, známy aj ako rádiový blackout typu R alebo fadeout typu I. Objavil ho americký fyzik John Howard Dellinger a už takmer sto rokov si drží reputáciu slnečného „vypínača“, ktorý dokáže v priebehu sekúnd položiť komunikáciu na krátkych vlnách.

What is Dellinger effect actually?

V jadre ide o sudden, sharp weakening to complete cessation of shortwave radio signal propagation. Nejde o jemné zhoršenie podmienok, ktoré rádioamatéri poznajú zo slnečných cyklov. Dellingerov efekt je skôr ako prudká clona svetla spadnutá na scénu: signály miznú, contestové pile-upy stíchnu a celý ionosférický most, ktorý obvykle spoľahlivo odráža KV signály späť k Zemi, sa zrazu prestáva správať podľa očakávaní.

Najviac sú zasiahnuté frequencies between 3 and 30 MHz, čo je presne krátkovlnné pásmo využívané rádioamatérmi, námornými službami či leteckou komunikáciou. Vyššie frekvencie (napríklad v pásme VHF) už stoja mimo dosah tohto javu a prežijú ho bez väčších škrtov.

How does it arise: a dramatic scene on the solar stage

Spúšťačom je silná erupcia na Slnku, typicky triedy M alebo X, ktorá vyšle do priestoru masívnu dávku of extreme ultraviolet and soft X-ray radiation. S týmto žiarením sa nedeje nič pomalé: keďže svetlo nepotrebuje na cestu od Slnka k Zemi nič iné než čas, daň za túto rýchlosť zaplatíme už o 8 minút, teda takmer okamžite.

When this intense radiation reaches Earth, it shines on ionosféru, konkrétne na D vrstvu. Za bežných okolností je D vrstva taká nenápadná služba pri dverách: trochu pohlcuje nízke frekvencie, no väčšinou nechá krátke vlny prejsť ďalej k E a F vrstve, kde prebieha odraz signálu.

However, after the arrival of a solar eruption, the D layer turns into a hyperactivated guard that pulls up the nets and slams shut all passages. Röntgenové a UV žiarenie dramaticky zvýši ionizáciu D vrstvy, čím z nej urobí extrémne efektívny absorbér KV signálu. Namiesto odrazu späť k Zemi dôjde k tomu, že signál je „zožratý“ hneď v najnižšej časti ionosféry.

Result: total damping of short waves.
Sometimes there is a deafening silence.

How does Dellinger effect manifest in practice?

Radio amateurs know it intimately well. Typical are:

• 

  sudden band silence, bez varovania a často počas pár sekúnd,

• disappearance of data from ionosond na KV frekvenciách,

• absolute reduction of propagating frequencies, MUF klesá prudko nadol,

• znefunkčnenie NVIS spojení on lower bands (1.8, 3.5, 7 MHz),

• aviation and maritime emergency frequencies na HF zrazu pôsobia opusteným dojmom.

The geographic extent typically mirrors the illuminated half of the Earth. On the night side of the planet, silence is still silent, but of a different kind: there is no D layer because it is kept alive only by solar radiation.

How long does it last?

Toto je jedna z najvzrušujúcejších častí fenoménu. The Dellinger effect typically lasts from a few minutes to tens of minutes. Väčšina bežných blackoutov sa zmestí do rámca 10 až 40 minút, hoci pri extrémnych slnečných erupciách vyšších tried X môže trvanie prekročiť aj hranicu hodiny.

The length is directly proportional to:

• the intensity of the eruption,

• the amount of X-ray radiation,

• the duration of the solar flare itself.

When the eruption burns out, ionization in the D layer begins to decay as quickly as it formed, and communication gradually returns to normal. The return is usually magnificent: HF bands come back to life abruptly and often chaotically, as if all signals decided to arrive at once.

Why is this phenomenon so crucial?

Dellingerov efekt patrí do rodiny tzv. R-veľkostí (Radio Blackout Classes), monitored by NOAA. It is one of those phenomena that affect not only amateur communications, but also:

• letecké KV okruhy in polar regions,

• maritime communication,

• military and diplomatic networks pracujúce mimo satelitov,

• time and navigation services prevádzkované na HF.

For radio amateurs, it is a reliable indicator that the Sun is currently in a noisy period and that the DX window may be much smaller than usual in the next few minutes.

How to recognize that it is Dellinger effect and not another issue?

In the middle of a contest, anything can happen, but Dellinger has a very clear signature:

1. The effect occurs immediately.
   It is not a gradual deterioration of conditions, but a sudden shutdown.

2. The illuminated side of the Earth suffers the most.
   If it is daytime for you, but all bands have dropped, it is very suspicious.

3. Even higher shortwave bands are declining, nie iba 80 m či 40 m.

4. After a few tens of minutes, the situation usually returns, často rovnako náhle.

5. NOAA reports increased X-ray activity, často v triede M alebo X.

Summary

The Dellinger effect is a rapid, dramatic, and uncompromising impact of solar energy on our shortwave world. It occurs after a powerful flash of X-ray and UV radiation from the Sun, which turbo-charges the D layer of the ionosphere and causes massive absorption of HF signals. It lasts from a few minutes to an hour and affects the entire illuminated hemisphere. For radio amateurs, it is clear evidence that the Sun occasionally plays its own improvisation, which is beautiful but unforgiving for HF DX.