I need some proof that the electric (E-field) and the magnetic component (H-field) of a lightning stroke both propagate at the speed of light, and that there is not a significant delay between them.

Please? :-)

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    $\begingroup$ As Glenn said, E and H field are strictly coupled. If you look at Maxwell's equations, you'll see that you can't have one field change over time without generating the other kind automatically. The combination of this mutual "implication" is what allows electromagnetic waves to exist and propagat. $\endgroup$ May 12, 2018 at 8:25
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    $\begingroup$ If static charges “build up”, then delta E can’t equal zero. Any change in E will cause an H field to propagate. If the change is slow (over an entire day) then H will be tiny, but non-zero, and propagate at the speed of light. $\endgroup$
    – hotpaw2
    May 13, 2018 at 11:57
  • $\begingroup$ Maxwell's E/M equations spells it out very clearly, like @Marcus says. You need the E field collapse to create the M field, which in turn collapses to induce another E field, and so on. They do not travel separately. Wikipedia has a pretty decent write-up on this subject. en.wikipedia.org/wiki/Maxwell's_equations Have you tried working the math yourself on this? If you show your attempt at doing so, then I am sure we have people here who can help with it and turn this into a great reference question on basic wavelet propagation. $\endgroup$
    – SDsolar
    May 14, 2018 at 5:16

1 Answer 1


The E and H fields of all RF signals travel at exactly the same speed - the speed of light. The phase relationship between the two fields remains constant as they travel through various mediums.

Lightning in itself is not an RF signal but it does emit RF (with E&H waves) as it propagates.


After reading some of the additional dialog provided by the OP in response to my answer, I believe the other party is talking about detecting the E field of a capacitor with the storm system being one "plate" and the earth forming the other "plate" of the capacitor. Note that this is quite different from the paired oscillating E and H fields of an RF signal propagating through space.

Inside of an ideal, charged capacitor there exists only an E field that is measured in Coulombs (shown as a unit of C). One proton has a charge of 1.6 x 10-19 C.

For a capacitor where the diameter of the plates are substantially larger than the gap between the plates, there will exist an equal charge in the space between the plates. When this charge reaches 3x106 N/C, the air inside the capacitor will break down and a spark (lightning in this case) is formed.

So it seems that the proposal is to measure the electric field of the capacitor formed by the storm system and the earth as a predictor of the potential of lightning. The referenced probe would form another plate in the capacitor - not to be confused with an antenna. This may work in principle although there will be a substantial difference in the E field as measured when between the plates (inside the storm system) and outside of the plates (near the edge of the storm). If prediction is not the goal, then edge detection of the collapsing E field, as a result of a dielectric breakdown of the air exhibited as lightning, may be a solution.

  • $\begingroup$ We know that, but the gentleman I'm debating with further stated: "Do not confuse the Electric component of an electromagnetic wave, with of the with the Charge Field we are detecting with the E probe. It is detecting the Charge density inside the Ionospheric / earth capacitor... not the RF wave. You can have a 'charge field'; buld up without generating an EM wave... when the charge breaks down and cascades, then you can have a stroke... $\endgroup$
    – Mike Waters
    May 12, 2018 at 12:39
  • $\begingroup$ "... In other words, the [~15' high] probe [10cm wire], board [preamp], and coax form a 'field density' sensor' and we monitor the changes or those charges at a rate at various rates of change.... ....... however E field can detect information that is NOT present in either the H or E planes of a 'polarized' 'RF' impulse.. It is most 'informative' when high frequency information, as in neary cells. ... $\endgroup$
    – Mike Waters
    May 12, 2018 at 12:42
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    $\begingroup$ well, what he's asking you to do is to differentiate between E-field and EM-wave, I'd guess. First is static, second exists only as change of something over time. Also, you two seem to be non-correctly communicating about "planes": When he says "planes", he means "planes" as in "the plane spanned by the XY axes", as in "the (E-Field) polarization of this wave is horizontal". $\endgroup$ May 12, 2018 at 13:27
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    $\begingroup$ @MikeWaters They are likely then measuring the collapse (de/dt) of the E field which would occur when the above N/C condition is met. $\endgroup$
    – Glenn W9IQ
    May 12, 2018 at 15:16
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    $\begingroup$ @MikeWaters Mike, I am not a lightning expert but I would theorize that the collapse of the E field would be the result of the leader as this forms the first equalizing breakdown. More broadly, I wonder how their technique detects cloud to cloud discharges. Could their description deviate from the method? $\endgroup$
    – Glenn W9IQ
    May 13, 2018 at 1:26

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