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I was talking with an acquaintance about lightning, and we came up with opposite theories and predictions for the frequency of lightning over ocean.

  • My theory is that since seawater is a fluid riddled with ions, the charges can move to equalize with whatever field is applied to it; therefore it should take a much higher, much faster increase in the magnitude of cloud charge to cause the dielectric breakdown necessary for a strike--in other words, the clouds have to beat the ocean to the punch before it dissipates the increase. So I predict less frequent lightning over the ocean.

  • His theory is that the composition of the lower surface is irrelevant; it's the insulating effect of the air that contributes to favorable conditions for lightning generation. He predicts more or less equal frequency of lightning over land or sea.

Wikipedia bears out my prediction (sourced from NASA data): NASA world lightning frequency

According to the distribution of lightning page, strikes occur most frequently in the tropics, on land. What makes this possible? More importantly, which of us is right? ;)

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  • $\begingroup$ Except for the Southern tio pf South America. $\endgroup$ – Abhimanyu Pallavi Sudhir Dec 21 '13 at 10:57
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This is not my area but I found an interesting article about lightning on the NASA web site. A key point from this article is that only 25% of lightning is cloud to surface and the rest is made up from strikes between clouds. Therefore changes in the surface or the insulating properties of the air near the surface could affect only 25% of the lightning strikes. But much larger differences are seen between land and sea, and this suggests that the explanation lies elsewhere.

I would guess the reason is that the special type of weather systems needed to generate lightning do not occur over the oceans and that is the reason for the dearth of lightning. The NASA article makes the point that lightning is most intense where air masses converge e.g. Florida and the Himalayas. Over the oceans where there are no topographic features to deflect the wind you would not get the air mass convergence that is required to generate lightning.

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    $\begingroup$ Hm, then what explains the largest region on the top-most scale being Central Africa? Which air - masses converge there? $\endgroup$ – Abhimanyu Pallavi Sudhir Dec 21 '13 at 10:52
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    $\begingroup$ The NASA articles says: And where does lightning strike most frequently? Central Africa. "There you get thunderstorms all year 'round," Christian says. "It's a result of weather patterns, air flow from the Atlantic Ocean, and enhancement by mountainous areas." $\endgroup$ – John Rennie Dec 21 '13 at 11:39

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