Re: Home ionizers and lightening storms

Steve, I don't have a firm answer, but I think that the ionizer will not have a noticeable effect. My reasoning rests more on engineering judgment than hard physics. That is, all things being equal (and they never are), lightning might prefer to strike an ionizer *if* it were of the proper polarity and *if* the ionizer electrode were the only feature in an otherwise featureless world (i.e., a perfectly flat plane of uniform properties) -- but that's not the real world, and other effects would tend to swamp out, or at least mask any potential attractiveness of an ionizer. I'll explain my deliberations below.

Lightning continues to be an area of active research, as the mechanisms for its production are still not well understood. I stumbled across a reference to a Ph.D. abstract on triggered lightning apparently using some sort of electrical apparatus, but I can't find the URL again (sorry).

Don't abandon your questions, as a version of it someday may be the basis for your own dissertation. The University of New Mexico, for instance, appears to be carrying out research on lightning, and other universities are as well, I'm certain.

Now, on to some tech discussion:

I found the technical specs for a home air ionizer, and it claimed 16 trillion ions per second per square centimeter emitted 2.5 cm from their "vortex generator". (Please note: this reference to a commercial product does not constitute a criticism or endorsement of that product; it was merely the first obvious response to a Web search engine query.)

This translates to a current of about 3 microamps, assuming the area above their vortex generator is about 1 cm**2 (about right, judging from picture). Note: 1 ampere is the flow of 1 coulomb of charge per second, and an electron has charge of 1.6 * 10**(-19) coulombs.

This leakage current is significantly higher than the background leakage current between earth and sky (the "electrosphere"), which is about 0.00001 microamps per square meter of earth surface under clear sky conditions. Thus the air ionizer current into the atmosphere is equals that of a patch of ground about 300 meters on a side. On the other hand, this current is similar to the current streaming from each of millions of sharp objects beneath a storm cloud (blades of grass, tips of leafs on trees). Current from an air ionizer would tend to get "lost in the crowd".

Another important idea is that the ions created by the ionizer will quickly (within a few meters) tend to be attracted to nearby objects, completing the circuit back to ground to the power station through the electric grid back to the ionizer. The ionizer may affect air conductivity locally, but again, this effect is minimal when you consider the other effects of terrain and the actual distance from the ionizer to the clouds.

According to data from a lightning fact sheet at the Princeton Plasma Physics Lab web site, the earth is negatively charged relative to the positively charged atmosphere, and this background leakage current acts to dissipate the charge. Lightning serves to recharge the earth with electrons, transporting them from the negatively charged base of clouds back to the earth (negative cloud to ground lightning is the most common type of cloud to ground lightning).

A negative ion generator, therefore, would tend to repel lightning, if anything. The ions would tend to be repelled by the cloud, rather than attracted.

So what if we reverse the polarity of the ion generator? Would it attract lightning? Maybe. I found an abstract to a Ph.D. thesis concerning research concerning a mechanism to trigger lightning. It doesn't say what voltages or currents are involved in their trigger. That's the abstract I can't find anymore.

Here's another thought. Lightning represents a flow of electrons made possible when the atmosphere ionizes in the presence of a sufficiently strong electric field. The threshold is somewhere in the vicinity of 50,000 volts/meter

The electric field from an air ionizer is not strong enough to cause this breakdown. The reason is that the electric field strength from a point source falls off with the square of distance; one will have to get very close (fraction of an inch) to the ionizer electrode to cross the breakdown threshold, at which a spark will be obtained. Again, this argues that the effect of an ionizer electrode, even of proper polarity, would not have great effect in the larger context of many other point sources of currents and the substantial distance to the clouds.

Finally, there's a bit of empirical data to consier (which in this case is the weakest argument of all -- it is arguably similar to an ostrich's legendary "head in the sand" defense against danger): ionizers have not been recognized to influence lightning strikes, nor are television sets or computer display CRTs, which operate at similar or higher voltages (although they aren't designed to intentionally emit ions, there will be some leakage). Advice to unplug TVs or computers during a lightning storm is intended to protect them agains voltage surges conducted by the power lines, not to forestall lightning strikes.

As I warned, my answer is a bit soft; this is why engineering is an art as well as a science -- many times there are no clear cut answers, and best judgment is required.

Steve Czarnecki