rich

Are clouds charged or polarized?

9 posts in this topic

I've read two accounts as to why clouds become attracted to the earth's surface, which is of course a precursor to lightning.

One hypothesis is that a cloud's water molecules, being polarized (oxygen atom carrying an effective negative charge and the two hydrogen atoms carrying an equal effective positive charge), all align inside the cloud with their oxygen atoms pointed toward the earth and the hydrogen atoms pointing away from the earth. This creates a large polarization of the cloud, that in turn polarizes the surface of the earth.

Another hypothesis is that as clouds move through the air, the friction between cloud and air knocks electrons off of the cloud, giving the cloud a net positive charge, creating a polarization on the earth's surface.

The first hypothesis assumes that clouds are not charged, but polarized; the second assumes they are indeed charged, and does not discount the possibility of polarization being present also.

One of these hypotheses has to be wrong. Anyone know which one?

Share this post


Link to post
Share on other sites

-----------

The first hypothesis assumes that clouds are not charged, but polarized; the second assumes they are indeed charged, and does not discount the possibility of polarization being present also.

One of these hypotheses has to be wrong. Anyone know which one?

What would polarize the water molecules to begin with? Is there some electric or magnetic field around? How would polarization account for lightning jumping from one cloud to another or from the ground up to the clouds, which has been known to happen.

Share this post


Link to post
Share on other sites

What would polarize the water molecules to begin with? Is there some electric or magnetic field around? How would polarization account for lightning jumping from one cloud to another or from the ground up to the clouds, which has been known to happen.

Maybe I wasn't clear enough. The water molecules themselves are already polarized; water molecules are polarized naturally, and each water molecule can be thought of as a tiny dipole. What I meant was, the water molecules as a group may be ordered in such a way as to polarize the cloud. In other words, somehow all the H2O molecules at the bottom of the cloud might have their O atoms pointed toward the earth, and their H atoms pointed away from the earth. I don't know how this might occur in the first place. There is, of course, the earth's natural magnetic field, but its strength is only of the order of 1 gauss, so I doubt it would effect the water molecules significantly.

Polarization, though, would account for lightning's jumping from one cloud to another, I think. If the positively polarized part of one cloud drifts near the negatively polarized part of another cloud, a strong electric field will arise -- eventually resulting in dielectric breakdown of the air in between the clouds, i.e., lightning.

Share this post


Link to post
Share on other sites

Maybe I wasn't clear enough. The water molecules themselves are already polarized; water molecules are polarized naturally, and each water molecule can be thought of as a tiny dipole.

It's been a long time since physics class, but water molecules are not polarized, they are polar; and they are randomly oriented. They become polarized when they align themselves in an electric field.

What I meant was, the water molecules as a group may be ordered in such a way as to polarize the cloud. In other words, somehow all the H2O molecules at the bottom of the cloud might have their O atoms pointed toward the earth, and their H atoms pointed away from the earth. I don't know how this might occur in the first place.

Neither do I.

There is, of course, the earth's natural magnetic field, but its strength is only of the order of 1 gauss, so I doubt it would effect the water molecules significantly.

Polarization, though, would account for lightning's jumping from one cloud to another, I think. If the positively polarized part of one cloud drifts near the negatively polarized part of another cloud, a strong electric field will arise -- eventually resulting in dielectric breakdown of the air in between the clouds, i.e., lightning.

What kind of electric field would be present in the atmosphere that would allow the water molecules to align in one direction yet in an adjacent cloud to align in the opposite direction?

Besides, the theory you've put forth doesn't explain how polarization would create a potential difference between the cloud and the ground. Polarization would result in a potential difference between the top and bottom of the cloud (assuming that the cloud somehow becomes polarized).

Share this post


Link to post
Share on other sites

Maybe I wasn't clear enough. The water molecules themselves are already polarized; water molecules are polarized naturally, and each water molecule can be thought of as a tiny dipole.

It's been a long time since physics class, but water molecules are not polarized, they are polar; and they are randomly oriented. They become polarized when they align themselves in an electric field.

What I meant was, the water molecules as a group may be ordered in such a way as to polarize the cloud. In other words, somehow all the H2O molecules at the bottom of the cloud might have their O atoms pointed toward the earth, and their H atoms pointed away from the earth. I don't know how this might occur in the first place.

Neither do I.

There is, of course, the earth's natural magnetic field, but its strength is only of the order of 1 gauss, so I doubt it would effect the water molecules significantly.

Polarization, though, would account for lightning's jumping from one cloud to another, I think. If the positively polarized part of one cloud drifts near the negatively polarized part of another cloud, a strong electric field will arise -- eventually resulting in dielectric breakdown of the air in between the clouds, i.e., lightning.

What kind of electric field would be present in the atmosphere that would allow the water molecules to align in one direction yet in an adjacent cloud to align in the opposite direction?

Besides, the theory you've put forth doesn't explain how polarization would create a potential difference between the cloud and the ground. Polarization would result in a potential difference between the top and bottom of the cloud (assuming that the cloud somehow becomes polarized).

Plus, if the water molecules in two clouds were polarized in opposite directions, the only thing that would happen is that the two clouds would be electrically attracted to each other. Where would the discarge come from? Polarization does not result in an imbalance of electrons.

Share this post


Link to post
Share on other sites

For a good description of how lightning works, read THIS.

Share this post


Link to post
Share on other sites

Polar, polarized -- call it what you will, the point is that the oxygen and hydrogen atoms that make up water do not share their valence electrons equally. Oxygen keeps the valence electrons for a greater share of time than the hydrogen atoms do, and so the molecule as a whole has a slightly positive end, and a slightly negative end. I'm sure we both agree on this.

And I've imagined clouds having this same feature -- a slightly positive end, and a slightly negative end, but neutral as a whole. I don't know how this would arise in the first place, as I've stated. But assuming it does occur, then I was thinking that if two clouds meet with their oppositely charged ends facing one another, then the attraction would be great enough to rip off some electrons, resulting in an electric current. But now, I realize, this is probably not physically reasonable, because as you said, polarization does not lead to a charge imbalance. So I'm still not sure what's going on with the clouds.

Share this post


Link to post
Share on other sites

Polar, polarized -- call it what you will, the point is that the oxygen and hydrogen atoms that make up water do not share their valence electrons equally. Oxygen keeps the valence electrons for a greater share of time than the hydrogen atoms do, and so the molecule as a whole has a slightly positive end, and a slightly negative end. I'm sure we both agree on this.

The polar nature of the water molecule is due to the assymetry of its shape, not how long the valence electrons are on one side or the other. The molecule is shaped like a "V" where the oxygen is at the apex and the hydrogen is on the legs. Thus, there are 2 positive charges on one side and 2 negative charges on the other side. The molecule as a hole is electrically neutral. If the molecule had a linear shape (H-O-H), there would be no polar nature to it.

--------

So I'm still not sure what's going on with the clouds.

Check out the link I sent you above.

Share this post


Link to post
Share on other sites

Thanks for the link, I'll check it out soon.

I had been taught years ago (in high school, I think) that water is polar because oxygen has a greater affinity for electrons than does hydrogen. But, this would not explain how why H2O is nonlinear.

Share this post


Link to post
Share on other sites