Ralph in Stanford asked:
Do all thunderstorms have lightning?
Chris - I think that actually, if you're going to have a thunderstorm, that means by definition you're hearing thunder. So if you're hearing thunder, you're hearing a shockwave, and what's happened during a thunderstorm to make that shockwave is that something has heated a patch of the air to a very high temperature. This has made the air expand supersonically, making a shockwave that then comes towards you through the air as a rippling roll of thunder. You can't really have the heating of the air without some kind of an electrical discharge which is what the lightning is.
In fact, I think when people have done calculations and measurements, a lightning bolt actually registers a temperature of about 30,000 degrees C which is 5 or 6 times hotter than the surface of the Sun. So I donít think you can have a thunderstorm without a lightning bolt because you wouldnít hear any thunder because something, some discharge has got to actually drive that happening in the first place. I think itís probably just that the lightning is masked behind a layer of cloud or something and you just donít see it.
The sound of thunder travels for quite some distance, so you may not see the lightening from your vantage point.