Heat lightning

[Lucretia]

Referencing this column, Is there such a thing as heat lightning? , I found it interesting that Cecil seemed to be saying that the reason the term is “heat” lightning is because it’s reddish colored.

I had always heard that it was called that because it was more likely to occur during hot weather.

[Barbarian]

I’ve never heard the term heat lightning, but that’s not the definition of sheet lightening where I grew up.

Sheet lightning is lightning that strikes over the horizon-- and turns that section of the sky white for a second-- hence the ‘sheet’.

The rule of thumb for soccer games was that we would play with sheet lightning, but stop the moment we saw ground or cloud strikes.

[Terrifel]

Frankly, after reading the column I’m more confused than ever.

Cecil agrees with Ed E. that there is no such thing as “heat lightning,” but then goes on to clarify that the phenomenon in question occurs on “warm summer nights.” This jibes well with my own observations from growing up in Florida (“The Lightning Capital of All the Parts of the World You’d Want to Visit,”) where my family and I would often sit out on the dock in the evenings to watch a particularly impressive light show. The “heat lightning” effect was not limited to the horizon (although it did seem to be most prominent in offshore thunderheads), but would also travel across the sky above us in reddish or greenish cascades (what Cecil seems to be describing as “sheet lightning”). It was always silent, save the occasional faint rumble, and would last for hours without ever turning into an actual storm. So what is it about summertime, specifically, that causes this effect? I don’t ever remember seeing it during colder weather, such as early spring (and there’s plenty of thunderstorms then as well).

[schizmaticism]

I was always taught that lightning went from ground to cloud, not the other way around.

:dubious:

[PhuQan_G_Nyus]

I live in a desert and in the summers we often will have “heat lightning” which is generally considered to be lightning that follows a particularly hot day and usually occurs with little or no cloud cover and little or no rain. I don’t know if it is a phenomenon caused by low humidity or what but it is different than the normal rain storm associated lightning. That is not to say that it is in any way different from normal lightning or acts any differently just that it can start suddenly. It may have to do with us being in a valley where weather can be almost self-generating when the prevailing winds die down for a few days, but it is different than the typical stormfront and not nearly as well forecast.

[Chronos]

The “heat lightning” effect was not limited to the horizon (although it did seem to be most prominent in offshore thunderheads), but would also travel across the sky above us in reddish or greenish cascades

Very different from the heat lightning I’ve seen in the northern Appalachians. There, it’s always restricted to the horizon, and lightning overhead is always associated with rain. So presumably, the lightning we saw on the horizon was somebody else’s actual storm. Horizon lightning doesn’t seem to occur at all in Cleveland, but there, we’re used to the Lake Effect screwing everything up.

[Irishman]

Here is How Stuff Works on lightning.

How Lightning Works

Note types of lightning:

How Lightning Works

Normal lightning - Discussed previously
Sheet lightning - Normal lightning that is reflected in the clouds
Heat lightning - Normal lightning near the horizon that is reflected by high clouds
Ball lightning - A phenomenon where lightning forms a slow, moving ball that can burn objects in its path before exploding or burning out
Red sprite - A red burst reported to occur above storm clouds and reaching a few miles in length (toward the stratosphere)
Blue jet - A blue, cone-shaped burst that occurs above the center of a storm cloud and moves upward (toward the stratosphere) at a high rate of speed

So they agree with Cecil.

schizmaticism, the above site explains that you are wrong. However, there is a ground contributing effect.

Lightning is caused by the molecules in the clouds bumping each other, liberating electrons. These electrons build up in the lower part of the clouds, with positive charges higher in the clouds. When the negative charges build up enough, they force electrons in the Earth down, creating a positive charge near the surface of the Earth. As the charge difference gets big enough, the clouds start sending down leaders. These are ionized air pathways, which fork in various directions trying to find a path. Meanwhile, the positive charges on Earth send up streamers, which is the part that reaches from ground to cloud. These streamers do not build, but only reach partway. The leaders then search around until they find the streamers, connecting the path and allowing the charges to discharge across the ionized path.

So why is lightning more common on hot days?

Why are there more thunderstorms during the summer?

Because moisture and warmth are crucial to thunderstorms, it makes sense that they would occur more often in the spring and summer, particularly in humid areas such as the southeastern United States. The high humidity, in conjunction with warm temperatures, creates massive amounts of warm, moist air rising into the atmosphere, where it can easily form a thunderstorm.

I did not see information for why sheet lighting happens more in summer. Perhaps in the summer, it is easier for the potential to discharge from cloud bottoms to cloud tops rather than to the ground.