For some people, lightning is a scary phenomenon, while for others, it’s a passion and part-time pastime chasing them. However, did you know that not all lightning is created equally? That is, there is a variety of lightning types that we see when studying thunderstorms.
Fascinating, isn’t it?
While meteorologically, I already know quite a bit about lightning – that is, the major lightning types – I found out that there is a wide range of visual varieties that are not even known by all meteorology enthusiasts. Or better, it should be wide – in bold – because there are really many variations.
Even more interestingly, many of those variations can help you estimate how the thunderstorm will behave – for example, some indicate that it is gaining strength.
Now, in this article, we’ll be taking a look at all those variations. Firstly, in order to provide the necessary context, we will take a look at lightning in general. What is it? Why does it happen, and how does it form? And, more relevant to the rest of this post: why are there so many different types? Answering those questions, we’ll build a nice framework from which we can explore lightning types.
And that’s precisely what we’ll do subsequently. We study the three major groups of lightning: intracloud lightning, cloud-to-cloud lightning and cloud-to-ground lightning.
Now, I think that this introduction is already long enough, so let’s take a look! 😎
Lightning: what it is, and why there are different types
While enjoying the beauty of all seasons, some people, me included, always love when the calendar approaches May again. From May on, until somewhere in September, my country faces some severe thunderstorms every now and then.
I then chase the storms together with some friends of mine.
Part of the reason why I love storm chasing is the unpredictability and thrill of lightning. Lightning, meteorologically, can be characterized as follows:
Lightning is a transient, high-current electric discharge with pathlengths measured in kilometers.AMS Glossary (n.d.)
Let’s now take a look at why lightning appears and why there are different types of lightning.
The appearance of a cumulonimbus cloud
If we want to understand why lightning occurs on Earth, we must take a look at how thunderstorm appear and grow.
We know that a thunderstorm can emerge due to buoyant air, which is keen to rise. Such convective movement in the atmosphere will eventually ensure that condensation occurs. As we know from another article, which covers the appearance of thunderstorms in more detail, this happens because rising air will cool down.
Eventually, the air that is getting cooler can no longer contain the amount of water vapor that it can hold at max for that temperature, and the surplus will condensate. A cumulus cloud appears.
When the updraft, i.e. the warm, upward moving air, is strong enough, the cumulus cloud will grow into mature forms of cumulus and eventually into a cumulonimbus cloud, or a thunderstorm cloud.
While at that stage there is no lightning yet, we’re not far away – rain is already falling.
Into a mature thunderstorm: elektrification
With really strong updrafts, the cloud continues to grow into what is eventually called a mature thunderstorm – a cumulonimbus incus.
Funnily, when this happens, the cloud breaks through the level where condensed water begins to freeze. While this sounds innocent, it’s one of the contributing factors to lightning formation.
As scientists have observed, water in clouds does not freeze immediately when it passes through freezing level. Instead, it will remain supercooled for some time. In one area of the cloud, in particular between 0 and -25 degrees Celcius (up to -13 degrees Fahrenheit), there will be a mixture of supercooled water, small ice crystals, and graupel/hail (Wikipedia, 2002).
From our article about why large hail can fall sometimes, we know that it’s kept in the cloud by the strength of the cloud updraft. At some point however, gravity working on the ice particle becomes stronger than the upward force of the downdraft, and the hail particle will fall.
At the same time, however, there are many other particles – those supercooled water particles and the small ice crystals – that move upward, because gravity working on them does not exceed upward motion because of their mass (Wikipedia, 2002).
Obviously, there will be collisions between the particles, and this is one of the primary factors of electrification of the cumulonimbus cloud. The process of colliding particles is visualized below, with two additional visual aspects: a ➕ and a ➖ symbol.
Those symbols mean the electrical charge of that particle.
When larger and smaller particles hit, the ice crystals that move upward become positively charged, while the falling graupel/hail becomes negatively charged (Wikipedia, 2002). As we can see, the positively charged particles will be moved upward into the cloud by the updraft, while the negatively charged ones fall downward.
As a result, the top of the cloud – which in the mature stage is often the anvil, or the incus – becomes positively charged, while the middle to lower parts of the storm become negatively charged (Wikipedia, 2002).
The lowest part of the storm, in return, becomes positively charged again, due to effects of ice turning into rain (Wikipedia, 2002). Since there is a large negative force in the lower parts of the cloud, the ground itself will also become positively charged.
This, in brief, is how a thunderstorm cloud electrifies once it becomes mature enough to freeze.
Why lightning occurs: downward-moving leader
Beyond electrification, understanding why exactly a lightning strike happens is complex (Wikipedia, 2002). It is therefore difficult to precisely but briefly explain here why lightning strikes happen, or why lightning in general appears from the electrified cloud.
Nevertheless, it’s worth to give things a try.
For a reason that is not yet understood by scientists, charged thunderstorms can form what is known as a leader. Here’s how they can be described:
Leaders are electrically conductive channels of ionized gas that propagate through, or are otherwise attracted to, regions with a charge opposite of that of the leader tip.Wikipedia (2002)
What happens within the thundercloud, which we know is negatively charged in the middle and lower regions while charged positively in the lowest regions, is that sometimes – the differences in charge become too large.
In those cases, the negative charge starts moving downward, to the positively charged area (National Weather Service, n.d.). However, the positive charge is insufficient to satisfy the negative charge that has accumulated over time. What then happens is that the downward flow continues, as we can see in the image on the right. This is called the leader we just introduced.
If you looked at the image critically, you saw that it is called a stepped leader. While it can sound strange, the leader does not move downward in a continuous fashion – but rather in a stepped way. This can also be seen in the image. The direction into which the leader moves is not determined by the positive charge near the surface (National Weather Surface, n.d.). Rather, the leader steps forward directly based on charges in the atmosphere surrounding the leader, within approximately 50 metres.
When the leader gets closer to the ground, the electrical forces between the tips of the leader and the ground get stronger. This is particularly true for the larger, positively charged objects such as buildings and trees. Eventually, air above those objects ionizes – charges – positively as well. The negative charge this also creates, moves into the ground.
We call this a streamer (National Weather Service, n.d). Many streamers can be there at once. They keep moving upward until one of them reaches the downward-moving leader.
When this happens, the negative charge can move towards the ground much faster. By result, a flash appears – which we see as the lightning flash (National Weather Service, n.d.).
Interestingly, the flash moves in the opposite direction of the negative charge – that is, upward.
This happens because the flash appears where charge starts moving quickly. As the charge moves downward, the flash beginning in the lower areas of the spectacle, the flash must move upward by definition. Here things are showed visually:
Now that we understand why lightning happens, we can take a look at different types of lightning that occur. In general, we can distinguish between those three types of lightning:
- Cloud-to-ground lightning (CG lightning)
- Intracloud lightning (IC lightning)
- Cloud-to-cloud lightning (CC lightning)
Cloud-to-ground lightning (CG lightning)
In the explanation above, we saw that a lightning strike occurs between the thunderstorm cloud and the ground.
We call this a cloud-to-ground lightning, or a CG lightning strike. Those strikes are the most powerful strikes that we see on Earth.
Generally, they can be divided into two groups of CG strikes (Wikipedia, 2002):
- Negative CG strikes, which are the ones that we covered above. With these strikes, current flows from the ground to the negative lower part of the cloud (Wikipedia, 2002).
- Positive CG strikes, where the opposite happens: the current flows from the cloud to the ground.
Positive strikes, while really rare (less than 5% of lightning strikes is a positive strike), are much stronger than negative ones, and hence much more dangerous. They are much more likely to cause fire upon striking an object, and they can travel greater distances. The strikes happen more often during winter and during the dissipation of a thunderstorm (Wikipedia, 2002).
Intracloud lightning (IC lightning)
When lightning moves from the cloud to itself, we talk about intracloud lighning, or IC lightning. This is by far the most frequent type of lightning (Wikipedia, 2002). It does not matter whether the lightning is within the cloud or whether it’s visible from the outside. What matters is whether the lightning moves between thunderstorm clouds that are located closely together, or whether it moves within one thunderstorm cloud.
The lightning bolt on this picture can thus both be an IC lightning or a CC lightning, which we shall cover next:
Cloud-to-cloud lightning (CC lightning)
Put very simply, a cloud-to-cloud lightning strike (or CC lightning) happens when a lightning bolt moves from one thundercloud to another thundercloud.
This happens often when multiple cells are close together, and strikes can move between areas with different charges within those clouds.
Now that we know why lightning occurs and what general lightning types there are, we can take a look at why we can observe them. Why is there simply not just one type of lightning? Let’s take a look.
Why there are different types of lightning
If we recall the explanations above, we can see that generally speaking, charges within a storm cloud are distributed as follows:
There is a main positive charge in the upper part of the storm cloud, possibly with a negative charge above it. In the middle to lower parts of the cloud, there is a negative charge, with a positive charge in the lowest parts of the storm cloud.
As we know, this yields a good opportunity for cloud-to-ground lightning, but it also describes why there are other lightning types.
Simply put, a lightning strike can happen between all differently charged wells within a thundercloud. This means that within the thundercloud, as in the case of intracloud lightning, a strike can occur between a positively and a negatively charged part of the cloud. If there is a multicell scenario, it’s of course also possible that lightning strikes occur between charged areas within two clouds, spawning the cloud-to-cloud lightning strikes that we covered before.
And finally, when a strike happens between the negatively charged part of the cloud and the positively charged round, we’re seeing a CG strike.
Now, that’s why there are many different types of lightning!
In this article, we studied lightning strikes – and more specifically, the large variety of types of lightning that occur during thunderstorms.
Firstly, we saw how a lightning strike emerges in the first place. Requiring convection, condensation, and the subequent maturation of the cloud’s updraft into a mature (i.e. icy) thunderstorm, a process of collisions between graupel/hail and smaller ice crystals starts occurring. Due to this process, parts of the cloud become positively charged, whereas others become negatively charged.
This, in return, will eventually lead to a lightning strike.
We also saw that there are three main types of lightning strikes: lightning from the cloud to the ground (both positive and negative), lightning from the cloud to another cloud, and lightning within the cloud (whether visible from the outside or not). Those types are all caused by the differently charged regions within the cloud.
I hope that you have learnt a lot from this article with respect to lightning and lightning types. Please do not hesitate to leave a comment below if you have any questions, remarks or suggestions for improvement. I’d love to hear from you! Anyway, thanks for reading MisterWeather today and enjoy the weather 😎
Lightning. (2002, July 10). Wikipedia, the free encyclopedia. Retrieved September 25, 2020, from https://en.wikipedia.org/wiki/Lightning
Lightning. (n.d.). AMS Glossary. https://glossary.ametsoc.org/wiki/Lightning
Understanding lightning: Initiation of a stepped leader. (n.d.). National Weather Service. https://www.weather.gov/safety/lightning-science-initiation-stepped-leader
Understanding lightning: Making connection with the ground. (n.d.). National Weather Service. https://www.weather.gov/safety/lightning-science-connection-ground
Understanding lightning: Return stroke. (n.d.). National Weather Service. https://www.weather.gov/safety/lightning-science-return-stroke