SINGAPORE - A lightning strike on the East-West Line near Bedok MRT station around 4pm on Monday (Nov 20) caused a delay in service between Tanah Merah and Paya Lebar.
The train captain said he was unwell and was taken to Changi General Hospital, where he was warded on Monday night.
Responding to queries from The Straits Times, the Meteorological Service Singapore said a lightning stroke was detected near Tanah Merah MRT station at 3.37pm on Monday.
A lightning stroke refers to a discharge of lightning between a cloud and the earth, especially one that causes damage.
What are the different types of lightning and which is most common in countries like Singapore? The Straits Times finds out.
1. How does lightning form?
Lightning is an electrical discharge caused by imbalances between storm clouds and the ground, or within the clouds themselves. Most lightning occurs within the clouds.
2. What are the lightning statistics in Singapore?
Singapore, which has been dubbed a lightning capital, has one of the highest occurrences of lightning activity in the world.
The country is situated near the equator and has warm and humid tropical conditions highly favourable for the development of thunderstorms.
On average, Singapore experiences 168 thunderstorm days per year - days in which thunder is heard over the island, and gives an indication of lightning activity. At any given time, more than 2,000 thunderstorms are estimated to be active around the globe.
3. When does lightning occur in Singapore?
Lightning is associated with thunderstorms and the frequency of thunderstorms can be used as a gauge for lightning frequency.
Thunderstorms are most frequently observed during the inter-monsoon months of April and May and October and November. Thunderstorms tend to occur between 2 pm and 6 pm in the afternoon as diurnal heating and convection play an important role in thunderstorm development.
The occurrence of thunderstorm is lowest in January and February in the later phase of the north-east monsoon.
4. What are the different types of lightning?
The most common types of lightning never leave the clouds but flash between differently charged areas within or between clouds.
a. Intracloud lightning
This is the most common type of discharge. Intracloud lightning occurs inside a single storm cloud, jumping between different charge regions in the cloud. It is sometimes called sheet lightning because a distant bolt lights up an entire cloud base with a "sheet" of light.
b. Bead lightning
Also called chain lightning, it is a form of lightning that lasts longer than more typical lightning. It appears as a string of luminous segments instead of a continuous channel. It occurs infrequently but has been observed many times.
c. Cloud-to-ground lightning
Cloud-to-ground lightning, also known as a lightning stroke, refers to a discharge of lightning between a cloud and the earth, especially one that causes damage.
There are two types of cloud-to-ground lightning strokes - negatively and positively charged ones, the former of which is more common.
Most of the lightning seen striking the ground in a storm is of the negative cloud-to-ground variety. These can be identified visually and in photographs by their distinctive downward branching. They commonly consist of multiple "return strokes", which are additional pulses of current that illuminate the channel again and again.
Positively charged cloud-to-ground lightning is less common and is usually associated with supercell thunderstorms. Thunder that accompanies it is typically very loud, and often sounds like a series of deep, low-frequency sonic booms.
d. Other rare forms of lightning
Other rare forms of lightning can be sparked by extreme forest fires, volcanic eruptions, and snowstorms.
Ball lightning, a small, charged sphere that floats, glows, and bounces along oblivious to the laws of gravity or physics, still puzzles scientists.
Witnesses report seeing luminous spherical objects that can be as small as the size of a pea to several metres across. It has been described by eyewitnesses but rarely recorded by meteorologists, and remains controversial.
Red sprites, which are described as shaped like jellyfish, carrots or columns, are mostly red and last just a few seconds. They usually happen at the same time as powerful positive cloud-to-ground lightning strokes and can extend up to 95km from the top of the cloud.
They can be seen only at night and are rarely spotted with the human eye, showing up only on highly sensitive cameras.
5. What is a lightning stroke?
A lightning stroke, also known as a cloud-to-ground lightning flash, refers to a discharge of lightning between a cloud and the earth, especially one that causes damage.
There are roughly five to 10 times as many lightning flashes within clouds as there are cloud-to-ground flashes, according to the National Severe Storms Laboratory, a US federal research laboratory under the National Oceanic and Atmospheric Administration.
6. What are the dangers of lightning strokes and strikes?
According to the National Environment Agency's (NEA) website, cloud-to-ground lightning poses a serious threat to lives and property.
Lightning strikes can be fatal and have critically injured many. Generally, there is no safe place outdoors when a thunderstorm is nearby.
A common misconception is that there is lightning only when there is rain. However, lightning can strike a distance away from the thunderstorm cloud where there is no rain or even where the skies appear to be clear.
These so-called "bolts from the blue" have been documented to strike even as far as 16km from the thunderstorm cloud.
7. What should one do if there is lightning?
NEA gives the following advice:
- Take shelter in a house, large building or car and remain inside for at least 30 minutes after the last sound of thunder is heard
- If no structure is available in open areas, head for the lowest elevation and crouch down as low as possible, supporting yourself on the balls of your feet with heels touching (Lightning Crouch position).
- In open water, head for the shore immediately
- Stay off bicycles, motorcycles or golf carts
- Avoid large, open areas and high ground
- Spread out if in a group
- On a golf course (without any nearby shelter), put down your clubs, take off spike shoes and adopt the lightning crouch position
- Stay away from isolated tall objects such as trees, towers or poles
- Stay away from metal conductors such as fences, pipes and rails
- Do not hold metal objects such as golf clubs, umbrellas or bicycles
- Do not handle explosive or inflammable materials
SOURCES: Britannica.com, National Geographic, NEA, Stormhighway.com, National Severe Storms Laboratory