Tag: cloud

Posted in Science & Nature

Thuder And Lightning

Posted on by Jinavie

The best or worst part (depending on your preference) about a dark and stormy night are the majestic flashes of lightning and booming thunder. Most people confuse the two terms, typically using “thunder” to describe both, but technically thunder is the sound produced by lightning, which is the flash of light. Lightning occurs when dense clouds become electrically charged due to the collision of water molecules. As charge builds up, the cloud becomes negatively charged. The negative charge becomes so intense that it begins to push electrons towards the surface of the Earth, creating a positive charge. Electricity always flows from a negative charge to a positive charge through a medium. The intensity of charges causes the air to become ionized (plasma), making it suddenly conductive and allowing the electricity to flow from the cloud to the ground. This is seen as a flash of intense light. As the electricity travels through this channel of air, it superheats the air and causes a massive expansion of air, much like an explosion. This creates an intense shockwave burst, producing a sound that we call thunder.

Lightning is a deadly force of nature. It clocks a peak voltage of somewhere between 30 million to billions of volts – far exceeding the electricity that can be generated by humans. When a lightning bolt strikes a human, it has a mortality rate of between 10~30%. The two effects of lightning on the human body is electrical shock and heat. As lightning flashes over the skin to reach the ground, it leaves a striking pattern known as Lichtenberg figures (see below), showing the path of the electrical breakdown. The intense electrical burst can cause loss of consciousness, arrhythmia or sudden cardiac arrest. The heat generated by the electricity can cause severe burns both externally and internally. It can literally fry internal organs causing permanent damage to the heart, lungs and brain. Neurological symptoms such as amnesia, confusion, sleep disturbance and chronic pain have also been reported. Strangely, there are also reported cases of lightning curing ailments such as blindness, deafness and baldness.

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Because lightning is light and thunder is sound, one can calculate how far away lightning struck using the time between the lightning flash and the sound of thunder. Sound travels at 340m/s, so by multiplying the number of seconds between the lightning and thunder by 340, you can deduce the distance in metres. For example, if you see a lightning strike and then hear thunder after 7 seconds, the lightning must have struck 340m x 7s = 2380m = 2.38km away.

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Posted in Science & Nature

Rain

Posted on by Jinavie

Let’s imagine that you are walking outside, when rain clouds catch you by surprise and suddenly pour down on you. Assuming that you have no umbrella or anything to cover yourself with, is it best to run back home or walk back? Or to elaborate, should you walk and spend more time in the rain, or should you run, which means you will run into rain sideways?

There are two ways you can get wet in the rain: it will either fall on top of your head, or you will run into it from the side. The amount of rain that falls on your head is constant whether you are walking or raining, as the entire field you are travelling through is full of raindrops. Therefore, one would naturally think that running would not add much benefit as you run into more rain by moving faster, as you essentially hit a wall of raindrops.

But this is not true. No matter how fast you travel, the amount of rain you hit sideways is constant. The only variable that affects the amount of rain you hit sideways is the distance you travel. This is because the amount of raindrops in the space between you and your destination is constant.

Summarising this, the wetness from rain you receive is:

(wetness falling on your head per second x time spent in rain) + (wetness you run into per meter x distance travelled).

Since you cannot really change how far you are from your destination, the best way to minimise getting wet is to run as fast as you can to minimise the time you spend in the rain.

Then again, this is only the most practical option to keep you dry. If you are feeling particularly romantic or blue, then feel free to stroll through the rain, savouring the cold drops on your face (or wallow in the sadness that is your life).

(Here’s a very good video explaining the maths/science of it all: http://www.youtube.com/watch?v=3MqYE2UuN24)

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Posted in Science & Nature

Forecast

Posted on by Jinavie

When the weather forecast says today will be sunny, it always seems to rain (and vice versa). In fact, according to a US study, forecasts are sometimes less accurate than flipping a coin. If not even professionals can accurately predict the weather, can ordinary people like you and I do it?
The key to this is observation. By carefully studying your surroundings, you can look in to the future.

There are many signs before rain comes. For example, if the sunset is unusually clear or if a mountain far away looks smaller or hazy then it is very likely that it will rain the next day. If you see a rainbow in the morning it suggests rain is coming from the west. On hot days without any wind, it is likely there will be a heavy shower.
Animals are also adept at telling the weather. Frogs crying, worms coming out and swallows flying low are all signs that the air is humid and rain is coming. Swallows are especially accurate, as they fly low to catch insects that cannot fly high due to the humidity weighing them down.
If you are at the beach and there is a swarm of jellyfish, avoid going out to sea. Jellyfish near the coastline is a premonition for a storm.

If a more accurate weather prediction is required, the most precise method is cloud observation. If you study them carefully they comprise three tiers, with some clouds rising vertically.

Clouds in the highest level

  • Cirrus: Very fine, white feathery clouds that almost look combed over. If these clouds are curvy and organised the weather will be fine, but if they appear banded or spread chaotically they can gather and form rainclouds and start a shower.
  • Cirrostratus: Looks like a veil of cotton curtaining the sky. They cause halos around the sun and moon, which is a sign of imminent rain.
  • Cirrocumulus: Looks like a spread of seashells on a beach. If you find these clouds over a beach in winter, it will rain soon.

Clouds in the middle level

  • Altocumulus: Either appears as an ordered stream of rounded clouds, or looks like a herd of sheep. If these clouds shrink in size, the weather gets better (and vice versa).
  • Altostratus: Shaped like streaks of veil across the sky. They are often light grey or very dark. If they become thicker or sink to a lower level, it is a sign that the weather will be cloudy with a chance of rain.
  • Nimbostratus: The common “raincloud”, bringing rain and snow.

Clouds in the lowest level

  • Stratocumulus: Clumps of clouds that appear in layers without clear boundaries. You can see clear sky through gaps between them. If you can see clouds that were cumulus in the afternoon changing to stratocumulus by sunset, the weather will be great the next day.
  • Stratus: Looks like fog covering a low sky. If they come in the morning and disappear by night, that day will be clear. However, if they lie between altostratus and a canyon, it will rain.

Clouds that rise vertically

  • Cumulus: Fluffy clouds that you can see on a clear sky. If they disappear by evening the next day is clear, but if they can be seen late at night or float north-westerly, it is a sign that it will rain.
  • Cumulonimbus: Massive cloud pillars that rise to the level of cirrus. It always brings heavy rain and sometimes a thunderstorm.

If you know how to observe and analyse cloud patterns, you can predict the weather even when stranded on a desert island.