Have you ever experienced really wanting to go out, say to play basketball, go biking around the neighborhood or just take a stroll in the park, when suddenly, it rains! This can really dampen your spirits. But why does it rain? What contributes to the formation of a storm? How about lightning and thunder?
Tropical cyclones
Tropical cyclones are storm systems with a closed circulation around a center of low pressure. They originate in the tropics and are called typhoons in most areas around the Pacific Ocean and hurricanes in the western hemisphere.
Tropical cyclones develop as a result of air pressure differences. When an air mass over a certain area is greater than its surrounding area, it is termed high pressure. When an air mass is lighter than its surrounding area, it is called low pressure.
Wind is formed as air travels from a high-pressure area to a low-pressure area as a result of the different air densities between the two. The greater the difference between the two, the stronger the wind that is formed.
Tropical cyclones get their energy from the evaporation of water in the oceans. The greatest evaporation occurs during summer equinox – when the equator receives the greatest amount of sunlight. Around this time, the surface water in oceans begins to warm up to above 26 C for a period of more then two months. In the northern hemisphere where the Philippines is located, tropical cyclones develop around the months of June and October.
Having warm ocean temperature is not enough to create a cyclone. There should also be a convergence of air over the area. This induces a rise of air and creates instability in the upper atmosphere.
In tropical cyclones, this instability is further induced by the latent heat of evaporation (or latent heat of vaporization). The latent heat of evaporation of ocean water at 26 C is 2425 kilojoules per kilogram. This means that a kilogram of ocean water evaporated at 26 C will use up to 2425 kilojoules of heat energy.
Evaporated water then rises up the atmosphere. As it rises, it cools and releases heat energy to its surroundings. The great amount of heat transferred causes convective instability which forces air to rise even higher. This instability will continue as long as a warm ocean is heated. This can then develop into the eye of a cyclone.
Thunderstorms
Did you know that there are about 1800 storms per hour or roughly 44000 per day occurring around the world? Thunderstorms (or electrical storms) are generally associated with heavy rainfall accompanied by thunder and lightning.
There are these basic ingredients needed to create a thunderstorm: (1) moisture found in the lowest level of the atmosphere; (2) unstable air; and (3) a “lift” (something that would push the moist air from near the ground up to where the air around it is cold). A lift can come in the form of fronts, sea breezes or even mountains.
When a mass of moist air is pushed up, it cools off and after a while, some water vapor turns into liquid droplets (which we see as clouds). The rest of the air in the mass warms up and does not cool off as fast as it would if the air was dry.
When the air mass gets to the part of the atmosphere where it is very cold, it will be warmer and less dense than the air around it. It will then start to rise faster without being pushed. More water vapor will turn into liquid. The mass will be warmer and will rise faster until all the water vapor are gone and the mass eventually reaches a part of the atmosphere where it is colder than its environment.
Lightning
Lightning is formed when charged ions build up in a cloud. This is called charge separation or polarization. During this process, positive ions go to the top of the cloud and leave the negative ions at the bottom. Positive charges also form between the negative base of the cloud and the positive surface of the ground.
When the negative charge at the base of the cloud becomes strong enough to overcome air resistance, electrons begin moving toward the ground. This electrical discharge is called a stepped leader. It is invisible to human eye.
Opposite charges attract, thus the positive charge from the ground moves up. When the charges meet, they form a complete circuit. After the formation of this circuit, it takes less than a millisecond before the actual lightning bolt can be seen.
Thunder
Lightning heats up the air to almost 30000 C. this causes air to expand from a few centimeters in just a few millionth of a second. Then, the air quickly cools after lightning flashes, causing it to contract.
The rapid expansion and contraction of air around the lightning causes air molecules to move back and forth, producing sound waves and the noise that we hear as thunder.
Storms may prevent you from enjoying outdoor activities. Still, there are many exciting things that you can do inside the house. Just ask your mother and for sure, she will give you a truckload of things to do.
James Lactao
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