Meteorology: Part 2
Clouds
When we look in the sky and see the different shapes in the clouds, we also see that the clouds float around at different levels and that there are different types. From heavy, gray clouds to big, white, fluffy clouds to light, wispy clouds, there are 3 main types of cloud.
Stratus clouds are low, flat, and gray (stratus means layer in Latin).
Cumulus clouds are mid-level, fluffy looking, and white.
Cirrus clouds are upper-level, thin, wispy clouds of ice crystals.
These types can be combined with each other or with prefixes to describe almost all of the clouds found in the sky. However, one type literally looms over all the others...cumulonimbus. These clouds are the nurseries for thunderstorms and are sometimes called thunderheads or thunderclouds.
When we look in the sky and see the different shapes in the clouds, we also see that the clouds float around at different levels and that there are different types. From heavy, gray clouds to big, white, fluffy clouds to light, wispy clouds, there are 3 main types of cloud.
Stratus clouds are low, flat, and gray (stratus means layer in Latin).
Cumulus clouds are mid-level, fluffy looking, and white.
Cirrus clouds are upper-level, thin, wispy clouds of ice crystals.
These types can be combined with each other or with prefixes to describe almost all of the clouds found in the sky. However, one type literally looms over all the others...cumulonimbus. These clouds are the nurseries for thunderstorms and are sometimes called thunderheads or thunderclouds.
Precipitation
Clouds can't hold on to the water forever. When the water (or ice) falls from the cloud, we call it precipitation. Precipitation can take a variety of forms.
Snow - ice crystals that fall from the clouds and stay frozen down to the surface.
Rain - ice crystals that melt after it leaves the cloud and does not refreeze.
Sleet - rain that hits a layer of freezing temperatures that causes it to turn into ice pellets.
Freezing rain - rain that encounters a layer of freezing temperatures at ground level.
Hail - ice crystals that accumulate layers of ice through condensation and freezing in a cumulonimbus cloud. In cumulonimbus clouds, there is a powerful updraft of air that pushes ice crystals that have accumulated condensed water back up into the upper parts of the cloud. Up here, the temperatures are cold enough to freeze the water into a new layer of ice. It falls and accumulates more water. If the updraft is strong enough, it pushes the crystal back up to freeze another layer. Eventually, an ice ball forms with multiple layers of ice and falls from the cloud as a hail stone.
Clouds can't hold on to the water forever. When the water (or ice) falls from the cloud, we call it precipitation. Precipitation can take a variety of forms.
Snow - ice crystals that fall from the clouds and stay frozen down to the surface.
Rain - ice crystals that melt after it leaves the cloud and does not refreeze.
Sleet - rain that hits a layer of freezing temperatures that causes it to turn into ice pellets.
Freezing rain - rain that encounters a layer of freezing temperatures at ground level.
Hail - ice crystals that accumulate layers of ice through condensation and freezing in a cumulonimbus cloud. In cumulonimbus clouds, there is a powerful updraft of air that pushes ice crystals that have accumulated condensed water back up into the upper parts of the cloud. Up here, the temperatures are cold enough to freeze the water into a new layer of ice. It falls and accumulates more water. If the updraft is strong enough, it pushes the crystal back up to freeze another layer. Eventually, an ice ball forms with multiple layers of ice and falls from the cloud as a hail stone.
Severe Weather
Severe weather is caused by low pressure systems and cold or occluded fronts. We'll take a look at thunderstorms, tornadoes, and hurricanes. All of them are similar in how they form and eventually die. The difference lies in the degree of severity.
Thunderstorms
Thunderstorms are created by the unstable air in the heart of a cumulonimbus cloud. In a low pressure system, remember that warm air rises up from the surface. This warm air fuels the storm system. As the air cools at the top of the cloud, it falls back down toward the bottom of the cloud. These two columns of air passing each other inside the cloud causes friction between them and separates the charges of atoms. This is essentially building up static electricity. When the cloud discharges the static, it creates a spark...a large one that we call lightning. Lightning is incredibly hot and the air around it heats up very quickly and expands. As it cools and contracts, the speed in which it does so breaks the sound barrier and creates a sonic boom that we call thunder. As long as the storm passes over warm air, it will feed off of this warmth. But rain cools the ground and ultimately kills the fuel for the system; causing the thunderstorm to die.
Thunderstorms
Thunderstorms are created by the unstable air in the heart of a cumulonimbus cloud. In a low pressure system, remember that warm air rises up from the surface. This warm air fuels the storm system. As the air cools at the top of the cloud, it falls back down toward the bottom of the cloud. These two columns of air passing each other inside the cloud causes friction between them and separates the charges of atoms. This is essentially building up static electricity. When the cloud discharges the static, it creates a spark...a large one that we call lightning. Lightning is incredibly hot and the air around it heats up very quickly and expands. As it cools and contracts, the speed in which it does so breaks the sound barrier and creates a sonic boom that we call thunder. As long as the storm passes over warm air, it will feed off of this warmth. But rain cools the ground and ultimately kills the fuel for the system; causing the thunderstorm to die.
Tornadoes
Tornadoes are essentially really nasty thunderstorms. In fact, tornadoes come from severe thunderstorm systems. However, they are not as common as you might think. Only about 1% of severe thunderstorms spawn tornadoes. Since we have thousands of severe storms throughout the year, tornadoes can number close to 100 in a given year. So, as with thunderstorms, tornadoes are caused by low pressure systems...very low pressure. Low pressure systems not only feed off of warm air, but this air rotates in a counter-clockwise motion (called cyclonic motion for obvious reasons). When streams of air cross paths in the atmosphere, they start to roll like a barrel. A strong updraft of warm air can tilt this barrel roll onto the vertical causing a funnel cloud. A tornado is born. Tornadoes typically do not last very long because, like a thunderstorm, the rain that falls cools the ground and will cut off the warm air feeding the system. Once that warm air is gone, the tornado and thunderstorm system die. We measure tornadoes using the Enhanced Fujita (EF) Scale. This measures wind speed and accounts for the structural integrity of the buildings getting damaged...or destroyed. |
Hurricanes
Like thunderstorms and tornadoes, hurricanes are formed by a low pressure system. In this case, a low pressure system forms on the west coast of Africa. As it moves over the warm waters of the equatorial Atlantic Ocean, it picks up a lot of energy and gets bigger. The low pressure gets so big, that it actually causes a depression in the atmosphere which we call a Tropical Depression. Then, when the winds reach 34 mph sustained, we call it a Tropical Storm and give it a name. At 74 mph sustained (not gusts), we call it a Category 1 hurricane. We use the Saffir-Simpson Scale for measuring hurricanes. Hurricanes are not as powerful in regards to wind speed as tornadoes are, but they last longer. The ocean provides a huge area of warm, moist air for it to feed on. When the hurricane makes landfall, it immediately begins to weaken, but it can weeks for it completely die off. The same type of storm can also occur in the Pacific and Indian oceans, but we have different terms for them. In the Atlantic and Eastern Pacific (around the US), we call them hurricanes. In the western Pacific (around Asia), we call them typhoons. And in the Indian ocean, we call them cyclones. They are all the same, just in a different location. |