Starter…Name these clouds… A B C DE F G H I

Answers… A. Cirrus B. Cirrocumulus C. Cirrostratus D. Altocumulus E. Altostratus F. Cumulonimbus G. Stratocumulus H. Stratus/Nimbostratus I. Cumulus

Air Pressure Air Pressure

What is air pressure? As we know, the air in the atmosphere is made up of a number of gases. These gases press down on the Earth’s surface, exerting a force that we call air pressure. Although we are usually unaware of this pressure, it actually presses down very hard – roughly equivalent to the force of an elephant balancing on a desk! As we know, the air in the atmosphere is made up of a number of gases. These gases press down on the Earth’s surface, exerting a force that we call air pressure. Although we are usually unaware of this pressure, it actually presses down very hard – roughly equivalent to the force of an elephant balancing on a desk!

Air pressure varies over time and from place to place. If we travel up a mountain or go up in a hot air balloon, for example, the air pressure gets less the higher we go. We can explain this difference by comparing air pressure to a pile of blankets on your bed. Air pressure varies over time and from place to place. If we travel up a mountain or go up in a hot air balloon, for example, the air pressure gets less the higher we go. We can explain this difference by comparing air pressure to a pile of blankets on your bed.

Air pressure at sea level is the equivalent of having many blankets, which would feel very heavy. Air pressure at sea level is the equivalent of having many blankets, which would feel very heavy. If you have only one blanket though, it would feel very light, and this is like the air pressure at the top of a mountain. If you have only one blanket though, it would feel very light, and this is like the air pressure at the top of a mountain. Each layer of air presses down on the layers below, and so the greatest pressure is at ground level where we have the maximum amount of air above. If we go above the height of mountains and into the stratosphere, the pressure will decrease until it reaches about zero, as here there is hardly any air above it. Each layer of air presses down on the layers below, and so the greatest pressure is at ground level where we have the maximum amount of air above. If we go above the height of mountains and into the stratosphere, the pressure will decrease until it reaches about zero, as here there is hardly any air above it.

Pressure and Temperature Air pressure also varies because of the differences in the temperature of the air. Air pressure also varies because of the differences in the temperature of the air. What do you think? Do high temperatures lead to high pressure or low pressure? What do you think? Do high temperatures lead to high pressure or low pressure?

HIGH TEMPS = HIGH PRESSURE As the temperature increases, so does the pressure. As the air heats up, the molecules move faster and run into each other more, which ends up increasing the air pressure. As the temperature increases, so does the pressure. As the air heats up, the molecules move faster and run into each other more, which ends up increasing the air pressure. The opposite occurs when temperature decreases…air pressure goes down. The opposite occurs when temperature decreases…air pressure goes down.

Cool air is denser (heavier) than warm air. Areas of high pressure can be caused when cool air is sinking and pressing on the ground. When there is high pressure, the weather is usually dry and clear. Cool air is denser (heavier) than warm air. Areas of high pressure can be caused when cool air is sinking and pressing on the ground. When there is high pressure, the weather is usually dry and clear. Warm air is less dense (lighter) than cool air and will therefore rise above it. When warm air rises, it causes a region of low pressure. With low pressure, the weather is often wet and cloudy. Warm air is less dense (lighter) than cool air and will therefore rise above it. When warm air rises, it causes a region of low pressure. With low pressure, the weather is often wet and cloudy.

“Winds blow from high to low!" Changes in air pressure bring changes in the weather and make winds blow. Air usually moves from areas of high pressure to areas of low pressure, and this produces winds. Changes in air pressure bring changes in the weather and make winds blow. Air usually moves from areas of high pressure to areas of low pressure, and this produces winds.

Barometer Changes in air pressure are measured on an instrument called a barometer. Most barometers give a reading in millibars (mb for short). Readings over 1010 mb indicate high pressure. Changes in air pressure are measured on an instrument called a barometer. Most barometers give a reading in millibars (mb for short). Readings over 1010 mb indicate high pressure.

What does a Barometer do? Air has weight, and a barometer measures the changes in air pressure above, so basically it measures the weight of the air. Air has weight, and a barometer measures the changes in air pressure above, so basically it measures the weight of the air. When there is a high-pressure area, the air sinks. When the air sinks, more force pushes down toward the ground, so the barometric pressure increases. When there is a high-pressure area, the air sinks. When the air sinks, more force pushes down toward the ground, so the barometric pressure increases. Conversely, when a low-pressure area moves in, the air rises. Since a rising column of air above weighs less, the barometric pressure falls. Conversely, when a low-pressure area moves in, the air rises. Since a rising column of air above weighs less, the barometric pressure falls.

Let’s Try This Concept Out… Let’s Try This Concept Out…

High Pressure Areas High pressure areas tend to be warmer. High pressure areas tend to be warmer. As we know, warm air can hold more moisture than cold, so the air of a high pressure area is not as humid as a low pressure area would be. As we know, warm air can hold more moisture than cold, so the air of a high pressure area is not as humid as a low pressure area would be. Due to low humidity, high pressure areas tend to have fair weather associated with them. These are the bluebird, fair weather days where nothing weatherwise is happening. Due to low humidity, high pressure areas tend to have fair weather associated with them. These are the bluebird, fair weather days where nothing weatherwise is happening.

Low Pressure Areas Low Pressure areas usually produce cloudy, stormy weather. This is due to the fact that low pressure areas tend to be cooler, and air is moving quickly into low pressure areas. Low Pressure areas usually produce cloudy, stormy weather. This is due to the fact that low pressure areas tend to be cooler, and air is moving quickly into low pressure areas. This movement of air causes winds, clouds and storms. This movement of air causes winds, clouds and storms.

Isobars On a weather map, lines called isobars join up areas where the pressure is the same. On a weather map, lines called isobars join up areas where the pressure is the same. These lines resemble those seen on topographic maps. These lines resemble those seen on topographic maps. The closer together the isobars are, the more windy it will be. The closer together the isobars are, the more windy it will be. Generally, there is a 4mb difference between each isobar Generally, there is a 4mb difference between each isobar

Can you find where the strong and weak winds are?