Atmosphere and Pressure

Unit 6

What are the layers of the atmosphere?

• There are 5 layers to the atmosphere: the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.
• It is thickest at the surface and thins out eventually into space.

Troposphere

• The troposphere is the first layer above the surface and contains half of Earth’s atmosphere. Weather occurs in this layer.
• The troposphere begins at Earth’s surface and extends to 4-12 miles (6-20 km) high.

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Stratosphere

• The stratosphere is the second layer of the Earth's atmosphere. Many airplanes fly in the stratosphere, because it is very stable.
• The bottom of the stratosphere is the coldest, and temperature increases in height. This is because heat is produced in the formation of ozone.
• The stratosphere extends from 4-12 miles high to around 31 miles (50 km).

Mesosphere

• The mesosphere is the third layer of the Earth's atmosphere. Meteors or rock fragments burn up in the mesosphere.
• This layer extends from 31 miles (50 km) to around 53 miles (85 km) high.

Thermosphere

• The thermosphere is the fourth layer of the Earth's atmosphere. It's the layer with auroras and where the space shuttle orbits.
• It extends from 53 miles (85 km) to around 375 miles (600 km) high.
• The thermosphere is the hottest layer, but there are too little molecules to heat up anything (so it’ll still feel cold).

Exosphere

• The exosphere is the fifth and last layer of the Earth's atmosphere. This is the layer where the atmosphere merges into space. This layer is extremely thin.
• In this layer, atoms and molecules escape into space and satellites orbit the earth.
• This layer is composed mainly of simple gases, like Hydrogen and Helium.

Tropopause

• The tropopause is the boundary between the thermosphere and the stratosphere.
• It is located somewhere around 4-12 miles high depending on location.

Stratopause

• The stratopause is located at the boundary between the stratosphere and the mesosphere.
• It is located about 31-34 miles (50-55 km) into the sky.

Mesopause

• The mesopause is the boundary between the mesosphere and the thermosphere.
• It is located around 53 miles (85 km) above the Earth’s surface.
• The mesopause is the coldest region on Earth, with temperatures as low as -100°C.

Thermopause/Exobase

• The thermopause is the boundary between the thermosphere and the exosphere.
• The exosphere is sometimes considered to be outer space because there is no clear boundary between the exosphere and outer space.

Composition

• The atmosphere is made up of 78% nitrogen, 21% oxygen, 0.9% Argon, 0.03% Carbon Dioxide, and 0.07% other gases.

What is Ozone?

• Ozone is a natural gas that is found in two different layers of the atmosphere. In the layer around the Earth's surface, otherwise known as the troposphere, bad ozone dirties the air and helps make smog. The troposphere extends up to the stratosphere layer, where good ozone protects life on Earth by absorbing some of the sun's UV rays. Stratospheric ozone is found most often between six to 30 miles above the Earth's surface.

The Ozone Layer

• The ozone layer forms a thin shield high up in the sky and is located in the stratosphere. It protects life on Earth from the sun's ultraviolet rays. In the 1980s, scientists began finding clues that the ozone layer was going away or being depleted. This allows more UV radiation to reach the Earth's surface. This can cause people to have a greater chance of getting too much UV radiation. Too much UV can cause bad health effects like skin cancer, eye damage, and get you sick easier.

What causes ozone depletion?

• Stratospheric ozone is often destroyed by manufactured chemicals containing chlorine and/or bromine.
• Chlorine and bromine can destroy ozone easily by breaking apart ozone.

Pressure

• Atmospheric pressure is the force per unit area exerted on a surface by the weight of air above that surface in the atmosphere.
• Low pressure areas have less atmosphere pushing down, while high pressure areas have high atmosphere pushing down.

High Pressure

• A high pressure system is a whirling mass of cool, dry air that generally brings fair weather and light winds. In the Northern Hemisphere, winds spiral out of the system in a clockwise direction.

Low Pressure

• A low pressure system is a whirling mass of warm, moist air that generally brings stormy weather with strong winds. In the Northern Hemisphere, winds spiral into the system in a counterclockwise direction.

How does pressure change with altitude?

• The higher you go, the lower the pressure. When you increase your elevation, less air is pushing down on you.

Air pressure at sea level

• The air pressure at sea level is:
• 1 atm (atmosphere)
• 1013.25 mb (millibar)
• 1013.25 hPa (hectopascals) = 101325 Pa = 101.325 kPa
• 14.7 psi (pounds per square inch)
• 760 mmHg (millimeters Mercury) = 29.92 inHg
• 760 Torr
• 1.01325 bar
• 14.7 psi = the air above us at sea level weighs 14.7 pounds on every square inch!

Humidity

• Humidity is the amount of water vapor in the air.
• Absolute Humidity is the total amount of water vapor present in a given amount of air. It does not take temperature into consideration.
• Relative Humidity is the ratio of water vapor contained in the air compared to the maximum amount of moisture that the air can hold at that specific temperature and pressure.

How can we feel humidity?

• Humans are very sensitive to humidity, as the skin relies on the air to get rid of moisture. The process of sweating is your body's attempt to keep cool and maintain its current temperature. If the air is at 100-percent relative humidity, sweat will not evaporate into the air. As a result, we feel much hotter than the actual temperature when the relative humidity is high. If the relative humidity is low, we can feel much cooler than the actual temperature because our sweat evaporates easily, cooling ­us off.

Temperature

• Temperature is a degree of hotness or coldness the can be measured using a thermometer. It's also a measure of how fast the atoms and molecules of a substance are moving. Temperature is measured in degrees on the Fahrenheit, Celsius, and Kelvin scales.

Wind Chill

• The wind chill index is the temperature your body feels when the air temperature is combined with the wind speed. The higher the wind speed the faster exposed areas of your body lose heat and the cooler you feel.

Heat Index

• The Heat Index is a combination of air temperature and humidity that gives a description of how the temperature feels. This is not the actual air temperature.

Wind Chill Chart

Heat Index Chart

Wind Chill Advisory

• Wind Chill Advisories are issued when the wind chill is expected to be between -15°F to -24°F.

Wind Chill Warning

• Wind Chill Warnings are Issued when the wind chill temperature is forecast to be -25°F or lower.

Heat Advisory

• Heat Advisories are issued when the Heat Index is greater than or equal to 105°F and less than 115°F for less than 3 hours per day. Also, nighttime heat indices should remain above 80°F for at least 2 consecutive days.

Excessive Heat Watch

• Excessive Heat Watches are issued when the heat index is expected to be greater than 115°F.

Excessive Heat Warning

• Excessive Heat Warnings are issued when the Heat Index is expected to be 115°F or greater for more than 3 hours per day for at least 2 consecutive days.

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Why can you see your breath when it is cold outside?

• Your breath is reasonably warm and humid and it has invisible water vapor as a large component of the gas. Warm moist air meeting the cooler air outside the body causes the invisible water vapor to condense the cooler air outside are visible and form the cloud that you see. The relative humidity which depends upon water content and temperature goes to 100%. As the breath gets further from the person's face the water content dilutes and the relative humidity goes down and the droplets go back into vapor form.

Crickets

• Crickets can be used to determine temperature based on their chirping.
• See Activities 261-266 in the Assignment sheet.

Hai

I really don’t know why there are a lot of empty slides.

# of chirps + 40 = °F

# of chirps/3 + 277.15 = K

# of chirps/3 + 4 = °C

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