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Meteorology: Air Masses, Temperature, and Humidity

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Emma Follman

on 11 April 2014

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Transcript of Meteorology: Air Masses, Temperature, and Humidity

Heat Transfer
Meteorology: Air Masses, Temperature, and Humidity
Humidity: the amount of water vapor in the air
Angle of Insolation
Air Masses
An air mass is a body of air with similar temperature and moisture content throughout it.
Air masses form at source regions.
Source regions affect the two factors that affect air masses:
Representing Air Masses
Air Masses that form near the equator and are warm are called "tropical."
Air masses that form towards the poles and are cold are called "polar."
Air Masses that form over water are called "maritime," and are wet.
Air Masses that form over land are called "continental"
Air Masses are abbreviated with two letters:
First Letter
Second Letter
The first letter represents where the air mass forms:
continental - c
maritime - m
The second letter represents the air masses' temperature:
tropical - T
polar - P
here are some examples
This Area is a continental tropical air mass.
It formed on the continent, so it is dry, and is near the equator, so it is warm.
Continental Tropical
Continental tropical is represented by "cT"
A warm, dry area describes a desert. This makes sense because there are lots of deserts in this area of the US.
*the second letter is CAPITALIZED
Maritime Tropical
This source region is where a maritime tropical air mass forms. Since it is over the Pacific ocean, it is maritime. This means it is moist. Also, it is near the equator, so it is warm.
Maritime Tropical is represented by mT.
Continental Polar
This source region is continental polar because it is over land and farther north than the previous two. Air masses that form here would be dry and cold.
This describes the current location, Canada.
Continental Polar is represented by cP.
Maritime Polar is represented by mP.
Maritime Polar
Last but certainly not least we have the maritime polar source region. This particular example is located in the northern waters next to Canada. Air masses here are wet and very cold, too.
Continental Arctic
Actually, there is one more: continental arctic. This source region forms very far north on land. It is extremely cold and very dry, just like the arctic is.
Continental Arctic is represented by cA.
Meteorology is not the study of meteors; it is the study of the atmosphere.
Weather is the condition of the atmosphere at a certain time and place. It changes every day and differs depending on the location on the earth.
Five factors affect the weather: temperature, pressure, humidity, wind, and precipitation.
As the temperature increases, the air can hold more water vapor.
Relative Humidity
Relative Humidity is the actual amount of water vapor in the air compared to the capacity of water vapor it can hold. It is represented with a percentage.
The air is called saturated is when it is holding its maximum capacity of water vapor. So, saturation is 100% relative humidity.
actual water vapor content
saturation water vapor content
Relative Humidity Percentage
Higher Temperature = Lower Relative Humidity
This is because the lower the temperature, the easier it is to become saturated and have a higher relative humidity.
Say a warm air mass and a cool air mass both have a relative humidity of 60%. Which one holds more water vapor?
The warm air mass would. Why?
This is because a warm air mass can hold more water vapor. If both air masses had the same percentage and a warm air mass can hold more, then the warm air mass actually holds more water.
Warm Air
Cold Air
The warm air mass holds more water even though they have the same percentage.
here's a visual
Quick Recap:
This is perihelion, when the earth is closest to the sun.
This occurs at 7:00 am on January 4th.
It is 147,098,074 km from the sun or about 91 million miles.
This is aphelion which is when the earth is at it's farthest point from the sun.
This occurs on July 4th every year at around 8pm.
At this point the earth is 152,171,522 km or about 94.5 million miles away from the sun.
Earth's tilt is 23.5 degrees
When is summer and winter in this diagram?
Most people would say that at perihelion it is summer and at aphelion it is winter.
This isn't actually the case. The earth's distance from the sun doesn't effect the season or temperature. The two factors affecting the season are:
Earth's Tilt
Earth's Shape
The Earth's Tilt
At perihelion, the earth is away from the sun. So, the northern hemisphere is receiving indirect sunlight and the southern hemisphere is receiving direct sunlight.
At aphelion, the earth is towards the sun. The northern hemisphere is receiving more intense direct sunlight and the southern hemisphere is receiving less intense indirect sunlight.
The northern hemisphere has winter at perihelion because it is receiving indirect sunlgiht.
The southern hemisphere and the equator are receiving direct sunlight so they have summer at this time.
The northern hemisphere is experiencing summer at this time. It's receiving direct and intense sunlight.
The southern hemisphere is experiencing winter at this time because it's getting indirect less intense sunlight.
The earth's shape effects the angle of insolation and the seasons of different places. The equator always gets direct sunlight and the northern and southern hemispheres have varying seasons depending on which way the earth is tilted relative to the sun.
Earth's Shape
For example, if the earth were a cube then the sun would be directly shining on every surface except for the top and bottom. This means it would always be summer.
If the earth had no tilt of its axis, then the equator would always be summer and the poles would always have winter no matter what. This is because no axis means the angle of insolation stays constant, so it's either always summer or always winter.
direct sunlight
always winter
always summer
always winter
always summer
Insolation is "incoming solar radiation"
There are three types of heat transfer: radiation, conduction, and convection
The sun releases energy through radiation. Radiation is transfer of energy through electromagnetic waves.
The sun releases all forms of electromagnetic waves but our atmosphere prevents the harmful waves to come through.
Another form of energy transfer is conduction. This is when thermal energy is transferred by contact through a material.
A person sitting is an example of conduction. This is because when someone sits in the chair they make the chair get warmer.
Some people argue that at the surface there is conduction because the earth heats the air.
However, this is debatable because it could also be called radiation. The earth is transferring its infrared waves/heat waves.
The last kind of heat transfer is convection. This is the transfer of thermal energy through circulation through a liquid or gas.
An example of convection is a convention current. Warm air is less dense and rises above cool air which is more dense.
This sounds like the convection current in the asthensosphere from the last unit. In the asthenosphere, as magma heats it comes up towards the surface because warm magma is less dense.
Ever wonder why babies or dogs can't be left in the car for an extended period of time during the summer?
This is an example of radiation. Fast electromagnetic waves come through the car's window and and slow down. They get trapped in the car and turn into infrared waves, which heats the car.
This is just like when someone dives in water. They start out fast until they hit the water which slows them down.
When someone walks on the street barefooted during a hot summer day, they are experiencing thermal conduction. The ground is hot and their feet touch it and feel pain.
The End. Tune in Next Time!
By Emma Follman
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