GY101 week 4 notes
GY101 week 4 notes GY 101
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This 6 page Class Notes was uploaded by Elle Notetaker on Saturday February 13, 2016. The Class Notes belongs to GY 101 at University of Alabama - Tuscaloosa taught by Eben Broadbent in Fall 2016. Since its upload, it has received 32 views. For similar materials see Atmospheric Processes & Patterns in Geography at University of Alabama - Tuscaloosa.
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Date Created: 02/13/16
GY101 Notes from 2/10/2016 Insolation in the Atmosphere *Warning. There will be some discussion of rainbows. If you are allergic to awesome colors, it is recommended that you avoid page 2 of this document. You’ll be missing out, though it’s a great picture. The sun gives us shortwave radiation, or radiation with high frequencies, and Earth sends out longwave radiation, or radiation with low frequencies. Radiative equilibrium is when the sun gives us energy and we send it back into space. The warmer Earth is, the more energy we send out. Atmospheric Influences on Insolation Absorption when energy is absorbed. Some of the gases, liquids, and solids in the atmosphere reduce the energy that reaches the earth’s surface by absorbing it. For the most part, though, the things in the atmosphere are bad at absorption. reflection energy is reflected/redirected by an object like a mirror. Different objects reflect different amounts of energy. Albedo the amount of energy an object or surface reflects. This is a percentage. A high albedo means that the object is very reflective. A white car and snow both have high albedos. Specular reflection when an object reflects energy in a concentrated beam, like a mirror Sensible vs Latent Heat Sensible Heat you can feel an object changing temperature (warming up or cooling down, both apply). There is NO change in state Latent Heat This is what changes the state of matter. When water goes from liquid to gas or gas to liquid, latent heat is involved. THERE IS NO CHANGE IN TEMPERATURE HERE. This is important for storms, because the condensing water gives out latent heat as it forms clouds. Interaction of Insolation with the Atmosphere Different layers of the atmosphere take out or reduce different types of radiation. The Thermosphere absorbs gamma and xray radiation, while the Ozone in the Stratosphere absorbs a lot of UV radiation. Components of Atmosphere As we all know, the atmosphere is made of gas (air), solids (dust), and liquid (drops of water). These bits interact with radiation and energy in different ways, by reflecting, absorbing, or scattering the energy. Scattering, or diffuse reflection is when energy is reflected into less intense beams. Gases in the atmosphere like to scatter radiation, hence the name. Rayleigh Scattering this is what makes the sky look blue. Things in the atmosphere that are smaller than 1/10 the wavelength of the incoming radiation turn back some of the radiation, scattering the nonblue wavelengths and sending that radiation back into space. Rayleigh Scattering is partial to shorter wavelengths, so because ‘blue’ light is on the short end of the color spectrum, the Rayleigh scattering tends to let that stuff through, creating the color of the sky. Mie Scattering this is what happens when it’s really foggy, there’s a lot of pollution in the air, or when the sun is rising/setting. It’s mostly forward scattering, so there’s not much energy that gets turned back to space, it’s just redirected in a way. Mie scattering is why sunrises are more red when there’s a lot of pollution, or what makes gray skies in cities sometimes. Nonselective Scattering this is where rainbows come from. Clouds scatter the incoming radiation (light) equally, sending the different waves out to make pretty colors after storms and whatnot. (Next time you see a rainbow, you should start yelling “Hey, come look at the Nonselective Scattering! It’s really cool!”) This picture is from abcNews. If you want to look it up, this is the link. http://abcnews.go.com/US/beachgoerssnapstunningphotosrarefirerainbowsouth/story? id=33209513 For those of you who want to know exactly what parts of the atmosphere gets what energy, you can go to page 64 in the book for information on the Earth’s energy balance. It’s got a nice diagram there that you can look at. For those on StudySoup, I would recommend finding ‘energy balance’ or ‘radiation balance’ in your textbook. It should be in roughly the same area. 2/8/2016 The Solar Constant (we’re starting out with a little review, here) Again, EMR doesn’t slow down or anything as it gets closer to the Earth it spreads out. (A flashlight’s illumination is stronger as you get closer to it, but it will cover a lot more area if you move the light back some. In the same way, radiation is inversely proportional to the distance between the objects of interest squared. In other words, radiation is proportional to 1/d² this is called the inverse square law. Solar constant a measure of flux density and the amount of Solar EMR the Earth system gets. It comes in constantly, at a rate of roughly 1,366 watts/m² on the big circle of the Earth system. If you’re having trouble understanding that, here’s a picture that might help a bit. Now, the solar constant measures the EMR for the plane that is 1 astronomical unit from the sun. An astronomical unit is the distance between the Earth and the Sun. As of 2012, said distance is 140, 597,870,700 meters, according to the International Astronomical Union As we all know, the Earth goes around the sun every 365.25 days. (The ‘.25’ is why we have February 29 every 4 years.) When the Earth makes a circle around the sun, that’s called a ‘Revolution.’ We go about 1° around the sun every day. If you think about it, that might be related to the 360° in a circle. 365 days in the year, 360 degrees in a circle it makes sense. Weirdly enough, we don’t quite go in a circle we go in an elliptical (oval) path around the sun, sometimes closer and sometimes farther away. When we’re closest to the sun, that’s the Perihelion, and when we’re farthest, that’s the Aphelion. Perihelion Earth is closest to the Sun. 91 million miles away. December 21. Aphelion Earth is farthest from the sun, at 94 million miles away, on July 21. Some people might look at that and think “Oh, so that’s where seasons come from” Nope! Seasons come from the fact that Earth is tilted. 23.5°, in fact. In the Northern Hemisphere’s summer, we’re farthest away from the sun Aphelion on June 21. Those 4 million miles have nothing to do with it. So, the seasons come from the earth’s tilt. In june, the Northern Hemisphere is tilted toward the sun summer. In December, we’re tilted away. If you’ll think about it, areas around the equator don’t really have seasons, but places farther north or south do. There’s a reason that in To Kill a Mockingbird, Scout says that Alabama doesn’t even have seasons. (That’s only true to an extent, though, given that six months ago we were all sweating, and now it’s freezing cold and windy outside). It takes us 24 hours to rotate (spin in a circle) on our 23.5° axis. If you stick a pole through our axis, it will line up with a star called Polaris the North Star. As we go around the sun, the Earth doesn’t change positions, so one hemisphere will face the sun at certain times, and away at others. When Earth is tilted just right between the perihelion and the aphelion, both hemispheres share the sunlight equally those are solstices, and we get one in the spring and one in the fall. Everywhere on Earth gets 12 hours of sunlight on March 21 and September 21. When you calculate the intensity of radiation, you need to consider the solar angle the angle the sun is hitting us at. At noon, we’ve got a higher solar angle than in the evening, and the solar angle is directly related to the radiation we get. When you have a high solar angle, there’s not as much beam spreading the light is more concentrated so it’s easier for the sun to make things warm. There’s a reason that noon is hotter than the evening. Now, we’ve got 2 angles for the sun: Zenith angle: the angle between the sun and, say, a tree. It measures the vertical angle. Angle of Incidence: the angle between the sun and the ground this is the horizontal angle. Insolation the amount of radiation Earth gets is spread out as a function of different Zenith angles between the equator and the poles. For those of you who’re a bit lost, I’m going to make a picture. It might be a bit… lacking in artistry, but I’m not an artist. And there are actually 2 pictures. SPF= Solar Protection Factor Weather Basics: The molecules in the air are always moving, and they’re always moving in every direction, which means that they exert pressure in every direction, too. Imagine you’ve got a box sitting on top of you. It’s putting out a lot of pressure, so you move away from the box. You’ve just gone from a high pressure spot to a low pressure spot. Air does the same thing when there’s a lot of pressure, it tries to go away to a low pressure area, thus we have wind. High Pressure air sinks, and there might be clearer skies Low Pressure the air rises, and helps form clouds. When mapping air pressure, we plot it with lines called isobars. The pressure is measured in either millibars in the US or kilopascals in Canada. Temperature changes based on time and location. When there’s a big change, it’s usually because of a front cold, warm, occluded, or stationary. That’s when a different sort of air is coming in. Fronts often bring along their luggage in the form of precipitation so when you have a front coming in, you might get a bit of snow. (Rain in Alabama we don’t get snow much, here.) Humidity is used to describe the water in the atmosphere. There’s a maximum amount of water vapor that can be in the air at different temperatures, and there’s the real amount that is in the air. Because of that, humidity is stated as a percent. If you go look at the weather report, you’ll see it’s true. Dew Points change based on temperature and humidity and that’s where the temperature has to get below for condensation to start on grass, cars, etc. Now for a brief history of meteorology Meteorology is the study of the atmosphere. Figuring out the future is both an art and a science you use computers and models for science, and your opinion and experience contribute to what you think will happen that’s the art part. There’s no routine that people use to figure out the weather, so when the weatherman is wrong, it’s because he’s not a psychic. Probably. And this concludes the 2/8 session of notes for GY 101. I hope these have helped and you visit again soon.
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