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OU ASTR 1514 - Atmospheres of Earth and Venus

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ASTR 1514 1st Edition Lecture 16Atmospheres of Earth and VenusChapter 7.3-7.4Equilibrium temperature of a planet depends in the distance from the sun and the albedo, reflectivity of sunlight. - Farther from the sun – Weaker sunlight – Less heating from sun- Higher albedo –les light absorbed – less heating from sunGreen-House Effect- Planet’s atmosphere produces a green-house effect that prevents the radiation from escaping- Visible light from the sun easily penetrates the atmosphere- Temperature of the planet is cool so infra-red light is radiated, however the atmosphere is not transparent to infra-red light, so the energy does not escapeEnergy Balance (Green-house Effect)- Energy in = Energy out – Energy planet absorbs = energy planet radiates- Temperature of planet adjusts until these two rates are equal- Green-house effect planet does not radiate as efficiently, so planet heats up more than it would without an atmosphere. - (Planet still in energy balance equilibrium, but at a higher temperature.)Energy in: Incoming sunlight heating planetEnergy out: Outgoing Infra-red radiation cools planetSome gases, especially Carbon Dioxide and Water vapor, block some infra-red radiation, preventing planet from cooling. Heated atmosphere will also heat the groundThis green-house effect means the planet is at a higher temperature due to extra energy needed tobe in equilibrium with the sunlight. Earth’s surface temperature is about 33K higher than it would be without an atmosphereWithout Earth’s atmosphere water on Earth would be frozen. Some Green-house gases1. Carbon Dioxide2. Water Vapor3. Methane4. Nitrous Oxide5. Chlorofluorocarbons6. Some of the gases are man-made, but many are naturally occurring gasesVenus and Mars- Both Venus and Mars have atmospheres dominated by Carbon Dioxide. - Carbon Dioxide on Venus raises surface temperature by about 400K (to 737K).- Carbon Dioxide on Mars raises surface temperature by only 5K- This depends on the total number of greenhouse molecules on a planet. Mars atmosphere is too thin to have an effective greenhouse effect. Why Earth is so different1. Mostly due to Its distance from the sun2. Volcanism causes gasses to be released into the atmosphere including water.3. Water rained from the sky, forming oceans4. Liquid water dissolved the carbon dioxide from the atmosphere, and carbon precipitated out and was taken out by life.5. Venus was too hot; liquid water could not exist and a runaway greenhouse effect developed. 6. On Earth, Greenhouse effect acts as a thermostatRunaway Green-House Effect- Venus: Hot when formed, so no water on surface- Earth: Water removes Carbon Dioxide from the atmosphere, forming limestone. - Earth: Life further removed Carbon Dioxide. - Water and carbon dioxide were contained on Earth (not in the atmosphere) but not contained on Venus, developing a runaway green-house effect. - If Earth moved to Venus’s orbit it would be hotter than Venus because Earth has more liquid water that would evaporate and form water vapor in the atmosphere causing a stronger greenhouse effect. Earth’s Atmosphere - Mostly Nitrogen and Oxygen- Life on Earth is responsible for the presence of oxygen- Other planets do not have oxygen in their atmosphereOxygen- Oxygen is a very reactive gas, Ex: Rust is a reaction between iron and oxygen.- Oxygen must be continually replenished to remain in our atmosphere- Plants: 1. Use Carbon Dioxide and Water and the energy of sunlight to perform photosynthesis, releasing carbohydrates and oxygen as waste products.2. If plants disappeared then atmospheric oxygen would disappear. Earth’s Magnetosphere - Earth’s magnetic field, the magnetosphere, extends out into space.- It blocks much of the solar wind (particles blown off by the sun)- Prevents solar wind stripping, the removal of atmosphere by solar windsHow does the magnetosphere protect us?- Solar winds consist of ions (atoms missing one or more electrons)- Ions interact with the magnetic field, ions do not cross magnetic field lines- But Ions travel along magnetic field lines.- Damaging Ions either avoid Earth altogether or get funneled to magnetic poles. - At the poles the Ions may come into contact with Earth’s atmosphere creating auroras. - The magnetosphere can trap charged particles.- Particles from solar winds collide with the atmosphere creating the Northern and Southern lights (aurora borealis and aurora australis)Weather on EarthHadley Circulation- Hot air at the equator rises- Displaces air above it, which flows towards the poles.- The air cools and sinks, flowing back toward the equator. Coriolis Effect- Caused by Earth’s rotation- Causes Hadley cells to break in to zonal winds- Diverts wind in the East/West direction.- Coriolis Effect is a pseudo force.- The earth rotates at different speeds under the north-south trajectory depending how far you are from the equator. - Parts of the Earth are heated differently- Vertical circulation of air (convection) distributes surface heating- Global winds carry heat from hot to cool regions- The circulation depends on heating patterns and rotation period. - These circulation patterns are responsible for the weather we experience as well as seasonal patterns. - Warm air hold more moisture than cool air- Hurricanes are influenced by the Coriolis Effect.- Foucalt Pendulum is an example of the Coriolis effect at work. Venus’s Atmosphere- Venus has a hot dense atmosphere completely covered by clouds- 96% of the Venus atmosphere is Carbon Dioxide, so strong greenhouse effect- Surface temperature of Venus is roughly 737K, hot enough to melt led.- Thick atmosphere means nearly uniform temperature over the entire planet. More on Venus- Venus rotates very slowly on its axis (once every 243 Earth days relative to the stars, but once every 117 days for the sun to come back to the same place) and in the opposite direction that it revolves around the sun. - Coriolis Effect is weak on Venus- Surface winds on Venus are like a classical Hadley Circulation, mixing hot equatorial air with polar air.- Surface area of planet is nearly constant- Surface winds are very weak- Venus has a weak magnetic field so it is very vulnerable to solar wind stripping- Orbital plane is the same as it’s rotational plane so there are no seasons on


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