Lecture 8 - Planetary Atmospheres Flashcards
what is an atmosphere?
layer of gas surrounding a planet
is there a boundary to an atmosphere?
there is no clear upper boundary –> exponentially falls off
how thick is the atmosphere? what is it made of?
10km
mostly N2 and O2
what happens >100km? what about >300km
> 100km is considered space
> 300km still has some small amounts of gas
what creates atmospheric pressure?
collisions of individual atoms or molecules in the atmosphere
what happens to pressure and density as altitude increases? why?
pressure and density decrease as altitude increases bc there is less weight from overlaying layers
what is Earth’s pressure at sea level in kg/in^2, lb/in^2, 1 bar?
1.03 kg/in^2
14.7 lb/in^2
1 bar
describe pressure balanced with balloon elasticity
STAYS INFLATED when inside/outside pressures are balanced
adding air molecules will increase the inside pressure so the balloon expands until balance is restored
heating the balloon increases the speeds of air molecules inside to increase the inside pressure so the balloon expands until balance is restored
what are 5 effects of the atmosphere?
- creates pressure that determines whether a planet has liquid water
- absorb and scatter light
- create climate, weather, and wind
- interact with solar wind to create a magnetosphere
- making planetary surfaces warmer thru greenhouse effect
what happens when the atmosphere scatters light?
bright daytime skies
what happens when the atmosphere absorbs light?
prevents dangerous radiation from reaching the ground
what occurs during the greenhouse effect?
visible light (small wavelengths) passes thru atmosphere and warms the planet’s surface
then atmosphere absorbs infrared light (long wavelengths) from the surface, trapping heat
what are 4 factors that cause long-term climate change?
- solar brightening
- change in axis tilt
- change in reflectivity
- change in greenhouse gas abundance
how does solar brightening contribute to long-term climate change?
sun is changing the amount of thermal energy it releases and grows brighter
how does a change in axis tilt contribute to long-term climate change?
makes seasons more or less extreme –> warmer summers prevents ice buildup which reduces reflectivity to make the planet warmer
how does a change in reflectivity contribute to long-term climate change? what causes a change in reflectivity (3)?
increased planet reflectivity = less sunlight absorbed
(i.e. change in amount of light entering the atmosphere)
due to increased:
1. cloud cover
2. ice cover
3. particles released from volcanoes
how does a change in greenhouse gas abundance contribute to long-term climate change?
more greenhouse gases = warmer planet
in general, what determines surface temp of a planet?
balance btwn energy from sunlight it absorbs and outgoing thermal radiation
what determines the amount of incoming sunlight to a planet?
distance from the sun
what determines the temperature differences btwn day and night on a planet?
planet’s rotation rate
what is a planet’s reflectivity? what is another name for reflectivity?
reflectivity is the fraction of incoming sunlight it reflects
aka ALBEDO
what happens if there is low albedo?
absorbs more sunlight –> hotter temp
what is a “no greenhouse” temperature?
surface temp without any changes in atmosphere –> no greenhouse
what planet has the greatest reflectivity? what does this indicate about its temperature?
venus
temp very high –> high greenhouse effect
- bc lots of sunlight absorbed and cannot escape
how would the temperatures of venus and earth change if there was no greenhouse effect?
Venus would be 510deg C colder
Earth would be 31deg C colder
what are the 4 layers of Earth’s atmosphere from low to high?
- troposphere
- stratosphere
- thermosphere
- exosphere
TROPOSPHERE
- how does its temp change with altitude?
- what causes it to warm up?
- what is found here (2)?
temp drops with altitude
warmed by infrared light from surface and convection
airplanes, highest mountains
STRATOSPHERE
- how does its temp change with altitude?
- what causes it to warm up?
- what planet is the only planet with a stratosphere? why?
temp rises with altitude in lower parts, then temp drops with altitude in upper parts
warmed from the top by absorption of UV sunlight
Earth is the only planet with a stratosphere bc of UV-absorbing O2 molecules which protect us from Sun’s UV light
THERMOSPHERE
- at what altitude is it located at?
- how does its temp change with altitude?
- what 2 types of light is found here and what do they do?
located at 100km altitude
temp rises with altitude
X-rays and UV light from the sun heat and ionize gases
EXOSPHERE
- what is it?
- how does temp change with altitude?
- what happens to atoms in exosphere?
- what 2 types of light play a role and what do they do?
highest layer in which atmosphere gradually fades into space
temp rises with altitude
atoms escape into space
warmed by X-rays and UV light
why is the sky blue? why are sunsets red?
the atmosphere scatters blue light from the sun, making it appear to come from different directions
at sunset, there is more atmosphere to get through so blue does not cross. RED will cross but red gets scattered less
what is the role of earth’s magnetic field?
acts as a protective bubble around the planet to deflect solar wind particles
what happens to particles at the North and South poles?
some particles can accumulate in charged particle belts at either poles
does the strength of magnetic fields stay the same or change over time?
strength of magnetic fields changes over time
what causes an Aurora? when are they larger?
particles from solar wind energize the upper atmosphere near magnetic poles
larger when the sun is more active
On mars, seasons vary btwn _______ and _______
On Mars, seasons vary btwn North and South
how does the orbit of Mars affect its seasons?
orbit is elliptical so seasons are more extreme in the Southern hemisphere
spends more time away from the sun so winter is long and cold
describe the evolution of the atmosphere on Mars
how has the core changed?
early atmosphere was preserved by magnetic fields from molten core that bent solar winds around it
then magnetic fields decreased due to interior cooling and the solar wind stripped the atmosphere
the core is now weaker
describe surface water on Mars
no evidence of recent surface water, but there likely was water at some point
must have had greenhouse effect leaving long wavelength light in
describe the south polar ice caps on Mars
Residual ice of the south polar cap remaining during the summer is mainly water ice
describe the role of CO2 on Mars
CO2 makes up the ice of polar ice caps in winter
it sublimates in summer and condenses at the opposite pole
in ICE FORM, not in atmosphere so cannot warm the planet
what is the evidence for water on Mars? where could liquid water be located?
radar imaging has found frozen waters in layers of dusty ice
liquid water may exist underground near sources of volcanic heat
what is unique about the axis tilt of Mars? what does this lead to?
axis tilt changes –> ranges from 0-60
leads to climate changes and is evident in alternating layers of ice and dust
describe the atmosphere and surface pressure of Venus
venus has a thick CO2 atmosphere with a surface pressure 90x that of Earth
why does Earth have less of a greenhouse effect compared to Venus?
most of the carbon and water on Earth is in rocks and oceans
is the rotation of Venus slow or fast? what 2 things does this lead to?
rotation of Venus is slow
produces:
1. weak Coriolis effect
2. little weather
could Earth have had a larger greenhouse effect at one point? why?
yes, because of more carbon in atmosphere
what is the runaway greenhouse effect?
as greenhouse effect gets stronger, there is feedback to make it MORE stronger
why does the runaway greenhouse effect occur? (3)
- higher temp = more evaporation = more water vapour in atmosphere and it is a greenhouse gas which strengthens the greenhouse effect
- higher temp = oceans evapourate and release CO2 into atmosphere
- melting ice caps = less sunlight reproduction = more heat trapped and materials in permafrost could produce more heat as they melt
how might runaway greenhouse effect affect Venus?
the runaway greenhouse effect could account for why Venus has so little water
