Chapter 5 Atmospheres

Question 1

Escape velocity equation and definition

Answer 1

This is the minimum speed needed before a body has enough kinetic energy to overcome the gravitational field of a planet.

V esc = sqrt((2GM)/R

Where M is the mass of a body, R is its radius and G is the gravitational constant.

Question 2

What is the exosphere?

Answer 2

The outermost region of the atmosphere where an outward traveling particle is more likely to escape than be bounced back by hitting another particle is known as the exosphere.

The temperature of escape is the same as the temperature of the exosphere.

Question 3

Why is Mercurys atmosphere so thin?

Answer 3

As mercury spins so slow the sun facing side gets heated to 740K, hot enough to excite CO2 enough to become lost into space.

Question 4

What is gas chromatography?

Answer 4

This is a process of separating a complex mixture of gasses into its chemically distinct components.

It works by pumping a gas mixture along a tube packed with material coated in liquid. The soluble gasses dissolve and therefore take longer to emerge from the tube. The instrument needs to be calibrated with authentic samples of each component gos to measure them.

Question 5

What is mass spectrometry?

Answer 5

This allows you to identify components of gas by measuring the masses of molecules (or parts of broken up molecules). They are then expressed as a relative molecular mass.

Question 6

Relative molecular mass definition

Answer 6

This is the mass of a molecule relative to the mass of a carbon 12 isotope.

RMM (molecule) = 12 x (mass of molecule) / (mass of C12 atom)

Question 7

What is an electric dipole?

Answer 7

An electric dipole is when a molecule has a positive and negative component, this happens because the electrons are more attracted to the atom with the most protons making it more negative, making smaller atoms more positive.

Question 8

What are heteronuclear molecules?

Answer 8

This are diatomic molecules made up of a different atoms ( i.e. CO). In these molecules electrons are shared unevenly causing electric dipoles. The electric dipole changes in strength as the molecule vibrates allowing the molecule to he detected by electromagnetic absorption.

Can he detected with infrared spectroscopy.

Question 9

What is a homonuclear molecule?

Answer 9

A homonuclear molecule is a diatomic molecule made from 2 of the same atoms. i.e. H2. These molecules share electrons equally so have no electric dipoles. So cannot he detected via their vibrational spectra.

Cannot be detected with infrared spectroscopy.

Question 10

What is an oxidised atmosphere?

Answer 10

Any atmosphere where carbon, for example, is predominantly combined with oxygen as opposed to hydrogen.

Question 11

What is a reduced atmosphere?

Answer 11

Any atmosphere where carbon, for example, is predominantly combined with hydrogen as opposed to oxygen.

Question 12

What is column mass? (Equation)

Answer 12

Column mass (mc), is the mass of atmosphere that sits above 1m^2 of a planets surface.

mc = Ps / g

Where mc is column mass, Ps is atmosphere pressure at the surface, and g is gravitational acceleration at the surface.

Question 13

What is oxidisation?

Answer 13

This is the loss of elections, but can also be described in this unit as the addition of oxygen.

Question 14

What is reduction?

Answer 14

Reduction is the process of gaining elections or in this unit the addition of hydrogen.

Question 15

What is the troposphere?

Answer 15

The lowest layer of an atmosphere heated by a planets surface.

Question 16

What is the thermosphere?

Answer 16

This is the outermost layer of an atmosphere characterised by the temperature rising with attitude.

Question 17

What is the mesosphere?

Answer 17

This is the middle layer of the atmosphere where the temperature decreases with altitude, but more slowly than the troposphere.

Question 18

What is the stratosphere?

Answer 18

Unique to earth the stratosphere is below the mesosphere, but above the troposphere where the temperature increases with altitude.

Question 19

What is the adiabatic lapse rate?

Answer 19

The slowest rate at which the temperature of a rising parcel decreases is that which results solely from the expansion of the gas with no heat lost to the surroundings.

Question 20

What is effective temperature? (equation)

Answer 20

Providing a planet doesn’t undergo any short term net heating or cooling, it is the temperature necessary for a planet to re-radiate all of the energy absorbed by the atmosphere and surface.

Te^4 = L / (4pi R^2 x 5.67x10^-8)

Where L is the total power radiated by the planet in watts and R is the radius of the planet in meters. The constant is units W m^-2 K^-4.

Question 21

What is albedo?

Answer 21

The total fraction of solar radiation that is reflected by a planet is referred to as albedo, a.

Albedo is a value between 1-0 with one being the most reflected and 0 being little reflected.

Question 22

What factors affect albedo on a planet?

Answer 22

• Surface colour, brighter surfaces reflect more radiation, dark surfaces absorbs more.
• cloud coverage, the more Cloud coverage, the more radiation that is reflected.

Question 23

Calculating the power of the sun absorbed by a planet (total power)

Answer 23

Total power = πr^2 x solar flux density x (1 - albedo)

Question 24

Calculate total power from radiogenic heating?

Answer 24

Total power = flux x mass (kg)

Question 25

Why don't N2 and O2 absorb infrared radiation?

Answer 25

As homonuclear diatomic molecules they do not contain an electric dipole, therefore do not absorbs infrared radiation. H2O and CO2 absorb infrared for more efficiently

Question 26

What causes the green house effect?

Answer 26

Visible light can penetrate the atmosphere and is absorbed by the surface. The planets surface then remits energy as infrared which can he absorbed by the atmosphere, causing it to heat up.

Question 27

Ozone key facts

Answer 27

Ozone is predominantly found in the stratosphere and is O3. Ozone is very good at absorbing wavelengths shorter than 350 nm, which means it is effective at absorbing UV radiation.

Question 28

Chapman scheme

Answer 28

O2 + photon > O + O O2 + O + M > O3 + M O3 + photon > O2 + O O + O3 > 2O2 Where the photon has to be a UV photon and M is any atom or molecule involved in this collision.

Question 29

How is the thermosphere heated?

Answer 29

Heating results from the absorption of high frequency UV radiation, which causes the ionisation of gasses. In the outer layers of the thermosphere a large portion of the gasses become ionised forming a plasma (free ions and electrons) that is conductive. This is known as the ** ionosphere**. Eventually the ions move to a lower energy level and emits a infrared photon. This is inefficient for homonuclear molecules so earths thermosphere is warmer than mars and Venus.

Question 30

What is a saturation vapour pressure diagram?

Answer 30

This is a diagram that can be constructed from laboratory studies that allows you to predict if liquid or solid particles will form in the atmosphere based on temperature and partial pressure. These diagrams only take into account a flat water surface, not rounded water droplets in which a higher partial pressure is required. Soluble particles also affect the diagram as they can dissolve in the liquid lowering the partial pressure required to form liquid.

Question 31

What is a Hadley cell?

Answer 31

This is where air is most heated by the seen at the equator and rises. The air then travesty travels away from the equator in the troposphere as it cools before returning to the surface at approximately 30° north and south.(convection currents)

Question 32

How does earths rotation effect the atmosphere? (equation)

Answer 32

The atmosphere rotates at the same speed as the earth. Due to the Hadley cycle, air from the equator moves closer to the earths spin axis causing it to spin faster due to the conservation of angular momentum. atmospheric speed at the equator can be calculated by 2πr / t where t is rotation period in seconds and r is earth radius at the equator

Question 33

Magnitude of angular momentum (equation)

Answer 33

Using the formula *mvr* (where m = mass, r is the distance of the mass from spin axis, v is angular momentum) we can calculate the momentum of the atmosphere at different latitudes by multiplying r by *cos(degree)*. The angular momentum must remain constant so as *rcos(degrees)* then *v/cos(degrees)* assuming m remains the same.

Question 34

What is condensation flow?

Answer 34

This is when the atmosphere flows from one pole to the other due to seasonal temperature differences between the poles. ( occurs on mars)

Question 35

What are thermal tides?

Answer 35

When the side of the planet is facing the sun it absorbs solar radiation. When the planet spins the face previously facing the sun turns away from the sun re radiating the energy and coating down. The large difference in temperature of the sun facing and dark side of a planet causes the atmosphere to flow around the planet, called thermal tides. This is most prominent on mars.

Question 36

What is the interplanetary magnetic field (IMF)?

Answer 36

The magnetic field lines from the sun extend so for that they appear to just travel away from the sun. These are referred to as the IMF. The IMF guide and influences the solar winds which consist of mainly protons, elections and some larger ions.

Question 37

What is bow shock?

Answer 37

This is where the solar winds wrap around the ionosphere or **magnetosphere** of a planet and produce "bow waves" similar to those produced by a boat.

Question 38

What is ionopause?

Answer 38

This is a region where very few ions from solar winds are found due to **bow shock**.

Question 39

What is the **magnetopause**?

Answer 39

This is the boundary between A planets magnetic field and the solar winds.

Question 40

What are the **van Allen radiation belts**?

Answer 40

These an two distinctive doughnut shaped regions where ions are trapped by earths magnetic field.

Question 41

What is a **magnetosheath**?

Answer 41

This is the region outside the **magnetopause** where solar winds can go.

Question 42

What are geomagnetic storms?

Answer 42

These are large variations to the suns magnetic field/ solar winds potentially caused by solar flares.

Question 43

How to remotely test the constituents of an atmosphere?

Answer 43

You can use infrared spectroscopy to measure absorption, emission and reflection of infrared radiation with a planets atmosphere. It is ineffective at identifying homonuclear molecules.

Question 44

How to test an atmosphere sample?

Answer 44

You can use mass spectrometry and gas chromatography.