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Atmospheric Sciences > Topic 1a - Dry Thermodynamics > Flashcards

Topic 1a - Dry Thermodynamics Flashcards

1
Q

What is a standard atmosphere?

A

1013.25hPa

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2
Q

From which direction does pressure act?

A

All directions

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3
Q

Pressure = ?

A

Force/area, 1013hPa at surface

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4
Q

the higher up you go the ___ the pressure

A

lower

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5
Q

Density = ?

A

mass/volume, 1.2 kgm^-3

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6
Q

The higher up you go the ___ the density

A

lower density changes in response to pressure as the atmosphere is compressible

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7
Q

What are three variables needed to describe dry air/

A

Pressure Density temperature

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8
Q

What is the Ideal gas law? What are the units of each component?

A

pV=mRdT

p = pressure in Pa, V = volume in m^3, Rd = constant: 287.04Jkg^-1K^-1,T = temperature in K, m = mass in Kg

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9
Q

What is the equation of state? What are the units of each component?

A

P=pRdT

p = pressure in Pa, p (rho), Rd = constant: 287.04Jkg^-1K^-1, T=temperature in K

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10
Q

Describe the hydrostatic balance.

A

Hydrostatic balance is the balance between the downward force of gravity and the upward acting pressure gradient force (pressure decreses with height)

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11
Q

What is the hydrostatic equation? What are its units?

A

dp/dz = -pg

p(rho) = density in kg/m^3, g = 9.81 ms^-2

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12
Q

If there is strong vertical acceleration ie. a cloud. what is the state of flow? (hydrostatic or non-hydrostatic)

A

non - hydrostatic

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13
Q

What is the hypsometric equation? assumptions?

A

p(z) = p(o)exp [-zg/RT]

Assumption: T is constant (isotermal)

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14
Q

What is the equation for Scale height? practical definition?

A

H = RT/g

height at which pressure is 1/e of its surface value

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15
Q

When incorporating scale height with the hypsometric equation what equation is made?

A

p(z) = p(0) exp [-z/H]

can also use density

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16
Q

Define atmospheric Thickness.

A

Thickness is the equivalent height change between two pressure levels.

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17
Q

What is the equation to find thickness? What is the scale height in this case?

A

p(z1) = p(z2) exp [- (Z1-Z2) /H] OR

p(z1) = p(z2) exp [- (thickness) /H] OR

Thickness = -H . ln(Z1/Z2)

H ~ Rd Tav /g

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18
Q

What can the hydrostatic balance calculate?

1.

2.

3.

4.

A
  1. calculate the approximate pressure as a function of height
  2. height as a function of pressure
  3. thicknesss between two pressure layers
  4. sea level pressure if you know above pressure
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19
Q

Why does the temperature profile over a desert have a higher rate of change of temperature?

A

More heating during the day -> more ascending motion -> troposphere expands more

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20
Q

Define temperature

A

Temperature is proportional to the mean moleculat kinetic energy of gas, given in Kelvin.

21
Q

what happens when you lift a parcel of air without exchanging energy between the parcel and its surroundings? (adiabatic process)

A

The parcel expands due to a reduction in pressure with height. This causes a reduction in molecular kinetic energy and a reduction in temperature.

22
Q

Describe the adiabatic process.

A

when a parcel undergoes a change in state (pressure, density or temperature) without an energy exchange? ascent of parcel = cooling. descent casues warming

23
Q

What is the first law of thermodynamics?

A

dq = du +dw

24
Q

What do the following represent:

  1. dq
  2. du
  3. dw
A

dq = external energy input. variation in heat content of the parcel

du = internal energy of the system (temperature)

dw = work donw by the system through expansion or contraction

25
Q

Define the internal energy (du) equation.

A

du = Cdt

C = specific heat

dt= change in temperature

26
Q

What is the first useful form of the 1st law of thermodynamics? when is it used?

A

dq = Cv dT + p da

Used at constant volume.

Cv = specific heat at constant volume.

da (alpha) = change in specific volume

27
Q

What is the second useful form of the 1st law of thermodynamics?

A

dq = Cp dT - a dp

Where Cp = Cv + Rd = 1004 JKg^-1K^-1 OR heat capacity at a constant pressure

28
Q

What are the values of the following:

Cv

Cp

Rd

A

Cv = 717JK^-1Kg^-1

Cp = 1004 JK^-1Kg^-1

Rd = 287.04 JK^-1Kg^-1

29
Q

What is the thrid useful form of the 1st law of thermodynamics?

A

dq = Cp dT + gdz

where gz = geopotential

30
Q

Define geopotential

A

Geopotential is the amount of work needed to lift 1kg of air from the surface to the height z

31
Q

what is the equation for adiabatic motion?

A

dT/dz = -g/Cp

32
Q

Give a physical interpretation of the vertical temperature profile.

1.

2.

3.

4.

A
  1. solar radiatio heats up the surface via short wave absorption and long wave radiation re-emission
  2. the warm surface air is less dense, rises and cools adiabatically
  3. if atmosphere is dry temperature will vary 10 degrees per km

4 . if it contains water vapour there will be latent heat release and cloud formation. Rate of cooling will be less

33
Q

What is the concept of bouyancy? formula?

A

potential vertical motion based on changes in density.

B = - g (rho - rhoe)/rho in ms^-2

34
Q

At constant pressure warm air is ___ dense than cold air

A

less

35
Q

Explain the state of the following

A

Parcel lapse rate is higher than the environmental lapse rate (Te < Td). This means that the parcel is colder than the environment. It has a negative buoyancy and will sink. This creates a stable environment, a parcel displaced will want to return to its original position.

36
Q

Explain the following

A

The parcel lapse rate is smaller than the environmental lapse rate (Te>Td). This means that the parccel if warmer than the environment. the parcel has a positive buoyancy and will want to rise further. This is an unstable environment, if displaced the parcel will coninue to move away from original position.

37
Q

Explain the following

A

The parcel lapse rate is the same as the environmental lapse rate (Te=Td). they will be the same temperature and the parcel will have no buoyancy. This is a neutral environment and a parcel moved vertically will remain there.

38
Q

What is the possion equation?

A

T0 = T1 (p0/p1) ^ Rd/Cp

39
Q

What can the possion equation tell us?

A

If we know the temperature and pressure at a particular height what would the temperature of that parcel be if i moved it adiabatically to a differnt height that has a known pressure

40
Q

Define potential temperature. formula?

A

the temperature a parcel of air would have if it were moved adiabaticall to a reference pressure of 1000hPa.

theta = T(100000/P)^RdCp

41
Q

What is the value of Rd/Cp?

A

0.286

42
Q

Describe the following stability

A

theta is constand with height. environment is neutral.

43
Q

Explain the stability of the following

A

theta increases with height. the environment is stable

44
Q

Explain the stability of the following

A

Theta decreases with height. The environment is unstable

45
Q

Why is potential temperature a conserved vairable for adiabatic process?

A

If there is no transfer of energy tothe parcel the parcel will maintain the same potential temeprature regardless of pressure.

46
Q

Describe the states of the following

A
  1. unstable
  2. neutral
  3. stable
47
Q

Define the Brunt-Vaisala frequency. formula?

A

N^2 = g/thetha dtheta/dz OR

N^2 = g (gamma dry - gamma)/T

maximum frequency oscillation if forced ascent occurs.

48
Q

What types of clouds are created by oscillation?

A

lee waves or mountain waves

lenticular clouds

Atmospheric Sciences (8 decks)

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