What can the hydrostatic balance calculate? 1. 2. 3. 4.

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

Topic 1a - Dry Thermodynamics Flashcards by Hellen Le Bacq

What is a standard atmosphere?

1013.25hPa

How well did you know this?

Not at all

Perfectly

From which direction does pressure act?

All directions

How well did you know this?

Not at all

Perfectly

Pressure = ?

Force/area, 1013hPa at surface

How well did you know this?

Not at all

Perfectly

the higher up you go the ___ the pressure

lower

How well did you know this?

Not at all

Perfectly

Density = ?

mass/volume, 1.2 kgm^-3

How well did you know this?

Not at all

Perfectly

The higher up you go the ___ the density

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

How well did you know this?

Not at all

Perfectly

What are three variables needed to describe dry air/

Pressure Density temperature

How well did you know this?

Not at all

Perfectly

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

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

How well did you know this?

Not at all

Perfectly

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

P=pRdT

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

How well did you know this?

Not at all

Perfectly

Describe the hydrostatic balance.

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

How well did you know this?

Not at all

Perfectly

What is the hydrostatic equation? What are its units?

dp/dz = -pg

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

How well did you know this?

Not at all

Perfectly

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

non - hydrostatic

How well did you know this?

Not at all

Perfectly

What is the hypsometric equation? assumptions?

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

Assumption: T is constant (isotermal)

How well did you know this?

Not at all

Perfectly

What is the equation for Scale height? practical definition?

H = RT/g

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

How well did you know this?

Not at all

Perfectly

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

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

can also use density

How well did you know this?

Not at all

Perfectly

Define atmospheric Thickness.

Thickness is the equivalent height change between two pressure levels.

How well did you know this?

Not at all

Perfectly

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

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

How well did you know this?

Not at all

Perfectly

What can the hydrostatic balance calculate?

calculate the approximate pressure as a function of height
height as a function of pressure
thicknesss between two pressure layers
sea level pressure if you know above pressure

How well did you know this?

Not at all

Perfectly

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

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

How well did you know this?

Not at all

Perfectly

Define temperature

Study These Flashcards

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

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

Study These Flashcards

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

Describe the adiabatic process.

Study These Flashcards

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

What is the first law of thermodynamics?

Study These Flashcards

dq = du +dw

What do the following represent:

Study These Flashcards

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

Define the internal energy (du) equation.

du = Cdt C = specific heat dt= change in temperature

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

dq = Cv dT + p da Used at constant volume. Cv = specific heat at constant volume. da (alpha) = change in specific volume

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

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

What are the values of the following: Cv Cp Rd

Cv = 717JK^-1Kg^-1 Cp = 1004 JK^-1Kg^-1 Rd = 287.04 JK^-1Kg^-1

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

dq = Cp dT + gdz where gz = geopotential

Define geopotential

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

what is the equation for adiabatic motion?

dT/dz = -g/Cp

Give a physical interpretation of the vertical temperature profile. 1. 2. 3. 4.

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

What is the concept of bouyancy? formula?

potential vertical motion based on changes in density. B = - g (rho - rhoe)/rho in ms^-2

At constant pressure warm air is ___ dense than cold air

less

Explain the state of the following

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.

Explain the following

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.

Explain the following

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.

What is the possion equation?

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

What can the possion equation tell us?

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

Define potential temperature. formula?

the temperature a parcel of air would have if it were moved adiabaticall to a reference pressure of 1000hPa. theta = T(100000/P)^RdCp

What is the value of Rd/Cp?

0.286

Describe the following stability