Lectures 3 & 4 Flashcards
What controls Qg
-the amount of energy required to raise the temperature object through 1°C
-thermal conductivity
How fast is Qg
Qg is a relatively slow responding flux due to conduction
How large is the laminar boundary layer
Very small - 5 to 50 mm thick around all objects
Breakdown of laminar boundary layer
speed, distance from source, and viscosity of air are reached.
Is low velocity more or less turbulent?
Less turbulent
Is shorter distance more or less turbulent?
Less turbulent
Is lower viscosity more or less turbulent?
More turbulent
Mechanically induced turbulence =
Forced convection
Thermically induced turbulence =
Free convection
Free convection is caused by
by unequal heating of the surface due to spatially varying surface conditions
What causes unequal heating of the surface?
-albedo
-wetness : is incoming radiation used for heating or evaporation?
Does the atmosphere get more or less dense with height?
Less dense due to reduced pressure
Adiabatic meaning
heat does not enter or leave system
Forced convection
air flows along the surface until it meets an obstacle
What is the Cook Strait an example of?
Forced convection
What is the rate of temperature change with height in dry unsaturated air?
9.8°C per km (DALR)
Is the SALR or DALR higher?
DALR is always higher.
What is the environmental lapse rate?
The measure of actual rate of temperature decrease with altitude for a given location.
Stability
the relative tendency of an air parcel to move vertically
ELR > DALR
Unstable, favours vertical mixing
ELR < DALR
Stable, little vertical mixing
ELR = DALR
Environment cools at 9.8°C per km.
Atmospheric stability
The actual cooling / heating (ELR) compared to the idealised cooling / heating (DALR) determines whether the atmosphere is stable or unstable
What controls the upper limit of turbulent activity?
Magnitude of surface forcing (surface roughness, surface heating)
Lost buoyancy from; mechanical mixing, condensation and latent heat release, reaching an inversion
What convection dominates most of the outer layer at day time?
Free convection
What convection dominates at night time?
Forced convection, with turbulence restricted to shallow surface layer
