stability of air Flashcards
what determines the pattern of weather and the type of cloud that will form?
the way in which temperature varies in conjunction with atmospheric humidity.
what happens in an adiabatic process?
in an adiabatic process, heat is neither lost nor gained by a gas
what is it called when in rising air currents, pressure and temperature decrease?
adiabatic lapse rate
what is environmental lapse rate?
the rate of temperature decrease with a gain in altitude.
Environmental lapse rate is a recording of what?
it is a recording of the atmosphere’s actual temperature with a gain in altitude
what is the average temperature lapse rate? (up to 35,000ft)
2 degrees per thousand feet.
what is dry adiabatic lapse rate (DALR)? And what is the rate?
The DALR is the rate at which the temperature of unsaturated air changes as a parcel ascends or descends through the atmosphere. The DALR is approximately 3°C/1000 feet.
how will saturation occur in a rising parcel of air that is DALR?
if the ascent is sufficiently high, when the parcel
of air’s temperature reaches the dew point temperature saturation will occur in the rising parcel of air. above this height, the now saturated air will cool as it rises.
what is saturated adiabatic lapse rate?
The rate at which saturated air cools when it ascends (when considering) the effect of latent
heat release.
what is the SALR rate?
1.5C per 1000ft
is SALR a fixed rate like DALR?
no, it depends on the amount of water vapour available for condensation.
what is required for SALR?
latent heat is required for the process, the heat is taken from the air parcel in which the droplets are evaporating, thus
counteracting the heating due to comp
what is stability?
stability refers to the the tendency of an object to return to its original position after a disturbance.
define stable
if a parcel returns to its original position after a disturbance
define unstable
if a parcel doesn’t return to its original position after a disturbance
define neutrally stable
If the parcel of air is forced to move either up
or down and then remains in the moved
position, after the disturbance has ceased, it
is said to be neutrally stable
the 3 types of stability are determined by?
temperature, humidity and environmental lapse rate
What are the conditions of stable air?
denisty of air is greater then surroundings, air tends to resist vertical movement and air is stable if ELR is less than SALR. and DALR is stable if the observed lapse is less than SALR
what are the conditions of unstable air?
Dry air is unstable, if the environmental lapse rate is
greater than the Dry Adiabatic Lapse Rate (DALR). And saturated air is unstable, if the environmental lapse rate is greater than the saturated adiabatic lapse rate.
what are the coniditions of conditional instability?
Conditional instability occurs when the Environmental Lapse Rate is between both the dry and saturated lapse rate. The air will become unstable if the air becomes saturated.
what is an inversion
an increase in temperature with height
what is an isothermal layer?
a vertical column of air having a constant temperature with height.
what is a subsidence inversion?
a slow downward motion of
air typically found in Anti-cyclonic
conditions.
Pollutants trapped in the inversion
layer means that a ‘Subsidence inversion’ is
commonly marked by what?
a layer of haze
the clear skies above, light winds and high humidity caused by subsidence inversion allows for what conditions to form?
the clear skies above, light winds and high humidity create ideal conditions for fog.
what causes radiation inversion?
After sunset, due to the lack of radiation from
the sun, the layer of air next to the surface of
the Earth is cooled by conduction, thereby
creating a warmer layer above.
what causes subsidence inversion?
when a widespread layer of air descends.
what does radiation inversion depend on?
Radiation Inversions depend upon clear nights, when the terrestrial radiation can quickly escape, and
light winds (6-8 Knots) create a mixing layer
that will determine the height of the inversion
what happens to radiation inversion if winds are strong?
If the wind speed is any stronger, the colder air will be dispersed over a wide area, preventing
the inversion from occurring.
where are radiation inversions usually found?
Radiation Inversions are usually found in anticyclonic
conditions and over land or swamp areas, but not over lakes or the sea, due to water’s higher
‘specific heat’ preventing the condition of rapid cooling necessary
when are radiation inversions strongest?
strongest around sunrise and when the temperature falls below the dew point temperature, frost or even fog may occur.
whats at the top of the radiation layer?
wind shear, due to a difference in wind speed and direction.
what are the effects of radiation inversion on a plane?(3)
A rapid decrease in density, associated with strong inversions, can also affect climb performance.
If descending to land, a ‘negative wind shear’ can be experienced as a decrease in airspeed and/or increasing rate of descent.
Carburettor Icing can also occur as temperatures may increase by up to 10 degrees C from the surface to the top of the inversion
what causes a frontal inversion?
A frontal inversion occurs when a cold
air mass forces the warm air mass to rise.
what happens during a frontal inversion? And what will frontal inversions create
Temperatures will decrease at the ‘Observed’ Environmental Lase Rate and an inversion marks a small transition layer between the cold and warm air.
Turbulence and wind shear frequently occur in this transition layer between the cool and warm air.
what causes turbulence inversion?(2)
if there is a temperature inversion, you may encounter turbulence or wind shear.
After sunrise, (Radiation Inversion) a Turbulence Inversion may form
what are the conditions required for turbulence inversion?(2)
Conditions required for formation is a light wind (8
– 10 Knots) and a Shallow
Environmental Lapse Rate
when the conditions required for turbulence inversion are met what happens? What can The mixing turbulence do?
conduction and convection cause thermal currents to rise. Assisted by the light wind, cold parcels of air are also forced to rise and cool adiabatically.
This vertical mixing can force downward movement of air from the upper level and create a turbulent mixing layer, as this air is then warmed adiabatically, as it descends
what is the overall effect of turbulence inversion?
The overall effect is a decrease in the temperature near the ground and the Environmental Lapse Rate
Steepening as a result.
what happens to the upper layer of turbulence inversion?
The unmixed air above is not cooled and eventually is warmer than the air below; an inversion
then exists. A layer of stratiform cloud often exists at the inversion layer, if sufficient moisture
content exists in the air near the ground.
what happens to turbulence inversion as the heat of the day increases?
As the heat of the day increases, greater conduction
and convection occurs and the cloud may become more unstable, rising higher and forming
stratocumulus until it dissipates around mid-morning.
what is the effect of turbulence inversion on visibility?
unlikely to be any restrictions to visibility unless there
is heavy precipitation
what is the effect of turbulence inversion on cloud creation?
Create cumulus clouds, possibly containing violent updraughts.
what is expected to occur in desert regions with dry air that experience turbulence inversion?
dust storms may be experienced
what is expected to occur in humid air that experiences turbulence inversion?
violent thunderstorms or tornaodes may develop.
what happens If conditional instability
exists and the air is saturated (turbulence inversion)?
cumulus cloud may develop
what happens If conditional instability
exists and the air is unsaturated (turbulence inversion)?
most likely going to be haze conditions
what is visibility like inside an inversion and above it?
Dust, moisture, smoke etc are trapped beneath the inversion and therefore the visibility below the inversion is less than the visibility in the air above, which is much cleaner and less moist.
what will flight conditions be like inside an inversion and above it?
Flight conditions above the inversion will be smooth and the temperature and dew point will be lower. Flying through an inversion layer, wind shear might be present if the wind change is significant above the inversion
what is the risk of carburettor icing like in an inversion?
High humidity and higher outside air temperatures associated with inversions, mean that the risk of Carburettor Icing should always be expected.
