Atmospheric Stability Flashcards
What 3 states can moisture exist?
- Liquid
- Solid
- Gas
What is the process of;
Gas to Solid?
Deposition
What is the process of;
Solid to Gas?
Sublimation
What is the process of;
Gas to Liquid?
Condensation
What is the process of;
Liquid to Gas?
Evaporation
What is the process of;
Solid to Liquid?
Melting
What is the process of;
Liquid to Solid?
Freezing
How is a change of state achieved?
Exchange of latent heat
What does humidity refer to?
Amount of water vapour contained in air sample
How is humidity measured?
Psychrometer
What is relative humidity expressed as?
Percentage
When is a sample of air said to be saturated?
When the air sample can hold no more water without condensation occurring
Relative humidity %=
Actual Mass of water x 100/ Mass of water vapour at saturation
What influences the amount of water being able to be held?
- Temperature
- Pressure
Increased temperature increases the stability of an air sample and is there for able to hold more or less water?
More
The relative humidity is decreased with….
An increase in temperature
What is dew point?
Temperature at which a sample of air must be cooled to reach saturation
As a parcel of air rises up through the atmosphere what happens to the surrounding air pressure?
Reduces
A parcel of air cools when it rises why is this?
The volume of parcels increases and the temperature reduces. Process called expansion
When an air sample changes temperature due to pressure or volume this is called?
Adiabatic
What is the lapse rate?
Lapse rate is the rate at which an air sample cools as it rises
What does the lapse rate depend on?
Whether the sample of air is dry or saturated
What is the lapse rate of unsaturated air?
3/1000ft
DALR
What is the lapse rate of saturated air?
1.5/1000ft
SALR
What causes saturated air to move more slowly?
As water vapour condenses to liquid, latent heat is released causing it to cool more slowly
What is the Dew point lapse rate?
.6/1000ft
What is considered a stable atmosphere?
One which an air parcel return to its original level after being forced vertically
What is the air said to be if it continues to rise on its own after being forced vertically?
Unstable
Stability or instability depends on?
Relative lapse rates and the air parcels being forced vertically
What is ELR?
Environmental Lapse Rate
When does stability exist?
When the ELR is less than the SALR
When does instability exist?
When ELR is greater than DALR
When does conditional stability exist?
ELR is less than DALR but greater than SALR
What does conditional stability mean?
The parcel remains dry and cools at the DALR, conditions will be stable. If dew point is reached the parcel will cool at the slower SALR and if sufficient lifting occurs become warmer than the environment resulting in instability
How do you find out the cloud base height?
Subtract the surface dew point from the actual surface temperature and divide by 2.4
When does an inversion exist?
Whenever a layer of warm air exists above cooler air
What is a surface inversion?
Air close to the surface is cooled at night by conduction
When is surface inversion most common?
Just before dawn when the surface temperature is lowest
What is a turbulence inversion?
Moderate winds at low level may cause adiabatic expansion and cooling in lower layers due to mixing
What is a frontal inversion?
Boundary between two air masses of different temperatures may form an inversion as the warm air slides up over the cooler air
What is a subsidence inversion?
As a column of air subsides the top of the column undergoes greater compression and heating than the bottom
Are inversions associated with stable or unstable conditions?
Stable
Are there bumpy or smooth conditions above or below the inversion layer?
Above- Smooth
Below- Bumpy
What is a fohn wind?
Hot, dry breeze blowing down lee side of a mountain
How is a fohn wind created?
Cloud base on lee slope is higher than on the windward slope due to precipitation on the Winward slope and a change in dew point
On the lee slope surface temperatures are higher because…
The air warms at the DALR from the higher cloud base through a greater depth than it cooled on the windward side
