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Part II: Weather and Climate
Water vapour has density of 1 kg/m3
Liquid is 1000 kg/m3
Solid is 900 kg/m3
The atmosphere is only 0.03% of fresh surface water
Saturation vapour pressure curve
As the pocket of air gets warmer you can hold more vapour, as it gets colder it holds less water vapour.
How to cool that parcel of air (20,5)?
Cool parcel of air until it gets to dew point
temperature. Or can add almost 20 mb of
Dew point temperature is the point on a
thermometer. It is the red line.
Dew point temp means pocket of air has
reached capacity of water vapour (saturation).
Relative humidity changes but actual doesn’t.
Condensation on a cooled surface
Water vapour on side of glass is cooling down,
so it cools to dew point temp. (relative humidity
With a hot cup you would be heating the air, so
you would make air dryer on surface.
Raise temperature and relative humidity goes
down. Lower temp and relative humidity
Daily Humidity Patterns
In colder months relative humidity is higher.
Sdown is the fuel that drives all processes:
As you go down atmosphere there is more pressure on parcel of air so relative humidity increases. This
is because of the pushing down of molecules above. As parcel of air rises through the atmosphere its
pressure is going down and temperature is going down and parcel of air is getting bigger.
As parcel of air goes down it expands and relative pressure goes up and it heats up.
These parcels of air are heating and cooling adiabatically
If parcel of air is below dew point than it will increase 10*C/km when going down.
3 Things happen as parcel of air rising, expanding(less dense), cooling, Rh goes up. All happens in turn.
When parcel is going down, compressing, heating, Rh goes down.
Dry air means air is not saturated. Less than 100% relative humidity than it is not saturated.
Environmental lapse rate is variable and depends on temperature surrounded parcel of air. Adiabatic
lapse rate tells temperature of parcel of air rising.
Goes from dry adiabatic lapse rate to saturated adiabatic lapse rate. Builds up condensation once it hits
dew point and goes up moist adiabatic lapse rate.
Becomes saturated at dew point.
Cool more slowly past dew point. From 10*C/km to 3*c/km. This caused because energy is released
past dew point. Latent heat that released offsets the rate of cooling. At some point you will run out of
moisture and latent heat will stop.
If rate of lifting is faster than that means it’s cooling more rapidly, and giving off heat more rapidly.
Lower number means a more rapid rise. 3*C/km is faster than 6*C/km. Ranges from 3 to 6. (Heater that
turns off at condensation point)
If environmental lapse rate is to the left than that means dry adiabatic lapse rate is warmer and parcel of
air is stable.
Once no more condensation than that means no more heat. Air parcel begins to descend and follows
the dry adiabatic lapse rate. When raising you follow dry and saturated lapse rate. When descending
only follows dry adiabatic lapse rate.
Orographic Lifting: Does the same thing when an air parcel is traveling up a mountain. Rises, expands,
cools, Rh goes up. Same thing but different process. Topographically different
Dew point temp is what you see on a thermometer.
When going up a mountain, the saturated adiabatic lapse rate is almost parallel to the dry adiabatic
lapse rate at the top. Releases more heat at bottom of SAR.
3 types of clouds: Cirro, Alto, Nimbo.
Bunches and formulation are cumulus. Stratus is more layered. Altostratus is a layered cloud at middle
Mix and match these, prefix and suffix.
Cumulonimbus clouds don’t fit under these. This is because they cut through all 3 levels of elevations. A
down draft to compensate for updraft in cloud. This causes lightening. Cloud of vertical development.
Nimbostratus causes snow.
Fog: cloud on the ground and same processes of cooling. Generally defined by formation process.
1) Cooling Processes
- Advection Fog
Cold air advection fog – Cold air passing over warm body of water. Creates sea smoke because causes
lower layer to move upward creating whisps.
Warm air advection fog – Warm air moves over cool water and lowest layer of air is cooled and
therefore condensates. Blanket layer which is fog over cool water.
- Radiation fog – Formed by the cooling of land after sunset by thermal radiation in calm
conditions with clear sky. The ground produces condensation in the nearby air by heat
conduction. More energy is going in than out so there is flux divergence. (a transfer of heat from
the ground to the air above which causes condensation)
- Upslope fog or hill fog forms when winds blow air up a slope (called orographic lift),
adiabatically cooling it as it rises, and causing the moisture in it to condense. This often causes
freezing fog on mountaintops, where the cloud ceiling would not otherwise be low enough.
- Valley fog forms in mountain valleys, often during winter. It is the result of a temperature
inversion caused by heavier cold air settling into a valley, with warmer air passing over the