Title: Condensation
1Condensation Clouds
- Condensation
- Condensation Processes
- Lapse Rates
- Stability Conditions
- Chapters 4.3 4.5
2Condensation
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- Conversion of water vapor to water
- A reverse of evaporation
- Results in a release of latent heat
- A warming process
- Saturation is achieved
- Clouds
3Condensation Processes
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- Three main condensation processes
4Condensation Processes (1)
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- Air mass mixing
- An air mass is a large body of air having little
horizontal variation in temperature and moisture - Air mass mixing occurs when two air masses with
different temperature and moisture contents
converge and mix - The mixture may be saturated with respect to the
new temperature
5Condensation Processes (2)
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- Cooling without vertical motion
- Radiation fog
- A low level cloud formed when the atmosphere
loses heat through radiation loss - Advection fog
- Fog formed when warm, moist air is blown
(advection) over a cool surface and chilled below
the dew point temperature
6Condensation Processes (2)
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Not in Book
Aguado and Burt Understanding Weather and
Climate
7Condensation Processes (3)
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- Cooling with vertical motions (convection)
- Forced (mechanical) convection
- Orographic uplift
- Frontal uplift
- Convergence
- Free (thermal) convection
- Heating of surface by sun
- Cold air over a warm surface
8Condensation Processes (3)
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- The cooling with an increase in height is called
an adiabatic process - Adiabatic process
- The process in which a rising parcel of air cools
through expansion or a sinking parcel warms
through compressionbut with no exchange of heat
between the parcel and its surrounding environment
9Adiabatic Processes
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10Adiabatic Processes
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- Why do we have adiabatic processes?
- Air is a poor thermal conductor
- Air parcels move quicker than heat can be
exchanged with the environment
11Lapse Rates
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- Environmental Lapse Rate (ELR)
- The observed temperature distribution with height
- Variable in time and space
- Can be anything
- Is not adiabatic
12Lapse Rates
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- Normal Environmental Lapse Rate
- The ELR averaged over the globe
- 6.4 C/1000 m
13Normal Environmental Lapse Rate
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Not in Book
14Lapse Rates
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- Dry Adiabatic Lapse Rate (DALR)
- The rate at which an unsaturated parcel of air
cools or warms - DALR 10 C/1000m
- Can be a decrease in temperature (rising air) or
an increase in temperature (sinking air)
15DALR (cooling)
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16DALR (warming)
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17Lapse Rates
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- Saturated Adiabatic Lapse Rate (SALR)
- Also called the Wet Adiabatic Lapse Rate (WALR)
- The rate at which a saturated parcel of air cools
- SALR 0.6 C/1000 m (slightly variable)
- Lower rate of cooling because of heat released
during condensation
18SALR (cooling)
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Relates to Figure 4.6
19Stability Conditions
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- Three types of Stability Conditions
- Stable
- Unstable
- Conditional Instability
20Stability Conditions
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- When an air parcel is warmer than the surrounding
environment, the parcel will be less dense than
its surroundings and will rise through the
atmosphere - When an air parcel is cooler, it will be more
dense and sink through the atmosphere
21Stable Conditions
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- The parcel of air is cooler than its surrounding
environment - The parcel will sink once the forcing mechanism
is removed
22Stable Conditions
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Figure 4.7
23Unstable Conditions
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- The parcel of air is warmer than its surrounding
environment - The parcel will continue to rise once the
initially forcing mechanism is removed
24Unstable Conditions
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Figure 4.7
25Conditional Instability
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- The parcel of air is stable when it begins
rising, but becomes unstable during ascent - Occurs when the ELR is between the DALR and the
SALR
26Conditional Instability
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Figure 4.7
27Conditional Instability
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- The air parcel starts rising and is stable
- Parcel cools at DALR until it becomes saturated
at the Lifting Condensation Level - Clouds start to form (Condensation Level)
Figure 4.7
28Conditional Instability
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- The air parcel starts to cool at the SALR
- The parcel eventually is warmer than the
environment at the Level of Free Convection - The air parcel is unstable
Figure 4.7
29Condensation Processes (3)
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- Cooling with vertical motions (convection)
- Forced (mechanical) convection
- Orographic uplift (stable air)
- Frontal uplift (stable air)
- Convergence (conditionally unstable)
- Free (thermal) convection
- Heating of surface by sun (unstable)
- Cold air over a warm surface (unstable)
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