Exam 2 Flashcards
Definition
Evaporation
Process by which water molecules break free from liquid surface
(latent heat of fusion)
Definition
Latent Heat
Enery required to be absorbed/released to change a substance from one phase (form) to another
*without changing temperature!!
Definition
Condensation
Process by which water molecules collide with liquid surface and bond to the liquid surface (latent heat of vaporization)
Definition
Sublimation
Process of converting a solid directly to a gas without going through the liquid state
Examples of Sublimation
Snow sublimates directly into water vapor
Definition
Deposition
Process of converting a gas directly to a solid without going through the liquid state
Example of Deposition
Frost on your windshield
Definition
Vapor Pressure
Partical pressure of water vapor in the air (Pascals)
Definition
Saturated Vapor Pressure
Vapor pressure the atmosphere would have if it were saturated
(temperature dependent)
Definition
Actual Vapor Pressure
Vapor pressure the atmosphere actually has
Definition
Saturation*
Occurs when rate of evaporation = rate of condensation
(very highly dependent on temperature)
Definition
Dew Point (Td)
Temperature at which the air is saturated
How to change the dew point temperature and vapor pressure
Change the amount of water vapor in the air
Definition
Air Parcel
A body of air that has specific temperature and humidity characteristics
Definition
Adiabatic Process
No exchange of heat or matter between air parcel and its surrounding environment
Dry Adiabatic Lapse Rate
Occurs in a unsaturated rising or sinking that is being forced up or down
- Consists of positive or negative buoyancy
Dry Adiabatic Lapse Rate (DALR)
-10 C
Moist Adiabatic Lapse Rate
Air parcel is being forced to rise -> its buoyant
- Soon as an air parcel cools it’s dew point, condensation occurs, releasing latent heat
Average MALR
-5 C
Definition
Environmental Lapse Rate
Actual change in temperature you would experience as you rise through the atmosphere
Definition
Dew Point Lapse Rate
Rate at which dew point temperature changes with elevation is a complicated function of the moisture content of the rising air parcel
Average Dew Point Lapse Rate
-2 C
Definition
Speed Convergence
Occurs when faster moving air slows down (deceleration)
Speed Divergence
Occurs when slower moving air speeds up
(acceleration)
Definition
Directional Convergence
Occurs when isobars get closer together
Definition
Directional Divergence
Occurs when isobars get further apart
Definition
Fronts
A boundary separating air masses of different densities, one warmer and often more humid than the other
Definition
Frontogenesis
(general terms)
The change iin the magnitude and orientation of the temperature gradient at a level or in a layer (eg. surface, 850-700mb, etc) due to directional and speed changes in the wind field
Definition
Frontogenesis
(Specific Terms)
To an increase in the horizontal thermal gradient with time
What causes Frontogenesis
The geometry of the horizontal flow has a strong influence on frontogenesis in most situations
Definition
Lifting Condensation Level
Altitude at which water vapor in a rising air parcel will beign to condense
Definition
Stability
Tendency of air parcel to remain in place or to change vertical position by rising or descending
Defintion
Stable
If parcel is colder than surroundings, its more dense and will resist displacement upwards
Definition
Unstable
If parcel is warmer than surroundings, its less dense and will rise and move away from its original position
Definition
Convection
Unequal heating causes pockets (parcels) of air to rise
Definition
Orographic
Air forced up and over mountains
Definition
Convergence
“Piling up” of horizontally-moving air
(leads to rising air motion)
Definition
Warm Front
(Frontal)
Lower density of warm air mass replacing cold air mass forces warm air over cold air, causing condensation and precipitation
Definition
Cold Front
(Frontal)
Higher density of cold air mass replacing warm air mass forces cold air under warm air, causing condensation and precipitation
Cloud Formation
Cloud Condensation Nuclei
- Very Small Particles
- Les than one-trillionth of a gram
- Microscopic dust, smoke, salt particles
- NEEDED for cloud formation
Cloud Formation
Hydroscopic Nuclei
Water Seeking
- Most effective sites for condensation
- Water droplets can form < 100% relative humidity
- Eg. Salts
Cloud Formation
Hydrophobic Nuclei
Water Repelling
- Water droplets won’t form until 100% humidity
Fog
A cloud with its base at or very near the ground
When is Fog reported?
When visibility is reduced to 1km or less
Fog Types Formed by Cooling
Radiation Fog
Results from nighttime radiative cooling of the ground and adjacent air
- Requires clear skies and fairly high relative humidity
Fog from Moving & Cooling
Advection Fog
When air in one place migrates to another place where conditions are right for saturation
- Warm moist air moves over a cold surface
Fog from Moving & Cooling
Upslope Fog
When relatively humid air move up a sloping plain or mountain slope and cools to saturation
Fog from Adding Water Vapor
Evaporation/Steam Fog
Evaporation from water to air
- “Seeing your breath” caused by this process
Fog from Adding Water Vapor
Frontal Fog
(warm front)
Rain evaporates in colder air thats already near the dew point and fog is produced
How are clouds classified
Form and height
Basic Forms of Clouds
- Cirroform
- Stratiform
- Cumuliform
Basic Cloud Types
High Clouds
- Cirrus
- Cirrostratus
- Cirrocumulus
Basic Cloud Types
Low Clouds
- Stratus
- Stratocumulus
- Nimbostratus
Basic Cloud Types
Middle Clouds
- Altostratus
- Altocumulus
Basic Cloud Types
Vertically Developed
- Cumulus
- Cumulonimbus
Cirrus (Ci)
- High, thin, wispy clouds
- Take a large variety of forms
- Can indicate everything from fair weather to a coming low pressure system
- Often occur above other cloud types
- Composed entirely of ice
Cirrostratus (Cs)
- High, thin clouds
- Form a relatively extensive, consistent layer
- Often indicative of a coming low pressure (especially snow, in winter)
- Can occur above other clou types
How are Cirrostratus clouds different from Cirrus clouds
Form a relatively extensive, consistent layer
Cirrocumulus (Cc)
- High, small, billowy clouds
- Rarely cover entire sky
- Indicative of instability and/or wind shear at high levels (coming low pressure)
- Often occur in parallel rows
Altostratus (As)
- Mid-level, often composed of liquid drops
- Extensive, consistent coverage
- Often occur ahead of nimbostratus (rain,snow)
- Dreary Day
Altocumulus (Ac)
- Mid-level, billowy clouds
- Can be extensive in coverage
- Wide range of appearances (random to organized, thin to thick)
- Often occur ahead of rain or snow and can be indicative of instability and a chance for thunderstorms in warmer weather
Stratus (St)
- Low, greyish, dreary clouds
- “Fog” that occurs above ground level
- Can produce drizzle
- Often “burn off” during morning
- Often develop when high humidity present at lower layers during night
Nimbostratus (Ns)
- Rainy or snowy day cloud type
- Extensive coverage, low base
- Layered, have range of thicknesses
- Often not visible due to precipitation
- Often form due to large scale lift
Cumulus (Cu)
- “Fair Weather Cumulus”
- Scattered, puffy clouds
- Indicates shallow instability and convection occuring (single, small air particles)
- Dissipate when air parcel stops rising
- Shallowo regions of air sinking occur in between clouds
Cumulus Congestus
- Extensive vertical development
- Low base
- Indicates deeper convection occuring
- May become a cumulonimbus (thunderstorm)
- Air parcel has become an “updraft”
Cumulonimbus (Cb)
- Thunderstorm, severe weather
- Low bases to as high as 70,000 feet
- Updraft can extend several kilometers into stratosphere (“overshooting top”)
- Liquid at low levels to ice at high levels
- Anvil at tropopause
- Can be isolated to extensive coverage
Whats a typical cloud droplet size
Very Small
(20 μm)
