Chapter 7 Flashcards
Atmospheric Stability
the tendency of air to ascend or descend vertically
Adiabatic Rate
warming or cooling rates for ascending or descending air masses.
Air cools at different lapse rates
(3) Environmental Lapse Rate Dry Adiabatic Rate (DAR) Moist Adiabatic Rate (MAR)
Environmental Lapse Rate
the actual lapse rate at a particular place and time - can vary by several degrees per thousand meters
Environmental Lapse Rate differs depending on what environmental factors?
(3) - location - season - atmospheric pollution
Dry Adiabatic Lapse Rate (DALR)
the rate at which dry air (RH <100%) cools by expansion as it ascends/warms by compression as it descends - 10 C° per 1000 m
Moist Adiabatic Lapse Rate (MALR)
the rate at which moist (saturated, RH=100%) air cools as it ascends/warms by compression as it descends - 6 C° per 1000 m
Lifting Condensation Level
the altitude at which the dew point temperature, saturation, and active condensation occurs
Clouds are fundamental indictors of ____
overall conditions including: - stability - moisture content - weather
how do clouds form?
Clouds form as air becomes saturated with water
Cloud
A cloud is an aggregation of tiny moisture droplets and ice crystals that are suspended in air and are great enough in volume and concentration to be visible
Three states of water
Liquid, Solid (ICE), Vapour
When does saturation occur?
- decrease in Air temp - addition of water vapour
Dew Point Temperature
Temperature at which net condensation occurs
Properties of Water
- Polar - Universal Solvent - Surface Tension that occurs due to hydrogen bonding - Capillarity (hydrogen molecules pulling on each other_
Phase change involves the absorption or release of what kind of heat?
absorption or release of latent heat
Sublimation
A process in which ice evaporates directly to water vapour or water vapour freezes to ice
Latent Heat
Energy required for a change of state.
Specific Humidity
mass of water vapour per mass of air at any specific temperature.
Relative Humidicty
Ratio of amount of water vapour actually in air to maximum amount possible at a given temperature.
Vapour Pressure
Portion of total air pressure that results from water vapour molecules (mb).
Two things necessary for raindrop/snow formation (condensation processes)
- Collision - Coalescence process 2. Bergeron ice-crystal process
Fog
Is a (generally stratiform) cloud that occurs at ground level
Maximum Specific Humidity
the maximum mass of water a mass of air can hold at a specific temperature
Condensation requires..
cloud condensation nuclei, microscopic particles (dust, soot, ash, particles from burned fuel, sea salts)
Cloud Names
- Stratus - Cumulus - Nimbostratus - Stratocumulus - Altocumulus - Cirrus - Cumulonimbus -
Stratus
Stratiform (flat) cloud generally below 2000m
Cumulus
Bright and puffy cumuliform cloud up to 2000m in altitude
Nimbostratus
Rain-producing stratus clouds (gentle dizzle)
Strato cumulus
Lumpy, grayish, lowlevel cloud (patchy) near end of the day
Altocumulus
Middle-level, puffy clouds. (Lenticular clouds, other forms)
Cirrus
High altitude, ice crystal clouds
Cumulonimbus
Towering cumulus cloud. Thunderhead.
Five types of Fog
- Radiation Fog - Rime Fog - Ice-Crystal Fog - Advection Fog - Evaporation Fog
Radiation Fog
When radiative cooling of a surface chills the air layer directly above that surface to the dewpoint temperature, creating saturated conditions, a radiation fog forms • This fog occurs over moist ground, especially on clear nights; it does not occur over water because water does not cool appreciably overnight
Rime Fog
• Similar to radiation fog, rime fog consists mostly of tiny supercooled droplets that turn into rime frost on contact with freezing objects It is very common in cold weather, when the air temperature near the surface is below freezing and the air is fairly moist. Rime fog usually happens when the sky is clear on cold mornings. When this type of fog occurs at airports, aircraft have to deice before takeoff.
Ice crystal fog
At low temperatures in a continental Arctic air mass, ice-crystal fog may develop, for example, when the air becomes full of ice crystals that formed by sublimation. Such an icecrystal fog seriously limits visibility
Advection Fog
When air in one place migrates to another place where conditions are right for saturation, an advection fog forms • Off all subtropical west coasts in the world, summer fog forms in the manner just described • One type of advection fog forms when moist air flows to higher elevations along a hill or mountain. • This upslope lifting leads to adiabatic cooling by expansion as the air rises • Another advection fog associated with topography is valley fog
Evaporation Fog
Another type of fog that is related to both advection and evaporation forms when cold air lies over the warm water of a lake, an ocean surface, or even a swimming pool. This wispy evaporation fog, or steam fog, may form as water molecules evaporate from the water surface into the cold overlying air, effectively humidifying the air to saturation, followed by condensation to form fog
Adiabatic process
warming or cooling of ascending or descending (and contracting or expanding) air masses
adiabatic cooling by ___
expansion
adiabatic warming by ____
contraction
conditionally unstable
DALR > ELR > MALR
stable
DALR > MALR > ELR
unstable
ELR > DALR > MALR
Cold Front
Leading edge of cold air mass. Almost always associated with thunderstorms and cumulonimbus clouds
Warm Front
Leading edge of warm air mass. Associated with showers or light rain.
Stationary Front
Occluded Front
Very stormy weather, intense precipitaion.
Occlusion
A cold air front moves faster than a warm air front. Once they meet, an occluded front occurs. This point is called the point of occlusion. Mixing will eventually create one single mass of cold air.
Cyclogenesis
The birth of a cyclone.
Formation of a cyclone
Cyclogenesis
Open Stage
Occluded Stage
Disslving stage
Jet Stream
Polar Jet Stream
Tornado
Wind
How are tornados formed?
Vertical wind shear causes a rotating column of air to spin along a horizontal axis. Updrafts then tilt the horizontal spinning vertical. Forms from a thunderstorm that is at least medium sized (mesoscyclone).
Vertical wind shear
Most tornadoes start from south and head
North East
