GHY 104:Chapter 7 & 8
85 Cards in this Set
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Cloud
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aggregation of tiny moisture droplets and ice crystals suspended in air, great enough in vol. and concentration to be seen
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Fog
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a cloud that is in contact with the ground
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Bergeron process
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Occurs in the higher parts of the troposphere.
Here, decreased pressure means both liquid water and solid water (ice) can co-exist.
Liquid water can be super-cooled below freezing.
Liquid water sheds water molecules which are absorbed by growing ice crystals.
Eventually snow fal…
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key to cloud classification
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Altitude and shape
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Clouds occur in 3 basic forms:
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flat, puffy, and wispy
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Clouds occur in 4 altitude classes:
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low, middle, high, and vertically developed
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There are ____ basic cloud types
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....
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Stratiform:
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horizontally developed, flat and layered
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Cumuliform:
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vertically developed, puffy
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Cirroform:
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wispy, high in alt., made of ice crystals
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Fog
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Fog formation is essentially “cloud” formation at or near the Earth’s surface.
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Fog can form almost the same way as clouds, but two main differences exist.
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Air cools, and once Ta cools down to the Tdp, condensation occurs. Fog does not usually form from upward motion.
Moisture source = higher amounts of water vapor in cooling areas. Note that clouds generally do not form this way.
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Fog
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Visibility restricted to >1km
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Advection fog (air in one place migrates to another where conditions are right for saturation)
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Evaporation fog
Upslope fog
Valley fog
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Radiation fog
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(radiative cooling of a surface chills air layer directly above that surface to Tdp creating saturated conditions)
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Advection Fog
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When warm, moist air moves over cooler body of water.
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Evaporation (or Steam) Fog
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Cold air lies over warmer body of water, and evaporation from water surface causes saturation and fog.
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Upslope Fog
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Air cools as it moves upslope... as in our Great Smoky Mountains.
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Valley Fog
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Air in valleys is denser and colder than surrounding air, causing fog.
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Radiation Fog
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Loss of longwave radiation at night over moist surface causes saturation.
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Weather
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the short-term, day-to-day condition of the atmosphere
A “snap-shot”
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Important elements to weather
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Temperature
Air pressure
Relative humidity
Wind speed and direction
Seasonal factors (e.g. Insolation receipt, daylength)
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Climate
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long-term average (over decades) of weather conditions and extremes in a region
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Air Mass:
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Homogeneous body of air with similar temperature and moisture properties to underlying land area
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Source region:
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Location from which an air mass originates.
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Classify air masses by:
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Moisture and temperature
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Moisture:
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These can be either maritime (m) = moist or
continental (c) = dry.
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Temperature:
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These can be equatorial (E), tropical (T), polar (P), Arctic (A), or Antarctic (AA).
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Lake Snow Effect
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As air masses migrate from source regions, temp. and moisture characteristics change and take on characteristics of the land over which they
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Atmospheric Lifting Mechanisms
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1. Convergent Lifting
Air coming together, no place to go but up.
2. Convectional Lifting
Uneven heating of the Earth’s surface
3. Orographic Lifting
Forcing over a mountain barrier
4. Frontal Lifting (cold and warm fronts)
Air masses colliding
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Orographic Uplift
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Air forced over mountain on windward slope cools at the Dry Adiabatic Rate.
Once Ta lowered to Tdp = saturation, condensation at the Lifting Condensation Level = clouds.
Air continues to rise over mountain, cooling now at the Moist Adiabatic Rate.
Once peak is reached, air then descend…
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chinook winds
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Dry hot leeward winds
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rainshadow
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Large dry area on leeward side of mountains
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Front:
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the leading edge of an attacking air mass
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Fronts are named after
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the attacking air mass
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Cold Fronts
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Cold air is denser, heavier
Cold air forces warm air aloft
Relatively narrow, but up to 400 km " wide (250 mi)
Blue triangles on a weather map
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Warm Fronts
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Warm air moves up and over cold air
1000 km wide (600 mi)
Red or orange half circles on a weather map
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Frontal Uplift
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Both cold and warm fronts cause air to be uplifted.
This causes adiabatic cooling, low pressure, cloud development, rainfall.
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Cold Front and Squall Line
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Fast-advancing cold front can cause violent lifting and create a zone right along or slightly ahead
of the front called a squall line.
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Weather with Passing Fronts:
Moisture
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cold air mass ↓
warm air mass ↑
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Weather with Passing Fronts: Temperature
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cold air mass ↓
warm air mass ↑
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Weather with Passing Fronts: Pressure
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cold air mass ↑
warm air mass ↓
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Weather with Passing Fronts: Wind Direction
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cold air mass from W-NW
warm air mass from S-SW
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Weather with Passing Fronts: Rainfall
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cold front: intense, short;
warm front: steady, long- lasting
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Weather with Passing Fronts: Cloud cover
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cold front: cirrus, cumulus, then cumulonimbus
warm front: cirrus, cirrostratus, altostratus, stratus, nimbostratus
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Life Cycle of a Midlatitude Cyclone
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Cyclogenesis or Early Stage
Open stage
Occluded stage
– Occluded front
– Stationary front
Dissolving stage
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1. Cyclogenesis
Early Stage
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Process in which L wave cyclones develop and strenghten
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2. Open Stage
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To the E of the developing L system center, warm air begins to advance N
As the MC matures, the CC flow draws cold air from N&W and warm air from S
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3. Occluded stage
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Cooler cP air mass denser than warmer mT air mass.
Cold front speed ~25 mph; warm ~ 10 mph
Precip. is mod. to heavy initially, then tapers off as warm air wedge is lifted higher.
Eventually it moves and dominating air mass results (either cold/warm front)
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Thus, cold front overtakes warm front, wedges beneath it, andproduces an __________
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occluded front.
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Stalemate between cooler and warmer air masses and airflow on either side of the front is II to the front = ______________
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stationary front.
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____ ASOS stations nationwide (Automated Surface Observing System)
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883
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NEXRAD Doppler Radar Installations, ____ nationwide
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158
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Violent Weather
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Thunderstorms
Tornadoes
Tropical Cyclones = Hurricanes
All operate on the same principles, but occur over different spatial scales
All can bring devastating weather
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Violent Weather: All of these are examples of ___ pressure
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L
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Lightning most often found in _____ clouds
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cumulonimbus
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Lightning
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Causes still largely unknown.
Collisions of water droplets and ice particles cause electrons to be shed.
Electrical charges now separated in the cloud.
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Lightning arc can heat air to _______ in a split second.
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50,000 F
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Thunder caused by _________ of air as it is ________.
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rapid expansion; heated
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Derecho
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Widespread, long-lived, violent, convectively-induced, straight-line windstorm.
Associated with a fast-moving band of severe thunderstorms, usually in late spring and summer.
• Sustained winds of 58 mph.
• Causes severe damage, extensive forest blowdown.
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Blizzard of 1993
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A midlatitude cyclone, began with deep trough of low pressure extending into Gulf of Mexico on March 12.
Clash of very warm mT air mass (from southwest) with very cold cP air mass (from northwest), PLUS mP air mass (from western US).
Unusually low pressure from very warm Gulf of Mexico …
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Mesocyclone and Tornado
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Speed of air above surface is slower than speed of air well above the ground.
This initiates a spinning motion, like a rolling barrel.
Encounters strong updrafts associated with thunderstorm activity.
Causes shift from horizontal rolling to vertical spinning.
Wind speeds increase as…
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Within the cumulonimbus cloud, a_______ will then form.
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mesocyclone
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Mesocyclone
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large, rotating body of air within a thunderstorm.
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Mesocyclone and Tornado:
When this happens, atilted __________ forms that can spawn __________.
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supercell cloud; supercell tornadoes
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Single cell VS. Super cell
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No tilt VS. tilt
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______Wind Damage Scale for Tornadoes
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Fujita
F-0 to F-6
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Tornado damage:
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Caused exclusively by high winds and not by low pressure blowing up houses (= urban myth).
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Tornado Alley
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Texas, Oklahoma, Kansas, and Nebraska, but also notice Florida, Indiana,
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Tornado peak season
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May; Late Spring or Early Summer
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The Inter-Tropical Convergence Zone (ITCZ) is characterized by _______ uplift.
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Convergent
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A type of fog that is formed when warm, moist air moves over cold water and is chilled to its dew point temperature is called:
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advection fog
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Which of the following clouds is formed at the highest altitude?
Stratus, Cirrus, Nimbostratus, Altostratus
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Cirrus
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The most likely source of a mT air mass is:
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The Gulf of Mexico
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When placed in sequential order, the main life stages of the midlatitude cyclone include the _____, open stage, occluded stage, and the closed stage.
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Cyclogenesis Stage
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Tropical Cyclones
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Powerful manifestation of Earth-atmosphere energy budget
Originate entirely within tropical air masses
80 occur annually
45 hurricanes, typhoons, or cyclones
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Tropical Cyclones form differently than midlatitude cyclones. How?
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Air of tropics is homogeneous, no fronts or conflicting air masses
Warm SSTs provides abundant water vapor (latent heat energy that fuels storms)
Tropical cyclones convert heat energy from the ocean into mechanical energy in the wind
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Easterly Wave:
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Precursor to a Hurricane
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Easterly Wave:
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Begin in April and May
Between 5° and 15° N
Move from Africa to the Americas
9% develop into tropical storms
Warmer waters in western Atlantic
85% of major hurricanes start as easterly waves
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Different names for Hurricanes
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Hurricane: Atlantic and E. Pacific
Typhoon: W. Pacific
Cyclone: Indian Ocean, Australia
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Hurricane Requirements
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Warm ocean waters > 27 °C
Unstable, warm, moist air
Away from the equator.
Weak upper level winds.
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Hurricane Properties
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Energy source = water
As hurricane hits land, they weaken
Intense low pressure = rising air
Weak upper level winds = strong storm
Winds weaken with height = upper level high, diverging.
Air in the eye actually sinks.
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Hurricane wind speeds
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Storm center velocity= speed of entire storm
Storm wind velocity= speed of winds
Additive on the right, subtractive on the left
The eastern side of a hurricane is most destructive; NE wall
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Hurricane season:
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June 1 to November 30
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Hurricane Probabilities (>10% hurricane strikes)
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Coastal Texas
LA, MS, AL, and FL
Southern Florida
North Carolina
Northeast US
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GHY 104:Chapter 7 & 8