Meteorology 206 Exam 3
Semi-permanent cells
These form because of land masses in the Northern Hemisphere (some in Southern) - Major features shift seasonally with sun - North in July - South in December
GEOSTROPHIC WIND
Upper level winds - Balance between PGF and Coriolis force - Winds flow parallel or along the isobars
During the winter as you travel toward a warm front, the most likely sequence of weather you would experience is:
snow, sleet, freezing rain, rain
At a given level: - Warm air aloft = - Cold air aloft =
warm = high atmospheric pressure cold = low atmospheric pressure
What type of weather front would be responsible for the following weather forecast? "Increasing high cloudiness and cold this morning. Clouds increasing and lowering this afternoon with a chance of snow or rain tonight. Precipitation ending tomorrow morning. Turning much warmer. Winds light easterly today becoming southeasterly tonight and southwesterly tomorrow."
warm front
Three Cell Model
• Allows Earth to rotate • Three cells: Hadley (center), Ferrell (middle upper), Polar (upper) - Hadley and Polar: thermally direct - Ferrell: thermally indirect • Warm air falls, cold air rises
What is general circulation?
• Refers to the average of the air flow over the globe - The basic cause of the general circulation is unequal heating of the Earth's surface
Isobars show what?
Lines of constant pressure
Iowa tornado climatology
Most evident in June around 5pm-8pm Most tornados in a year: 25 Least tornados in a year: 6
Dry line
Narrow boundary of steep change in dew point but very little temperature change
North American cP and cA
Northern Canada, Alaska - Dry, cold, stable - Extremely cold associated with upper-level winds typically with a strong north-south
Doldrums
On the equator - Calm because almost no winds
Sunvex parry arch
Right above the sun right after it's gone below the horizon - V shape of (orange) light usually
Low pressure systems are associated with _____ air, High pressure systems are associated with ______ air _____ air is associated with clouds and precipitation
Rising Sinking Rising
How do you know where a front is?
Sharp temp change, sharp dew point change, shift in wind direction, sharp pressure change (kinks in isobars), clouds and precipitation
Horizontal pressure variations
Short column of dense, cold air weighs the same as a taller column of less dense, warm air
On a weather map, the transition zone between two air masses with sharply contrasting properties is marked by:
a front
The word "frontogenesis" on a weather map would mean that:
a front is regenerating or strengthening
Cold front
- Clouds with vertical development - Showery precipitation (blue triangles point in direction it's moving)
Pressure gradient force
- Created by a change in pressure over a distance (pressure gradient) - Directed perpendicular to the isobars from high to low pressure
Coriolis force
- Deflection is to the right in northern hemisphere and left in southern hemisphere • No Coriolis effect at the equator, greatest at poles • Only has significant impact over long distances
Newton's Second Law of Motion
- F = m x a
How do rainbows form?
- Face away from the sun - Sun's light reflects into the rain - Light is bent while entering raindrop - Light reflected off back of the drop - Light is bent again while leaving the drop - Rainbow is created (40-42 degrees) - The higher the sun, the flatter the bow
Corona brightness
- Face sun - See light reflection in wet clouds
Warm fronts
- Horizontal clouds with steady rain
How to determine a front
- Movement of cold air alone - Needs to be blowing toward boundary
Centripetal force
- Net result of all the forces above - Determines the direction the air will move
Stationary fronts
- No movement - Cold air blows parallel to the front - Weather varies
What is a typical pressure change across the state of Iowa?
- North/South: 215 miles or 346 km - East/West: 330 miles or 531 km
SURFACE WINDS
- Reduces Coriolis - No longer a balance between PGF and Coriolis • Stand with your back to the surface wind and then turn clockwise about 30 degrees, the center of lowest pressure will be to your left
North American cT
- Source region: Southwest United States, Mexican Plateau - Hot, dry, stable - Responsible for summer heatwaves in the western half of the United States
Sea level pressure vs. station pressure
- Station pressure is the actual barometric pressure at the reporting station. - Sea-level pressure is the station pressure adjusted for the elevation of the station using a standard formula, and the difference between them will be a constant percentage for each station. The only time they will both be the same is when the station is at sea level, in which case they will *always* be the same.
Secondary Rainbow
- Sun beam being reflected twice (52-54 degrees) - Never brighter than primary cause you lose light from each reflection
Glory lights
- Sun reflected directly over clouds
Initially causes the air to start moving
- The larger the PGF, the stronger the winds - Closer Isobars are together = stronger the winds
WINDS ON UPPER LEVEL CHARTS 1. Winds flow _____ to height contours 2. Heights decrease from ___ to ___
1. Parallel 2. North to south
How far do you need to go in the vertical to get that same horizontal change?
1mb for every 8m
Ethil Arcs
Above the sun in the winter time
Why doesn't mA exist?
Arctic air is so cold that you can't classify it as maritime
Single Cell Model
Assume: - Uniform water surface - Sun directly over the head at the equator - Earth does not rotate Result: - Huge thermally direct circulation cell - Thermally direct: warm air rising, cold air falling - Hadley cell
Air mass classification
Based upon temperature and humidity using two letters - Humidity given first (lower case) - Temperature second (upper case) Moisture - m (maritime - moist) - c (continental - dry) Temperature - P (polar) - A (arctic) - T (tropical)
Occluded front
Cold front catches up to and takes over a warm front (triple point)
What does an upper level chart show?
Constant pressure surface (500 mb for example)
Air masses
Extremely large body of air whose temperature and humidity are similar horizontally and vertically Source region: area where air mass originates, usually flat and uniform composition with light surface wind
Newton's First Law of Motion
First law: an object at rest will remain at rest and an object in motion will remain in motion as long as no force acts on the object
Horizontal Arcs
In the summer time
Large change in pressure over a short distance =
Large PGF
Intertropical Convergence Zone
Where the Hadley cells meet causing upward motion - By the equator
Jet streams
Where you get overlaps of circulation cells Polar jet - between polar and Ferrell Subtropical jet - between Hadley and Ferrell
Hadley cell
Wind flows clockwise (S-->N)
Polar cell
Winds flow clockwise (W-->E)
Ferrell cell
Winds flow counterclockwise (N-->S)
What type of air mass would be responsible for refreshing cool, dry breezes after a long summer hot spell in the Central Plains?
cP
The greatest contrast in both temperature and moisture will occur along the boundary separating which air masses?
cP and mT in summer
Which air mass forms over North America only in summer?
cT
In winter, which sequence of clouds would you most likely expect to observe as a warm front with precipitation approaches your location?
cirrus, cirrostratus, altostratus, nimbostratus
One would expect a cP air mass to be:
cold and dry
Sea Level pressure chart:
constant height
Before the passage of a cold front the pressure normally __________, and after the passage of a cold front the pressure normally __________.
drops, rises
Pressure changes vertically much ____ than horizontally
faster
When comparing an "average" cold front to an "average" warm front, which of the following is not correct? - especially in winter, cumuliform clouds are more often associated with cold fronts - generally, cold fronts move faster than warm fronts - generally, precipitation covers a much broader area with a cold front - generally, cold fronts have a steeper slope
generally, precipitation covers a much broader area with a cold front
Which one of the descriptions below is not correct concerning a warm front? 1. is colored red on a weather map 2. in winter it is usually associated with stratified-type clouds 3. has warm air ahead (in advance) of it 4. it normally moves slower than a cold front
has warm air ahead (in advance) of it
Flow around high and low pressure systems
high - anticyclonic flow (longer clockwise) (Northern) low - cyclonic flow (shorter counterclockwise) and air parcel rises to start flow (Northern)
Upper Level chart: - High heights = - Low heights =
high = warm low = cold
Which one of the descriptions below is not correct concerning a cold front? it marks a zone of shifting winds it is colored purple on a weather map it marks the position of a trough of low pressure it has cold air behind it
it is colored purple on a weather map
During the winter, an air mass that moves into coastal sections of Oregon and Washington from the northwest, would most likely be:
mP
North American Maritime Air Masses
mP - North Pacific, North Atlantic - Cool, moist, unstable mT Source region: Gulf of Mexico, Caribbean, Southeast Pacific - Wet, warm, unstable - Bermuda High, Pineapple Express
A warm, moist air mass that forms over water is:
mT
During the spring, which air mass would most likely bring record-breaking high temperatures to the eastern half of the United States?
mT
In Southern California, which air mass is mainly responsible for heavy rains, flooding in low-lying valleys, and melting of snow at high elevations? cP cT mT cA mP
mT
What type of air mass would be responsible for hot, muggy summer weather in the eastern half of the United States?
mT
The rising of warm air up and over cold air is called:
overrunning