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