Reading Assignment
Moran&Morgan Ch5, Ch6 p95-106 Ch7, Ch9
Reader p296-304

Weather map

If 15z, subtract 7 =8am
If 03z, subtract 7=8pm

Cyclone : Low pressure area that is encircled by an isobar.
Trough: Low pressure area that is not completely encircled by an
isobar
Anticyclone: High pressure area that is encircled by an isobar
Ridge: High pressure area that is not completely encircled by an
isobar

Surface Pressure System

- Air flows counterclockwise and inward with respect to low pressure areas
and clockwise and outward with respect to high pressure areas.
- Air flows fastest the greater the pressure difference across an area. (
the closer the isobar)

Pressure System at all levels except the surface

- Air flows parallel to the isobars( or height contours), counterclockwise
around low pressure and clockwise around high pressure.
- Air flows fastest the greater the pressure( or height) difference across
an area ( the closer the isobars or height contours)

Dew point temperature

The temperature at which the condensation of water vapor occur is the dew
point temperature.

Severe Thunderstorm

Definition: a thunderstorm that is violent and life-threatening
(a) Hail 3/4" or larger
(b) Straight line wind of 50 knots (57mph) or greater
(c) Tornado
"Lightening is not included because all thunderstorm produce lightening"

Front

Front is a boundary between warm air and cold air

Cold front has triangles pointing toward which the cold air is moving

Warm front has semi-circles pointing toward which the warm air is moving

Wave cyclone : Cyclone with fronts

Dry line is a dashed line with unfilled semi-circles

Jet Stream: Area that high and low pressure area are close
together
Pressure force: Air moves from high pressure area to low
pressure area

Coriolis Effect

1 deflects all Frictionless moving objects to the right in the Northern
Hemisphere. Examples: air planes, ocean currents, projectiles, the winds.

2 is maximum at the poles and zero at the equator

3 is, for a given time interval and at a given latitude, greater the faster
the speed of the moving object. Example: Over 1 hour interval , a plane
moving 1000mph is deflected more than a ship moving 20 mph.

4 is, for a given speed and at a given latitude, greater the longer the time
interval an object is in motion. Example: a 5 mph ocean current acting over
a month long period is deflected more than a plane moving 400 mph for three
hours.

Coriolis Effect is important in understanding air motion for
- jet streams( circle the globe)
-extra tropical storm systems(500 to 1000 miles diameter)
-hurricanes (500 miles diameter)

Coriolis Effect
- is less important in understanding air motion for thunderstorms (10 to
100 miles diameter)
- is hardly important at all in understanding air motion for tornados (10s
of yards to 1/2 mile in diameter)
- is not important at all in understanding motion of water into a drain

Coriolis Effect

Corilois Effect deflects all FRICTIONLESS MOVING OBJECTS to the RIGHT in the Northern Hemisphere, observer perceives movement of the object to be left ward. Dr Monteverdi provided the class with a handout that documents the relevancy of the Coriolis Effect. Highlighted are four observations of this phenonomen that are important to know when considering synonymous weather events that lend to the formation of California Advection Fog. It is imperative that the first three factors listed are known and understood.... refer to handout!

In order to understand the coriolis effect, you need to remember from previous lecture:   We live on a planet that is rotating If you are looking downward onto the earth, it looks like a rotating record, where the center is stationary and the speed increases the further you are from the center. the rotation is in a counterclockwise rotation Some approximate speeds: — at equator: 1035 mph — at 60° latitude: 518 mph — at northpole: 0 mph We are unaware of the motion because we are "fixed" to the earth's surface — We are fixed on the earth due to gravity and friction Newton's Second Law of Motion  states that objects move at a constant speed in a straight line forever if not acted on by an outside force (actually, the acceleration experienced by an object is due to the sum of the forces acting upon that object.  An object unaffected by outside forces will be unaccelerated--move in a straight line at a constant speed forever!!) An Example: Say there is a person standing at the north pole and another person is standing at 60° north latitude. If there are no outside forces acting and the person at the pole throws a baseball to the person at 60° north latitude., the ball goes in a straight line.  Say it takes approximately an hour for the ball to reach the latitude where the other person is standing. Within that hour's time, the person standing at 60° moves about 518 miles east of his or her initial position.  Since that person does not THINK that he or she has moved, so it looks as if the ball is moving away at the right from its initial straight line path. Of course, what has happened is that the ball DID move in a straight line.  The person preparing tol catch the ball just rotated out of the path of the ball. This is an example of how Coriolis Effect works.

Coastal Upwelling:

During Summer, in the morning the continent heats up creating a Thermal Low

By 4:00 pm, NW winds have picked up and the coriolis effect causes surface waters to move off shore

Cold waters move up from the ocean floor causing upwelling

A Upwelling is important to fisheries, some fish die or leave the area when upwelling stops During El Nino, there is a decreased coastal upwelling from mid Summer through fall.

Weather Map Interpretation

1. Remember the Rule of Thumb in relation to wind direction around pressure systems: Wind direction around a surface Low moves counter-clockwise and inward while wind direction around a surface High moves clockwise and outward.
2. Encountered in our reading are synonyms for High and Low pressure systems that we need to be aware of: Low Cyclone* (where at least one isobar completely encircles the region of Low pressure); High = Anticyclone (where at least one isobar completely encircles the region of High pressure)* This use of the term "Cyclone" is not the same as a "Cyclone" as it is used locally to name hurricanes in the Indian Ocean and Bay of Bengal or "cyclone" as it is used locally as a term for tornadoes in the Midwest.
3. A region of air pressure unenclosed by an isobar has two types:Ridge: an area of High pressure; Trough: an area of Low pressure.* It is reduntant to say "a ridge of High pressure" or" a trough of Low pressure" for the terms are synonymous. You only need to say, "a ridge/trough".

The question was raised, "What characteristics would you expect to find from air that is moving towards a Low pressure system." To answer this we used an example of a Low pressure system located in the Northern United States; therefore, the different air masses moving into the Low are warm/moist air from the Gulf and cold/dry air from the North.

Fronts

A front is a boundary between a warm air mass and a cold air mass. A line is drawn to indicate the boundary. The polar front is the boundary between a polar air mass and a tropical air mass.

Symbols are used on the front line to indicate whether the line is moving or stationary. A stationary front line is indicated by blue triangles on one side of the line alternating with red semi-circles on the opposite side of the line. The triangles point away from the colder air while the semi-circles point away from the warmest air.

A cold front is a front that is moving in the direction of the warmer air. A cold front is indicated on the line by blue triangles pointing away from the colder air. A warm front is a front that is moving in the direction of the colder air. A warm front is indicated on the line by red semi-circles pointing away from the warmer air.

A wave cyclone in a region of low pressure completely encircled by an isobar. As the air moves counter clockwise and inward, a wave like form is created in the front.Wind direction in Low Pressure areas should say something about the temperature - the air drawn southward from Canada into the US should be cool. Air being drawn Northward into the Mississippi River Valley from the Gulf of Mexico should be much warmer. The air coming in from Canada has a very low dewpoint temperature, whereas the air coming in form the Gulf of Mexico has a much higher dewpoint temperature. The air is moist in the "collision zone" where the two different air temperatures meet. This creates a Front. This particular front is called a Cold Front - cold air hitting the warm air from the side. Warm air is lighter and less dense. When cold air thrusts underneath it the hot air rises. We can see this happening in the use of a hot air balloon. The cold front in this area results in much precipitation around Kansas. Air can also be traced back to the Atlantic in between other areas of temperature on the map. More about fronts will be discussed later on in class.

High Pressure Areas:

The air around the high in the Great Basin (1116, 1020, 1024) should be blowing clockwise and outward. In this case it doesn't work well because of the surrounding mountains. Physical obstacles are not exceptions to the rules of thumb. Instead, the air must blow around the mountains.