Note: use this set of notes as a style and format guideline. Note that there should always be an "Assignments" and "Housekeeping" section. Note that the notes themselves are not just a run-on list of items covered or outline, but connections and synthesis are used to show discussion.

ONLY AN EXAMPLE. THE CONTENT IS NOT THE CONTENT OF THE FIRST LECTURES.

Assignments

Reader; pp.31-35, pp.39-41, pp.68-81

Housekeeping and Announcements

- reviewed more of the class website

- received information detailing what is expected of the class notes to be posted on the website.

Homework

The Mac lab will be open so that one can work on the homework assignment.

Latitude and Longitude

What are the lines that form a grid on the satellite images for? As in all maps of quality we see a grid made up of latitude on longitude lines. In the realm of weather the principal form of communication is by the use of maps.

Latitude lines run East/West and measure distance North/South. These lines are concentric circles which are parallel to one another. They are sometimes called parallel lines. How do they measure anything? Seventeenth century cartographers devised a system, based on geometry, by which measurements can be made from the equator which bisects the Earth into equal Northern and Southern halves. The measurement of the equator is called zero degrees. The North pole then becomes "90 degrees North" and the South pole is called "90 degrees South." Imagine each hemisphere as a protractor that only measures from 0 to 90 degrees. Latitude lines are assigned and named according to the respective angle between 0 and 90 degrees and the hemisphere. For example, San Francisco is latitude 38.5 degrees North. This means San Francisco is North of the equator at the angle, between the equator and the North pole, 38.5 degrees.

Longitude lines run North/South and measure distance East/West. Lines of longitude form circles of equal size and also use geometric measures of degrees. Again there needs to be a line which will be called 0 degrees. We call it the Prime Meridian or the International Date Line which runs through both the North and South poles and Greenwich, England. Imagine looking down at the North pole of the Earth (imagine the Earth as a circle with the North pole is the center). The Prime Meridian bisects the Earth into equal West and East halves. Since both the North and South poles fall on the Prime Meridian the pole's location is called "0 degrees longitude." Both the East and West halves are measured from 0 degrees to 180 degrees with due East and West are called "90 degrees" respectively. For example, San Francisco's longitude is approximately "122 degrees West"

When we refer to the location of San Francisco or any point on the globe we refer to the location in terms of its latitude and longitude. When sharing the location with others latitude is always mentioned before longitude. For example, San Francisco is located on the Earth at latitude 38.5 degrees North and 122 degrees West or 38 N 123 W.

Geographic Regions:

Hurricanes are tropical storms that form in the tropics or subtropics; clouds from such storms can affect California rarely (as did the fringes of Tropical Storm Lane on September 14). The tropics are located within a band on either side of the equator from 23.5° North, and 23.5° south. This is also known as the tropic of Cancer, and the Tropic of Capricorn.

Composition of the Atmosphere

The atmosphere is mostly the result of volcanic eruptions. Today our atmosphere is mostly nitrogen (78%), even though most people think that oxygen is the most dominant component (20%). Also of great importance to our atmosphere is water vapor (1%-4%), carbon dioxide (much less than 1 %) as well as ozone (much less than 0.05%) which prevents us from getting melanoma.

Temperature Scales

Temperature is the energy of vibration. The more the vibrations the warmer the temperature. Therefore, the more vibrations the temperature will increase, the less the vibrations, the temperature will decrease.

There are a few important temperatures mentioned in class that we need to remember. One is the easy conversion that 61 degrees F = 16 degrees C, all you have to do is switch the numbers around. The freezing point of water is 32 degrees F = 0 degrees C 273 degrees K. The boiling point of water is 212 degrees F = 100 degrees C = 373 degrees K.

Temperature is a measure of how much molecules are "vibrating."  The nerve endings on our skin perceive these vibrations and transmit the sensation of warmth or cold to our brains.  

For example, say the room was 76 degrees F, we would feel it because molecules press against our skin vibrating at a rate of 76 degrees. If you wanted to stop the vibration you'd have to cool the room down to -273 degrees C = 0 degrees K. Any object that possesses temperature (above 0 degrees K) emits energy. The warmer it is the more energy it emits and the shorter its wavelength (discussed next time).  So all warm objects (above 0K) emit electromagnetic energy.  

In the next class, we will discuss how these ideas relate to satellite sensors.

Condensation and Evaporation

The last thing we looked at was page 285 in the reader. It shows the concept of condensation and evaporation.  Like molecules attract one another. However the vibrations of warm molecules (any molecule with a temperature greater than 0K) opposes this connection.  In our atmosphere, the temperature is just right for water vapor to condense if temperatures cool enough.  In fact. the dewpoint temperature is the temperature to which air must be cooled (at a given pressure) in order for condensation to occur (cloud forms).

Condensation is water vapor changing to liquid water. There are lots of water molecules in the air, but they don't connect because they are vibrating too fast and they end up bouncing off each other. If you wanted them to connect you'd have to cool the room until you reached the Dew Point Temperature, or the temperature at which condensation will occur.

Satellite Images

In order to begin to evaluate weather someone has to make an observation. Looking at any map of tbe North American West coast we see a difficulty in making weather observations of California. Using observation, we agree, our weather here usually comes from the West. We find our difficulty in making observations of weather to the West of us is there is no land from which to make observations.

In order to view weather off the coast we rely on two types of satellite images sent to us by weather satellites. These satellites are positioned in geosynchronous (at a constant distance from the Earth these satellites orbit at the same rate of speed that the Earth rotates) orbits above the equator.

The first of these two types of images are made possible because the satellites are capable of sensing visible radiation (light) from the sun which is reflected by the water vapor in clouds. The equal combination of the three primary colors of solar light red, green and blue create the color we call white. In the day time clouds reflect solar radiation and our eyes perceive white clouds. So does the satellite. When we experience night time the sun's solar radiation is blocked by the earth (because of its rotation) and cannot be reflected by the clouds. Although the images we receive are clear enough to offer significant amounts of information, visible light cannot be detected at night time.

The second type of image we receive from the same satellite detects heat radiation within the clouds themselves. The water vapor in clouds differ in temperature according to the altitude of the clouds. The satellite is able to detect these temperature differences by using infa-red sensors. The information about the temperature of the clouds is sent to a ground based computer which assimilates temperature with cloud thickness (based on altitude) and creates an image which can, finally, be perceived by human eyes. These night time images can be colored or in black and white.

We know, from observation, that clouds move with the wind. When viewing either satellite image we can see where the clouds are or aren't and make estimates about the clouds thickness. Look at the satellite images on the class website. We see that low lying clouds (fog) stops at the coast. Coastal mountains stop coastal breezes from moving clouds Eastward. The exception to coastal mountains stopping cloud movements depends on two things. The first is the presence of gaps in the mountains. The Golden Gate is a example of a gap that allows low lying clouds through the coastal mountains. The second thing would be if clouds are forming at altitudes and being pushed by winds that are higher than the coastal mountains.

This concept is true for clouds, wind and mountains throughout California. We can see in indicator of cloud where wind and clouds are stopped by mountains when we look at a map of rainfall throughout the state. Be familiar with the mountain ranges and mountain peaks in the state; Rockies, Coast, Cascades, Sierra Nevada, Trinities, Klamath, Mt. Tamalpais, Santa Cruz, Mt. Hamilton, Mt. Shasta, Mt. Diablo.

Use of such images has allowed meteorologists to learn, for example, a great deal about fog and its motion. California summer fog outlines the coast because the fog layer is more shallow than the tops of the mountains, which are generally on the order of 200 to 400 meters (600 ft to 1200 ft). Since the fog layer is less deep than the tops of the mountains, the fog will not generally go up a mountain range; it moves to the sides--mainly southward but sometimes northwards--or around mountains.