Notes for Meteorology 356

September 3, 2004

Jennifer Robbins

Alek Butler

Assignments

Williams: Chp. 1; Chp. 2

Reader: Section I

Browse---Section II, 10, 15, 27, 28

Browse---Section III, 30-41

Read---Section IV, 67-80

Browse---Section V, 280-285

Housekeeping

-Reviewed links on class website of condensation, dew point, and Hurricane Frances along with general facts about hurricanes, tropical storms and depressions.

Homework

-Keep up the reading assignments and take a look at the Gyre (circulation of ocean currents).

Condensation

Condensation is the “connection” of single vapor molecules to form a liquid droplet. Like molecules attract one another, when close enough together they bond together.

** Refer to handout in reader and class website…

(Shown below, under the “Dew Point” section)

**In-Class Experiment: At room temperature (75 degrees F, for September 3, 2004) there are many molecules vibrating, but we can’t see them. For a better understanding, Professor Monteverdi created an in-class experiment, so we could “see” water vapor. We visualized two molecules represented as circles, which Professor Monteverdi held in his hand while vibrating (the molecules vibrate because of temperature). Then the molecules were brought close together to “connect,” which represents condensation through a natural binding. This connection brings the molecule together, where the bonded molecules are still vibrating. If the temperature heats up enough the vibration increases. If the vibration is so strong that the bond is broken, it is called evaporation.

Dew Point

The dew point is the temperature air is cooled to make condensation. You may usually notice the effect of this after a cooling period during the night. When you wake up in the morning you will see water droplets on such things as car windshields, grass and plants.

Water vapor in the atmosphere condenses.

** Refer to handout in reader and class website…

Concepts Related To Dew Point Temperature

(From link on class website)

All gases can be "forced" to become liquid (condense) by the process of cooling. For conditions on the earth, only one gas can be condensed by cooling, water vapor. The temperature at which such condensation would occur is called the DEW POINT TEMPERATURE.

The difference between the dew point temperature and the actual temperature is related to RELATIVE HUMIDITY. When the temperature is cooled to the dewpoint then the relative humidity is 100%. If there is a large difference between the temperature and the dewpoint temperature, then the relative humidity is very low (e.g., 10%).

It can be shown that the dew point temperature is also related to the total number of water vapor molecules present. In essence, the dew point temperature also is a rough measure of how much water vapor is present. This is why dew point temperatures are characteristically higher over oceans and in areas that have access to air flowing from the oceans.

Rules of Thumb:

The higher the dew point temperature, the greater the amount of water vapor is present (source for clouds).

The smaller the difference between the temperature and the dew point temperature, the higher the relative humidity (the closer the atmosphere is to a state in which water vapor would condense).

(### End of website text)

Link to site above:

HYPERLINK "http://tornado.sfsu.edu/geosciences/classes/m356/Dewpoint.htm"

http://tornado.sfsu.edu/geosciences/classes/m356/Dewpoint.htm

Discussion about Hurricane Frances

Summaries of the difference between hurricanes, tropical storms and tropical depressions

In class we referred to the Navy website of satellite images of Hurricane Frances, “US Navy Tropical Cyclone Page:” ( HYPERLINK "http://www.nrlmry.navy.mil/tc_pages/tc_home.html" http://www.nrlmry.navy.mil/tc_pages/tc_home.html)

We looked at the “track and image” of the hurricane. We first looked at an image of reflected light in black and white of the hurricane, visible sensor. The brightest white resembles cold temperatures and the black resembles warm temperatures. It was difficult to distinguish the various types of clouds analyzing only this image, so we referred to the IR color satellite image. Now we could tell the difference between stratus clouds, cumulonimbus and other cloud types by referring to a scale of the various temperatures of the clouds. In a hurricane, as Hurricane Frances, the clouds are warmest at top and coldest around the eye. Looking at this image you can see where the heaviest precipitation will occur. On the image, clouds –80 degrees are orange/yellow, -70 degrees are red, -60 degrees are green and –50 degrees are blue.

A hurricane is a tropical storm with winds sustaining 74mph or more. Gust are much stronger and can be well over 100mph. On the map it is symbolized as a filled circle with two swirled lines.

A tropical storm is a weaker system with winds between 39-73mph. On the map it is symbolized as a open circle with two swirled lines.

A tropical depression is the start or the death of a tropical storm with winds under 39mph. On the map it is drawn as just an open circle, no swirled lines.

On September 3, 2004, meteorologists from the National Weather Service have forecasted that Hurricane Frances will weaken from a category four hurricane to a category three. Meaning from 130 mph winds to now 110 mph winds. They are highly concerned with heavy amounts of rain and flooding. Wind is not the chief hazard on land during a hurricane. Flooding is actually going to be a huge threat after Hurricane Frances hits due to storm surges, and especially since Florida is flat. The rainfall does not easily run off, causing flooding.

The NWS informs the public about weather hazards that are a nuisance and are life threatening. The NWS is one of the best sources for weather reports and forecasts.

The future forecasts for this hurricane implies once the hurricane gets inland it will weaken, like most hurricanes do when they get inland, and turn into a tropical storm. Finally, as it moves more inland it will weaken enough and become a tropical depression.

Florida is expected to have 18.610 inches of rain after this system hits. Florida will likely have flash floods.

California is unique. Looking at precipitation numbers on the class website, you can see that ninety-eight percent of the world’s wettest month is July. This is not the case in California. San Francisco’s average rainfall per year is about 21 inches, and Florida is expected to receive a little more than 18 inches of rain in one weekend alone. California keeps dry during summer months, as many residents living in other states have to make use of their umbrellas.

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