Homework Assignment
Read Morgan and Morgan pgs. 31-34, 50-53, 62-63
Appendix 3, 152-156
" " Reader pgs. 39-51
Overview
-Wind direction is the direction from which the wind COMES, not the direction it is going. Wind
brings with it, the characteristics of the continent.
-61 degrees Farenheit is equal to 16 degrees Celsius
-The difference between temperture and dewpoint in the air, is an approximate measure of the relative humidity present. If dewpoint and temperture are the same amount, the result is 100% relative humidity. The smaller the difference between the two, the higher the relative humidity. Dewpoint is the measure of how much water vapor is in the air. The higher the dewpoint measurement, the greater amount of water vapor there is.
-The Pacific Gyre is the whole system of air currents in the Pacific.
-The Clockwise Gyre is the way winds move.
-Water is forced to condense by air cooling.
-A Cummulonimbus Cloud is a cloud formed from several smaller clouds which are "piled-up" on top of each other. Such cloud formations create rain, lightening and thunderstorms.
-A Stratus Cloud is a flat "pancake of a cloud" which is basically fog. Drizzle can also result from this cloud formation, but not rain.
Weather Maps
-Weather maps generally divide the state of California into three sections. Central California extends from Point Conception to the middle of the Golden Gate Bridge. Northern California is the area above this, and Southern California the area below it.
-Maps used to synopsize weather indicate fronts by using red and blue lines. Fronts mean areas with a noticable increase or decrease in temperture, i.e. warm and cold fronts.
-Temperature is also dependent on elevation as well as the geographics of the area. Reno is colder in Winter then Sacramento because of the higher elevation. In order to properly compare the temperture of two separate areas, they must have the same elevation.
-Semicircles on the map point to the area in which the air is moving.
Air Pressure
-A barometer measures the weight of the air. A high pressure area is one in which air is present, a low pressure area is one which exhibits no air, such as a vacuum.
-A millibar is used to measure air pressure. Dyne (the unit of weight) over cm squared is the formula for calculating the measurement of air pressure. Pressure is measured to the tenth.
-Millibars are coded on a weather map, by either adding a 9 or 10 to the listed amount. The limits of measurement, however, are 1050 millimars as the highest possible amount, and 960 millibars as the lowest. Thus, a reading of 86 4, would be 986.4, because 1086.4 exceeds the possible amounts.
-Earth-like planets like Venus and Mars have atmosphere, but low pressure. Mars has a measurement of about 50.5 millibars, while Venus exhibits twenty times Earth's pressure, enough to crush a human being. Different air contents in each, however, make them both unliveable.
-Lines called isobars, organize millibars on a map.
-A clear circle with a line going straight down the middle, on a weather map, indicates an area which is almost clear, but with scattered clouds.
Atmospheric pressure is basically the weight of the atmosphere (i.e. air) pressing down on a given area. This is measured in units of millibars by a device called a barometer.
At sea surface elevation, the average atmospheric pressure is around 1000 millibars. Pressure decreases with altitude. The jet stream is usually found at the 500 millibar level. Since the atmosphere is composed of gases, which are very compressible, the 500 millibar level is around 18,000 feet altitude, rather than half way to the top of the atmosphere. In fact, most of the gases comprising the atmosphere are below 36,000 feet.
Surface pressures vary, however, and this is what causes wind.
The rule of thumb to remember is thus: "Nature abhors a vacuum." Air at a given elevation will move automatically to fill vacuums. Areas of low atmospheric pressure therefore can be thought of as partial vacuums.
-Different weather maps, including images and animations, are accessable through the class website.
Interpretation of the Dew Point Temperature
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The two rules of thumb regarding dewpoint temperature are:
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The ocean is the largest source of water vapor. Dew Points in Calif are usually in the 5O's as compared to the Gulf Coast, for instance, which is usually around 70 degrees. It turns out that the dewpoint temperature in coastal areas is generally the same as the temperature of the ocean from which the air passes. Thus, dewpoint temeperatures along the California coast are generally in the 50s and along the Gulf Coast in the 70s.
Relative humidity relates to condensation. 100 % Relative Humidity (when the temperature has been cooled to the dewpoint temperature) is important because visible condensation will occur (a cloud will form). However, the relative humidity on the ground does not have to compare/correspond to the cloud coverage, since clouds form many thousands of feet above the ground. Thus, the relative humidity at the ground may be far below 100%, yet clouds may be present and rain may be occuring.