INTRODUCTION (Moran and Morgan, 1997)

All of us are immersed in the atmosphere, and as such, we continually experience changing weather on a daily basis.  As a consequence, we may be acquainted with some of the terminology used to describe the weather, since many of us have ready access to current weather information sources as through television media. Rather than having you wait until near the end of the course to look at weather maps, you can start by looking at the weathercast on television.  Consequently, the purpose of this Introduction is to help us learn some of the fundamental terminology that is used to describe the current weather.  We can then from the current weather while taking the course. 
One of the other aspects of this introduction is to identify some of the sources of weather information.  Many of us obtain our weather information from local television weathercasts or from the networks, to include the "Weather Channel" on cable television.  Some of us also have the capability of accessing current weather from the Internet (World Wide Web). 

IN Lesson 1

Read the introduction

Weather and climate elements

Moving from a qualitative or subjective account of the weather, such as warm or blustery to a more quantitative description of the atmosphere requires measurements of several "weather elements".  Briefly, these weather elements include:
	Air temperature;
	Air pressure;
	Atmospheric humidity (a measure of the water vapor content in the air);
	Winds (both speed and direction);
	Clouds (types and amounts).
	
Sources of Weather Information
	What current weather and climate information is available to you.
		Regular
	You should make an effort to look at the current weather information in your hometown, across the nation and around the world.
Tools of Meteorology
	Visualizing the Weather
		Weather Maps
	Weather Instruments and Instrument Platforms
		Satellites, Radar
Probing the Atmosphere
Atmospheric Constituents

STUDY NOTES

Read the Introduction, noting the set of numbered items that can be thought of as guides to reading and interpreting a surface weather map.  Some of these items may not appear to make sense at this time, but as you go through the book, you will begin to understand these points.  Rather than memorizing these "rules", you should frequently return to these lists when watching the weathercasts to see if the current weather maps reflect some of the items. 

Figure I.3 -- Take time to inspect a sample surface weather map appearing in Figure I.3.  You may be familiar with this type of map since these may appear in a similar format on television or in the newspaper. This map displays some of the weather features that many observers located across the country have observed at a particular time.  
Use the accompanying legend to identify the various symbols used to locate the centers of high and low pressure, as well as the standard symbols used to describe the fronts.  These basic symbols typically appear on most weather maps that you would see either in the newspaper or on television.  Symbols used to describe the precipitation and "weather" are shown here in the standard meteorological format.  However, many of the weather maps that you may encounter in the media contain stylistic symbols rather than the standard weather symbols.

Look at Figure I.4, which shows a map or floor plan of the flow of air from a surface high pressure cell (as indicated by the large block letter H) and into the surface low pressure cell (the block L).  The point to remember is that in many of the weather maps that you will see, air will flow out in a clockwise direction from the high pressure system, while air flows into the low in a counterclockwise manner.  While the particulars as to why this observed motion takes place will be discussed later in the course, you can still follow the basic atmospheric flow patterns on most weather maps that may see now.

To help you remember how the winds circulate around each type of system, try the following "hand-twist model".
Place your right hand just above a flat table, with your palm facing downward.  Move your hand downward and while spreading your fingers outward, twist your hand in a clockwise direction (in the same direction as the hands of a clock).  Try this twisting motion several times.  Note that as you push down toward the table, essentially you would be creating more pressure (that is a greater force on a given area of the table) and the clockwise motion of your fingers would duplicate the flow pattern in Panel A of Figure I.4.  Thus, you have seen how air spreads outward in a clockwise direction from a high pressure system.

Next, place your hand palm down on the table with fingers spread apart. With a counterclockwise twisting of your hand, lift it off the tabletop and at the same time bringing your fingers together.  As you lift your hand upward, you are in essence reducing the pressure upon the tabletop.  This twisting motion is meant to simulate the counterclockwise inflow and upward motion of the air coming into a surface low pressure system as shown in Panel B of Figure I.4. 

Spend a few minutes looking at Figure I.5 that provides a vertical slice through a warm front (left) and a cold front (right).  In other words, instead of looking at a map view, you are viewing what is called a "vertical cross-section", or an atmospheric block from the side view.  Specifically, the bottom of each panel is along the ground, while the top of the panel may be at an altitude of several thousand feet above the ground.  In Panel (A), the warm front proceeds from left to right.  Visualize that this vertical cross-section would cut across the warm front appearing in Figure I.3 from the warm air in the Middle Atlantic states (which would be on your left in Figure I.5) toward cooler air over eastern Canada (on your right in Figure I.5).  A vertical cross-section of a cold front appears in Panel (B) of Figure I.5, with the cold front progressing from left to right.  The orientation of this panel would correspond to traversing from the cold air in the Mississippi Valley across the front to the warm air along the Eastern Seaboard.

You may wish to refer back to these diagrams, as well as the numbered items, as you watch the television weathercasts to gain an appreciation of the current weather.

If you have ready access to the Internet (World Wide Web) you could obtain current weather and climate information from some of the sites listed in Table I.1.   However, since the Internet remains in a relatively high state of flux, some of the addresses appearing in the table may be no longer valid.  If you wish, contact your instructor for help finding appropriate current weather links on the Web.
 
Figure I.7 -- Take a moment to inspect these satellite images. The image in the left panel is a visible image with the white over the Southeastern United States representing highly reflective clouds.  The panel on the right is a color-enhanced image where different colors represent different temperatures.  In this example, the blue would portray cold clouds in a storm system offshore of Canada's Maritime Provinces and the red region would contain the warmest temperature. 


Look at Figures I.8 through I.11 -- These photographs show some of the common types of clouds that you may observe.  At this point you may not be familiar with the names that will be described in more detail later in the course.
You should make a mental note of those clouds that may appear filmy or those that appear layered or puffy. Inclusion of these photographs here is meant to encourage you to take an active role in watching the sky as you proceed through this course.