METR Quiz Prospectus
Review for Quiz 3. 1 | Page What is the relationship of air pressure to increasing altitude? Winds are caused by difference in pressure across a surface. 8. Two belts of winds, air in this region sinks, warms and moves toward the equator in an easterly direction. Wind & Pressure Relationship. Quiz: Air Pressure & Winds – STUDY GUIDE. Use the word bank to iii. ___ Elevation____. 2) What is the relationship between Temperature and Air Pressure?.
Although these two physical variables may at first glance appear to be quite different, they are in fact closely related.
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Wind exists because of horizontal and vertical differences gradients in pressure, yielding a correspondence that often makes it possible to use the pressure distribution as an alternative representation of atmospheric motions. This pressure is usually expressed in millibars mb; 1 mb equals 1, dynes per square cm or in kilopascals kPa; 1 kPa equals 10, dynes per square cm.
Distributions of pressure on a map are depicted by a series of curved lines called isobarseach of which connects points of equal pressure. At sea level the mean pressure is about 1, mb kPavarying by less than 5 percent from this value at any given location or time. Mean sea-level pressure values for the mid-winter months in the Northern Hemisphere are summarized in this first diagram, and mean sea-level pressure values for the mid-summer months are illustrated in the next diagram.
Quiz #1 Study Guide
Since charts of atmospheric pressure often represent average values over several days, pressure features that are relatively consistent day after day emerge, while more transientshort-lived features are removed.
Those that remain are known as semipermanent pressure centres and are the source regions for major, relatively uniform bodies of air known as air masses.
Warm, moist maritime tropical mT air forms over tropical and subtropical ocean waters in association with the high-pressure regions prominent there. Cool, moist maritime polar mP air, on the other hand, forms over the colder subpolar ocean waters just south and east of the large, winter oceanic low-pressure regions.
Over the continents, cold dry continental polar cP air and extremely cold dry continental arctic cA air forms in the high-pressure regions that are especially pronounced in winter, while hot dry continental tropical cT air forms over hot desertlike continental domains in summer in association with low-pressure areas, which are sometimes called heat lows.
What creates wind horizontal motion of air? Principle of Conservation of Momentum Newton's 2nd Law Forces that we know push and pull on air in the atmosphere: How do we measure pressure?
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What units do we use to measure and express pressure? What are typical values of observed pressure? What does atmospheric pressure have to do with wind? What determines the strength of the net force on air due to pressure differences the pressure gradient force?
How can we use weather maps to visualize relations between pressure and wind patterns? How should we interpret isobars on a contour map of pressure map?
How can we interpret the pressure-gradient force on a pressure map? Winds and Pressure Patterns: Over land, winds do generally blow faster where the PGF is stronger isobars are closer together Over oceans, winds do generally blow faster where the PGF is stronger isobars are closer together Winds over oceans are generally faster than winds over land for the same PGF can explain this by noting that friction is greater over land than oceans because land is rougher--it has vegetation, hills and mountains, buildings, etc.
Near the earth's surface in the Northern Hemisphere, maps showing winds and pressure patterns isobars show that winds don't typically blow perpendicular to isobars toward their lower pressure side, but instead blow at an angle skewed somewhat to the right clockwise relative what we'd expect. In the Northern Hemisphere aloft the discrepancy is even greater: Coriolis effect We observe moving things for example, air parcels and lots of other things from the perspective of the earth, which is rotating while we make our observations.
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Hence we, the observers, are following a gradually curving path through space while we watch things move relative to us. Even if no net force acts on a moving object, so that its motion doesn't change according to the Principle of Conservation of Momentumwe observe it to follow what appears to be a curved deflected path the object is following a curved path--instead, we are, but we just don't perceive it!
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Illustrations of the Coriolis effect YouTube Movie: Some guys play catch on a rotating merry-go-round According to the Principle of Conservation of Momentum, any object that follows a curving path is changing its motion and therefore must have a net force pushing on it. To account for the apparent deflection of moving objects, we invent a fake force, the Coriolis force: Aloft, the winds blow so that the Coriolis "force" pushing on moving air to its right appears approximately to balance the PGF pushing on it toward lower pressure animation of combined effects of PGF and Coriolis force without friction the resulting wind is called the geostrophic wind examples at mb level there is a relatively narrow zone of large PGF aloft at midlatitudes, where the geostrophic winds are correspondingly faster and blow eastward on the average the jet stream At the surface, the winds blow so that the Coriolis "force" pushing on moving air to its rightthe PGF pushing on air toward lower pressureand friction pushing against the direction of the wind, trying to slow it downproduces distinctive wind patterns Lab Exploration 6: Pressure at any level in the atmosphere must approximately support the weight of air above that level that is, approximately balance the force of gravity pulling down on the air above that level.
Since the total weight of air above you decreases as you go higher in the atmosphere, it follows that the pressure must decrease as you go higher, too. Of course, this is what we observe. When air in the lower troposphere warms, it expands and lifts air sitting on top of it upward.
At any particular level above the warmed air below, some air that started below that level will be lifted up past that level. This increases the amount of air above that level, and hence the weight of air above that level. This requires that the pressure at that level, pushing upward, must increase to support the increased weight of air above that level.
When air in the lower troposphere cools, it contracts and air sitting on top of it drops lower At any particular level above the cooled air below, some air that started above that level will drop below that level. This decreases the amount of air above that level, and hence the weight of air above that level.
This requires that the pressure at that level, pushing upward, needed to support the decreased weight of air above that level, must decrease. Consequently, there must be a relationship between the temperature of air in the lower troposphere relative to surrounding areas and the pressure aloft relative to surrounding areas at the same level aloft. Where the lower troposphere is relatively warm compared to surrounding areasthe pressure aloft, above the relatively warm air, must be relatively high compared to surrounding areas at the same level aloft Where the lower troposphere is relatively cool compared to surrounding areasthe pressure aloft, above the relatively cool air, must be relatively low compared to surrounding areas at the same level aloft As observational evidence that this is true, note how similar the patterns shown on these two maps are: Can't add air through the top of a column it has no true top Can't add air through the bottom up through the ocean or land surface Can add air through the sides of the column wind!
However, wind by itself isn't enough, because air can be entering and leaving different parts of the column at the same rate, producing no net change in the amount of air in the column Must have air entering the column faster than it is leaving convergence of winds or leaving faster than it is entering divergence of winds.
Winds converging in an areas adds air to a column, increasing its weight and increasing the surface pressure. Relatively high surface pressures develop where winds aloft converge Relatively low surface pressures develop where winds aloft diverge. To summarize so far see class summary for Monday, May 2: Pressure differences between places at the surface push air at the surface into motion.
Friction and the Coriolis effect modify the motion of air at the surface The resulting surface winds tend to spiral counterclockwise inward converging into low pressure areas and spiral clockwise outward diverging out of high pressure areas. As air within the polar front spirals clockwise around and into low pressure areas, colder air from the north moves south on the west side of the low, while warmer air from the south move north on the east side of the low.
The result is temperature advection cold advection west of the low and warm advection east of the low The leading edge of the advancing cold air west of the low is a cold front The leading edge of the advancing warm air east of the low is a warm front Air tends to be pushed up in advance of these fronts.
When air rises, the pressure on it drops, it expands, it cools, and if it cools enough then water vapor condenses to form clouds. Hence, clouds tend to form along fronts.