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Why does the wind blow?
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What is the mass of air above a given level?
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Weather Test 4;Sec1
| Question | Answer |
|---|---|
| Why does the wind blow? | air moves in response to horizontal differences in pressure to equalize imbalances in air pressure |
| What is the mass of air above a given level? | air pressure |
| What is one way to change air pressure? | move up or down in the atmosphere |
| What is the instrument that detects and measures pressure change? | barometers |
| What is the unit of pressure commonly found on surface weather maps? | millibar |
| What is the common pressure unit used in aviation? | inches of mercury |
| What is a common pressure unit used at sea level? | standard atmospheric pressure |
| What is the unit of pressure designated by the Internation System (SI) that is the force of 1 newton acting on a surface area of 1 square meter? | pascal |
| What is is a unit of measure that is gradually replacing the millibar because it is the preferred unit of pressure on surface weather maps? | hectopascal |
| What is a barometer created by Galileo? | mercury barometer |
| Why is mercury rather than water used in the mercury barometer? | convenience; water evaporates; mercury rarely rises to a height above 80 cm |
| What is the most common type of home barometer that contains no fluid? | aneroid barometer |
| What is the small, flexible metal box inside an aneroid barometer that expands or contracts with change in air pressure? | aneroid cell |
| What are the two different types of aneroid barometers? | altimeter and barograph |
| What is an aneroid barometer that measures pressure, but are calibrated to indicate altitude? | altimeter |
| What is an aneroid barometer that consists of a pen attached to arm that marks a continuous record of pressure on chart paper? | barograph |
| What are lines connecting points of equal pressure on maps that are drawn at intervals of 4 mb? | Isobars |
| What is a sea-level pressure chart that represents the atmospheric pressure at a constant level? | constant height chart |
| What are charts that are constructed to show height variations along an equal pressure surface? | isobaric chart (constant pressure charts) |
| Why are isobaric charts convenient? | because the height variables they show are easier to deal with in meteorological equations than the variables of pressure |
| High heights on an isobaric chart correspond to (higher/lower) than normal pressure at any given altitude, and low heights on an isobaric chart correspond to (higher/lower) than normal pressures? | higher; lower |
| What are lines connecting points of equal elevation that tells us the atlitude above sea level at which we can obtain a pressure reading? | contour lines |
| When are contour lines crowded together in the middle of the chart? | where the pressure surface drops rapidly due to the changing in temperature |
| What are elongated highs where the air is warm and indicating depression? | ridges |
| What are elongated lows where the air is cold? | trough |
| How are upper-level chars a valuable tool? | they show wind-flow patterns that are extremely important in forecasting the weather, can also determine movement of weather systems and to predict the behavior of surface pressure areas |
| What is the direction from which the wind is blowing? | direction |
| What are large blue H’s on a map that indicate the centers of high pressure? | anticyclones |
| What are the large L’s represent centers of low pressure? | mid-latitude cyclonic storms (depressants) |
| The northern hemisphere winds blow in what directions? | counter clockwise and inward toward the center of the lows; clockwise and outward from the center of the highs |
| What is the difference in elevation between each contour line? | contour intervals |
| What are superimposed red dashed lines which represent lines of equal temperature? | isotherms |
| What direction do winds flow compared to contour lines? | parallel |
| What do horizontal differences in atmospheric pressure cause? | causes air to move and hence, the wind to blow |
| Pressure gradient –x/y? | difference in pressure/distance |
| If we compute the amount of pressure change that occurs over a given distance, what do we get? | the pressure gradient |
| What is a relatively short distance where the condition would produce a rapid change in pressure? | steep (strong) pressure gradient |
| What is it called if the pressure were to change such that the isobars spread farther apart, then the difference in pressure would be small over a relatively large distance? | a gentle (or weak) pressure gradient |
| What is a force directed from higher toward lower pressure at right angles to the isobars? | pressure gradient force |
| What is the force that causes the wind to blow? | pressure gradient force |
| Closely spaced isobars on a weather map indicate what? | steep pressure gradients, strong forces, and high winds |
| Widely spaced isobars on a weather map indicate what? | gentle pressure gradients, weak forces, and light winds |
| What is a force observed on any free-moving object in a rotating system? | Coriolis force |
| What does a Coriolis force result from? What does it cause? | the earth’s rotation and causes moving particles (including to wind) to deflect to the right in the NH and to the left in the SH |
| The magnitude of the Coriolis force varies with what? | with the speed of the moving object and the latitude and rotation of the earth |
| The stronger the wind speed, the (lesser/greater) the deflection? | greater |
| The Coriolis force increases for all wind speeds from a value of what? | zero at the equator to a maximum at the poles |
| The Coriolis force acts at right angles to the wind, only influencing what? And never influencing what? | only influencing wind direction and never wind speed |
| What do evenly spaced isobars indicate? | a constant pressure gradient force directed from south toward north as indicated by the red arrow at the left |
| Above the level of friction, air initially at rest will accelerate until what? | until it flows parallel to the isobars at a steady speed with the pressure gradient force (PGF) balanced by the Coriolis force (CF) |
| What is a theoretical horizontal wind blowing in a straight path, parallel to the isobars or contours, at a constant speed? | geostrophic wind |
| What does geostrophic wind result from? | when the Coriolis force exactly balances the horizontal pressure gradient force |
| What direction to the geostrophic winds blow in the NH with low pressure? High pressure? | low |
| What happens when the flow of air is purely geostrophic? | the isobars(or contours) are straight and evenly spaced, and the wind speed is constant |
| Geostrophic wind direction can be determined by what? | orientation of isobars |
| The speed of a geostrophic wind can be estimated from what? | the spacing of the isobars |
| The counterclockwise flow of air around cyclones are called what? | cyclone flow |
| The clockwise flow of air around a high, or anticyclone? | anticyclonic flow |
| In the SH, the pgf starts the air moving, and the Coriolis force deflects the moving of air to the (left/right), thereby causing the wind to blow how (clockwise/counterclockwise) around lows and (clockwise/counterclockwise) around highs? | left; clockwise; counterclockwise |
| What is the wind where the Coriolis force is considered negligible where the winds may blow around intense tropical storms with the centripetal force being almost as large as the pgf? | cyclostrophic |
| On a map, why do winds tend to parallel contour lines in a wavy west to east direction and the contour lines decrease in elevation from south to north? | because the air at the level is warmer in the south and colder to the north |
| What is a type of atmospheric circulation pattern in which the north-south component of the wind is pronounced | meridional |
| What is a wind that has a predominate west to east component | zonal |
| Why do surface winds normally cross the isobars and why do they blow more slowly than the winds aloft? | friction- the frictional drag of the ground slows the wind down |
| What happens because the effect of friction decreases as we move away from the earth’s surface | wind speeds tend to increase with height above the ground |
| What is the atmospheric layer that is influenced by friction that usually extends upward to an altitude near 1000 m above the surface? | friction layer (planetary boundary layer |
| Friction (increases/reduces) the wind speed, which in return (increases/reduces) the Coriolis force? | reduces reduces |
| What happens when the Coriolis force weakens? | The force no longer balances the pressure gradient force, and the wind blows across the isobars toward lower pressure |
| The angle at which the wind crosses the isobars varies, but averages at about what? | 30 degrees |
| At the surface the pressure gradient force is balanced by what? | thesum of the frictional force and the Coriolis force |
| In the NH, we find surface winds blowing counterclockwise (into/out of) a low; they flow clockwise and (into/out of) a high? | into; out of |
| In the SH, winds blow clockwise and (inward/outward) around surface lows; counterclockwise and (inward/outward) around surface highs? | inward; outward |
| Because of friction, what do we know about surface winds? | surface winds move more slowly than do the winds aloft with the same pressure gradient & surface winds also blow across the isobars toward lower pressure |
| The angle at which the winds cross the isobars depends upon what? | surface friction, wind speed, and the height above the surface |
| If you stand with your back to the wind, then turn clockwise about 30 degrees what happens? | the center of lowest pressure will be to your left |
| What does not change as long as the upper-level diverging air balances the converging surface air? | the central pressure in the surface low does not change |
| The surface pressure will change if what happens? | if upper-level divergence and surface convergence are not in balance |
| What will happen if upper-level divergence exceeds surface convergence (more air is removed at the top than is taken in at the surface)? | the air pressure at the center of the surface low will decrease, and isobars around the low will become more tightly packed |
| Surface winds move outward (diverge), away from what? | away from the center of a high-pressure area |
| What happens when surface winds move outward away from the center of a high-pressure area? | to replace this laterally spreading of air, the air aloft converges and slowly descends |
| Why does air not rush off into space? | air does not rush off into space because the upward directed pressure gradient force is nearly always exactly balanced by the downward force of gravity |
| What is the state of the atmosphere when there is a balance between the vertical pressure gradient force and the downward pull on gravity with no net force acting upon it? | Hydrostatic equilibrium |
| What is force due to differences in air pressure within the atmosphere? | pressure gradient force |
| The speed of wind depends on what? | the steepness of the slope (or pressure gradient) |
| Pressure gradient is shown on weather charts by what? | the spacing of Isobars |
| What are lines on a weather map joining places reporting the same air pressure? | isobars |
| What do widely space isobars indicate? | a gentle gradiant-Lighter Winds |
| What do closely spaced isobars indicate? | steeper gradiant-Stronger winds |
| On parallel isobars, how do winds blow? | perpendicular to the isobars (or at right angle) |
| What is a force caused by the rotation of the earth on its axis? | Coriolis Force |
| What is the influence of Coriolis force on wind? | Deflects wind to the right in the Northern Hemisphere, and to the left in the Southern Hemisphere |
| Coriolis Force is ZERO at equator, but increases with increasing latitude, reaching a maximum at where? | the poles |
| Coriolis Force increases when? Resulting what? | wind speed increases, resulting to greater wind deflection |
| Coriolis force deflects what? But does not change what? | wind direction, but does not change the wind speed |
| What is “Force caused by frictional drag of winds by landforms near earth’s surface”? | frictional force |
| What are winds aloft, usually above 600 meters, that blow parallel to isobars? | Geostrophic winds |
| Geostrophic winds result from what? | a balance between PGF and CF |
| What is it called when winds are coming together to the surface? | convergence |
| Converging flow of air around low pressure center creates what? | a cyclone |
| Air converges where, then does what? | at the surface, and rises, and diverges above |
| Diverging flow of air around High Pressure, creates what? | an anticyclone |
| What happens as air diverges from a High Pressure on the surface? | air above converges and sinks down |
| Weather chart also shows direction and speed of the upper through what? | air winds |
| Pressure of 500 b is measured at what? | different elevations at different latitude |
| Pressure is measured at higher elevations in what and at lower elevations toward what? | in low latitudes; toward the poles |
| Pressure decreases more rapidly with what? | height near the poles |
| PGF is directed from what to what? | low latitudes to higher latitudes |
Created by:
arcall