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Meteorology Test Two
| Question | Answer |
|---|---|
| What is the primary cause of wind | Atmospheric pressure differences |
| Where does wind flow | Wind flows from areas of higher pressure to lower pressure |
| How does a mercury barometer work | Air pressure pushes on a pool of mercury, which forces the mercury up a tube |
| The best explanation for the cause of atmospheric pressure is | The weight of the air above |
| What is the primary force that causes ALL winds | The pressure gradient force |
| How does the Coriolis effect influence wind | By changing the direction of the wind |
| High air pressure zones are usually associated with | Relatively dry conditions |
| Low pressure zones are usually associated with | Stormy weather |
| Planetary scale flow such as trade-winds are best classified as | Macroscale |
| Winds are usually named for | The direction from which they are blowing |
| Is the United states completely unaffected by monsoons | No |
| The greater strength of jet stream winds during winter is due to | Greater horizontal temperature contrasts |
| With rainfall, areas of persistent high pressure tend to cause | Desert regions |
| How does temperature affect pressure | The bigger the temperature difference, the bigger the change in pressure |
| Pressure gradient force | Change in pressure measured across a given distance |
| What is air pressure measured in | Millibars |
| How does an Aneroid barometer work | Uses an evacuated metal chamber that compresses with pressure increases and expands with pressure decreases |
| What is falling pressure associated with | Increasing clouds and storms |
| What is rising pressure associated with | generally clearing conditions |
| Why do we use sea level-pressure | Use sea level equivalents to account for changes in elevation |
| What is average sea-level pressure | 1013.25 mb |
| What are high pressure systems typically called | Anti-cyclones |
| What weather is associated with anti-cyclones | Dry weather |
| What are low pressure systems called | Cyclones or mid-latitude cyclones |
| What type of weather is associated with cyclones | Stormy weather |
| What direction does wind flow in a cyclone | Counter-clockwise |
| How do areas of high pressure flow | Flow outwards toward lower pressure |
| What direction does wind flow in an anti-cyclone | clockwise |
| What are lines of equal pressure called | Isobars |
| How does the PFG develop | When air is subject to greater pressure on one side than another |
| Why is the 500 mb chart important | Represents the middle atmosphere (half air above and half air below) |
| What are ridges | High pressure warm air moving toward poles |
| What are troughs | Cold air moving toward equator |
| What direction does air move | From higher pressure in warm column toward the area of low pressure in the cold column |
| As air aloft leaves the column how does the mass change | Mass decreases, causing a decrease in surface pressure |
| How does pressure change with height | Decreases with altitude, increases with depth |
| How does pressure change in the cold column vs the warm column | Air transferred from warm column to cold column increases pressure in cold column |
| How does temp variations affect pressure | Leads to pressure differences, which leads to wind |
| What is convergence | When the net air flow into a region causes pressure to rise |
| What is divergence | When there is net outflow of air from a region and surface pressure drops |
| What do close isobars mean | steep gradient and high wind |
| What do far apart isobars mean | low gradient and low wind |
| How does convergence affect air pressure | Should lead to rising air and lower pressure |
| How does divergence affect air pressure | Can exceed convergence at the surface accelerating vertical motion and intensifying surface inflow |
| How does divergence and convergence affect anti-cyclones | Need to be maintained from above with convergence aloft and divergence at the surface |
| What are the scales of wind | Microscale, mesoscale and macroscale |
| What are microscale winds | Small and chaotic circulation. Can be simple gusts, downdrafts and small vortices |
| What are mesoscale winds | Things such as thunderstorms, tornadoes, local winds, and can have a strong vertical component |
| What are macroscale winds | The largest wind patterns that extend around the entire clobe |
| What are the two types of macroscale winds | Planetary-scale and synoptic scale |
| What are planetary-scale winds | Patterns that can remain unchanged for weeks at a time |
| What are synoptic scale winds | Smaller microscale circulations, about 600 miles in diameter (tropical storms and hurricanes) |
| How long do microscale winds last | From seconds to minutes |
| How long do mesoscale winds last | Can last from minutes to hours, in rare cases days |
| How large are mesoscale winds | Usually less than 60 miles (100km) across |
| What are global winds | A composite of motion on all kinds of scales |
| What are local winds | Examples of mesoscale winds. Land and sea breezes, mountain and valley breezes |
| What are Chinook winds | Warm dry winds that sometimes move down slopes of mountains |
| What are katabatic winds | Winds that originate when cold, dense air begins to move enough to displace the air downward. |
| What are country breezes | Mesoscale winds, caused by the uneven heating of urban and country areas. Results in the flow from country to urban areas |
| What is a monsoon | Refers to a season reversal of winds and wind direction change |
| What happens in the winter with monsoons | Wind blows primarily off shore (leads to drier conditions) |
| What happens in the summer with monsoons | Wind blows from sea to land |
| Why does the Polar Jet Stream stronger in winter vs summer | Moves faster in winter due to larger temp contrast |
| What does the polar jet stream do | Provides energy that drives storms, while also directing the path of storms |
| What is El Nino | The gradual warming of the eastern pacific waters in December or January |
| What is La Nina | The opposite of El Nino and refers to colder than normal ocean temperatures |
| What is an Air mass | An immense body of air, usually about 1000 miles or more across |
| What two things need to be similar when defining an air mass | Must have similar temps and humidity throughout |
| What makes a good source region | Must be an extensive and physically uniform area, with a general stagnation of atmospheric circulation |
| What are the two factors of classification of air masses | Latitude (temperature) and surface area |
| What are the three categories for latitude | Polar, Artic, and Tropic |
| What are the two surface area categories | Marine and Continental |
| Characteristic of Polar air | Cold |
| Characteristic of Artic air | Very cold |
| Characteristic of Tropic air | Warm |
| Characteristic of Marine air | Wet |
| Characteristic of Continental air | Dry |
| What would continental polar air be | Cold and dry |
| What would continental artic air be | Very cold and very dry |
| What would continental tropic air be | Warm and dry |
| What would marine arctic air be | Cold and wet |
| What would Marine tropic air be | Warm and wet |
| What air masses have the most moisture | Maritime Tropic |
| What air masses have the least moisture | Continental Arctic |
| What causes lake effect snow | The result of a cold air mass over warm water (cP air moves oer land, cools and drops snow in large amounts) |
| What side of the lake is impacted by lake effect snow | The leeward side when the cold air moves over the warm water |
| What are the five basic fronts | Warm fronts, cold fronts, stationary fronts, occluded fronts and drylines |
| What is a warm front | When warm air moves into a region of colder air |
| What weather comes with a warm front | Most of the time clouds are shallow and produce light to moderate precipitation. Temps gradually rise after the warm front passes. |
| What is a cold front | The zone of discontinuity when cold air advances sinto warm air |
| How are steep are slopes compared to warm fronts | Slopes are about twice as steep and travel 50% faster |
| What weather comes with a cold front | Dominated by subsiding air within a cP air mass. Cold advection usually offsets the warming and keeps things coller near ground |
| Why is there shorter/violent weather with cold fronts | The forceful lifting of warm, moist air along the front is often rapid enough that the released latent het increases the airs stability |
| The typical amount of time it takes for an air mass to pass over a given area is on the order of a few | Days |
| An air mass source region | Characterized by a general stagnation of atmospheric circulation |
| Lake effect snow is associated with what kind of air mass | cP, continental Polar |
| Is a region dominated anti-cyclone or a cyclone more like to produce an air mass | A region dominated by anti-cyclones |
| On a weather map, what kind of fronts are shown with blue triangular points along a blue line | Cold fronts |
| What is common to both cold and warm fronts | Lifting of warm air over cold air |
| In the US what air mass is most commonly found at the back of a cold front | cP, continental Polar |
| Thunderstorms can be generated when a cT air mass meets and mT air mass creates a frontal boundary called | Dryline |
| How do thunderstorms form | When warm humid air rises in an unstable environment |
| What are the three stages involved in the development of air mass thunderstorms | Cumulus stage, mature stage, and dissipating stage |
| What time of day is an air mass thunderstorm more likely to develop | Midafternoon |
| Roughly what percent of thunderstorms in the US become severe | 10% |
| Where does the gust front occur | At the leading edge of a thunderstorm downdraft |
| On a weather map, what kind of fronts are shown with red half-moon shapes on a red line | Warm fronts |
| On a weather map, what kind of fronts are shown with red half moons and blue triangles on a red and blue line | Stationary fronts |
| On a weather map, what kind of fronts are shown with purple triangles and half moon shapes on a purple line | Occluded fronts |
| On a weather map, what kind of fronts are shown with orange half moon shapes on an orange line | Drylines |
| When do stationary fronts occur | When airflow is neither toward cold air nor a warm air mass |
| What happens after a stationary front | Depending on which air mass moves first, they become either cold fronts or warm fronts |
| What is an occluded front | When rapidly moving cold air overtakes a warm front |
| When does a dryline occur | When cT air meets moist mT air from the Gulf of Mexico |
| What weather can come with a dryline and where | Often form thunderstorms in the Great Plains |
| What is a mid latitude cyclone | A synoptic scale low pressure system |
| What is overrunning | Warmer, less dense air being forced upward |
| Where do the warm and cold front extend from | The extend from the center |
| Where is the warm front located | Normally to the east |
| Where is the cold front located | Normally to the west of low pressure |
| What is a cut off low | Low pressure that is cut off from the jet stream |
| What kind of weather is associated with cut of lows | Dreary weather and large quantities of precipitation |
| What is a blocking high | High pressure that persists over an area for days to weeks |
| What kind of weather is associated with a blocking high | One part of nation is kept dry, while other part remains unsettled |
| How do midlatitude cyclones develop | When air masses of different temps move parallel to a front in opposite directions |
| What direction does the air begin to flow in a mid latitude cyclone | Moves in a counter-clockwise circulation, toward the center of the low |
| When is the peak performance of a mid latitude cyclone | During the mature stage |
| In a midlatitude cyclone how does a warm front form | Warm air advances poleward forming a warm front |
| In a midlatitude cyclone how does a cold front form | Cold air moves toward equator and forms a cold front |
| Where does the occluded front come from in a midlatitude cyclone | At the end of the mature stage, the cold front gradually takes over the warm front, producing the occluded front |
| What are the two types of thunderstorms | Air mass thunderstorms, and severe thunderstorms |
| How do air mas thunderstorms form | Warm, humid air that rises in convectively unstable environments |
| How do severe thunderstorms form | The result of uneven heating, frontal lifting and diverging winds |
| What environment is favorable for thunderstorm development | Conditionally unstable enviornments |
| What weather/time of day is best for thunderstorm development | Hot, humid, summer afternoons |
| What are the three stages of thunderstorm development | Cumulus stage, mature stage, and dissipating stage |
| What is the cumulus stage of thunderstorms | The development stage |
| What happens in the cumulus stage of thunderstorms | Unequal heating leads to cumulus clouds that begin to grow vertically once the air becomes humid enough. Cloud passes the freezing mark and produce precipitation. Stage is dominated by updraft, until falling raindrops develop drag and lead to downdraft. |
| What is the mature stage of thunderstorms | The most intense stage |
| What happens in the mature stage | Updrafts and downdrafts coexist, and continue to enlarge the cloud. Once they reach the tropopause, updrafts spread laterally for anvil shape. Gusty winds, hail, heavy precipitation are common |
| What happens during the dissipating stage | Drag of raindrops begin to strengthen and enlarges the downdraft. Rain eventually turns updraft into another downdraft. Cooling effect of falling precip and colder air aloft end thunderstorm activity |
| What is wind shear | Change in wind speed/direction with height |
| What defines a severe thunderstorm | 58 mph or greater wind, hail 1 inch in diameter or larger, or tornadoes |
| How does wind shear help the storm | The updrafts that provide the storm with moisture become tilted |
| How does the tilting of the updraft help the storm | The precipitation that forms in the top of the cloud does not fall into the updraft, allowing the updraft to continually supply the cloud with moisture to keep it building upward |
| What is an overshooting top | Momentum from updrafts that allow a clod to push its way into the lower stratosphere |
| What does the gust front do | Acts as a mini cold front, providing lift needed for additional thunderstorm development |
| Where do roll clouds and shelf clouds form | Along the leading edge of the parent cloud above the gust front |
| What is a roll cloud | Horizontal tube shaped cloud often detached from the parent cloud. Forms between the areas of cold downdraft and warm air flowing into the storm |
| What is a shelf cloud | Low horizontal wedge type clouds, accompanied by the strong, cool winds of the gust front |
| What is a squall line | A narrow band of thunderstorms |
| What is a derechos | A long-lived widespread straight-line wind event that exceeds 58 mph |
| What is an MCC | A mesoscale convective complex, a larger oval or circular cluster consisting of many individual thunderstorms |
| Where do MCC's form | Mostly in the great plains from a group of ordinary thunderstorms or behind a weakening squall line after sunset and into early am |
| What is required to transform ordinary thunderstorms into MCC | Strong low-level flow and warm moist air, enhancing instability and cloud development |
| What is a supercell thunderstorm | A single powerful cell that can extend to heights of 65,000 ft or more |
| Where do supercell thunderstorms form | Along the frontal boundaries, separating warm and cold air masses |
| What is a mesocyclone | A column of cyclonically rotating air formed by directional wind shear that develops vertically and may cause updraft to rotate |
| What is the most common type of lightning | Lightning within a cloud, or from one cloud to another |
| How does cloud to ground lightning occur | Occurs when the charge difference is between the cloud and the ground |
| What is the order of the lightning phases | Charge separation, step-leaders, stroke begins to carry charge, return stroke completes, dart leader re-ionizes the conductive path, after several strokes the negative charge is drained from the cloud |
| What is heat lightning | Lightning that is so far away you can't hear thunder |
| What is the rate of time and distance associated with lightning and thunder | When listening for thunder after lightning, every 5 seconds after lightning is approximately 1 mile |
| What is the leader in lightning | The ionized air |
| What is a tornado | Violent wind storm with a rapidly rotating column of air or vortex |
| What is directional shear | A change from southerly winds at the surface to westerly winds aloft |
| What direction do tornadoes most often move | Most travel southwest to northeast |
| What are the maximum wind speeds of a tornado | More than 300 mph |
| What is the range of winds speeds of a tornado | From less than 90 mph to more than 300 mph |
| What is responsible for the strong wind speeds in tornadoes | The mesocyclone is stretched vertically and narrowed horizontally, causing wind speeds to accelerate in an inward vortex |
| What type of thunderstorms do tornadoes usually develop in | Most often super cell thunderstorms |
| What is a hurricane | Intense center of low pressure |
| Where do hurricanes form | Over subtropical or tropical oceans |
| What determines the wind speed of a hurricane | The pressure gradient |
| What temperature must the water be to form a hurricane | 80 degrees or higher |
| Where are the worst conditions in a hurricane | The eye wall |
| How fast must winds be to qualify as a hurricane | They must have sustained winds of 74 mph or more |
| What is the storm called before it reaches hurricane status | Tropical storm or Tropical depression |
| What are some factors that cause a hurricane to weaken | Latent heat being cut off, hurricane moving over cold water or land, wind shear, |
| What impacts from a hurricane cause the most deaths | Storm surge and wind |
| Why does the eye of the hurricane occur | It occurs when air flows inward toward the center of the storm creating an area of low pressure |
| What causes the fast winds of a hurricane | The steep pressure gradient generates the wind and allows the velocity to increase as it moves inward |
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