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65 Cards in this Set
- Front
- Back
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• Troposphere
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o Adjacent to the Earth’s surface.
o Varies in height form an average 55,000 feet over the equator to 28,000 ft over the poles. o 50% by weight, lies below 18,000 ft and 90% within 53,000 ft. o Temp normally decreases with increasing altitude. |
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• Tropopause
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o Transition zone between troposphere and stratosphere.
o Temp is isothermal with increase in altitude. |
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• Stratosphere
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o Characterized by increasing temp with increasing altitude due to the gas zone, which plays a major part in heating the air at this altitude
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Describe the flight conditions associated with the troposphere
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o Large amounts of moisture and condensation nuclei are found there because of its closeness to Earth’s surface and nearly all weather occurs here.
o Winds are generally light and increase with altitude. |
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the flight conditions associated with the tropopause
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o Strongest winds, those of the jet stream, occur just below the tropopause. Moderate to severe turbulence is sometimes associated with the wind shear caused by the jet stream.
o Can identify tropopause by: anvil tops of thunderstorms will spread out at the base of the tropopause. Haze layer with a definite top exists at the tropopause |
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• Lapse Rate
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o Decrease in atmospheric temperature with an increase in altitude.
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State the average lapse rate in degrees Celsius.
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• 2°C (3.5°F) per 1000 ft
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• Atmospheric (barometric) Pressure
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o Is the pressure exerted on a surface by the atmosphere due to the weight of the column of air directly above that surface.
o The average weight of air on a square inch of the Earth’s surface at sea level conditions is 14.7 lbs. |
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State the standard units of pressure measurement
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• Inches of mercury (in Hg)
• Millibars (mb) |
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Define the standard atmosphere to include temperature and pressure.
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• Standard day conditions at sea level
o 29.92 in-Hg (1013.2 mb) and 15°C (59°F) |
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Differentiate between sea level pressure and station pressure
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• Station Pressure
o Is the atmospheric pressure measured directly at an airfield or other weather station. • Sea Level Pressure (or Reported Altimeter Setting) o Is the pressure measured from the existing weather if the station were at MSL. |
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• Indicated Altitude
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o Read directly from the altimeter.
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• Calibrated Altitude
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o Indicated Altitude corrected for instrument/position error.
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• Mean Sea Level (MSL) Altitude
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o Actual height above mean sea level, also called True Altitude.
o MSL/True altitude is Calibrated Altitude corrected for temperature deviations from the standard atmosphere. |
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• Above Ground Level (AGL) Altitude or Absolute Altitude
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o Is the aircraft’s height above the terrain directly beneath the aircraft and is measured in feet AGL.
o Can be found by subtracting the terrain elevation from the true altitude or with a radar altimeter. |
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• Pressure Altitude
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o Height above the standard datum plane.
o The standard datum plane is the actual elevation above or below the Earth’s surface at which the barometric pressure is 29.92 in-Hg. o Pressure Altitude is the height above the place in the atmosphere where the pressure is 29.92 in-Hg. |
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• Density Altitude
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o Pressure Altitude corrected for nonstandard temperature deviations.
o DA is not a height reference; rather, it is an index to aircraft performance. High DA results in decreased aircraft performance. |
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Describe the effects of pressure changes on aircraft altimeters
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Flying toward lower MSL pressure Indicates higher than actual
Lower than indicated by the altimeter Flying toward higher MSL pressure Indicates lower than actual Higher than indicated by the altimeter. |
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• High to Low, look out below
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o Aircraft is lower than indicated, thus the indicated altitude is higher than the aircraft.
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• Low to High, plenty of sky
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o Aircraft is higher than indicated, thus the indicated altitude is lower than the aircraft.
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State the effects of temperature deviations from the standard lapse rate on aircraft altimeters.
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• When accounting for altimeter error attributed to temperature use the rules shown for pressure above (High to Low).
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Explain the term pressure gradient.
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• The rate of pressure change in a direction perpendicular to the isobars (horizontal distance) is called the pressure gradient.
• Isobar spacing represents the size of the pressure gradient force (PGF). o PGF is the initial movement of air from high pressure to low pressure, thus initiating force for wind. o PGF is steep or strong when isobars are close together – strong winds o PGF is shallow or weak when isobars are far apart. |
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Explain Coriolis force and its apparent effect on wind
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• Coriolis force, created by the Earth’s rotation, diverts the air to the right with respect to its initial direction of motion regardless of whether the air is near a high or low pressure system.
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Explain and identify gradient winds with respect to the isobars around high and low pressure systems in the Northern Hemisphere.
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• The result of PGF and Coriolis force is gradient winds, which flow perpendicular to the PGF.
• This means gradient winds flow parallel to the isobars and results in circulation flowing clockwise around highs and counterclockwise around lows. • Gradient winds are found above 2,000 ft AGL. |
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Define Buys Ballot’s Law.
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• States that if the wind is at your back, the area of lower pressure will be to your left.
• It’s a rule of thumb to help remember the direction of the wind in relation to a pressure system |
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Explain and identify the surface wind direction with respect to the gradient winds in a high and low pressure system in the Northern Hemisphere.
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• Coriolis force still tries to turn the wind to the right, from its initial intended direction of the PGF, but it does not turn to the right quite as much as with gradient winds, due to surface friction.
• Thus, surface winds still move clockwise around highs and counterclockwise around lows, but since they blow across the isobars at 45° angle, they also have a component of motion that moves air out of the high pressure and into to low. |
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Describe the jet stream
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• The jet stream is a narrow band of strong winds of 50 knots or more that meanders vertically and horizontally around the hemisphere in wave like patterns.
• Average winds are 100 to 150 knots, but may reach speeds in excess of 250 kts. • It is found in segments from 1000 to 3000 miles in length, 100 400 miles in width, and 3,000 to 7,000 feet in depth. • Average height is about 30,000 feet MSL • During winter, the position of the jet stream is further south, the core rises to higher altitudes, and its speed is faster than in the summer. |
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• Sea Breezes
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o During the day, the pressure over the warm land becomes lower than over the colder water.
o The cool air over the water moves toward the lower pressure, replacing the warm and rising air over the land. o This results in an onshore wind, blowing from the sea. |
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• Land Breezes
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o During night, the circulation is reversed so that the air movement is from land to sea, producing an offshore wind called the land breeze.
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• Valley Winds
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o Occur during daytime when the sun heats the mountain slopes.
o As the air adjacent to the slopes is heated, it rises and is replaced by warmer air near the ground. o Since that wind is flowing from the valley, it is called a valley wind. |
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• Mountain Winds
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o Occur at night, when the air adjacent to the slopes is cooled by outgoing terrestrial radiation and becomes more dense than the surrounding air.
o The denser air flows downhill, from the top of the mountain and is called a mountain wind. |
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• Saturation
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o When air contains the maximum amount of water vapor for a given temperature.
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• Dew Point Temperature (TD)
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o Temperature at which saturation occurs. The higher the dew point, the greater chances for clouds, fog, or precipitation.
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• Dew Point Depression or Dew Point Spread
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o Difference between the air temperature and dew point temperature.
o This spread provides a good indication of how close the atmosphere is to the point of saturation. Saturation occurs when Dew Point = Temperature |
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• Relative Humidity (RH)
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o Is the percent of saturation of the air.
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State the relationships between saturation, air temperature, dew point temperature, and dew point depression necessary for the formation of clouds, fog, and precipitation.
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• Saturation occurs when Dew Point Temp and air temperature are equal.
• When the dew point depression/spread reaches about 4° F, the air is holding close to the maximum amount of water vapor possible. • If the spread continues to decrease, moisture will begin to condense to form clouds or fog and when saturation is reached, precipitation will result. |
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what are the 3 characteristics of percipitation
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showers, continuous, intermitent
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• Showers (percipitation)
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o Characterized by a sudden beginning and ending, and abruptly changing intensity and/or sky conditions. Showers are associated with cumuliform clouds.
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• Continuous (percipitation)
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o Also known as steady (not showery). Intensity changes gradually, if at all. Continuous or steady precipitation is associated with stratiform clouds.
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• Intermittent (percipitation)
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o Stops and restarts at least once during the hour. Intermittent precipitation may be showery or steady, and therefore may be associated with cumuliform or stratiform clouds
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• Drizzle
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o Very small droplets of water that appear to float in the atmosphere.
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• Freezing Drizzle
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o Drizzle that freezes on impact with objects
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• Rain
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o Precipitation in the form of water droplets that are larger than drizzle and fall to the ground.
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• Freezing Rain
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o Rain that freezes on impact with objects
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• Hail or graupel
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o Form of precipitation composed of irregular lumps of ice that develop in severe thunderstorms, consisting of alternate opaque and clear layers of ice in most cases. It does not form structural ice.
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• Ice Pellets or Sleet
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o Small translucent and irregularly shaped particles of ice. They form when rain falls through air with temp below freezing. Ice pellets do not produce structural icing unless mixed with super cooled water.
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• Snow
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o White or translucent ice crystals, usually of branched hexagonal or star like form that connect to one another forming snowflakes. When condensation place at temperatures below freezing, water vapor changes directly into minute ice crystals.
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• Snow Grains
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o Very small white, opaque grains of ice. They usually fall in small quantities from stratus type clouds, never as showers.
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Identify 4 cloud groups
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low clouds, middle clouds, high clouds, special clouds.
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• Low Clouds
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o Ranging form just above the surface to 6,500 feet AGL.
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• Middle Clouds
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o Bases between 6,500 and 20,000 feet AGL. Prefix alto-
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• High Clouds
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o Bases usually above 16,000 feet AGL. Prefix Cirro- or the word cirrus
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• Special Clouds
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o Extensive vertical development. Consist of Towering Cumulus and Cumulonimbus Clouds.
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Identify the weather conditions associated with Low Clouds
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o Mainly composed of water droplets, may hide thunderstorms
o If clouds are below freezing, icing may result. Icing accumulates faster in low clouds since they are generally denser than middle or high clouds. o Turbulence varies from none to moderate. o Precipitation is generally light rain or drizzle. |
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Identify the weather conditions associated with Middle Clouds
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o Names of middle clouds will contain prefix alto-.
o Rain, rain and snow mixed, or snow can be encountered in thick middle clouds. o Visibility depends on cloud density from ½ mile to a few feet. o Frequently these clouds are dark and turbulent enough to make formation flying difficult. |
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Identify the weather conditions associated with High Clouds
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o Will contain the prefix Cirro- or the word cirrus.
o They have little or no precipitation and do not constitute an icing hazard. o Severe or extreme turbulence is often found in the anvil cirrus of thunderstorms. |
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Identify the weather conditions associated with Special Clouds with Extensive Vertical Development
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o Consist of Towering Cumulus and Cumulonimbus Clouds.
o Towering Cumulus are clouds nearing the thunderstorm stage and produce heavy rain showers and moderate turbulence. o Cumulonimbus Clouds are thunderstorm clouds and produce severe to extreme turbulence, hail, icing, lightning and other hazards. |
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• Atmospheric Stability
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o Lifted air that is colder than the surrounding air settles when the lifting action is removed, since it is denser. This indicates a stable condition.
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• Atmospheric Instability
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o Lifted air that is warmer than the surrounding air continues to rise when the lifting action is removed because it is less dense. This indicates an unstable condition.
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• Atmospheric Neutral Stability
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o Lifted air having the same temperature as the surrounding air after it is lifted will simply remain at the point where the lifting action was removed.
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what are the 4 types of lifting
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convergence, frontal orographic, thermal
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• Convergence
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o Convergence of 2 air masses, or parts of a single air mass, force the air upward because it has nowhere else to go.
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• Frontal
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o The shape of cold fronts, as they move through an area, will lift air ahead of the cold air mass.
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• Orographic
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o Term indicating the force of the wind against a mountain side pushing the air upward.
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• Thermal
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o Thermal lifting also known as convective lifting, is caused when cool air is over a warm surface and it is heightened by intense solar heating on a clear day.
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