WEAX 201 Study Guide - Atmospheric Structure

what is density?

• how much () is () in a given space or volume

• () to the number of molecules per volume

• mass divided by volume (how much matter is packed in a given space or volume)

• proportional to the number of molecules per volume

• averages 1.225 kgm³ at MSL

• how does it affect flight performance?

• lower density gives less power, less lift, less drag because there are few air molecules to work with

• density () with height and what is the rate? - every () ft

• decreases

• every 20,000 ft you ascend, density reduces by about 50% because the air gets thinner as you get higher

how does density vary with pressure and temperature?

• density is () to pressure to temperature so at a constant pressure, if density was () then temperature would be ()

• density is proportional to pressure to temperature so at a constant pressure, if density was increased then temperature would be cooler

what is pressure?

• pressure = ()/()

• a change in a molecule’s () exerts a ()

• results from molecular ()

• acts in () directions

• pressure = force/area

• a change in a molecule’s momentum exerts a force

• results from molecular collisions

• acts in all directions

what causes an increase or decrease in air pressure?

• increase: add () to a closed container, add more (), or make the container ()

• decrease: () a gas, remove (), and make the container (), also go () in elevation, also adding more ()

increase: add heat to a closed container, add more gas particles, or make the container smaller

decrease: cool a gas, remove gas particles, and make the container larger, also go higher in elevation, also adding more water vapor

what causes an increase or decrease in air pressure when considering altitude?

• increase: Air pressure increases as you go () toward sea level. The stack of air above is (), () more molecules together.

• decrease: Air pressure drops as you go () up a mountain or fly in a plane. There are () air molecules above you, meaning () weight pressing down.

• increase: Air pressure increases as you go lower toward sea level. The stack of air above is taller, packing more molecules together.

• decrease: Air pressure drops as you go higher up a mountain or fly in a plane. There are fewer air molecules above you, meaning less weight pressing down.

what causes an increase or decrease in air pressure when considering temperature?

• increase: () air molecules () down and () tightly together. This makes the air () and (), raising the surface pressure.

• decrease: () air molecules () up and () apart. This makes the air () and less (), lowering the pressure.

• increase: Cold air molecules slow down and pack tightly together. This makes the air dense and heavy, raising the surface pressure.

• decrease: Warm air molecules speed up and spread apart. This makes the air lighter and less dense, lowering the pressure.

what causes an increase or decrease in air pressure when considering moisture (humidity)?

• increase: () air is () than moist air, which () the overall pressure

• decrease: () air has () pressure than dry air. (..) molecules weigh () than nitrogen and oxygen molecules, making humid air () dense.

• increase: Dry air is denser than moist air, which raises the overall pressure

• decrease: Humid air has lower pressure than dry air. Water vapor molecules weigh less than nitrogen and oxygen molecules, making humid air less dense.

what causes an increase or decrease in air pressure when considering air movement?

• Increase: Air that moves () gets () and pushes () on the ground, creating high-pressure systems.

• Decrease: Air that moves () leaves () less weight at the surface, creating low-pressure systems and stormy weather.

• Increase (Sinking Air): Air that moves downward gets compressed and pushes harder on the ground, creating high-pressure systems.

• Decrease (Rising Air): Air that moves upward leaves behind less weight at the surface, creating low-pressure systems and stormy weather.

what causes an increase or decrease in liquid pressure?

• increase: you go deeper () because the () of the water creates more ()

• decrease: a fluid moves () through a () space and () speed lowers the pressure

increase: you go deeper underwater because the weight of the water creates more pressure

decrease: a fluid moves faster through a narrow space and faster speed lowers the pressure

what is the average air pressure at MSL?

• () lbs/in²

• () in. Hg

• () mb (or hPa)

• drops about () Hg per () ft in the () atmosphere

• 14.7 lbs/in²

• 29.92 in. Hg

• 1013 mb (or hPa)

• drops about 1 Hg per 1000 ft in the lower atmosphere

what is temperature?

• proportional to average kinetic energy of molecules

how do you find Celsius from F?

• T(C) = 5/9(T_F -32)

how do you find fahrenheit from C?

(°C × 9/5) + 32

how do you calculate kelvins from C?

T(K) = T(C) + 273.15

how do you calculate kelvins from F?

1. convert F to C

2. then use the C to kelvins formula

What’s the significance of

32°F, 212°F, 0°C, 100°C, & 0 K, and the number -40?

32 F: freezing point of water

212 F: boiling point of water

0 C: freezing point of water

100 C: boiling point of water

0 K: when the molecules stop vibrating (all molecular motion stops)

-40: the temperature at which all water will freeze in both F and C

how are pressure and temperature interrelated?

• when temperature goes (), pressure goes ()

• If you heat up a gas in a closed container, the particles move faster and hit the walls harder. This makes the pressure go up.

• when temperature goes up, pressure goes up

how is density and temperature interrelated?

• if temperature goes (), density usually goes ()

• temperature and density are inversely related

• if temperature goes up, density usually goes down vice versa

how is pressure and density interrelated?

• when pressure increases, density usually ()

• directly related

• when one increases, the other generally increases as well

how is density measured?

• D =

• D = Mass divided by volume

how is temperature measured?

• you can measure using a thermometer and measure in C, F, or K

how is pressure measured?

• P =

• pressure = force divided by area

what is the ideal gas law?

• relates (), (), and ()

• pressure is () to density and temperature

• at a given altitude, () air is less dense than () air

• warm air ()

• relates temperature, density, and pressure

• pressure is proportional to density and temperature

• thus, at a given altitude, warm air is less dense than cold air

• warm air rises

what is the standard temperature?

• at MSL?

• what is the standard lapse rate?

• 15 degrees C at MSL

• standard lapse rate is 2 degrees C per 1000 ft up to 36000

how do altimeters work?

• by measuring changes in ()

• Air from outside the aircraft enters the altimeter case through a special opening called a ()

by measuring changes in atmospheric air pressure

Air from outside the aircraft enters the altimeter case through a special opening called a static port

Kollsman Window: Pilots use a small adjustment knob to type or dial in the local barometric pressure. This calibrates the device so it shows the correct height above sea level rather than just raw pressure

what are the four layers of the atmosphere?

• thermosphere

• mesosphere

• stratosphere

• troposphere

what is the troposphere?

• between surface & about 36,000 ft

• where weather occurs

• pressure ranges between 200 to 1030 mb

in the troposphere, what happens with the temperature and height?

• () temperature with height

• heated from () because the () absorbs more of the sun’s rays than air

• decreasing temperature with height

• heated from below the earth because the ground absorbs more of the sun’s rays than air

what do things does the troposphere have?

• vertical..

• turb…

• vertical air currents

• turbulence

what is it like in the troposphere with clouds and moisture?

• () and ()

• there are clouds where air is (), it is clear where air is ()

• moisture content () with height because the earth’s main source of water vapor is () through (), (), and vegetation. as you move higher into the atmosphere, you gain () from moisture sources, temperatures (), and () & () take moisture from the air

• cloudy and moist

• there are clouds where air is rising, it is clear where air is sinking

• moisture content decreases with height because the Earth's surface is the main source of water vapor through evaporation from oceans, lakes, and vegetation. as you move higher into the atmosphere, you gain distance from moisture sources, temperatures drop, and there is condensation and precipitation which takes moisture from the air

what is the stratosphere?

• between () ft and () ft

• pressure ranges from () to () mb

• Temperature () with height in the stratosphere due to the absorption of () by ()

• sm…, non…, cloud…

• between 36,000 ft and 160,000 ft

• pressure ranges from 1 to 200 mb

• Temperature increases with height in the stratosphere due to the absorption of UV radiation by ozone

• smooth, non-turbulent, cloud free

Why is the marked annual variation of temperature in polar regions near top of stratosphere?

• what is the temperature in polar winter? why?

• what is the temperature in polar summer? why?

• what forms here?

• what is a health hazard for aviatiors?

• that region experiences the most extreme shift between complete continuous darkness in winter and 24 hours of direct solar ultraviolet absorption by ozone in summer

• winter: less than -100 degrees C because during the polar night, there is zero incoming solar radiation. Because ozone no longer absorbs ultraviolet (UV) sunlight to generate heat, radiative cooling causes the air at the top of the polar stratosphere to plummet to its lowest seasonal values

• summer: greater than 0 degrees C because during polar summer, the sun remains above the horizon all day (the midnight sun). Continuous solar UV radiation is heavily absorbed by ozone molecules at this high altitude, strongly heating the upper stratospheric layers

• Nacreous (pearl-like) ice clouds in polar regions between 20 and 30 km

• Ozone

what is the mesosphere?

• between () and ()

• () region

• temperature () with height

• pressures range from () to () mb

• thin (noctilucent) () sometimes are observed at high latitudes in summer (rare)

• () also occurs in the upper portion of mesosphere

• between 160000 and 280,000

• middle region

• temperature decreases with height

• pressures range from 0.005 to 1 mb

• thin (noctilucent) ice clouds sometimes are observed at high latitudes in summer (rare)

• ionization also occurs in the upper portion of mesosphere

what is the thermosphere?

• above () ft

• () molecules but () energize

• temperature () with height due to absorption of () and () rays

• temp () when solar activity is high

• above 280,000 ft

• few molecules but highly energize

• temperature increases with height due to absorption of xrays and gamma rays

• temp rises when solar activity is high

why are molecules ionized and escape earth’s gravity?

• molecules are ionized above about () ft by () and () ray radiation

• molecules that become (…) and () escape earth’s gravity

• what refracts radio waves more when ion concentrations are high?

• molecules are ionized above about 250,000 ft by xray and gamma ray radiation

• molecules that become highly energized and surpass escape earth’s gravity

• ionosphere

what causes the northern lights?

• electrically () particles from the () colliding with () in earth’s upper atmosphere

• electrically charged particles from the sun colliding with gases in earth’s upper atmosphere

what is the tropopause?

• boundary between () and ()

• altitude varies with () and with ()

• location of () temp and () wind (near jet stream)

• () tops and high () extend to the tropopause

• boundary between troposphere and stratosphere

• altitude varies with latitude and with season

• location of lowest temp and max wind (near jet stream)

• thunderstorm tops and high clouds extend to the tropopause

where and when is it highest and coldest?

() in () regions because:

• () solar heating

• air () because the air is warm and it rises into the atmosphere

• extremely cold because as the air () and () that high, it () down significantly

summer in tropical regions because:

• intense solar heating

• air expansion because the air is warm

• extremely cold because as the air expands and rises that high, it cools down significantly

where and when is it lowest and warmest?

() in () regions because:

• () of sunlight

• air (): cold air is () and ()

• milder boundary temperatures since the troposphere is () and much () here, the temperature here stays warmer

winter in polar regions because:

• lack of sunlight

• air contraction: cold air is dense and shrinks

• milder boundary temperatures since the troposphere is compressed and much shallower here, the temperature here stays warmer

What factors cause the indicated altitude to differ from the true altitude?

• nonstandard ()

• nonstandard ()

• aircraft static ()

• instrument ()

• nonstandard temperatures

• nonstandard atmospheric pressure

• aircraft static pressure systems

• instrument error

explain nonstandard temperatures

• () than standard: () air expands, () pressure levels. The altimeter shows an indicated altitude that is () than your actual true altitude

• () than standard: () air compresses, () pressure levels. The altimeter shows an indicated altitude that is () than your actual true altitude, which can be dangerous near terrain ("high to low, look out below").

• Warmer than standard: Warm air expands, raising pressure levels. The altimeter shows an indicated altitude that is lower than your actual true altitude ("low to high, clear the sky"). [1, 2]

• Colder than standard: Cold air compresses, lowering pressure levels. The altimeter shows an indicated altitude that is higher than your actual true altitude, which can be dangerous near terrain ("high to low, look out below").

explain nonstandard atmospheric pressure

• () pressure: If local pressure is () than standard (above 31.00 "Hg), an altimeter might not adjust () enough, making the true altitude () than indicated.

• () pressure: If local pressure is abnormally () (below 28.00 "Hg), the true altitude will be () than what the altimeter indicates

• High pressure: If local pressure is higher than standard (above 31.00 "Hg), an altimeter might not adjust high enough, making the true altitude higher than indicated.

• Low pressure: If local pressure is abnormally low (below 28.00 "Hg), the true altitude will be lower than what the altimeter indicates

explain aircraft static pressure systems

• if you have a blocked static port, aerodynamic disruptions, etc, it can cause an incorrect reading

explain instrument error

• if the instrument reads incorrectly or is malfunctioning, etc

How do troposphere characteristics change with latitude?

• uneven () heating

• equator: () solar heating which causes () air to () vertically (maximum height), usually (), () water vapor content

• poles: much () layer so () air () and is (), very (), () water vapor content

• uneven solar heating

• equator: intense solar heating which causes warm air to expand vertically (maximum height), usually warmer, high water vapor content

• poles: much shallower layer so cold air contracts and is denser, very cold, low water vapor content

How and why do pressure vary with height on average?

• it () rapidly the() you go because () pulls air down and () levels are () by the weight of all the air above them so () up there is () air pressing down

• it decreases rapidly the higher you go because gravity pulls air down and lower levels are compressed by the weight of all the air above them so higher up there is less air pressing down

How and why do temperature vary with height on average?

• it () in the troposphere because the ground () the air from the () up and as air () into () pressure, it () and () down

• it drops in the troposphere because the ground heats the air from the bottom up and as air rises into lower pressure, it expands and cools down

How does the average wind speed vary with height in the atmosphere?

• wind speed generally () with height

• surface wind speeds typically…

• wind speeds near tropopause…

• () wind speed at tropopause

• strongest wind shear just () and () tropopause

• wind speed generally increases with height

• surface wind speeds typically 5-20 kt

• wind speeds near tropopause 50-200 kt

• maximum wind speed at tropopause

• strongest wind shear just above and below tropopause

what is temperature inversion?

• a layer where temp () with height

• ELR is () than 0

• a layer where temp increases with height

• ELR is less than 0

what is isothermal layer?

• a layer having () temperature

• ELR = ()

a layer having constant temperature

ELR = 0

what is lapse rate?

• the rate of temperature () with height

• average standard lapse rate is?

• the () the lapse rate, the () turbulence

• lapse rate is () in an inversion layer

• the rate of temperature decrease with height

• average is 2 degrees C per 1000 ft

• the bigger the lapse rate, the more turbulence

• lapse rate is NEGATIVE in an inversion layer

what is the environmental lapse rate equation?

• ELR =

ELR = (T^1 - T²) / (H² - H^1)