Atmosphere of Earth: Composition & Equator
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What is the atmosphere
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The collection of gases, particles, and clouds that comprise the envelope of air that surrounds the Earth
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What elements make up the atmosphere, and at roughly what percentage?
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78% Nitrogen 21% Oxygen 1% Argon 0 - 4% Water vapor ~0.04% Carbon dioxide
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What is the line of 0 degrees in latitudinal measurements?
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Equator
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What is the line of 0 degrees in longitudinal measurements?
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Prime Meridian
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How do you convert UTC to EST (Eastern Standard Time)?
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EST = UTC - 500
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How do you convert UTC to EDT (Eastern Daylight Time)?
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EDT = UTC - 400
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What is temperature?
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Temperature is a measure of the average kinetic energy, or motion, of molecules
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How can you identify strong gradient regions in an isopleth?
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Many isopleth lines appear near one another (change in a quantity over a distance
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What is an isopleth called for temperature? For pressure? For wind?
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Temp: Isotherm Pressure: Isobar Wind: Isotach
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How is wind named?
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Wind is named by the direction from which it blows
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What is the difference between weather and climate?
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Weather is the measure of temporary weather systems, while climate is over an extensive period of time
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What is radiation?
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Radiation is energy transferred by photons, and it travels at the speed of light
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How is radiation generated?
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Electrons oscillate and distort electromagnetic (EM) field
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Molecules ALWAYS both absorb and emit radiation simultaneously. How does a molecule heat up or cool down then?
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If emission > absorption = cools down If absorption > emission = heat up
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What does Wien's law state?
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Every object emits some radiation at all wavelengths, but the PEAK wavelength of emission depends on temperature. Higher temperature = shorter peak wavelength
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What does Stefan Boltzman's Law state?
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The total energy emitted by an object also depends on temperature. Higher temperature = more total energy emitted
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What is back-scattering with radiation?
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When radiation bounces off a surface and heads in different direction.
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What is transmission with radiation?
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When radiation makes it through a given surface
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What is absorption with radiation?
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When radiation is absorbed by the given surface?
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True or False: All 3 of these processes happen at the same time.
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TRUE
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What is albedo?
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The amount of radiation units reflected by clouds, air units and the surface.
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What heats up more: the ground or the atmosphere
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Sun heats the ground more than it heats the atmosphere
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How does radiation heat the ground and air?
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Shortwave radiation comes from the Sun and heats the ground, hotter ground emits longwave radiation, the clouds and atmosphere absorb and scatter some radiation, and the atmosphere absorbs some longwave radiation so the air heats below.
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Why are cloudy days cooler than a clear day?
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Clouds absorb some radiation that would heat the ground, which would in turn heat the air
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Does higher in the troposphere increase or decrease temperature? Why?
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Higher in the troposphere is decreasing temperature because the air heats from below.
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How does radiation affect the temperature at night?
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The ground emits longwave radiation which cools the ground, ground cools the air directly next to it, so the temperature increases with height.
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Are cloudy nights warmer or cooler than clear nights? Why?
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Warmer; because clouds hold temperature and emit longwave radiation which provides some energy to the ground.
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What are capabilities of greenhouse gases?
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Because Earth's surface emits longwave IR to space GHGs in the atmosphere absorb (intercept) some of this IR, GHGs then re-emit the radiation, some of which goes back to Earth's surface!
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What is conduction?
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Direct transfer of energy between things that touch
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What is convection?
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Movement of air due to density differences
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Why can too much greenhouse gas be bad?
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It would make the Earth too hot in a high enough concentration
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What is active remote sensing? What are examples?
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Measuring device emits energy Energy reflects off of object being measured Measuring device detects reflected energy Examples: Sonar & radar
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What is passive remote sensing? What are examples?
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Measuring device detects energy naturally emitted, reflected, or scattered by objects Measuring device sends data to computer for interpretation Examples: IR thermometers, human eyes, or common weather sattelites.
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What are the 3 types of passive satellites?
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Visible, water vapor, and infrared
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What does a visible satellite do?
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Measures solar radiation (sunlight) scattered by clouds and ground. Radiometers measure back-scattered sunlight (albedo) and assign a shade based on intensity. Dark for higher and lighter for lower intensity.
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What does an infrared satellite do?
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Measures IR radiation emitted by clouds and ground. It measures IR radiation (longwave) emitted by ground and clouds.
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What does a water vapor satellite do?
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Measures IR radiation emitted by water vapor in atmosphere
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What are the pros and cons of visible satellites?
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Pros: Determine cloud thickness Thicker clouds reflect more sunlight and thus are whiter on visible satellite imagery Cons: Snow can look like thick clouds (both have high albedo), and it is useless at night (no incoming solar radiation)
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What are the pros and cons of an infrared satellite?
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Pros: IR imagery is used to determine cloud temperature, and if there are no clouds it can actually show surface temperature. It also works night and day.
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What are the pros and cons of a water vapor satellite?
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Pros: it measures moisture/clouds in mid/upper troposphere. Also it works day and night. Cons: It does not measure WV in the lower troposphere
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What are the uses of radar/ how are they interpreted?
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It detects precipitation and snowfall. Interpretation:Power of return signal determines precipitation intensity== Higher DBz means heavier snow/rainfall Lower DBz means lighter snow/rainfall
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What does the Doppler Radar do?
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Measures wind However, it needs to hit a target to do so, meaning it only measures component of wind parallel to radar beam.
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What are astronomical seasons based off of?
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Earth is tilted 23.5° on its axis of rotation Result: At different times of the year, different latitudes get more direct sunlight than others.
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What are meteorological seasons?
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They are based on average monthly temps Temps \"lag\" annual solar cycle because of water (which has a very high heat capacity) and oceans cover 70% of Earth's surface. Therefore, the seasons in the NH are opposite to those in the SH.
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What 3 main factors measure average surface temperature patterns across the globe ?
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Latitude, proximity to large bodies of water, elevation
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What effect does latitude have on air?
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Sun angle always high over tropics = warm year round Sun angle always low over poles = cold year round Sun angle varies in mid-latitudes, so we're constantly on the battlefront between cold and warm air
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Why is it light in Alaska 24 hours a day during Summer, but rarely gets above 50 degrees F?
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It is very close to the South pole, where the Sun angle is always low
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What effect does proximity to large bodies of water have on temperature?
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Surface temps over large bodies of water change much more slowly than surface temps over land because water has 3x bigger heat capacity than land.
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What is seasonality? And how are areas close to large bodies of water affected by this?
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The range of temperatures a given location will experience, on average, throughout the year. And areas close to large bodies of water will normally experience less seasonality than areas in the middle of the continent.
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How does elevation affect temperatures?
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Because the Sun heats the ground, then the ground heats the air the temperature decreases with height in the troposphere. Therefore a city on a mountaintop would be cooler than a city in a valley.
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How does all of this affect the climate (as opposed to weather)?
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High latitudes (poles) are colder than low latitudes (tropics), areas downwind of large bodies of water have less seasonality, ocean currents affect a region's average temp, and higher elevation = colder climate
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Why aren't temperatures always average?
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Weather is the departure from average because anything can happen over a short period of time. Climate is the average scale because it takes place over a long period of time.
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What is an air mass?
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A very large region of air in which temperature and moisture are fairly uniform. The center of an air mass has high pressure.
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How can air masses be classified?
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By temperature (tropical, polar, arctic) or by moisture (maritime, continental)
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What is a front?
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The boundary between two air masses, where there are large gradients of temperature and moisture and are located in areas of low pressure.
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How are fronts classified?
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Cold front: Cold air advances Warm front: Cold air retreats Stationary front: Cold air moves parallel to front (neither advancing nor retreating)
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What is advection?
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The transport of an atmospheric quantity (pollution, temp, moisture) by the wind. It requires wind and a gradient (change over distance) of the atmospheric quantity
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What is the diurnal range?
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Range between high and low temp on a given day
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What are the geographical effects on the diurnal range?
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Latitude: Lower sun angle - lower high temp - smaller range Proximity to water: Decreases diurnal range (just like seasonality) Elevation: Cold air drains into valleys at night - lower low temp in valleys - larger range in valleys
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What is the effect of clouds on the diurnal range?
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It reduces it because: Day: Clouds absorb/reflect some incoming solar radiation - cooler high Night: Clouds emit longwave radiation to surface - warmer low. Also water vapor is a greenhouse gas, so it reduces diurnal range
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What are weather effects on the diurnal range?
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Precipitation (rain or snow) Evaporational cooling Clouds are necessary for precipitation Snow cover Night: Snow prevents heat energy in topsoil from escaping much colder lows Day: Snow has high albedo somewhat colder highs
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What is the distribution of water on Earth?
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Oceans- 97% (Cover 70% of Earth) On Land- 3%
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What happens when you add energy to H20 molecules?
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Surrounding air cools
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What happens when you remove energy to H20 molecules?
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Surrounding air warms
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What happens when precipitation evaporates?
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Moistens the air which increases dew point, and cools the air which lowers temperature
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What is vapor pressure?
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Force exerted by gaseous H2O molecules. Also, more vapor (gas) molecules = higher vapor pressure, and vapor pressure is proportional to the condensation rate
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What is equillibrium vapor pressure?
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The pressure at which the condensation rate = evaporation rate. When VP EVP: net condensation = supersaturated air
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What is the formula for relative humidity?
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(Vapor pressure/ Equillibrium vapor pressure) * 100%
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What is the dew point? (Td)
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Temperature to which air must cool to become saturated (condensation = evaporation) Lowering T decreases EVP, but doesn't change VP So RH increases to 100% when T = Td
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What is the relation between temperature and relative humidity?
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RH depends on T, and cooling increases RH
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What keeps clouds from dropping ice crystals and water particles?
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There's usually an updraft (rising air) within a cloud
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What are the components needed for a cloud?
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Big MAC = Moisture, Aerosols, Cooling
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How does moisture change in the air?
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Moisture advection: When winds blow from a moist area (high Td) to a drier area (low Td) Example: Change from maritime (moist) to continental (dry) air mass after frontal passage Evaporation Liquid H2O (ocean/lake/etc.) evaporates and moistens atmosphere
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What is an aerosol?
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A small, solid particle suspended in the atmosphere
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What is the purpose of cooling within a cloud?
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To get a cloud, let's lower T T lowers to Td, RH = 100%, air is now saturated Cool a bit more (Td > T; RH > 100%) → Net condensation
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What is the purpose of air parcels in cooling air?
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A rising air parcel (blob of air) encounters lower pressure, so it expands outward to adjust, and this expansion uses energy so the rising parcels are cooling. This leads to saturation.
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What is the Lifting Condensation Level?
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Level at which a rising (and thus cooling) parcel becomes saturated and cloud droplets begin to form
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What is the Bergeron- Findeisen process?
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Ice crystals coexist with H20 molecules in a cloud in a cold area, then the ice grows by stealing H2O molecules from liquid causing rain.
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True or False: All precip. outside of tropics starts as snow - even in summer!
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True
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What is the definition of air pressure?
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Force (weight) per unit area of the column of air above you
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Where is pressure the highest?
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At the ground level because the air above compresses the air below
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What is sea level pressure?
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The surface pressure a location would have if it were at sea level
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What is a ridge? A trough?
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A ridge is an elongated area of high pressure. A trough is an elongated area of low pressure.
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What is the pressure gradient force (PGF)?
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It sets wind in motion
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What is the Coriolis Effect (CE)?
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An \"apparent\" force (due to Earth's rotation and curvature) that deflects the wind
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What does friction do?
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Slows down the wind
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Where does PGF point in NH and SH?
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Always points from high to low pressure. Also, high PGF = faster wind
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What does the CF do?
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Deflects moving parcels (or other objects)... To the right in the Northern Hemisphere To the left in the Southern Hemisphere
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General rules of the CF?
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Only acts on moving things and is smallest at the equator
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What does friction do, and where is its effect the strongest?
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Friction acts against the wind, and slows it down. Highest effect in higher areas (Mountains).
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How does the amount of friction determine angle of spiral?
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Low friction= small angle High friction = larger angles
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How does the Sfc air spiral inward in low pressure for NH and SH?
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Sfc air spirals cyclonically inward (converges) Northern Hemisphere: Spirals in counterclockwise Southern Hemisphere: Spirals in clockwise
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How does the Sfc air spiral inward in high pressure for NH and SH?
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Sfc air spirals anticyclonically outward (diverges) Northern Hemisphere: Spirals outward clockwise Southern Hemisphere: Spirals outward counterclockwise
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True or false? Objects that have a peak wavelength of emission in the visible are warmer than objects that have a peak wavelength of emission in the infrared
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True
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What happens to slightly more than half of all sunlight (on average) that enters the top of the atmosphere
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It is absorbed by the Earth's surface (sun heats the ground, ground then heats the air from below)
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Rank the following types of radiation in order from shortest wavelength to longest wavelength: Infrared Visible Ultraviolet
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UV, Visible, Infrared
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Which has a higher albedo? Fresh snow, or grass?
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Fresh snow
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Why is the northern hemisphere summer warmer than the southern hemisphere summer?
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The northern hemisphere has more land than the southern hemisphere; land has a lower heat capacity than water, and thus a hemisphere with more land gets hotter in the summer
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Would the seasonality of State College change if the Earth's axis was tilted more than 23.5°?
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The seasonality would increase because summers would have more intense (direct) sunlight and the winters would have less intense sunlight
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Suppose a mP air mass is retreating and being replaced by a cT air mass. What kind of front separates these two air masses?
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Warm front because cold air is retreating
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For fog or clouds to form, the relative humidity must ever so slightly exceed 100%
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True. NET condensation (i.e., cloud formation) only occurs when the atmosphere is supersaturated (RH > 100%, VP > EVP, Td > T)
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Name an absolute measure of humidity
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Dew point or vapor pressure
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On a hot and humid summer day, why does liquid form on the outside of a cold drink glass?
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On a hot, humid day, both T and Td are high (say, 90°F and 70°F respectively). If the cold glass has a temperature of 50°F, then the outside of the glass is colder than the dewpoint, causing net condensation to occur on the outside of the glass.
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What are the 3 ingredients necessary for cloud formation?
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Moisture, aerosols, and cooling
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Describe the Bergeron-Findeisen process, and explain why it is important for precipitation in places outside the tropics
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The Bergeron-Findeisen process is when ice crystals grow by stealing water molecules from liquid water drops. Away from the tropics, this allows ice crystals to grow fast enough to fall out of clouds as precipitation in a timely manner
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Why do we convert from surface (station) pressure to sea level pressure?
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To remove the effects of elevation
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What is the definition of pressure that we have used in this class?
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Force per unit area; the weight of the column of air above you
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Is it possible for pressure to increase with height?
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NEVER; always decreases
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For each of the following, state whether it is found in high pressure or low pressure: Air mass Front Trough Ridge
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Air mass: high Front: low Trough: low Ridge: high
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Where does PGF point in each of the following: Northern Hemisphere Southern Hemisphere Equator
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NH = towards low pressure SH = towards low pressure Equator = towards low pressure
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When we say there is a northeasterly wind, what exactly do we mean?
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The wind is coming from the northeast
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Where does the Coriolis force point in the northern hemisphere? What about the southern hemisphere?
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NH = 90° to the right of the current parcel motion in the northern hemisphere SH = 90° to the left of the current parcel motion in the northern hemisphere
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State whether each of the following forces affects the wind speed PGF CF Friction
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PGF = yes CF = no Friction = yes
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Rank the following locations in terms of the amount of friction experienced by a moving air parcel, from least amount of friction to most amount of friction. Mountains Ocean Ten thousand feet above the ground A grassy plain
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10,000 feet, ocean, grassy plain, mountains
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Describe how rising air can lead to clouds and precipitation
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Rising air always cools; cooling air leads to (super)saturation (assuming parcel dew point stays constant); (super)saturation leads to condensation (cloud formation and possibly precipitation)
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What types of weather are associated with surface low pressure? What about surface high pressure?
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Surface low pressure = clouds and precipitation; surface high pressure = clear skies
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Name the three types of satellite imagery used by meteorologists (100 points each)
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Visible, infrared, and water vapor
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What is the fundamental difference between weather and climate?
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Climate is over a long period of time whereas weather is over a short period of time.
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Explain how greenhouse gases are both good and bad for life on Earth
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Greenhouse gases help to heat the earth and keep the temp relatively constant, but too much would cause the Earth to be way too hot
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What is the fundamental cause of weather?
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Large scale differential heating between the equator and the poles
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What is the Ideal Gas Law theory
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Ideal gas law: Pressure = constant*density*temperature At the same pressure, warmer air is less dense!
