Ch 2 - Heating Of The Atmosphere Flashcards
Temperature Conversions
C -> F F = 32.0 + 5/9(C)
F -> C C = 9/5(F) -57.6
C -> K K = C + 273
Boiling 100C or 212F or 373K
Freezing 0C or 32F or 273K
Stevenson Screen
Measures Temp and Humidity
1-2m (roughly 4ft) above the ground
Conduction
Heat transfer through contact (air is a poor conductor)
Immediate air above the surface of earth it is heated up this way
Convection
Vertical movement of air (parcels)
Heat -> Less Dense -> Rise up
Cool -> More Dense -> Sink
(*Lava Lamp)
Forced Convection
Mountain or any object that forces air up (orographic lifting) terrain -> high to low pressure
Mechanical Convection
Rotors
- Coming down the lee side of a mountain, due to friction, the air comes back up on itself, forcing to rotate
Creates turbulence
Parcels of convection rotors
Can happen when wind interferes with normal convection
Radiation
Heat transfer by the absorption of long wave radiation
- Sun gives out short wave radiation (DOES NOT HEAT UP ATMOSPHERE)
Long wave Radiation is what the earth gives out after being heated up by the SWR from the sun. Known as Terrestrial Radiation which heats up the earths atmosphere
Latent Heat
Hidden Energy from state change (solid-> liquid)
Sublimation
Must have a nuclei - impurity in the atmosphere
Dumps excess energy heat -Latent heat released into surround atmosphere (no rise/decrease when going from ice to gas)
Latent heat released and surrounding temp increases when going from gas to ice.
Advection
Heat transfer by horizontal movement of air
*Wind - Low level due to pressure gradient
Insolation
Amount of solar radiation energy being absorbed per unit area over time
- Less at the poles as they are at an angle to the radiation and snow/ice sheets reflect them
- More at EQ - Concentrated amount
3 Main things: Latitudes, season and time of day
Earths’ Axis and Orbit
23.5 Degrees tilted
Elliptical Orbit
Anti-clockwise orbit
Perihelion
Roughly 4th of Jan (N. Hemisphere winter)
- 91 millions miles away from the sun (closest it gets)
Aphelion
4th July (N. Hemisphere Summer)
95 Million miles away from the sun (furthest away)
Earth’s Spin
Anti-clockwise
15.04 degrees per hour
Equinox
When the earths EQ passes through the centre plane of the sun
23rd September
21st of March
Solstices
When the sun reaches its most northerly or southerly excursion relative to the earths EQ
21st of December
21st of June
Declination
Angle of the star (Sun) relative to the earth’s EQ
EQ - The Celestial EQ
Surface Temperature Variations
Large land masses have potentially large temperature variations due to the low specific heat of land
Sea temperatures remain fairly constant throughout the year
Impacts; Sea currents and Global winds (*Gulf Stream)
Heat
The Energy Required to Drive the Activity
Temperature
Measure of the heat of energy associated with movement and collisions of molecules
Calorie (Cal)
Heat needed to raise 1g of water by 1 degrees C
Specific Heat
Ratio of heat needed for some temperature rise
- Water needs 1 cal to raise 1g by 1C
(* Hence sea temp. stays relatively constant)
Ice = 0.5 Rock = 0.25
Diurnal Variation
The daily temperature changes
- Hottest part of the day is 2-3pm (2-3 hours after mid day
- Coldest time of the day is roughly 30 minutes after sunrise (dawn)
Factors that affect diurnal variation:
Wind - Stronger wind = less temperature fluctuations
- Day time temp = cooler as cool air being dragged down by mechanical convection from higher layers
- Night - temp doesn’t drop as much as it brings warm air in from layers above
Cloud - more cloud = Less SWR = Less surface temp
- Keeps LWR (terrestrial) in at night = Increased surface temp
- over cast = colder days, warmer nights
- clear sky = warmer days, colder nights
Low Clouds
Thicker, More moisture
Impact diurnal variation more than high level, whisky clouds
Temperature Inversions
Temperature increases with altitude
Mid Level inversion
Low Level inversion (nocturnal surface inversions)
Isothermal layer (stays at a constant temp with altitude)
Ground Inversion (Nocturnal / Radiation Inversion)
At night, ground cools, through conduction the first couple of layers of air heat up to about 500ft (can start on surface), then gets trapped by the warmer air sitting on stop of it. This creates the inversion.
Layer of smog or impurities sitting below the warmer air.
Only forms in very light wind leading to FOG, Stratus (St) or Stratocumulus (Sc) cloud, on or beneath the inversion.
With moderate wind the fog can be lifted.
As the air is cooled, it may reach the Dew point at which the air becomes 100% saturated with moisture. (100% Relative Humidity)
If temp drops even lower and the moisture condenses, it leads to clouds suspended in the air or Radiation Fog on the ground.
Valley Inversion
Same process as a Ground Inversion (Radiation or Nocturnal Inversion).
- Ground cools, air immediately on top of the ground cools and condenses, causing it to sit at the bottom of the valley with the warmer air sitting on top. It can cool to the Dew Point which would cause the moisture in the air to condense - lead to Fog, Stratus or Stratocumulus clouds
In cooler air, there is poor visibility but better aircraft performance because of the cooler dense air.
Warmer air = good vis. But bad aircraft performance
Subsidence Inversion
Only happens in a High Pressure System
- Warm air column descends (subsides) on cooler air which gets trapped beneath it (along with impurities) at roughly 2-3000ft creating a friction/boundary layer where the impurities get trapped.
The subsiding air gets heated by compression.
Column or air diverges (moves out from the centre as it has nowhere else to go)
Clear sky’s, with poor visibility.
Summer - happens quite a lot, massive high pressure sits on top
Frontal Inversions
Red lines with semi circles are warm fonts
Blue lines with triangles are cold fronts
Both take with them inversion layers
Between the lines is warm tropical air (warm sector)
Polar air sits behind the warm/cold fronts
mP/T = Maritime Polar/Tropical cP/T = Continental Polar/Tropical
Tropopause Inversion
The isothermal layer sits between 11km and 20km
- Staring point is the top of the isothermal layer in the stratosphere
- Very stable air above it
- Most hot air wont manage to break through the tropopause
