Meteorology - The Atmosphere Flashcards
The Atmosphere
What are the main component gases of the atmosphere in DRY air?
Nitrogen 78%
Oxygen 21%
Argon 0.9%
Traces of CO2 and other gases
What are the three gases which play the most important part in weather?
CO2
Ozone
Water vapour
Describe water vapour
Carries large amounts of latent heat energy
A light, transparent gas
Averages less than 1%, but local concentration can vary from 0% to 4%
Where is most of Earth’s water vapour found?
Low altitudes and areas of high temperature
In what form does the Sun’s energy reach the Earth?
Short wave radiation
How’s the Sun’s energy reflected back?
As long wave radiation
What causes the Greenhouse effect?
Carbon Dioxide and water vapour absorbing some of the long wave radiation reflected back from the Sun
Describe the general gas law as a formula. What does R stand for?
Pressure x Volume = R x Temperature
A gas constant for the gas or mix of gases we’re dealing with
How is density defined?
The mass of a unit volume of a gas
How does density relate to volume in a fixed mass of air?
Density is inversely proportional
Volume increases, density reduces
How is pressure defined?
A unit of force per area
A Hectopascal is equal to one…
Millibar
What’s the average pressure of the atmosphere at sea level in hPa? And in inches of mercury?
1013.25 millibars
29.92
What’s the most common type of barometer?
A mercury barometer
Describe how an aneroid barometer works
Using a closed, evacuated capsule that expands and contracts under changing pressure
What’s a barograph?
An aneroid barometer that records changing pressure in graphical form
What are recorded on surface weather charts?
Barometric pressures from hundreds of observation stations
How does one get a good overview of pressure distribution on a surface pressure chart?
By joining points of equal pressure
What secondary thing do we get from surface weather charts besides seeing pressure distribution easily?
An estimation of the wind direction and speed at any given point
What’s the most commonly measured weather parameter?
Temperature
What does temperature describe?
The kinetic energy or energy of morion, of the gases that make up the air
Name four major atmospheric phenomena which are affected by temperature
Rate of evaporation
Relative humidity
Wind speed and direction
Precipitation patterns and types
For calculations in thermodynamics…must be used
°A( Absolute temperature) or Kelvin
How does one convert to Kelvin from °C?
+273
What are the key temperatures in Fahrenheit?
Freezing point of water: 32°F
Boiling point of water: 212°F
How does one convert from °C to F°?
T(°C) x 1.8 + 32
How does one convert from Fahrenheit to Celcius?
(T(°F) -32) / 1.8
How is density measured in meteorology?
Grams per cubic metre
What’s the average temperature at sea level in °C and K?
15°C
288K
What’s the correct gas constant for dry air at sea level?
1225 g/㎥
What will happen to the msl air density constant if water vapour is present?
There will be a lower density for the same conditions of temperature and pressure
What’s the sea level density of water vapour?
About 760 g/㎥ (over half the density of the dry atmosphere)
Air density…with altitude
Decreases
At roughly what altitude is air density of that of at sea level? And quarter?
22,000 ft
40,000 ft
T or F
The rate of change of pressure with altitude is linear
F
How is upper air data usually collected?
By a Radiosonde
A balloon with an instrument pack that records temperature, pressure and humidity and radios it back to a ground station
How might radar tracking be used in conjunction with a radiosonde?
As a means of collecting upper air data
Which two atmospheric conditions always reduce with height?
Pressure and density
How does temperature affect pressure and density?
Only the rate at which they fall
Pressure and density fall…rapidly in cold air as height increases
More
In warm air, the pressure aloft is always…
Higher
What’s the feet per mb at 10,000 ft? And the pressure at ISA?
36 ft
700 mb
What’s the feet per mb at 18,000 ft? And the pressure at ISA?
48 ft
500 mb
What’s the feet per mb at 30,000 ft? And the pressure at ISA?
72 ft
300 mb
How are feet per mb calculated?
Feet per hPa = 96T (K) / P(hPa)
Pressure is approximately 50% of MSL pressure at…
18,000 ft
Density approximately 50% of MSL at…
22,000 ft
Density is approximately 25% of MSL density at…
40,000 ft
What’s the lowest level of atmosphere called? What are its extremities in feet?
The Troposphere
Approx. Ground to 8-16 km
How’s the Troposphere characterised?
Air cools adiabatically as it rises
Temperature falls as altitude rises until the Tropopause
Almost all weather occurs here
At the poles the troposphere is…than at the equator, reaching altitudes of approximately…
Lower
8 km
Why does temperature decrease with height?
In response to the reducing air density/thinner air
Which layer occurs above the Tropopause?
The Stratosphere
Describe the Stratosphere’s composition and temperature characteristics
What are its extremities?
The upper two thirds are ozone
The temperature stays constant just above the Tropopause then steadily increases to a maximum at the Stratopause, then reducing again as the atmosphere thins further
16 - 50 km
The stratosphere holds about…of the atmosphere’s gases but very little…
19%
Water vapour
What is above the mesosphere? How else is it known?
The thermosphere
The ionosphere
What’s above the stratopause?
The mesosphere
What’s the highest layer of Earth’s atmosphere?
The exosphere
…% of the mass of the atmosphere lies in the bottom…of the…
50%
20,000 feet
Troposphere
Why does temperature increase in the ozone layer? From what to what?
Heat is produced in the formation of Ozone
From an ISA average of -56.5° to approximately -15°C
Describe how ozone is formed
Diatomic oxygen absorbs UV radiation with wavelengths less than 240 nm and is split into two oxygen atoms
This is exothermic and results in 2 ozone molecules from every three diatomic oxygen molecules and light to heat conversion
What happens to zone when exposed to UV?
It absorbs UV with wavelengths up to 290 nm
This UV causes it to decompose into O2 molecules and oxygen atoms
This is exothermic
What’s the result of the stratosphere’s temperature profile?
Very stable atmospheric conditions
Almost completely clear of clouds/weather
How might the stratosphere benefit long distance flight
It’s above stormy weather
It has strong steady horizontal winds
Why does most commercial flight tend to cruise near the top of the tropopause?
Low temperatures and low air density, reducing parasitic drag
How does ozone pose a threat to commercial flight? How can this be mitigated?
It’s poisonous
By fitting catalytic converters to aircraft aircon, which break the ozone down into oxygen
What are the extremities of the mesosphere?
50 km to 85 km
Why does the mesosphere switch back to cooling with altitude?
As air becomes progressively less dense with altitude
Where do meteors tend to burn up? Why?
In the mesosphere
The gases are thick enough to slow them down
Which layers are considered to be the middle atmosphere?
The stratosphere and the mesosphere
Which layer lies between 85 km and 600 km?
How else is it known?
The thermosphere
The upper atmosphere
Why does the thermosphere increase in temperature with height?
UV and X-ray radiation from the sun heats the atmosphere/exosphere’s molecules as they first make contact
What can the extremities of temperature be in the thermosphere?
-120°C to 2000°C
What’s notable about the high temperatures in the thermosphere?
They would still feel cold to the skin as there are so few molecules here
What’s the outermost layer of the atmosphere? What are its extremities?
The exosphere
600 km to 10,000 km
