Chapter 1 - Air pressure & density+Vert structure of the atmosphere Flashcards
True or False?
Any sample volume of air consists of billions of tiny fast-moving molecules that have some mass
True
Any sample volume of air consists of billions of tiny fast-moving molecules that have some mass
How many molecules there are per cm3 of air?
2.7 x 1019 molecules
What is the Avogadro’s constant?
1 mol = 6.022×1023 molecules = NA (Avogadro’s constant)
Define density
the concentration of mass
-Density(ρ):mass/volume;[kg/m3]
What is the density of air at sea level?Standard pressure?
-density of air at sea level: ~ 1.2kg/m3
-1013.25hPa(“hecto-Pascal”)
= 1013.25 mbar (millibar, non-SIunit)
= 1 atm (“atmosphere”; an olderunit)
What is the density of liquid water at 25 degrees?
density of liquid water at 25°C: 997kg/m3
Define weight
the force exerted by the mass due to gravity
*Weight (wt): mass × gravitational acceleration; [kg m/s2] = N
Define pressure
Atmospheric pressure is the weight of the overlying air column per unit area
*Pressure (p): force/area = weight/area; SI unit “Pascal”, [Pa] = [kg/(ms2)]
How does the atmospheric pressure compare to the one in typical car tires?
-Car tire = 30psi
-atmospheric pressure at sea level = 14.7 psi (= 1013hPa)
-Note: 1 hPa (hectoPascal)=100Pa(= 1mbar)
What is the relation btw height & pressure/density?
Both air pressure and density decrease exponentially with height
the average mass per square metre of all the air molecules above Earth’s surface is 10,339.3kg, which produces an avergae pressure of 1,013.25 hPa
Why are aircraft cabins pressurized?
to supply enough oxygen to passengers at 11 km altitude
Why don’t we feel air pressure?
Since it acts in all directions, the body’s internal pressure adjusts to atmosphere
-Also: lungs are never fully emptied when exhaling
-spheres vs -pauses
*“-spheres” are layers
*“-pauses” are interfaces between layers
How is described change in temperature with a change in height?
Lapse rate
Define a positive lapse rate?
A positive lapse rate means temperature decreases with increasing height
Define a negative lapse rate
Temperature INVERSION means temperature increases with increasing height. Lapse rate is negative
What is the lapse rate of an isothermal environment ?
Isothermal environment implies no change in temperature with height. Lapse rate in this case is 0(°C/km)
Which layer is called the weather layer?
Troposphere since weather occurs in this layer
*Thunderstorm clouds often reach up to the tropopause
*Sometimes temperature inversions near surface present (warmer air on top of colderair
What is the upper boundary of troposphere?
Tropopause
What is the tropospheres usual lapse rate?
*Temperature decreases with height at ~ 6.5 °C/km (the lapse rate)
True or False?
The lapse rate of troposphere is always negative
False
Sometimes temperature inversions near surface present (warmer air on top of colderair) but lower Temperature decreases with height at ~ 6.5 °C/km (positive lapse rate)
True or False?
Temperature in the stratosphere increases with height
Temperature initially isothermal (constant with height), then increases up to ~50km (boundary of layer)
Which layer of the atmosphere contains an ozone layer? And how does it affect temperature
-Stratosphere (10-50km so 40km)
-Ozone layer is the main reason for temperature increase (absorption of solar UV radiation leads to heating up)
Which layer of the atmosphere is defined as the stable layer?
Stratosphere
-stratos: stratified, stable layer
Is the lapse rate of the mesosphere positive of negative?
Positive lapse rate
-Temperature decreases with height up to ~ 85km
Is the lapse rate of the thermosphere positive of negative? Is there a specific reason?
Temperature increases again with height due to absorption of energetic solar radiation by oxygen molecule
Why does it not feel “warm” in the thermosphere while there is a temperature increases with height?
Even though there is a absorption of energetic solar radiation by oxygen molecule that cause the temperature increase, there are very few molecules per unit volume at this altitude (density)
*temperature = average kinetic energy of molecule
Which layers of the atmosphere does the homosphere contain?
-Troposphere (0-12)
-Stratosphere (12-50)
-part of Mesosphere (50-85)
How is defined the homosphere?& what is composed of?
-Homosphere: well mixed “lower”atmosphere
-78% N2, 21%O2
How is defined the heterosphere? & what is composed of?
-Heterosphere: poorly mixed “upper” atmosphere
-different molecular mass of air constituents becomes important for mixing /un-mixing
Which layers of the atmosphere does the heterosphere contain?
-part of Mesosphere
-Thermosphere
Which layers of the atmosphere does the ionosphere contain?
-most of the Mesosphere
-Thermosphere
Define the Ionosphere? What is the ionosphere composed of?
An electrified region with ions and free electron
Contains large fraction of electrically charged atoms(ions)
*above ~ 60 km altitude
How does the ionosphere play a major role in radio communication?
Reflects AM radio signals, allowing transmission over large distances
-D region: absorbs radio waves, weakening surface signal (Much stronger during the daytime due to photo-ionization)
What are the regions of ionosphere? Define the inner region
F region (180km)
E region (120km)
D region (60km): absorbs radio waves, weakening surface signal
When is the efficiency of the D region much stronger? Why
Much stronger during the daytime due to photo-ionization
Lapse rate vs Inversion
(+)Lapse rate: The rate at which the air temperature decreases with increasing height
(- lapse rate) Inversion: A measured increase in temperature with increasing height
In which layers of the atmosphere is found the highest vs lowest temperatures?
Lowest temperatures = mesosphere
Highest temperatures = thermosphere
