Chapter 1 - Air pressure & density+Vert structure of the atmosphere

Question 1

True or False?
Any sample volume of air consists of billions of tiny fast-moving molecules that have some mass

Answer 1

True
Any sample volume of air consists of billions of tiny fast-moving molecules that have some mass

Question 2

How many molecules there are per cm3 of air?

Answer 2

2.7 x 1019 molecules

Question 3

What is the Avogadro’s constant?

Answer 3

1 mol = 6.022×1023 molecules = NA (Avogadro’s constant)

Question 4

Define density

Answer 4

the concentration of mass
-Density(ρ):mass/volume;[kg/m3]

Question 5

What is the density of air at sea level?Standard pressure?

Answer 5

-density of air at sea level: ~ 1.2kg/m3
-1013.25hPa(“hecto-Pascal”)
= 1013.25 mbar (millibar, non-SIunit)
= 1 atm (“atmosphere”; an olderunit)

Question 6

What is the density of liquid water at 25 degrees?

Answer 6

density of liquid water at 25°C: 997kg/m3

Question 7

Define weight

Answer 7

the force exerted by the mass due to gravity
*Weight (wt): mass × gravitational acceleration; [kg m/s2] = N

Question 8

Define pressure

Answer 8

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)]

Question 9

How does the atmospheric pressure compare to the one in typical car tires?

Answer 9

-Car tire = 30psi
-atmospheric pressure at sea level = 14.7 psi (= 1013hPa)
-Note: 1 hPa (hectoPascal)=100Pa(= 1mbar)

Question 10

What is the relation btw height & pressure/density?

Answer 10

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

Question 11

At ~ 5500 m above sea level…

Question 12

Why are aircraft cabins pressurized?

Answer 12

to supply enough oxygen to passengers at 11 km altitude

Question 13

Why don’t we feel air pressure?

Answer 13

Since it acts in all directions, the body’s internal pressure adjusts to atmosphere
-Also: lungs are never fully emptied when exhaling

Question 14

-spheres vs -pauses

Answer 14

*“-spheres” are layers
*“-pauses” are interfaces between layers

Question 15

Balloon soundings? 30km?

Question 16

How is described change in temperature with a change in height?

Answer 16

Lapse rate

Question 17

Define a positive lapse rate?

Answer 17

A positive lapse rate means temperature decreases with increasing height

Question 18

Define a negative lapse rate

Answer 18

Temperature INVERSION means temperature increases with increasing height. Lapse rate is negative

Question 19

What is the lapse rate of an isothermal environment ?

Answer 19

Isothermal environment implies no change in temperature with height. Lapse rate in this case is 0(°C/km)

Question 20

Which layer is called the weather layer?

Answer 20

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

Question 21

What is the upper boundary of troposphere?

Answer 21

Tropopause

Question 22

What is the tropospheres usual lapse rate?

Answer 22

*Temperature decreases with height at ~ 6.5 °C/km (the lapse rate)

Question 23

True or False?
The lapse rate of troposphere is always negative

Answer 23

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)

Question 24

True or False?
Temperature in the stratosphere increases with height

Answer 24

Temperature initially isothermal (constant with height), then increases up to ~50km (boundary of layer)

Question 25

Which layer of the atmosphere contains an ozone layer? And how does it affect temperature

Answer 25

-Stratosphere (10-50km so 40km)
-Ozone layer is the main reason for temperature increase (absorption of solar UV radiation leads to heating up)

Question 26

Which layer of the atmosphere is defined as the stable layer?

Answer 26

Stratosphere
-stratos: stratified, stable layer

Question 27

Is the lapse rate of the mesosphere positive of negative?

Answer 27

Positive lapse rate
-Temperature decreases with height up to ~ 85km

Question 28

Is the lapse rate of the thermosphere positive of negative? Is there a specific reason?

Answer 28

Temperature increases again with height due to absorption of energetic solar radiation by oxygen molecule

Question 29

Why does it not feel “warm” in the thermosphere while there is a temperature increases with height?

Answer 29

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

Question 30

Which layers of the atmosphere does the homosphere contain?

Answer 30

-Troposphere (0-12)
-Stratosphere (12-50)
-part of Mesosphere (50-85)

Question 31

How is defined the homosphere?& what is composed of?

Answer 31

-Homosphere: well mixed “lower”atmosphere
-78% N2, 21%O2

Question 32

How is defined the heterosphere? & what is composed of?

Answer 32

-Heterosphere: poorly mixed “upper” atmosphere
-different molecular mass of air constituents becomes important for mixing /un-mixing

Question 33

Which layers of the atmosphere does the heterosphere contain?

Answer 33

-part of Mesosphere
-Thermosphere

Question 34

Which layers of the atmosphere does the ionosphere contain?

Answer 34

-most of the Mesosphere
-Thermosphere

Question 35

Define the Ionosphere? What is the ionosphere composed of?

Answer 35

An electrified region with ions and free electron
Contains large fraction of electrically charged atoms(ions)
*above ~ 60 km altitude

Question 36

How does the ionosphere play a major role in radio communication?

Answer 36

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)

Question 37

What are the regions of ionosphere? Define the inner region

Answer 37

F region (180km)
E region (120km)
D region (60km): absorbs radio waves, weakening surface signal

Question 38

When is the efficiency of the D region much stronger? Why

Answer 38

Much stronger during the daytime due to photo-ionization

Question 39

Lapse rate vs Inversion

Answer 39

(+)Lapse rate: The rate at which the air temperature decreases with increasing height
(- lapse rate) Inversion: A measured increase in temperature with increasing height

Question 40

In which layers of the atmosphere is found the highest vs lowest temperatures?

Answer 40

Lowest temperatures = mesosphere
Highest temperatures = thermosphere