The approximate composition of dry air by volume in the troposphere is 21% oxygen, 78% nitrogen, and the rest other gases.

The atmosphere is primarily heated by heat from the Earth’s surface.

Solar radiation passes through the atmosphere and warms the ground. The Earth then radiates this heat back into the atmosphere, warming it from below.

The lapse rate in the troposphere is produced by terrestrial radiation and rising air, and in the stratosphere by absorption of solar radiation.

Short Notes:

Troposphere Lapse Rate:
* Earth’s surface absorbs solar radiation and emits terrestrial (long-wave) radiation.
* Air heated at the surface becomes less dense and rises (convection).
* Rising air expands and cools adiabatically, contributing to the lapse rate.
Stratosphere Temperature Increase:
* Ozone layer in the stratosphere absorbs ultraviolet (UV) radiation from the sun. This absorption warms the stratosphere, causing temperature to increase with height.

The percentage of oxygen in dry air by volume is approximately 21%.

Nitrogen makes up the majority at about 78%, with the remaining 1% consisting of trace gases.

Water vapor is a greenhouse gas.
– Methane is a greenhouse gas.
– Ozone contributes to the greenhouse effect but has a lesser impact than water vapor and carbon dioxide.
– Carbon dioxide is a major greenhouse gas.

Since the greenhouse effect of water is specifically due to water vapor, if “Water” in the question includes its liquid or solid forms, then Water would be the best answer to “Which of the following is not a greenhouse gas?” in this context.

The stratosphere is the atmospheric layer above the troposphere, extending from the tropopause to about 50 km. It is characterized by a temperature inversion, where temperature increases with altitude due to ozone absorbing ultraviolet radiation. This temperature increase contributes to the stability of the stratosphere, limiting vertical air movement.

In contrast, the troposphere, the lowest atmospheric layer, has a temperature that generally decreases with height and is relatively unstable. The tropopause is the boundary between the troposphere and stratosphere, where the temperature stops decreasing and begins to level off.

Key Points:

Stratosphere: Temperature increases with height, caused by ozone absorption of UV radiation, and is stable.

Troposphere: Temperature decreases with height, making it unstable.

Tropopause: Boundary between troposphere and stratosphere, where the temperature lapse rate changes.

The maximum concentration of ozone is at a height of 20-25 km.

Short Notes:
– Maximum ozone concentration: Approximately 25 km altitude in middle latitudes.
– Location: Stratosphere.
– Variation: Peak concentration in polar regions found at lower levels.

The reason 99% of the atmosphere’s mass is concentrated below 35 km is due to gravity. The Earth’s gravitational pull keeps the denser air molecules closer to the surface. As you go higher, the air becomes thinner, and the concentration of air molecules decreases significantly. This rapid decrease in density is why the majority of the atmosphere’s mass is in the lower layers.

The correct answer is Stratosphere. This is because mother-of-pearl clouds, also known as nacreous clouds, form at high altitudes in the stratosphere under extremely cold conditions.

The environmental lapse rate (ELR), which is the actual rate of temperature decrease with altitude in the atmosphere, is variable.

– The ISA lapse rate in the troposphere is about 2°C per 1000 ft (6.5°C per 1000 m).
– However, the actual lapse rate fluctuates and can be greater or less than the average.
– It can even be zero (isothermal layer) or negative, where temperature increases with height (temperature inversion).
– Conditions can range from very stable (small ELR or inversion) to very unstable (large ELR, potentially superadiabatic where ELR > DALR).

Short Notes:
– ELR is the actual temperature change with height.
– ELR is variable and fluctuates.
– ELR can be positive, zero (isothermal), or negative (inversion).
– Stability depends on the relationship between ELR, DALR, and SALR.

To find the ISA deviation, we need to calculate the standard temperature at 2 km and then compare it with the given temperature.

Here’s how:

ISA Temperature at Sea Level: The International Standard Atmosphere (ISA) defines the temperature at mean sea level as 15°C.

Standard Lapse Rate: The temperature decreases at a standard lapse rate of 6.5°C per kilometer in the lower troposphere.

ISA Temperature at 2 km:

Temperature decrease = 2 km * 6.5°C/km = 13°C

ISA Temperature at 2 km = 15°C – 13°C = 2°C

ISA Deviation:

ISA Deviation = Actual Temperature – ISA Temperature = 05°C – 2°C = 3°C

Therefore, the ISA deviation is +3°C.

CO2 and H2O keep the atmosphere Warm.

Short Notes:

– CO2 and H2O are greenhouse gases.
– They absorb heat (infrared radiation) emitted by the Earth.
– This process, known as the greenhouse effect, warms the atmosphere and the Earth’s surface.
– Without these gases, the Earth would be much colder.

In jet standard atmosphere the Lapse rate is 6.5-degree C per km.

Short Notes:
* JSA lapse rate is 2°C per 1000 ft.
* This is approximately equal to 6.5°C per kilometer.

Most of the water vapor in the atmosphere is confined to the lower troposphere.

The troposphere is the lowest layer of the atmosphere, and it’s where the majority of water vapor resides. This is primarily because water vapor originates from the Earth’s surface through evaporation from water bodies and transpiration from plants. The temperature in the troposphere decreases with altitude, which leads to condensation and precipitation, further limiting the vertical extent of water vapor.

ICAO Standard Lapse Rate: In the troposphere, the temperature decreases by 2°C for every 1000 feet in altitude.

Altitude Difference: From FL110 (11,000 ft) to FL140 (14,000 ft), the altitude difference is 3000 feet.

Temperature Change:

For every 1000 feet, the temperature decreases by 2°C.

3000 ft ÷ 1000 ft = 3 increments.

3 increments × 2°C/increment = 6°C decrease.

Starting Temperature at FL110: -12°C.

Temperature at FL140: -12°C – 6°C = -18°C.

Final Temperature at FL140: -18°C.

Explanation:

Altitude to Freezing Level:
* Temperature difference between FL250 (-38°C) and freezing (0°C): 38°C.
* Altitude change required to warm to freezing: 38°C / (2°C/1000 ft) = 19,000 ft.
* Since the temperature at FL250 is already below freezing, the freezing level is below this altitude.

Estimated Freezing Level:
* Freezing level ≈ FL250 – 19,000 ft = 25,000 ft – 19,000 ft = 6,000 ft, which is FL060.

correct answer is Nitrous Oxide (N₂O).

Explanation:
Greenhouse gases are those that absorb and emit infrared radiation, trapping heat in the atmosphere.

Nitrous Oxide (N₂O) is one of these gases, contributing to the greenhouse effect.

Other important greenhouse gases include:
Water vapor (H₂O)
Carbon dioxide (CO₂)
Methane (CH₄)
Ozone (O₃)
Chlorofluorocarbons (CFCs)

Short Notes:
Oxygen (O₂) is not a greenhouse gas.
Carbon monoxide (CO) is a pollutant, not a primary greenhouse gas

To find the outside air temperature, we first need to calculate the International Standard Atmosphere (ISA) temperature at FL250.

* The ISA temperature at Mean Sea Level (MSL) is 15°C.
* The ISA temperature lapse rate from MSL to 36,090 ft (approximately FL361) is 1.98°C per 1000 ft.

At FL250 (25,000 ft):
ISA Temperature = 15°C – (1.98°C/1000 ft × 25,000 ft)
ISA Temperature = 15°C – (1.98 × 25)
ISA Temperature = 15°C – 49.5°C
ISA Temperature = -34.5°C

The air mass is 5°C warmer than ISA. Therefore:
Outside Air Temperature = ISA Temperature + 5°C
Outside Air Temperature = -34.5°C + 5°C
Outside Air Temperature = -29.5°C

Rounding to the nearest option, the outside temperature is likely to be -30°C.

Latent heat is the primary mechanism for heat transfer in the atmosphere. It involves the absorption and release of heat during water’s phase changes, such as evaporation and condensation. When water evaporates, it absorbs heat, cooling the surface. When the water vapor condenses, it releases heat, warming the atmosphere.

Approximately 77% of heat transfer to the atmosphere occurs through latent heat processes (evaporation, condensation, sublimation), which is much greater than the 23% contributed by sensible heat transfer (conduction, convection, radiation). This release of latent heat plays a major role in warming the atmosphere.

Key Points:
– Latent heat is responsible for most heat transfer in the atmosphere.
– Evaporation absorbs heat (cooling the surface); condensation releases heat (warming the atmosphere).
– 77% of atmospheric heat transfer is through latent heat.

Positive Lapse Rate (Normal Condition): Temperature decreases with height in the troposphere.

Negative Lapse Rate (Inversion): Temperature increases with height, known as a temperature inversion.

Incorrect Descriptions:

Temperature rise with lowering height: Opposite of an inversion.

Isothermal rate: Temperature remains constant with height (lapse rate is zero).

Temperature fall with height: Normal condition in the troposphere, not an inversion.

How Inversions Form:

Surface Inversions: Occur on cool, clear nights.

Inversions Aloft: When warm air moves over cooler air near the surface.

Subsidence Inversions: Occur in high-pressure systems due to descending, warming air.

Effects of Inversions:

Stability: Resists vertical air motion.

Pollution Trapping: Can trap pollutants, causing poor air quality.

Cloud Inhibition: Limits convective cloud formation.

Tropopause and Stratosphere: Inversions are common at the tropopause and in the stratosphere due to ozone absorption of UV radiation.

In the ICAO standard atmosphere, temperature decreases with increasing altitude below the tropopause.

Stratosphere is Stable.
Temperature inversion in the stratosphere (temperature increases with height) contributes to its stability.
Stable air resists vertical movement

The approximate ratio of O2 to N2 in the atmosphere by volume is 1:4.

Nitrogen makes up about 78% of the atmosphere, while oxygen is around 21%.

The remaining 1% consists of trace gases like argon, carbon dioxide, and others

Explanation:

1. Calculate the ISA temperature at FL300:
* ISA temperature at MSL = 15°C.
* ISA lapse rate = 1.98°C per 1000 ft up to 36,090 ft.
* Altitude = 30,000 ft (FL300).
* ISA temperature at FL300 = 15°C – (1.98°C/1000 ft × 30,000 ft) = 15°C – 59.4°C = -44.4°C.

2. Calculate the ISA deviation:
* ISA Deviation = Actual Temperature – ISA Temperature
* ISA Deviation = -42°C – (-44.4°C) = -42°C + 44.4°C = +2.4°C.

3. Determine if warmer or colder:
* A positive deviation indicates the actual temperature is warmer than ISA.

4. Final Answer:
* Rounding +2.4°C, the temperature deviation is approximately 3°C warmer than ISA.

We will use the International Standard Atmosphere (ISA) lapse rate to calculate the temperature difference. The ISA lapse rate below 11 km (approximately FL361) is 1.98°C per 1000 ft.

1. Altitude Difference:
FL270 is 27,000 ft.
FL170 is 17,000 ft.
Altitude difference = 27,000 ft – 17,000 ft = 10,000 ft.

2. Temperature Change:
Temperature decreases with height at a rate of 1.98°C per 1000 ft.
Over 10,000 ft, the temperature difference would be: 1.98°C/1000 ft × 10,000 ft = 19.8°C.

3. Expected Temperature at FL170:
The temperature at FL270 is -35°C. Since FL170 is lower, the temperature should be higher.
Expected temperature at FL170 = Temperature at FL270 + Temperature difference
Expected temperature at FL170 = -35°C + 19.8°C = -15.2°C.

Rounding to the nearest option, the expected temperature at FL170 is -15°C.

Explanation:

1. Standard Lapse Rate: The standard temperature lapse rate in the troposphere (below 11 km) is 6.5°C per 1000 meters.

2. Altitude Difference:
* Summit altitude: 5000 meters above MSL.
* Initial altitude: 1000 meters above MSL.
* Altitude difference = 5000 m – 1000 m = 4000 meters.

3. Temperature Change:
* Over 4000 meters, the temperature will decrease by (4000 m / 1000 m) × 6.5°C = 4 × 6.5°C = 26°C.

4. Temperature at the Summit:
* Temperature at 1000 meters = +20°C.
* Temperature decrease over 4000 meters = 26°C.
* Temperature at the summit = +20°C – 26°C = -6°C.

Explanation:
To find the ISA temperature at FL200:

ISA Temperature Formula: Starting at 15°C (sea-level temperature), reduce it by 2°C per 1000 feet for every 1000 feet of altitude.

At FL200 (20,000 ft):

ISA Temperature = 15°C – (2°C/1000 ft × 20,000 ft)

ISA Temperature = 15°C – 40°C = -25°C

Given the actual temperature at FL200 is -30°C:

ISA Deviation = Actual Temperature – ISA Temperature
ISA Deviation = -30°C – (-25°C) = -5°C

The negative deviation indicates that the actual temperature is 5°C colder than the ISA temperature.

Short Explanation:
The standard atmospheric lapse rate is 2°C per 1,000 feet (or approximately 6.5°C per 1,000 meters). Since the altitude increases by 2,000 meters (from 500m to 2500m), the temperature drops by:
2,000×6.5/1,000=13°𝐶
Thus, the temperature at the summit = 15°C – 13°C = 2°C.

Long Explanation:
The standard atmosphere assumes a temperature lapse rate of approximately 6.5°C per 1,000 meters in the troposphere. Given an initial temperature of +15°C at 500 meters above mean sea level, we need to determine the temperature at 2,500 meters.

Calculate the altitude difference:

2500m – 500m = 2000m (or 2 km)

Apply the standard lapse rate:

Temperature decrease = 6.5°C per 1000m × 2 = 13°C

Final temperature:

15°C – 13°C = 2°C

Thus, the correct answer is 2°C.

Explanation:
The tropopause, which marks the boundary between the troposphere and the stratosphere, has a height that varies with latitude. The sources consistently state that the tropopause is highest over the Equator and lowest over the poles. As you move from the Equator (southern part of the Northern Hemisphere’s perspective in this context) towards the North Pole (northern part), the height of the tropopause gradually decreases. For example, the tropopause is approximately 16 km (around 52,000 ft) over the Equator and about 8 km (around 26,000 ft) over the poles.

Short Notes:
– Tropopause height:
– Highest over the Equator (~16 km / 52,000 ft)
– Lowest over the Poles (~8 km / 26,000 ft)
– Variation with latitude (Northern Hemisphere): Decreases from south to north

Troposphere is generally unstable.

Explanation:
The troposphere is characterized by relatively low stability and frequent overturning of air. It is the layer where most weather occurs, and unstable air promotes the vertical motion necessary for weather development. While stable layers can exist, the troposphere as a whole is a dynamic and often unstable environment. The average lapse rate in the troposphere typically results in conditionally unstable conditions.

Short Notes:
– Contains almost all weather.
– Unstable air allows vertical motion.
– Average lapse rate leads to conditional instability.

ISA temp at 30000 feet is -45C.
OAT is 15 degree warmer = -30 C Ans.

The statement that applies to the tropopause is: It separates the troposphere from the stratosphere.

Short Notes:
* The tropopause is the boundary between the troposphere and the stratosphere.
* It marks where the temperature ceases to decrease with height.
* It is not defined as a strong temperature lapse rate itself, but as the location where the lapse rate changes.
* It is not defined as a temperature inversion (temperature increasing with height), although this often occurs in the stratosphere above it.

One of the characteristics of Earth’s atmosphere is that it is a poor conductor of heat and electricity.

Here’s why: Air molecules are relatively far apart, especially in the higher layers of the atmosphere. This spacing makes it difficult for heat to transfer efficiently through conduction, which requires direct molecular contact. Similarly, air is a poor conductor of electricity because it lacks a high concentration of free electrons to carry an electrical current.

In relation to the total weight of the atmosphere, the weight of the
atmosphere between mean sea level and a height of 10km is
approximate 75%

Short Notes:

– Troposphere extends to an average height of 11 km.
– Troposphere contains over 75% of the mass of the total atmosphere.
– Since 10 km is within the troposphere and very close to its upper limit, the weight of the atmosphere below this altitude is approximately 75%.

The lapse rate is the rate at which temperature decreases with altitude.

In the standard atmosphere, the lapse rate is 6.5°C per 1,000 meters or 2°C per 1,000 feet.

It is a key factor in meteorology and aviation, influencing weather patterns and flight conditions.

Isothermal rate refers to a condition where temperature remains constant with altitude.

Instability rate is not a standard atmospheric term

Most of the atmospheric mass is contained in Troposphere.

Short Notes:
– The troposphere contains over 75% of the total atmospheric mass.
– The troposphere is the lowest layer of the atmosphere.
– Almost all weather occurs in the troposphere.

The boundary between the troposphere and the stratosphere is called the Tropopause.

Short Notes:
* The tropopause separates the troposphere from the stratosphere.
* It is the upper boundary of the troposphere.
* At the tropopause, the temperature ceases to decrease with height.
* It is a transition zone characterized by an abrupt change in temperature lapse rate.

Troposphere is generally unstable.

Explanation:
The troposphere is characterized by relatively low stability and frequent overturning of air. It is the layer where most weather occurs, and unstable air promotes the vertical motion necessary for weather development. While stable layers can exist, the troposphere as a whole is a dynamic and often unstable environment. The average lapse rate in the troposphere typically results in conditionally unstable conditions.

Short Notes:
– Contains almost all weather.
– Unstable air allows vertical motion.
– Average lapse rate leads to conditional instability.

The temperature in ISA at 17 km is -56.5°C.

– ISA temperature profile:
– Decreases 1.98°C per 1000 ft (6.5°C per km) from MSL to 11 km (36,090 ft).
– Constant at -56.5°C from 11 km to 20 km (65,617 ft).
– 17 km falls within the constant temperature layer of the ISA.

The tropopause is discontinuous at about 40° lat.

Short Notes:
– Breaks in the tropopause occur where significant temperature changes happen.
– These breaks are located at approximately 40° latitude and between 60° latitude.
– The discontinuity at 40° latitude is where warm air from the equator meets colder air from higher latitudes.
– Another abrupt change or “fold” occurs around 60° latitude.

The height of the tropopause at the equator is typically 16-18 km.

This is due to the strong convective activity and rising air currents caused by intense solar heating in the equatorial region. This upward movement of air expands the troposphere, resulting in a higher tropopause compared to the poles.

By volume, the proportion of CO2 in the atmosphere is approximately 0.03%.

While CO2 is a crucial greenhouse gas, it’s a trace gas, meaning it’s present in relatively small amounts compared to nitrogen (78%) and oxygen (21%).

The height of the tropopause at the poles is typically 8-10 km.

At the poles, the troposphere is thinner due to less solar heating and weaker convection. This results in a lower tropopause compared to the equator.

Deviation = actual – ISA = 1002.25 – 1013.25 = -11 hPa

FAA recommends auxiliary oxygen above 10,000 feet.
This is to prevent hypoxia (oxygen deficiency).
Effects of hypoxia include fatigue, impaired judgment, and unconsciousness.

Short Explanation:
The correct answer is “Varies with Latitude.” This is because the tropopause is higher at the equator (around 16-18 km) and lower at the poles (8-10 km) due to differences in surface heating and atmospheric circulation.

Long Explanation:
The question asks about the height of the tropopause. The correct answer is that it varies with latitude. The tropopause is the boundary between the troposphere and stratosphere, and its height depends on atmospheric conditions. Near the equator, strong solar heating causes more convection, lifting the tropopause to around 16-18 km. Near the poles, cooler temperatures and weaker convection result in a lower tropopause, around 8-10 km. This variation influences weather patterns, jet streams, and turbulence, making it a critical factor in aviation and meteorology.

he expected temperature at the tropopause is approximately -50°C.

Explanation:
Altitude Difference: From FL260 (26,000 ft) to the tropopause (36,000 ft), the altitude difference is 10,000 ft.

Temperature Change: Using the standard lapse rate of 2°C per 1000 ft:

10,000 ft / 1000 ft/increment = 10 increments

Temperature change = 10 increments × 2°C/increment = 20°C decrease.

Expected Temperature: Starting from -30°C at FL260, we subtract the 20°C decrease:

-30°C – 20°C = -50°C.

The expected temperature at FL240 would be -38°C.

Explanation:
We can use the standard temperature lapse rate in the troposphere, which is approximately 2°C per 1000 feet.

1. Altitude Difference: The altitude difference between FL240 (24,000 ft) and FL150 (15,000 ft) is 24,000 ft – 15,000 ft = 9,000 ft.
2. Temperature Change: For a lapse rate of 2°C per 1000 ft, over 9,000 ft the temperature will decrease by (9,000 ft / 1,000 ft/increment) * 2°C/increment = 18°C.
3. Expected Temperature: Subtract this temperature decrease from the temperature at FL150: -20°C – 18°C = -38°C.

Stratosphere extends from Tropopause to 50 km.

Short Notes:
– Stratosphere: Layer above the tropopause.
– Upper limit: Approximately 50 km altitude.
– Boundary with mesosphere: Stratopause at around 50 km.

To determine the ISA deviation, we need to calculate the ISA temperature at 19 km and compare it with the actual temperature.

Here’s the breakdown:

ISA Temperature at Sea Level: The ISA temperature at mean sea level is 15°C.

ISA Lapse Rate: The standard lapse rate in the troposphere is 6.5°C per kilometer.

Tropopause Height: The tropopause is around 11 km, and above it, the temperature remains constant at -56.5°C up to approximately 20km.

ISA Temperature Calculation:

Up to 11 km: Temperature decreases at 6.5°C/km.
Above 11 km: Temperature is constant at -56.5°C.
Since 19 km is above the tropopause, the ISA temperature at 19 km is -56.5°C.

ISA Deviation Calculation:

ISA Deviation = Actual Temperature – ISA Temperature
ISA Deviation = -60°C – (-56.5°C) = -60°C + 56.5°C = -3.5°C
Therefore, the temperature differs from ISA by -3.5°C

First, find the altitude difference in feet:

FL300 is approximately 30,000 feet, and FL220 is approximately 22,000 feet.

Difference = 30,000 ft – 22,000 ft = 8,000 ft

Next, use the standard lapse rate, which is about 2°C per 1000 feet:

Temperature change = 8,000 ft * (2°C / 1000 ft) = 16°C

Since we are descending, the temperature will increase:

Temperature at FL220 = -40°C + 16°C = -24°C

Therefore, the expected temperature at FL220 is -24°C.

The International Standard Atmosphere (ISA) assumes that the temperature will reduce at a rate of 1.98°C per 1000 feet up to 36,090 feet, after which it remains constant to 65,617 feet.

In the ISA model, the temperature decreases linearly with altitude in the troposphere at a lapse rate of 1.98°C per 1000 feet (or 6.5°C per kilometer). This continues up to the tropopause, which is at 36,090 feet. Above the tropopause, in the lower stratosphere, the temperature is assumed to remain constant up to 65,617 feet.

The stratosphere extends from the tropopause (the boundary between the troposphere and stratosphere) to about 50 km (31 miles) in altitude. The “lower part” generally refers to the region just above the tropopause, roughly up to about 20 km (12 miles).

In this lower stratospheric region, temperature remains relatively constant with increasing altitude. This is a key characteristic that distinguishes it from the troposphere, where temperature generally decreases with height. The reason for this constant temperature profile in the lower stratosphere is that it’s below the primary influence of the ozone layer, which absorbs UV radiation and warms the upper stratosphere.

Long Explanation:
The question asks about the extent of the stratosphere in mid-latitudes. The correct answer is 11 to 50 km. The stratosphere begins at the tropopause, where temperature stops decreasing with altitude, and extends up to 50 km. This layer contains the ozone layer, which absorbs ultraviolet radiation, leading to a temperature increase with altitude. The stratosphere is also important for aviation, as commercial jets often fly near its lower boundary to avoid weather disturbances in the troposphere. Understanding the structure of the stratosphere helps in studying climate patterns and atmospheric circulation.

The tropical tropopause is characterized by very cold temperatures. The tropopause temperature is typically -80°C over the equator, making -75°C the closest and most likely option.

At 50° latitude, the average height of the tropopause is approximately 11 km (36,090 ft).

### Key Points:
– The tropopause at 50°N latitude is generally around 11 km.
– It typically ranges between 35,000 ft and 38,000 ft depending on the season.
– The International Standard Atmosphere (ISA) defines the tropopause at 11 km.

This height can vary slightly due to seasonal changes but remains close to the 11 km mark.

The reversal of temperature in the atmosphere at 8 km is because Lapse rate reverses at poles and becomes negative.

Short Notes:

* At approximately 8 km, you are likely near the tropopause, especially over the poles.
* At the tropopause, the temperature stops decreasing with height (lapse rate becomes zero). In the stratosphere (above the tropopause), temperature remains constant or increases with height (lapse rate becomes zero or negative – a temperature inversion).

In a standard atmosphere, the temperature decreases at a rate of approximately 6.5°C per 1000 meters.

First, find the temperature difference between 6000 meters and 3000 meters:

Difference in altitude = 6000 m – 3000 m = 3000 m

Next, calculate the temperature change:

Temperature change = 3000 m * (6.5°C / 1000 m) = 19.5°C

Since we are going down in altitude, the temperature will increase.

Temperature at 3000 m = -50°C + 19.5°C = -30.5°C

Therefore, the temperature at the summit of the mountain 3000 meters above mean sea level is -30.5°C.

The term “troposphere” originates from the Greek word “tropein”, which means “to turn” or “to change”. This refers to the constant mixing and changing of air within this lowest layer of the atmosphere due to rising and descending air currents.

Short Notes:
– Tropos derived from Greek “tropein”.
– “Tropein” means “to turn” or “to change”.
– Reflects the turbulent and mixing nature of the troposphere.

The most important constituent in the atmosphere from a weather standpoint is Water vapour.

Short Notes:
* Water vapour is the only substance in the atmosphere that exists naturally as a gas, liquid, and solid (ice).
* It is essential for the formation of clouds and precipitation (rain, snow, etc.).
* Changes in water vapour content lead to humidity, which is a key weather element.
* The condensation of water vapour releases latent heat, a significant source of atmospheric energy, especially for storms.
* Water vapour is a potent greenhouse gas, playing a crucial role in the Earth’s energy balance.
* Aviation weather reports include information about water vapour through dew point and temperature-dew point spread, which are important for anticipating fog and frost.

The correct answer is approximately 50%. This is because the density of air decreases rapidly with altitude. Therefore, about half of the atmosphere’s mass is concentrated in the lower 5500 meters.

1. Temperature Difference:
* Actual temperature at FL140 is -8°C.
* Freezing point is 0°C.
* Temperature difference = -8°C – 0°C = -8°C (meaning the air needs to warm up by 8°C to reach freezing).

2. Altitude Change to Reach Freezing Level (from FL140):
* Using the ISA lapse rate of approximately 2°C per 1000 ft, an 8°C change in temperature corresponds to an altitude change of (8°C / 2°C per 1000 ft) = 4000 ft.
* Since the temperature at FL140 is -8°C (warmer than freezing), the freezing level is below FL140.
* Freezing level ≈ 14,000 ft – 4000 ft = 10,000 ft, which is FL100.

The approximate ratio of O2 to N2 in the atmosphere by weight is 1:3.

While the volumetric ratio of nitrogen to oxygen is about 4:1, oxygen molecules are slightly heavier than nitrogen molecules. This difference in molecular weight shifts the ratio to approximately 3:1 when considering the mass proportions of these gases in the atmosphere.

16 km

Explanation:
The average height of the tropopause over the Equator is approximately range of 16-18 km. In feet, this is around 52,000 feet. While there can be variations, 16 km is the closest average value presented in the sources for the tropopause height at the Equator.

Short Notes:
– Average height over Equator: ~16 km
– Range: 16-18 km
– Equivalent in feet: ~52,000 ft

The decrease in temperature with height below 11 km in the International Standard Atmosphere is 0.65°/100 m.

Short Notes:
* ISA temperature lapse rate below 11 km is 0.65°C per 100 meters.
* This is equivalent to 1.98°C per 1000 feet. for some practical calculations, a rounded value of 2°C per 1000 ft is used.
* This lapse rate applies from Mean Sea Level up to 11 km (36,090 ft).

The knowledge of the height of the tropopause is important for a pilot because weather is mainly confined up to this level.

The tropopause acts as a lid on the troposphere, where most weather phenomena occur. Pilots need to know its height for flight planning, altitude selection, and understanding weather patterns.

Half of the atmosphere’s air mass is contained below approximately 18,000 ft. The closest option provided is 20,000 ft.

Short Notes:
– 50% of atmosphere’s molecules (and thus mass) are below ~18,000 ft.
– Troposphere (up to ~36,000 ft) contains over 75% of the atmosphere’s mass.
– Air density decreases with altitude.

CO2 and H2O are also called Greenhouse Gases.

Explanation:
Think of our atmosphere like a greenhouse for the entire planet. Certain gases act like the glass in that greenhouse, allowing sunlight (shortwave radiation) to pass through and warm the surface. However, these same gases are less permeable to the heat emitted by the Earth (longwave or infrared radiation), trapping some of it and keeping our planet warmer than it would otherwise be. Water vapor (H2O) and carbon dioxide (CO2) are two of the most significant gases responsible for this “greenhouse effect”. They play a crucial role in regulating Earth’s temperature, much like how you manage the temperature inside the aircraft.

Short Notes:
– CO2 and H2O: Key components of the atmosphere. Allow sunlight in, absorb outgoing heat.
– Significance: Regulate Earth’s temperature.

Higher the surface temperature, the higher would be the tropopause.

The tropopause is the boundary between the troposphere and the stratosphere. As the surface temperature increases, the troposphere expands, leading to a higher tropopause.

find the average lapse rate, we need to calculate the change in temperature over a change in altitude.

Change in Altitude: FL240 – FL090 = 150 (which represents 150,000 ft)
Change in Temperature: -30°C – (-45°C) = 15°C
Lapse Rate = (Change in Temperature) / (Change in Altitude)

Lapse Rate = 15°C / 150,000 ft = 1°C / 10,000 ft

Since the answer choices are in terms of 1000 ft, the correct answer is 1 degree C per 1000 ft.

*Noctilucent clouds occur in the Mesosphere.*

Explanation:
Noctilucent clouds are observed at very high altitudes, specifically in the upper mesosphere, at altitudes above 75 km (46 mi). According to the sources, these clouds are found at heights probably around 75 to 90 kilometers. The mesosphere is the atmospheric layer where such altitudes are reached; it extends from the stratopause to approximately 80 to 90 km above the Earth’s surface. Therefore, noctilucent clouds occur in the mesosphere.

Short Notes:
– Noctilucent clouds location: Upper Mesosphere
– Altitude: 75-90 km
– Mesosphere altitude: Extends to approximately 80-90 km

Above 8 km the lower temperatures are over Equator.

Short Notes:
* The tropopause is higher over the Equator (approximately 16 km or 52,000 ft) and lower over the Poles (approximately 8 km or 26,000 ft).
* The temperature at the tropopause is typically colder over the Equator (-80°C) than over the Poles (-50°C).
* Since 8 km is closer to the tropopause at the poles and further from the generally colder tropical tropopause, the temperatures above 8 km are lower over the Equator.

Homosphere (surface to ~80 km): Uniform gas composition, above ~70-80 km (heterosphere): Composition varies with height due to less mixing and gravity

Nacreous clouds occur in the Upper Stratosphere.

Short Notes:
* Nacreous clouds form in the stratosphere.
* They are found at altitudes above 30 km (100,000 ft).
* They are also called mother-of-pearl clouds.
* They are best viewed in polar latitudes during winter.

In ICAO ISA the atmosphere is assumed to be isothermal 11 to 20 km.

Short Notes:
* ISA temperature decreases with height up to 11 km (36,090 ft).
* From 11 km to 20 km (65,617 ft), the ISA temperature remains constant at -56.5°C.
* This constant temperature layer is within the lower stratosphere.
* Above 20 km, the ISA temperature starts to increase with height.

Explanation:

1. Altitude Difference:
* FL300 = 30,000 ft
* FL180 = 18,000 ft
* Altitude difference = 30,000 ft – 18,000 ft = 12,000 ft

2. Temperature Difference:
* Temperature at FL300 = -45°C
* Temperature at FL180 = -15°C
* Temperature difference = -15°C – (-45°C) = 30°C

3. Average Lapse Rate Calculation:
* Average Lapse Rate = (Temperature Difference) / (Altitude Difference)
* Average Lapse Rate = 30°C / 12,000 ft = 0.0025°C per foot
* To express in °C per 1000 ft: 0.0025°C/ft * 1000 ft = 2.5°C per 1000 ft

The lowest layer of the atmosphere is Troposphere.

Short Notes:

* The troposphere extends from the Earth’s surface upwards.
* It contains most of the weather.
* Temperature generally decreases with altitude in this layer.
* The tropopause is the boundary above the troposphere.
* The stratosphere is above the tropopause.

The lowest temperature in the International Standard Atmosphere (ISA) between mean sea level and 20 km is -56.5°C.

This minimum temperature is reached at the tropopause, which is around 11 km. In the ISA model, temperature decreases with altitude in the troposphere at a rate of 6.5°C per kilometer. At the tropopause, this decrease stops, and the temperature remains constant in the lower stratosphere. So, the -56.5°C value represents that stable temperature in the lower stratosphere, following the temperature decrease in the troposphere.

In the International Standard Atmosphere (ISA), the mean sea level temperature is 15°C. This standard is used for aviation, meteorology, and engineering calculations.

Other ISA Parameters:
Sea-level Pressure: 1013.25 hPa (hectopascals) or 1013.25 mb.

Sea-level Density: 1.225 kg/m³.

Lapse Rate: In the troposphere, the temperature decreases by 2°C per 1000 feet.

Tropopause Altitude: Approx. 36,000 feet (11 km) where temperature becomes constant.

Tropopause Temperature: Typically -56.5°C.

ISA provides a reference for atmospheric conditions, helping with aircraft performance, navigation, and weather predictions.