L1 Properties of the Atmosphere

Flashcards about Meteorology Lesson 1: Properties of the Atmosphere Met 01

What should the meteorological section of the PPL course equip you to do?

To interpret weather information and make safe planning decisions based on it; and assess the actual weather occurring, and make sound decisions based on what you see.

Dealing with bad weather is all about what?

Pilot judgement

The root cause of 'weather' accidents is nearly always what?

Lack of judgement

What is the approximate proportion of Nitrogen (N2) in a dry atmosphere?

78%

What is the approximate proportion of Oxygen (O2) in a dry atmosphere?

21%

What is the approximate proportion of Carbon Dioxide (CO2), Ozone (03), and other gases in a dry atmosphere?

1%

How does the amount of water vapor in the atmosphere vary?

Close to zero in the cold, dry polar regions to a maximum of around 4% in the hot and humid parts of the world adjacent to tropical seas.

What relatively small amounts of gases have the greatest influence over the weather?

Water Vapour (H2O), Carbon Dioxide (CO2), and Ozone (03)

Which layer of the atmosphere is of most interest to the light-aircraft pilot?

The troposphere

What region marks the upper boundary of the troposphere?

The tropopause

What 'weather' phenomena are primarily found in the troposphere?

Clouds, fog, mist, rain, snow etc.

How does the height of the tropopause vary seasonally?

It is higher in summer than in winter.

Where is the troposphere most shallow and deepest?

On average, the troposphere is most shallow over the poles and deepest over the equator.

What layer lies above the tropopause?

The stratosphere

Apart from certain types of what, there is less in the stratosphere to interest pilots?

Wind

What are the three main properties of a gas or mixture of gases like the atmosphere?

Temperature, pressure, and density.

What is the ICAO standard unit of temperature?

Degrees Celsius (°C)

What term is defined as the pressure exerted by the weight of the atmosphere?

Atmospheric pressure

What is the ICAO unit for pressure?

Hectopascal (hPa)

What unit do the UK Met office and other weather forecasting agencies often use as a measure of pressure?

Millibars (Mb)

What does Boyle's law state about the relationship between pressure and volume of a gas?

A gas's pressure and volume are inversely proportional.

In what units is air density measured in the context of the atmosphere?

Grams per cubic metre (g/m3)

How does the density of dry air compare to moist air?

The density of dry air is greater than moist air.

Describe the relationship between air density, pressure, and temperature.

Air density is directly proportional to pressure and indirectly proportional to temperature.

What is the vertical movement in the atmosphere called?

Convection

How does temperature affect air movement (rising or sinking)?

Air which is warmer than its surroundings will be less dense and so will rise, whilst air that is colder than its surroundings will sink.

What force holds most of the air molecules close to the surface of the Earth?

Gravity

How does air pressure change with increasing altitude?

The further away from the surface of the Earth, the lower the air pressure.

Under normal circumstances, how does temperature vary throughout the atmosphere?

Temperature decreases with height.

What is the approximate rate of temperature change with altitude?

About 2°C for every 1000 ft of altitude change.

What is the rate of temperature change through the atmosphere known as?

The lapse rate

What is the lapse rate in the stratosphere?

There is no lapse rate in the stratosphere. The temperature is assumed to remain constant regardless of altitude.

Why does the density of the atmosphere decrease with altitude, even though temperature also decreases?

The change in pressure has a more marked effect on density than the change in temperature.

How do you convert °C to °F?

Divide by 5, multiply by 9 and add 32.

How do you convert °F to °C?

Subtract 32; divide by 9, multiply by 5.

Who needs a constant calibration to work to?

Those who need a constant calibration to work to - for example instrument manufacturers, aircraft designers and so on.

What is the 'International Standard Atmosphere' (ISA)?

An 'average' set of atmospheric conditions.

In an ISA atmosphere, what is the mean altitude of the Tropopause?

11 km or 35 000 ft

Given an ISA sea-level air temperature of what and a lapse rate of 1.98°C/1000 ft, the ISA temperature at any altitude up to 36 090 ft can be calculated?

+15 °C

What are the basic parameters of the ISA at sea level?

Temperature: +15°C; Pressure: 1013-25 mb/hPa (29.92 inHg or 760 mmHg); Temperature Lapse Rate: 1.98°C/1000 ft; Density: 1-225 kg / cubic-metre

What is the ISA's temperature lapse rate?

1.98°C/1000 ft Or in SI units 0.66°C / 100 m.

What temperature does the ISA remain constant at above 36 090 ft?

At a constant -56.5°C.

What is Outside Air Temperature or OAT?

The actual air temperature.

How does the difference between ISA conditions and the ambient (actual) conditions affect aircraft performance?

It can have a marked effect on aircraft performance and the accuracy of aircraft instruments.

What is the ISA deviation?

The difference between the calculated ISA value for temperature at a specific height and the actual OAT.

What happens to widespread descending air?

Widespread descending air will warm up as it descends, this may trap cooler denser air below.

When warm air and cold air mix we can find ourselves in a situation where as we climb we may enter a layer of the atmosphere where the temperature remains constant, what would this be?

An Isothermal layer. the temperature remains constant.

What is it called when you enter a layer where the temperature rises as you climb?

A temperature Inversion. The temperature rises as you climb.

What should you appreciate to treat weather forecasts with a reasonable degree of caution?

The unpredictability of weather systems and their complex interactions.

What are the primary gases that make up the Earth's atmosphere?

Nitrogen, Oxygen, Carbon Dioxide, Ozone, and Water Vapor

Why is water vapor's variability important in weather patterns?

The amount can vary significantly based on geographic location and temperature.

How does the tropopause affect weather phenomena?

It acts as a lid, keeping most water vapor and weather phenomena contained within the troposphere.

How do temperature, pressure, and density relate to each other?

The three main properties are interconnected; a change in one can affect the others.

How is the relationship between pressure and volume as described by Boyle's Law important for understanding air behavior?

It is inversely proportional. When temperature is constant, an increase in volume leads to a decrease in pressure, and vice versa.

How does air density change with altitude, and why is this relevant to aviation?

The density of the air decreases, impacting aircraft performance.

What is the definition of 'lapse rate'?

The rate at which temperature decreases with increasing altitude in the troposphere.

How does the temperature profile of the stratosphere differ from that of the troposphere?

There is no significant temperature change in the stratosphere.

Why is the International Standard Atmosphere (ISA) necessary?

It provides a baseline for calibrating instruments, designing aircraft, and other applications.

Why is understanding ISA deviations important for pilots?

ISA conditions are rarely perfectly met in the real atmosphere.

What is an isothermal layer?

A layer of the atmosphere in which temperature remains constant as altitude increases.

What is temperature inversion?

A layer of the atmosphere in which temperature increases with altitude.

What methods can pilots use to avoid mental math to more accurately convert temperature between Celsius and Fahrenheit?

Using resources such as conversion tables or flight computers.

Air density is directly proportional to what?

Pressure.

Air density is indirectly proportional to what?

Temperature.

True or false, there is no lapse rate in the stratosphere?

True, this is because the temperature is assumed to remain constant regardless of altitude.

True or false, the weather is a powerful and ruthless force when it turns against you and inviting the inevitable conclusion to a one-sided contest.

True, nature always wins.

Why do words like 'tend', 'may', 'can' and 'often' appear much more in meteorology than in other subjects?

It is difficult to make definitive statements about day-to-day weather.

What does a sound understanding of meteorological principles do?

It makes the rest of the course that much easier.

Is weather entirely predictable?

No.

Give an example of interactions between many elements.

The slight shift of an ocean current re-routing a major depression or an isolated factor triggering cloud and rain many miles downwind.

What is 78% Nitrogen, 21% Oxygen, and 1% CO2, Ozone, and other gases an example of?

The approximate proportions of gases in a dry atmosphere.

What is the scientific symbol for water vapour?

H2O

What is the scientific symbol for carbon dioxide?

CO2

What is the scientific symbol for ozone?

O3

What area contains virtually all the water in the atmosphere?

The troposphere.

Where can the top of a thunderstorm push?

It can push upwards through the tropopause.

Above what is the stratosphere?

The tropopause.

Most of the water vapour - and so virtually all weather - is in the troposphere thanks to the tropopause acting as a lid, which means there is less here to interest pilots. Where does this apply to?

The stratosphere

What is a measure of the degree of heat present?

Temperature.

What is the resulting force, defined as the pressure exerted by the weight of the atmosphere called?

Atmospheric pressure.

What is density?

The amount of matter in a given volume.

At a constant temperature, if the pressure reduces what happens to the density?

The density also reduces.

At constant pressure, if the temperature of the air is higher what happens to the density?

It is less dense.

Air which is warmer than its surroundings will be what?

It is less dense and so will rise.

Air that is colder than its surroundings will do what?

Will sink.

What is the individual molecular forces resulting in?

Atmospheric pressure.

Given there are more molecules at the surface of the Earth there will also be what?

There will also be a higher air pressure at the surface of the Earth.

The further away from the surface of the Earth the what?

The lower the air pressure.

How does the temperature change according to altitude?

The temperature change is about 2°C for every 1000 ft of altitude change.

Why does temperature decrease with height?

The troposphere is heated by the earth from below.

Other things being equal, the density of a gas reduces as its pressure is reduced. However, its density increases as temperature is reduced. What is this?

It is one expression of Boyle's Law.

Throughout this book temperature is referred to in terms of degrees what, which is the most commonly used unit in aviation?

Celsius.

To overcome the problem of the atmosphere constantly changing at any one location, what has been established?

A 'average' set of atmospheric conditions.

What does the text refer to on page 13?

Variations for the ISA and Aircraft Performance.

OAT can also be a limitation in a flight manual e.g. "Flight in what not permitted"?

Conditions beyond ISA +30°C.

If the same aircraft is at Denver in the USA, (elevation 5600 ft) when the temperature is +25°C, its take-off distance required is likely to be around 1100 m - how much more is this?

Almost double!

Increased altitude usually means what?

Reduced density, which reduces aircraft performance.

Note: distance above the earth's surface may be given in 'height', 'altitude' or flight level (FL) in exam questions. For the purposes of this type of question they should be considered how?

They should be considered the same, converted to 1000's of feet if necessary and then the 2°C per thousand feet approximate lapse rate applied.

What will warm up as it descends, this may trap cooler denser air below?

Widespread descending air.

The layer closest to the earth of most interest to the light-aircraft pilot?

The troposphere.