050 01 00 00 THE ATMOSPHERE

65,000 ft or 20 km.

From the surface to 11km or 36 090 ft (average in the mid-latitudes) the temperature reduces by 1.98°C per 1000 ft, this is the troposphere. From there temperature remains largely constant at -56.5°C until you hit the stratopause at 65 000 ft or 20km

At the surface up to 36 090ft is the troposphere, where, temperature reduces with height, this is where most of the weather is. About 75% of the mass of air lives here. The upper limit is where the temperature lapse rate is no longer roughly 1.98°C per 1000 ft or 0.65°C per km.

This upper limit is called the tropopause.

The isothermal layer ends at roughly FL650

Next is the stratosphere where the temperature begins to increase with height after an initial isothermal part. The top is warmer than the bottom, the stratosphere is essential an inversion. This is because O₃ is present which absorbs the sun’s shortwave UV light.

The troposphere contains most of the weather and water vapour. It is characterised be a fall in temperature with height.

The earth heats this layer with long wave re-radiation.

75% by mass of the air sits here.

The tropopause marks the end of the troposphere and where temperature no longer decreases with height. This air is stable, vertical movement is restricted. Its height varies with season, latitude and weather.

78% Nitrogen

21% Oxygen

1% other gasses, carbon dioxide, argon etc.

Due differential solar insolation, the height of the tropopause varies.

1 km is roughly 3,300 ft

Polar tropopause: 8 to 10 km or FL260 to FL310

Mid latitude tropopause: 11 km FL360

Tropical tropopause: 16 to 18 km or FL520 to FL590

11 km or FL

The breaks in the tropopause are due to large temperature differences at the surface (twice at 40° to 60° latitude) , this causes the jet streams to exist. Air masses keep their tropopause as the warmer the air, the higher the tropopause.

The height can vary by a few thousand feet, there is not much detail on how pressure affects this.

The stratosphere marks the point where the temperature is isothermal to FL 650 then rises due to Ozone absorbing some of the high energy, shortwave UV radiation from the sun. This LO only asks about the isothermal bit.. -56.5°C. This is a stable layer like the tropopause.

Jet liners can cruise in the stratosphere and it is a good place to be because of the lack of weather. It does however contain Ozone which is not good for the flesh inside the jetliner. Filters are needed to be here.

Is the degree of heat present and is really a description of the energy present in a molecule.

Kelvin is absolute zero, where all molecular movement ceases.

Celsius, water freezes at 0 and boils at 100

Fahrenheit, water freezes at 32o F and boils at 212o F

0K = 273.15°C

To convert F to C, subtract 32 and multiply by 5/9

T convert C to F, multiply by 9/5 and add 32

Already covered but temperature decreases by 1.98°C per 1000 ft until the tropopause where it is isothermal up to FL 650.

The lower atmosphere is heated by reradiating from the Earth, so further away gets heated less… The pressure drop with height will also play a part.

What is the temperature (ISA) deviation at 8,500 ft if the actual temperature is +5° C?

ISA temperature at 8,500 ft = ISA temperature at sea level – (ELR x height (in 1,000) ft)

= 15–(2×8.5)
= 15-17
= -2°C

Actual temperature at 8,500 ft =+5° C

The temperature deviation = The difference between ISA and actual temperature is 7°

This is written as ISA +7 because the actual temperature is warmer than ISA

A slightly odd LO. I think the general answer to this is quite simple. If you put a heater in a cold room it will warm the room. Similarly if you open the window on a cold night, it will get cooled.

It could be referring to specific heat capacity of various surfaces. ie, water and

These processes are described below.

As specific radiation is described below the dictionary definition is: ‘The emission of energy as electromagnetic waves or as moving subatomic particles”. Very useful..!

The solar radiation that reaches the Earth is high energy, short wave radiation. A process called insolation. The intensity of this depends on the angle of the area concerned with the sun – the angle of incidence. Basically at a large angle, i.e when the sun’s rays are at 90° to the surface, lots of energy is concentrated on a small area. Conversely at a small angle, the same energy is spread over a larger area.

The atmosphere is quite transparent to the direct shortwave radiation from the sun, half of it goes straight through to heat the Earth. The other half is absorbed, scattered re-radiated or reflected back out to space.

Some radiation is absorbed by gases (mainly oxygen and ozone) in the high atmosphere. Some is absorbed by water vapour and clouds in the lower atmosphere. Clouds will also reflect radiation, possibly as much as 70%.

This is the re-radiation of long waves from the Earth having been received as short wave insolation directly from the sun. This is how the atmosphere is heated and also why temperature decreases with height.

It is readily absorbed by the atmosphere especially by clouds, water vapour and carbon dioxide than solar radiation due to its longer wavelength. The absorption of heat by the atmosphere from the Earth is the main heat exchange mechanism that causes weather.

Any terrestrial radiation not absorbed or reflected by the atmosphere escapes back into space.

Clouds play an important role in this process; by reflection they cut off a substantial proportion of incoming radiation and by absorption and re-radiation they reduce the loss of outgoing radiation.

In this context it is heating by direct contact. Terrestrial radiation will heat a thin layer of air over the surface (air is a poor conductor). If this air is subsequently moved, it will take the heat with it.

As above, but also if this air is mixed with other layers of the atmosphere, conduction can again happen between these two layers. Conduction and the poor conduction of air causes low level inversions.

Because relatively warmer air is less dense it is lighter. It will therefore rise relative to its surrounding cooler air. It also occurs in water by the way.

Because of differential local heating or wide scale heating convection occurs. For example, a dark road has a lower specific heat capacity, it takes less energy to heat it up, making it hotter than its surroundings and therefore can trigger convection. This is also true of water next to land.

Advection is the transfer of heat by flow of a liquid or air in our case… So when the wind blows, it can become warmer or colder depending on where the wind has come from.

When the wind blows, i.e a pressure difference…

Turbulence is the chaotic mixing of airflows, the mixing transfers heat by conduction as well as advection.

Latent heat is heat released or absorbed without change of temperature.

Evaporation is the process of a liquid (e.g. water) changing into a gas (water vapour). For this to happen heat energy is required, known as latent heat. The significance of latent heat is that it does not change the temperature of the substance but does change the state of the substance; i.e. water to water vapour. Comparing the same amount of heat supplied to equal areas of land and water, evaporation of the water will use much of the heat without raising its temperature.

Within the troposphere:

The dry (<100% humidity) adiabatic lapse rate is 3°C/1 000 ft or 1°C/100 m

The saturated adiabatic lapse rate is 1.8°C/1 000 ft or 0.6°C/100 m

The ISA or theoretical environmental adiabatic lapse rate ELR is 1.98°C/1 000 ft or 0.65°C/100 m. This however is location and condition specific and will never be this exact figure, for example the presence of inversions proves this. A glance at a tephigram or skew-t diagrams shows this.

Where temperature increases with height.

Surface Inversion

There are two ways of forming; nocturnal or radiation inversion.

A surface inversion is caused by radiation cooling of the ground. As the ground radiates heat to the atmosphere, the lowest layers immediately above the surface are cooled by conduction to the ground. Because air is a poor conductor the cooling is restricted to a shallow layer and a strong surface inversion can be formed which can be just a few tens of feet deep. The cooling can be quite intense with a rise in temperature of as much as 10° C. Surface inversions tend to form on clear nights with no surface wind and are most noticeable around sunrise. They can be a couple of thousand feet high depending on what you read..

The other way a ground inversion can occur is advection from the sea. As a warm air mass blows from the sea, the lower layers are cooled by the cooler ground.

Surface Turbulence Inversion

This type is really an extension of the surface inversion. The surface inversion requires calm conditions to form but if a light wind is introduced, the cool surface air is mixed with the warmer air aloft. The depth of the inversion increases to a few hundred feet (probably no more than 300 ft) and the temperature rise is reduced to as little as 1° C. This type of inversion is important because it is a necessary requirement for fog to form. An increase in wind speed to over 5 kt will cause the inversion to dissipate.

Upper Air Turbulence Inversion or friction layer inversion

This type occurs at the top of the layer of air containing turbulence and a weak temperature lapse rate. Air that is lifted by turbulence cools at the Dry Adiabatic Lapse Rate (DALR) and air caused to descend by the turbulence will warm at the DALR. The combined effect of these movements is to increase the ELR through the layer. Assuming that the temperature above and below the turbulence layer is not affected; a weak inversion will develop just above the top of the layer. This inversion can be visible with sufficient moisture in the air forming a layer of cloud just under the inversion and by dust particles that are trapped.

Subsidence Inversion

(areas of high pressure). The air in the top layers of the troposphere tends to subside more, with greater adiabatic warming due to compression, than air in the lower levels. The result is relatively warmer air overlying the lower layer. Typically subsidence inversions occur between 4,000 ft and 6,000 ft and are quite strong with up to a 15° C temperature rise. They are generally up to 500 ft deep and provide a lid to haze and smoke layers which causes a reduction in visibility during descents through them. Also, they tend to inhibit thermal development so that low level convective cloud has limited vertical development if the inversion is strong enough.

Frontal Inversion

A front is the boundary between two air masses with the most significant feature being the temperature difference between them.

The colder, more dense air will lie under the warmer less dense air mass. An inversion will exist along the boundary where the warm air overlies the cooler air. The strength of the inversion depends upon the width of the boundary zone and the physical temperature difference. The boundary of a cold front is usually quite sharp and may only be a few hundred feet deep.

Sea Breeze Inversion

A sea breeze inversion is very similar to a frontal inversion as it occurs at the boundary of a warm body of air and a cooler body; the sea breeze itself.

As the sea breeze is usually close to the surface, the inversion will also occur there, between 100 ft and 1,000 ft above the ground. The strength of the inversion will depend upon the temperature difference between the sea breeze and the warmer air ahead of it. The rising warm air will be cooled adiabatically so the temperature above the inversion might be slightly less than expected, but still could be about 10° C through a couple of hundred feet.

Valley inversions

At night cooler air fills the valleys (a katabatibc wind) causing warmer air to be displaced and the only way it can go is up! They can last a long time.

Tropopause Inversion

It is possible for an inversion to exist at the tropopause. If ozone is present immediately above the tropopause, because the gas absorbs UV radiation from the Sun and is warmed by it, there may be a rise in temperature forming a tropopause inversion. If one exists it may not be strong and might only result in a temperature rise of between 1° C and 5° C but it might extent through a depth of several thousand feet.

Pretty much covered above.

I suppose this is referring to the short wave insolation from the sun heating the surface and the simultaneous reradiating love wave heat which warms the atmosphere. When there is an imbalance of heating, i.e at night time, the Earth continues to re-radiate this long wave radiation but also cools down as it is not being topped up when the sun has gone to bed.

Clouds can reflect and/or absorb some incoming shortwave radiation which results in the land getting less short wave energy and is therefore cooler.

However, water vapour being a greenhouse gas and as clouds are essentially water, they serve as a blanket trapping the heat in by reflecting and also re-radiating terrestrial radiation.

Cloud cover basically reduces the diurnal temperature variation.

By day, wind will cause turbulent mixing of the warm air at the surface with cold air above, reducing the temperature. Wind will also reduce the time the air is in contact with the warm ground.

At night with a nocturnal inversion, wind will cause cold air to be turbulently mixed with warm air above, increasing the temperature.

Defined as force per unit area

Is…the static pressure of the atmosphere.

It has mass and therefore gravity acts upon it…

Because air is compressible there is a much greater proportion of the air in the lower levels…

hPa

inHG

Mercury: Atmospheric pressure pushes down on a bowel of mercury which then gets pushed up a tube that is evacuated.

Aneroid: Flexible, partially evacuated capsule, atmospheric pushes down moving a mechanically connected needle.

…are lines of equal pressure..

High – or anticyclones. Pressure decreases from the centre.

Low – or depressions. Pressure increases from the centre.

Trough – An extension of a low.

Ridge – An extension of a high.

Col – Between two highs and two lows.

Again, air has mass so gravity acts upon it.

Pressure reduced with height in a non-linear way – because as you ascend there is progressively less air pushing down.

Or the air pressure is proportional to the mass of air above it.

The rate of change of pressure reduces with increasing height

See table above.

• QFF is the barometric pressure at an observation point – reduced to MSL using the observed temperature assuming an isothermal layer from the point to MSL.

Actual pressure change depends on actual temperature, i.e not using ISA conditions. Temperature affects the pressure lapse rate. Higher in cold air, lower in warm air.

Above, not the use of isothermal layer i.e same temperature at the station.

Not set in aircraft.

The MSLP charts use QFF.

Brain twister:

Because of temperature pressure levels can be very different at height.

At the surface pressure levels always slope down towards the low pressure. (A defined pressure will be at a higher height AGL in a high pressure area and will therefore be at a lower height AGL in a low pressure area. Hence the slope downwards.

At height, because of temperature, there can be varying differences:

A warm high pressure to a cold low pressure: The difference in height becomes larger. The cold air on the cold side pushes that pressure level lower and the on the high side the same pressure level increases with the warm air.

So, cold air above pushes pressure level down, warm air above allows the pressure level to rise.

With a cold high and a warm low, the slope towards the low starts to slope up as cold air pushes the high pressure level down.

It’s all about relative pressure levels affected by temperature and air mass. Pressure or the weight of the air has a larger effect.

Temperature up, density down.

Temperature down, density up.

Pressure increase, density increase.

Decreases with altitude. The rate of density reduction increases with altitude and temperature affects this.

Aircraft and other stuff are calibrated to the same set of values to make things easier and consistent.

1013.25 hPa

+15ºC

0.65ºC/100m or 1.98ºC/1000′ up to 11km or 36,090′

Then a constant temperature of -56.5ºC to to FL650 or 20km

Height – distance above the ground – QFE.

Altitude – Indication above MSA – QNH.

Pressure Altitude – Altitude on 1013.25 hPa

Flight Level – Heights above 1013.25 hPa with the last two zeros removed and FL aded at the front.

Pressure level – Flying along an isobaric line, will result in actual altitude varying.

True altitude – Actual vertical distance above mean sea level.

True height – Actual vertical distance above ground at a point.

Elevation – Vertical distance of a point above MSL.

Standard – 1013.25

Transition altitude – The altitude at or below QNH. Above SPS

Transition layer – Between transition altitude and transition layer. Depth varies.

Transmission level – Lowest available flight level. Guarantees (500′) vertical separation from an aircraft flying at the highest assignable altitude on QNH. Set by ATSU and depends on pressure.

Terrain clearance – Terrain clearance is the required safe distance in the area concerned.

QFE, QNH, RPS/SPS

Above transition altitude is SPS.

Descending – set QNH, RPS or QFE before reaching the transition level.

Roughly 27′ or 30′ per millibar.

Increasing pressure setting increases indicated altitude.

Above.

This is just playing around working out the indicated altitude with various settings. Practice, practice, practice…..

So when flying along an isobaric line from a warm area to a cold area, you will gradually descend.

Any deviation from ISA conditions will cause an altimeter error.

Temperature affects the lapse rate, cold air squashes the atmosphere so the pressure changes more rapidly.

Conversely, warm air expands the atmosphere and pressure changes more gently.

So colder air means the altimeter over reads = danger.

Cold Air: True < Indicated

Warm airL True > Indicated

Refer to the ICAO cold Temperature Error Table.

High pressure to low pressure, true altitude reduces. High to low beware below and all that….

4% rule I think…

4% error for each 10°C deviation.

Or:

For every 1°C deviation from ISA, altimeter error is 4′ per 1000′.

1 – Take the given transition level, i.e. FL35. The lowest assignable flight level would be +500′ so FL40.

2 – Temperature correction.

3 – Pressure deviation and correction against SPS. 

Calculate IAS then apply te

Remark: The following rules should be considered for altimetry calculations:

a) All calculations are based on rounded pressure values to the nearest lower hPa.

b) The value for the barometric lapse rate between MSL and 700 hPa to be used is 30 ft/hPa as an acceptable approximation of the barometric lapse rate.

c) To determine the true altitude/height, the following rule of thumb, called the 4 %-rule, shall be used: the altitude/height changes by 4 % for each 10 °C temperature deviation from ISA. 4′ per 1000′ per degree difference.

d) If no further information is given, the deviation of the outside-air temperature from ISA is considered to be constantly the same given value in the whole layer.

e) The elevation of the aerodrome has to be taken into account. The temperature correction has to be considered for the layer between the ground and the position of the aircraft.

Accelerated airflow caused by undulating terrain or valleys causes a reduction in pressure, therefore the altimeter will over read.