Earth's Atmosphere: Composition and Layers

ATMOSPHERE

• Meteorology studies the atmosphere.
• A dry atmosphere primarily comprises nitrogen (N2) and oxygen (O2), totaling around 99%.
• Nitrogen and oxygen exist in a 4:1 volume ratio and a 3:1 weight ratio.
• Air is never completely dry, always containing varying amounts of water vapor, behaving similarly to a gas.
• The maximum water vapor content typically ranges from 3% to 4%.
• The atmosphere consists of multiple layers of air surrounding Earth.
• All weather phenomena occur within the atmosphere.

Composition by Volume and Weight

• Nitrogen (N2) accounts for 78% of the atmosphere by volume and 75% by weight.
• Oxygen (O2) makes up 21% of the volume and 25% of the weight.
• Argon constitutes 0.95% by both volume and weight.
• Inert gases contribute 0.93% by volume and 1.3% by weight.

Atmospheric Layers and the Troposphere

• The atmosphere can be divided into layers, with the troposphere being particularly significant due to its frequent weather events.
• The layer of Earth's atmosphere where temperature decreases with height is known as the troposphere, and this rate of temperature decrease is called the lapse rate.
• The troposphere is unstable and contains about one-fourth of the total atmospheric weight.
• The troposphere extends up to 8 km at the poles and 16 km at the Equator.

Tropopause

• The tropopause marks the boundary between the troposphere and stratosphere, which is characterized by temperature ceasing to fall.
• The location of the tropopause is not uniform and varies with latitude, season, prevailing temperature, and time of day.

Tropopause Height

• The average tropopause height is 36,000 feet or 11.12 km.
• Tropopause height is lower at the poles.
• The temperature at the tropopause is lower over the Equator compared to the poles.
• The height of the tropopause is roughly 16 km near the equator.
• The height of the tropopause is roughly 8 km near the poles.
• The tropopause height signifies the maximum height of clouds, presence of jet streams, clear air turbulence, and maximum wind speed.

Breaks and Folds

• Breaks in the tropopause are more prominent at 40° to 60° latitude and are where jet streams occur due to heavy temperature differences.
• The tropical tropopause ranges from the Equator to 35-40° latitude, is at 100 hpa level.
• The tropical tropopause sits over India at 15-16.5 km.
• The polar tropopause ranges from 90° to 45-60° latitude at 300 hpa level.
• The polar tropopause fronts over the southern end during the winter.
• The middle tropopause is between the polar and tropical tropopauses and sits over India at 11.5 km.
• The middle tropopause may be at 23°N over India and at the southern end of the Subtropical Jet during the winter.

Atmospheric Layers: Stratosphere

• The stratosphere spans from the tropopause up to 50 km.
• Temperature is steady up to 20 km and then increases with height.
• The stratopause marks the upper limit of the stratosphere and has a temperature around 0°C.
• An ozone concentration at about 25 km absorbs ultraviolet radiation, causing the increase in temperature in this layer.
• The stratosphere is stable, has low humidity, and experiences very little weather.
• Nacreous clouds reside between 20 to 30 km during winter.

Ozone Formation

• Solar radiation break down O2 molecules to form O3.

Mesosphere and Thermosphere

• The mesosphere extends from 50 to 85 km and decreases in temperature with height.
• The thermosphere begins above 85 km, and temperature increases with height due to ultraviolet radiation.

Exosphere and Ionosphere

• The exosphere sits above 700 km.
• The ionosphere exists above 60 km.

International Standard Atmosphere (ISA)

• A standard atmosphere describes temperature, pressure, and density variations with altitude.
• ISA is needed for calibrating aircraft instruments and for aircraft design and testing.

ISA Definition (ICAO)

• Mean sea level (MSL) temperature is +15° Celsius and MSL pressure is 1013.25 hpa/millibars or ​29.92 inches of mercury.
• MSL density is 1225 grams per cubic meter.
• The lapse rate is 1.98°C per 1000 ft or 6.5°C per km, up to 36,090 ft (11 km).
• A constant temperature of -56.5°C exists up to 65,617 ft (20 km).
• An increase of temperature of 0.3°C per 1000 ft or 1°C per km, up to 104,987 ft (32 km).
• Gravity is 980.665 newtons/cm².
• Air is dry.
• ISA Deviation = (actual temperature) - (ISA temperature)

Atmosphere Properties

• Earth's atmosphere varies in pressure, temperature, density, and humidity both vertically and horizontally.
• Earth's atmosphere is a poor conductor and is fluid.
• Earth's atmosphere supports life only at lower levels.

Atmospheric Pressure

• Atmospheric pressure is the force exerted on a unit area by the air; when air is at rest, it is static or barometric pressure, acting uniformly in all directions.
• In meteorology, only static pressure matters.
• Air is held to the Earth by gravitational attraction.
• Pressure decreases with height.
• Pressure is measured using an aneroid or mercuric barometer, in hectopascals (hPa) or millibars (mb).
• 1 hPa is equivalent to 1 mb, and 1013.25 hPa equals 1013.25 mb.
• Changes in air pressure cause ear discomfort or a "popping" sensation in aircraft and when traveling over significantly varying topography.

Vertical Variation of Pressure

• Pressure decreases with height at a decreasing rate such as sea level to 600m at 4%, up to 1.5km at 3%, up to 3 km 2.5%.
• The pressure reduces to half its sea level value at 6km.
• Pressure is negligible at 100km high which leads to a vacuum
• Pressure varies from an altitude of Mean Sea Level to 40,000 ft.

Temperature Effect on Pressure

• Cold air leads to a more rapid decrease in pressure with height because it is denser and falls slowly and gradually in warm air.
• Pressure is lower in cold air than in warm air at same heights.
• Pressure at a given height is higher over warm air than over cold air.

Isobars

• Indicates a rise from low to high pressure from cold to warm and a dip from high to low pressure in a warm to cold environment.

Semi-Diurnal Pressure Variation

• Maximum pressure occurs at 1000 and 2200 hours.
• Minimum pressure occurs at 0400 and 1600 hours.
• Variations are minimal at the poles and maximal at the equator.
• Afternoon high temperatures lead to low pressure.
• Low temperatures just after sunrise result in high pressure.
• Semi-diurnal variations have almost a 12-hour period.
• One side of the globe has high pressure; the opposite has low pressure.
• There are two maxima and two minima within 24 hours.

Pressure Measurements

• A mercury barometer accurately measures pressure.
• Aneroid barometers are used in altimeters but are not as precise as mercury barometers.
• Barographs record pressure continually.

Contours and Thickness

• A contour connects points of equal height, and thickness refers to the height interval between upper and lower levels.
• 700 hpa - 500 hpa = 40 gpm and 300 hpa - 200 hpa = 80 gpm are set intervals.

Pressure System Terms

• Lines joining places of equal pressure are called isobars.
• Lines joining places of equal pressure change are called isallobars.
• Surface lows tend to move toward the isallobaric low.
• An isallobaric high indicates weakening of a pressure system.

Types of Isobars

• A steep pressure gradient means closed isobars.
• A weak pressure gradient implies isobars are further apart.

Pressure Gradient

• It's the horizontal rate of pressure change perpendicular to isobars, directed from high to low pressure.
• Sharp pressure gradients signify closed isobars, and weak gradients indicate that isobars are wide apart.

Pressure Tendency

• Variation of Pr with time is called Pr Tendency, and determined by comparing current levels to 3 hour earlier measuremnts calculated from the the present pressure.
• India calculates using 24hrs.

Anticyclones or Highs

• They are areas of high pressure characterized by circular, concentric isobars.
• The highest pressure is at the center and are referred to as a high
• Isobars tend have wide spacing compared to depressions.
• Air moves out from the center of high pressure toward lower pressure zones, which translates to divergence
• Air descends to replace the diverging air, termed subsidence, and causes a relatively low pressure at height.
• Air circulates clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere, flowing out from the high.
• Winds are light.

Types of Anticyclones

• Blocking anticyclones either move slowly or stay stationary, obstructing movements and migrants of the cyclone.
• Cold anticyclones occur over the colder region behind the cyclone.

Ridges

• Ridges, extensions of high-pressure systems, look more like a longer "U" shape and referred to as wedges
• Ridges = An Elongated HIGH

Anticyclonic Weather (Summer)

• No clouds except edges in winter
• No precipitation
• Good moderate visibility with haze
• winds are light

Winter Anticyclonic Weather.

• (warm anticyclones)
• It consists of Extensive stratus with a low base and limited vertical extent alongside possible drizzle.
• Visibility is generally moderate to poor with mist and fog.
• Temperatures are relatively warm.
• Winds are light..

Depressions, Lows, or Cyclones

• They are low-pressure regions that cause air movement into the low.
• Surface winds are counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
• Bad weather and good visibility are associated with a low
• Wind strength depends on the depth of the depression and the proximity of isobars.

Wind Direction Terms

• Wind backs are where northerly wind changes to northwesterly winds.
• Low winds are in the Northern and Southern Hemispheres

Troughs

• Troughs are extensions of isobars from a depression shaped like a V, or an extended area of low pressure.
• Pressure is typically lower on the trough than on either side of it.
• Wind shifts and backs abruptly.
• low pressure = An Extended low
• Pr along the trough is lower than on either side.
• Wind direction abruptly changes and backs.

Cols

• It is region enclosed by two highs and two lows.
• It has almost uniform pressure
• Mix of high and low weather types
• Light and variable winds.
• It is an area of stagnation.

Altimetry Definitions

• MSL: Mean sea level reference.
• Height: Vertical distance from a specific reference point, usually the ground.
• Altitude: Vertical distance from mean sea level.
• Elevation: The vertical distance of a fixed point above mean sea level.

Atmospheric Altitude types

• Pressure Altitude: Altitude when the altimeter is set to 1013.2 hpa or 29.92 inches of mercury for flight level 80.
• Transition Altitude (TA): an altitude where aircraft switch over to local QNH.
• Transition Level (TL) :the lowest Flight Level where an Standard ONH 10132 hPa is used (hundreds of feet).
• Transition Layer: the airspace between Transition Altitude and Transition Level
• Flight Level: Constant pressure at or above TL with 500 ft intervals, set to 1013.25 hPa (e.g. FL50 =5,000 ft.

Alimeter Pressure settings

• QFE: Pressure at a aerodome, called ZERO SETTING.
• QFF: Station level pressure reduced to mean sea level under existing conditions, mainly used in on Synoptic charts & drawing isobars.
• QNH: Station level pressure reduced to mean sea level assuming ISA CONDITION.
• Regional QNH- : Lowest estimated weather (issued every hrs) valid for one hr, ensures adequate terrain clearance.
• QNE Subscale : 1013.25 hpa. Used for instrument take offs

Setting rules

• Flying to High to Low High over reads, High+Dangerous and Warm to cold is over reads
• Flying from low pressure to high pressure = the altimeter under reads. LOW - HIGH = LOW. Cold to warm = under read

Temperatures

Fahrenheit Conversion

• Can be achieved by (C * 9/5) + 32

Standard Isobaric Levels

|Measurement | 850 | 7 |500 | 400 | 300 | 200 |100 |0| |---------------------------- |-------|-------|-------|-------|-------|-------|-------| | Level (hPa)| |Pressure Altitude (Ft)| 5,000 | 10,000 | 18,000 | 24,000 | 30,000| 38,000| 53,000| |Flight Level| 50| 100| 180| 240| 300| 380 | 530 |

Measurement

• Is the degree of hotness or coldness of a body. The scales generally used to measure temperature is Centigrade, Fahrenheit and Kelvin

Heat transfer

• is a form of energy where the Molecules when contracting a substance then this causes it to slow down. There will also be a minimum temperature that goes to all substances

Instruments used for measurement

-A minimum thermometer where the upper temperatures use a thermometer to measure. Stevenson screens which have measurements of 4 ft( 1.24m) above ground, are kept in the shade and face away from the Sun

Types of Temperature measurements

• It was stated that surrounding the air is called the Ambient Temp
• Vt is where a moist Air parcel would have the same pressure and density as that of parcel of air. -Heat can be generally be found measured to molecules that are within the subject

Heat and Temp

• Temperature is the average kinetic energy of all molecules/atoms in a substance. In terms of degrees or Kelvin measurement
• Heat is the sum total kinetic energies of all molecules/atoms in a substance. In terms of Joules and Calories measurment

Radiant Heat

is where there is solar radiation heats up at the top without affecting the sun

Solar Radiant Heat

• Consists of shortwaves with wavelengths (vibgyor) where Red has the longest and Violet has the shortest
• Consists of 46% ir, 45% visible, 90% uv

How much Earth Absorbs and reflects

Absorbed by Total Earth surface 51% Water Vapour, Dust, Ozone 16% Clouds 3% 70% Back Scattered by Air 6% Clouds 20% Earth Surface 4% 30%

Albedo

• Is where light of sorts can be a refectory

Surface temp Dv Maxi

Over land. Winds off the land near the cost , large as inland Wind is calm. In clear sky

Surface temp Dv Min

Over sea Wind off the sea Winds are strong When lower clouds present

Surface temps

Occurs at 0500, but for DGCA 30 Min after Sunrise.

##Temp Conversion

• Temp = occurs 1 to 1hr after the sunrise or dawn, The lowest temperature

Performance on height

Height increases, then temperature increases over 1.96°c ##IsoTherm is where constant height is maintained of a Isothermal layer

Temperature

Is affected by density, higher meaning that the longer a runway is required for takeoff

##Air density

Air Mass

• Mass in cubic volume measured via cubic metres

When the temp is constant there there will be pressure increasing with temp More humidity decreases density

• High Altitudes show lower density, and low altitudes show higher density Density sea level is lower closer to equator and poles therefore they more towards the surface ##Effects of Density on performace

• Low density then you have a: A reduced thrust rate of climb. Increased longer landing, and reduced takeoff

Density altitude

Density is expressed depending upon where it is at At any height there wil mean higher density If atmpos is warmer thatsa if higher density is warmer thens the Isa

Surface areas

• Reduced is 1% reduction with 10 hpa reduced
• 3. C increased then 300 ft increases

How the temperature affects air content

##Humidity water increases when you increase water , however it decrease density instead and it lessense due dry air

humidity content

Will be in upper Troposphere Saturated air is then is can not longer hold much, so it becomes maxed at that point there is vapour (vp) state

Latent heat is

• When a when heat is subtracted/released that is referred to something changes and there is absorption

evaporation

• Change from a state of liquid Condensation- a change from vapour , to liquid requiring forms then nuclei becomes forms then super humid

Sublimation

• There change of state water/vapours in the form of ice that has been released

#saturation

• As water evaporates into the air, there comes a point in which the air can no longer accept any more water vapour.
• SuperSaturation* Condensation that requires for any water to vapour then what is described This creates means humidity above 100%

Humidty measurement

• can come in the form relating to realiti ve volume is measured the amount of water that present

Rel volume

In the air with can be released due to evaporation Low is an the evaporation

#wet bulb temp

• can be cooled

Hygrometer or psychrometer

Measured in terms of 💧 with water evapouriting that lowers the temp with lower heat

• The different of dryness and weather is from humans and we see that there is a set atmospheric

Wind

Is a way horizontal of the way Air affects its self to the ground

General terms

Velocity is a combination wind speed 0,2 is 0,7 etc

• Speed km=40