Meteorology One PDF

1 Meteorology One 6ENT1169 Navigation, Human Factors and Meteorology Dr Ivan Sikora  2 Today’s Lecture Content  Today’s Lecture Content 3 ❑ The Atmosphere ❑...

1 Meteorology One 6ENT1169 Navigation, Human Factors and Meteorology Dr Ivan Sikora  2 Today’s Lecture Content  Today’s Lecture Content 3 ❑ The Atmosphere ❑ Atmospheric Pressure EASA Part-FCL / eRules Dec 2021 (Subpart C) ❑ Altimetry ❑ Pressure Systems ❑ Temperature ❑ Density ❑ Humidity ❑ Atmospheric Stability and Instability  Definition of Meteorology What is Meteorology? 4 Science of earth’s atmosphere and the physical processes occurring in it. Why do we need to study about Meteorology? ▪ Because it is the medium through which an aircraft flies. ▪ To understand the potential hazards that can affect the performance and safety of the flight. ▪ To acquire knowledge of the processes in which the weather forms which is useful for predicting what conditions may encounter by the aircraft during flight.  5 The Atmosphere  The Earth’s Atmosphere What is Atmosphere ? 6 The gaseous envelope that surrounds the Earth or any heavenly body. Properties of the Earth’s Atmosphere The atmosphere acts as a fluid, is a poor conductor of heat, and only supports life in lower levels. The earth’s atmosphere varies vertically and horizontally in: ▪ Pressure ▪ Temperature ▪ Density ▪ Humidity The Composition of the Earth’s Atmosphere (By Volume) Other trace elements include: Neon, Helium, Krypton, Xenon, Hydrogen, Methane, Iodine, Nitrous Oxide, Ozone, Sulphur Dioxide, Nitrogen Dioxide, Ammonia, Carbon Monoxide.  The Earth’s Atmosphere TROPOPAUSE7 8 Km 11 Km TROPOSPEHRE 16 Km  The Earth’s Atmosphere STRATOSPHERE STRATOPAUSE 8 20 -25 Km 50 Km OZONE  The Earth’s Atmosphere MESOSPHERE 9 MESOPAUSE 80 TO 90 Km  The Earth’s Atmosphere 10 THERMOSPHERE  The Earth’s Atmosphere The Structure of the Earth’s THE EARTH’S ATMOSPHERE IS MADE UP OF 11 Atmosphere SEVERAL LAYERS Troposphere ▪ The lowest layer of the atmosphere. ▪ Temperature decrease with increase in height. ▪ Contains over 75% of the mass of the atmosphere. ▪ Contains almost all the weather. ▪ Extends from the surface up to an average height 11km. Tropopause: The boundary between the troposphere and the stratosphere. ▪ The height of the tropopause varies with latitude, season of the year the weather conditions. ▪ It is lowest over the poles at 8km with average temperature of -40⁰C. ▪ It is highest over the equator at 16km with average temperature of -75⁰C to -80⁰C. ▪ The average height of tropopause is 11km (36090 ft) with a temperature of -56.5⁰C.  The Earth’s Atmosphere Stratosphere The Structure of the Earth’s Atmosphere 12 ▪ Layer above tropopause to approximately 50km above the earth’s surface. Relatively stable layer. ▪ Temperature remains constant for average height of 20km and the starts to increases to reach -2.5⁰C at a height of 47km, then above 51km starts to decrease. ▪ Temperature variation is due to absorption of ultra violet radiation by ozone layers of the stratosphere and the retransmission of this radiation as infra-red heat. ▪ The boundary between stratosphere and next layer, the mesosphere is known as stratopause. Mesosphere Thermosphere ▪ The layer above the stratosphere ▪ The outermost layer of the earth’s atmosphere above ▪ Temperature decreases with height. mesopause. ▪ Lowest temperature is approximately -90⁰C ▪ Holds exosphere in its upper regions at height greater occurs between 80km to 90km. than 700km and holds ionosphere in its lower regions. ▪ The boundary layer between mesosphere and ▪ Temperature increases with increase in height. At the next layer, thermosphere (ionosphere) is 200km temperature runs around 600⁰C. known as mesopause. ▪ At times of sunspot activity, can be up to 2000⁰C.  International Standard Atmosphere INTERNATIONAL STANDARD ATMOSPEHERE (ISA) 13 Because atmosphere is constantly changing, it is necessary, in aviation, to have a standard set of conditions to give a common datum for: ▪ The calibration of the aircraft pressure instruments. ▪ The design and testing of the aircraft. The ICAO (International Civil Aviation Organisation) ISA is purely hypothetical atmosphere that represents an average picture of the actual atmosphere and has been in use since 1964. It possesses the characteristics laid out below. Mean Sea Level (MSL) Temperature +15⁰C (Celsius) Pressure 1013.25 hPa (hectopascals) Density 1225 g/m3 From MSL to 11km (36090 ft.) Temperature decreases at 1.98⁰C/1000ft (6.5⁰C per km). From 11km to 20km (65617 ft.) Temperature remains constant at - 56.5⁰C. From 20km to 32km (104987ft.) Temperature rises at 0.3⁰C/1000ft (1⁰C per km)  14 Atmospheric Pressure  Atmospheric Pressure What is Atmospheric Pressure? 15 Atmospheric Pressure is force per unit area exerted by the atmosphere on any surface in contact with it. UNITS OF MEASUREMENTS ▪ The SI unit for force is Newton. Hence, the SI unit of Pressure is N/m2. (Pressure = Force/Unit Area). ▪ The N/m2 is also known as Pascal (Pa). ▪ 100 000 N/m2 is known as Bar. Within one Bar is 1000 millibars. The millibar (mb) may also be known as the hectopascals (hPa). ▪ The ISA values at MSL are: 1013.25 mb = 1013.25 hPa = 29.92 inHg = 101325 N/m2 = 760 mmHg Consider the column of the air on the above: ▪ The height (h2) of the column above s2 is less than above s1 (h1). ▪ There is a larger weight of the air above s1, hence a larger pressure. ▪ The cross – sectional area of both the surfaces are the same.  Atmospheric Pressure Measurement of Atmospheric 16 Pressure MERCURY BAROMETER ANEROID BAROMETER Scale Atmospheric pressure is exerted on the surface of the This consists of a partially evacuated capsule that mercury in the reservoir. The mercury in the tube then expands and contracts as the air pressure outside sinks to about 760 mm above the reservoir at mean sea the capsule changes. A scale indicates these level. The atmospheric pressure is therefore said to be changes by using a system of linkages. The 760 millimeters of mercury (760 mmHg). As the diagram shows the basic ideas behind the system. atmospheric pressure varies, so does the height of the mercury.  Atmospheric Pressure Measurement of Atmospheric Pressure THE BAROGRAPH 17 Time To continuously record the pressure changes, a paper cover rotating drum is substituted for the scale and the instrument becomes the barograph. This instrument is widely used by meteorologist to measure what is known as Pressure Tendency, the rise and fall of the pressure over time. Pressure tendency is a vital tool for forecasting weather phenomenon.  Atmospheric Pressure Variation of Atmospheric Pressure 18 Atmospheric Pressure varies horizontally, vertically and diurnally. Horizontally: Pressure changes from place to place and changes over time. Horizontal pressure differences lead to movement of air and hence, the weather. Vertically: Pressure decreases with increase in height. In ICAO ISA, we assumed that the MSL pressure is 1013.25 hPa. From this we can calculate pressure change at any height. The table below shows numerous values of pressure at different heights. Pressure (hPa) Approximate Height (ft) 850 5 000 amsl 700 10 000 amsl 500 18 000 amsl 400 24 000 amsl 300 30 000 amsl 200 40 000 amsl 100 53 000 amsl 50 68 000 amsl  Atmospheric Pressure Variation of Atmospheric Pressure 19 Diurnally: Pressure has a 12 hour oscillation period. In one day, there are two peak pressure values occurring at 1000 & 2200 and two lows pressure vales occurring at 0400 & 1600 hours. There is a small change, about 1 hPa in temperate latitudes and about 3 hPa in tropics. Max Pressure at 1000 & 2200 hours Min Pressure at 0400 & 1600 hours  20 Altimetry  Altimetry Altimeter 21 Altimeter is an instrument which measure altitude, or height, by using the fact that pressure reduces with height. The altimeter presents the local pressure (hPa or mb) as an altitude (ft). 10,000s ft 1000s ft 10,000s ft 100s ft Subscale Subscale Window Window Adjusting knob Fail Flag window (showing FAILED)  Altimetry HOW AN ALTIMETER WORKS 22  Altimetry 23 Terminology ▪ Altitude: Vertical distance above mean sea level (MSL) ▪ Height: Vertical distance of a level or point measured from a specific datum, e.g. above aerodrome surface. ▪ Elevation: Vertical distance of a fixed object above mean sea level (MSL) (e.g. aerodrome or obstacle) ▪ Flight Level (FL): Surface of a constant atmospheric pressure measures from 1013.25 hPa datum used for vertical separation by specified pressure intervals. Flight Level is measured in hundreds of feet.  Altimetry 24 Altimeter Settings ▪ QFE: Airfield level pressure. When set on altimeter, it reads “zero (0) ft” on the ground, or the height of the aircraft above the airfield. ▪ QNH: Airfield level pressure reduced to MSL in accordance with the ICAO ISA. The altimeter will read the height of the airfield above MSL, or the aircraft's height AMSL. (Note: QNH is always rounded to the nearest integer) ▪ QNE: The height indicated on the landing at an airfield when altimeter subscale is set to 1013.25 hPa. ▪ QFF: Airfield level pressure reduced to MSL by means of the actual atmospheric conditions (i.e. in accordance with isothermal conditions using the observed temperature at the surface and it’s corresponding pressure lapse rate).  Altimetry Pressure Calculations 25 When making calculation in altimetry, you can assume 1 hPa = 27 ft. Example: An aircraft is flying at an altitude of 3500 ft. The QNH is 1010 hPa. The QFE is 988 hPa. What is the aircraft’s height? Sol: 1010 - 988 = 22 hPa. Using 27 ft per hPa, the elevation of the airfield must be 22 x 27 = 594 ft. Hence, the aircraft height must be 3500-594 = 2906 ft.  Altimetry Pressure Calculations 26 When making calculation in altimetry, you can assume 1 hPa = 27 ft. Example: An aerodrome has an elevation of 1500 ft. The QFE is 965hPa. Calculate an approximate QNH? Sol: 1500 / 27 = 56 hPa The airfield is above the sea level so the QNH will be higher. Hence, QNH = 965 +56 = 1021 hPa.  Altimetry Temperature Calculations 27 ❖ The Altimeter is calibrated according to ISA conditions. ❖ If the conditions are non-ISA, the altimeter reads incorrectly. ❖ The altitude at which the aircraft is actually flying is called the true altitude. True altitude is higher than Indicated Altitude True altitude is lower than Indicated Altitude  Altimetry Temperature Calculations 28 When converting between indicated altitude and true altitude, use: 4 feet per 1000 ft per 1⁰C deviation from ISA. Add if warmer than ISA, subtract if colder than ISA. Example: You are flying at 6000 feet on a QNH of 1008 hPa. The temperature is 8⁰C. What is your true altitude? Sol: At 6000 ft the ISA temperature is 15 – (2 x 6) = 3⁰C. Hence the temperature is ISA + 5. Using the formula you get: 4 x 6 x 5 = 120 ft. It is warmer than ISA, so the true altitude is 6000 + 120 = 6120 ft.  Altimetry Temperature Calculations 29 When converting between indicated altitude and true altitude, use: 4 feet per 1000 ft per 1⁰C deviation from ISA. Add if warmer than ISA, subtract if colder than ISA. Example: You are flying at FL 300. The QNH is 976 hPa. The temperature is -58⁰C. What is your true altitude? Sol: First convert FL to altitude. The QNH is lower, therefore altitude will be lower than FL. (1013 -976) x 27 = 999 ft. Altitude is 30 000 – 999 = 29001 ft. ISA temperature is 15 – (29 x 2) = -43⁰C. So it is ISA – 15. Temperature correction is 4 x 29 x 15 = 1740 ft. Colder than ISA so true altitude is 29001 – 1740 = 27261 ft.  Altimetry Horizontal Pressure Variation 30 Aircraft flying through Constant QNH value from departure to destination airfield. True Altitude is equal to Indicated Altitude  Altimetry Horizontal Pressure Variation 31 Aircraft flying from High to Low QNH value from departure to destination airfield. HIGH TO LOW --- HIGH (Altimeter reads high) True Altitude is Less than Indicated Altitude  Altimetry Horizontal Pressure Variation 32 Aircraft flying from Low to High QNH value from departure to destination airfield. LOW TO HIGH --- LOW (Altimeter reads low) True Altitude is more than Indicated Altitude  Altimetry Temperature Variation 33 Aircraft flying from Warm to Cold air from departure to destination airfield. HOT TO COLD --- DON’T BE BOLD True Altitude is Less than Indicated Altitude  Altimetry Temperature Variation 34 Aircraft flying from Cold to Warm air from departure to destination airfield. True Altitude is more than Indicated Altitude Break 35  36 Pressure Systems  Pressure Systems What is Isobar ? 37 A line on weather synoptic chart joining places of equal atmospheric pressure (usually MSL pressure QFF). What is Isallobar? A line on weather synoptic chart joining places of same pressure tendency. Pressure Systems There are certain patterns formed by Isobars and Isallobars on the synoptic chart. These are called “Pressure Systems”. An understanding of the properties of these systems can help us forecast the weather. Types of Pressure Systems: ▪ Depressions or Lows or Cyclone. ▪ Anticyclones or Highs. ▪ Troughs. ▪ Ridges. ▪ Cols.  Pressure Systems Buys Ballot’s Law 38 In the 19th century the Dutch scientist and meteorologist, Buys Ballot, produced a law based on his observation of the wind direction and pressure systems. It states: “If an observer stands with his back to the wind in the Northern Hemisphere then the low pressure is on his left, and to his right in southern hemisphere”. A Corollary of Buys Ballot’s Law  Pressure Systems Depressions or Lows or Cyclones 39 A depression or low or cyclone is region of comparatively low pressure shown by more or less circular and concentric isobars surrounding the centre, where pressure is lowest. In a depression air is converging at the surface, rising from the surface to medium to high altitude then diverging at the medium to high altitude.  Pressure Systems Depressions or Lows or Cyclones 40 In the northern hemisphere, wind circulate anticlockwise around a low. Flying towards a low, an aircraft will experience starboard (right) drift. Weather associated with a Depression or Low or Cyclone ▪ Cumuliform clouds - Cu/Cb ▪ Good visibility ▪ Showers - rain or hail ▪ Turbulence - moderate or severe ▪ Icing - moderate or severe There are two type of depressions, frontal (large scale) also known as Polar Frontal Depressions which are found in temperate latitudes and non-frontal (small scale) depressions which can be found virtually anywhere.  Pressure Systems Anti-Cyclones or Highs 41 An anti-cyclone or high is a region of relatively high pressure shown by more or less circular isobars similar to a low but with high pressure a the centre. In an anti-cyclone, air is converging at the high altitude then descent of the air within the anticyclone (subsidence) and divergence at the surface.  Pressure Systems Anti-Cyclones or Highs 42 In the northern hemisphere, the wind circulate clockwise around the centre of a high. Flying towards a high an aircraft will experience port (left) drift. Weather associated with an Anti-Cyclone or High (warm anticyclone) ▪ Clear skies. ▪ Poor visibility (particles forced to stay near surface). ▪ No precipitation. ▪ No turbulence. ▪ No icing. ▪ Surface conditions; warm by day, cold by night. There are five types of anticyclone: warm, cold, temporary cold, ridges (or wedges) and blocking.  Pressure Systems Troughs (of low pressure) 43 A “V” - shaped extension of the isobars from a region of a low pressure is called a Trough (of low pressure). They bring similar weather to that associated with depressions. Ridges (of high pressure) A “U” - shaped (round shaped) extensions of the isobars from a region of a high pressure is called a Ridge (of a high pressure). They bring similar weather to that associated with anticyclones. Cols Cols are regions of almost level pressure between two highs and two lows. It is an area of stagnation. In autumn and winter cols produce poor visibility and fog, whilst in summer thunderstorm are common.  44 Temperature  Temperature What is Temperature? 45 Temperature is the measure of warmth of a substance. ▪ The temperature changes that occur on Earth’s surface initiates both the vertical air movement (leading to formation of clouds) and horizontal movement of air (wind). ▪ Temperature value normally decreases with increase in height from the earth surface. In case, where temperature rises with increase height, then it is called Inversion. If the temperature remains same with change in height, then it is called Isothermal Layer. Three scales of measurement of Temperature: The figure below shows the melting point of ice and boiling point of water. ▪ The FAHRENHEIT scale: +32 and +212 degrees. ▪ The CELSIUS scale: 0 and +100 degrees. ▪ The KELVIN scale: +273 and +373 Kelvin. Conversion factors: Fahrenheit to Celsius Celsius to Fahrenheit Celsius to Kelvin 5 9 ⁰K = ⁰C + 273 ⁰C = (⁰F - 32) x ( ) ⁰F = ( x ⁰C) + 32 9 5  Temperature Heating of the Atmosphere 46 The main source of heat for the atmosphere is the Sun. The atmosphere is heated by five different processes. ▪ Solar Radiation: Radiation from the sun is of short wavelength (less than 2 microns) and passes through the Earth’s surface almost without heating it. Some of the solar radiation is reflected back to the upper air from clouds and water surfaces on the earth. The rest heats the surface of the earth. This process is called Insolation.  Temperature Heating of the Atmosphere 47 ▪ Terrestrial Radiation: The earth surface absorbs large amount of solar radiation by the process of insolation and radiated back to the atmosphere by long wave radiation (between 4 and 80 microns). This is the main method by which the atmosphere is heated. As, the atmosphere is heated from below, it gets colder as you climb up from the surface of the earth. Hence, giving a temperature lapse rate. (Environmental Lapse Rate – ELR is 2⁰C/1000 ft under ISA conditions)  Temperature Heating of the Atmosphere 48 ▪ Conduction: Conduction occurs when two bodies are touching each other. At night, the ground cools quickly due to lack of insolation from sun. The air in contact with the ground loses heat by conduction. And as air is poor conductor, air at high levels remains warm, and hence we have an Inversion. ▪ Convection: Air heated by the conduction will be less dense and tends to rise and produce up currents called thermals or convection currents. Likewise, cold air is more dense and tend to subside. This process helps heat the upper levels of the atmosphere. Convection currents or thermals rising from a warm surface during the day  Temperature Heating of the Atmosphere 49 ▪ Condensation: The rising air will be cool by the adiabatic process and the water vapour in the air will condense out as visible droplets forming clouds. As this occurs latent heat will be released by the water vapour, and it adds to the heating of the atmosphere.  Temperature Variation of Temperature 50 Surface temperature is subjected to considerable variation: Latitude Effect, Seasonal Effect, Diurnal Variations and multiple effects due to clouds and wind. ▪ Latitude Effect: As can be seen from the picture, at Equator only a small area is heated and therefore more heat/unit area. Conversely, at the poles, the sun ray’s cover larger area and there fore less heat/unit area. However, the actual distance of polar regions from the sun is only fractionally more than from the equator, the effect is ignored. ▪ Seasonal Effect: Sun’s heating effect is not constant as the earth’s axis is tilted and the way the earth revolves around the sun.  Temperature Variation of Temperature 51 ▪ Diurnal Variation: Earth’s surface has highest amount of Insolation at around noon. But as the earth surface takes some time to heat up, there is slight lag to transfer the heat to the atmosphere. The high temperature occurs at about 1500 local time and the lowest occurs just about half an hour after the sunrise. Max Temperature at 1500 local time Min Temperature just half an hour after sunrise  Temperature Variation of Temperature 52 Effect of Wind by Day: Wind will cause turbulent Cloud cover by Day: By day some of mixing of the warm air at the surface with cold air the solar radiation is reflected back by above, reducing the T max. the cloud tops and T max is decreased. Cloud cover by Night: By night Effect of Wind by Night: There will be an inversion above terrestrial radiation is absorbed and the surface and wind will cause cold air to be turbulently radiated back to the surface from mixed with warm air above thus increasing the T min. the cloud. T min is increased.  53 Density  Density What is Density ? 54 Density,  (rho) can be defined as mass per unit volume. It is expressed in any of the following; ▪ Grams or kilograms per cubic meter i.e. g/m3or kg/m3.  Density Relative Density 55 ▪ ISA Density is 1225g/m3. 1225𝑔 1000𝑔 ▪ = 100 %. Than = 82%. 𝑚3 𝑚3 ▪ The altitude in the standard atmosphere to which the observed density corresponds – density altitude. The Table below shows the effect of change of various variables on Density: Variable Increase Decrease Relationship Pressure   Directly proportional Temperature   Inversely Proportional  Humidity  Inversely Proportional  Inversely Proportional Altitude  (Pressure has more effect on Density)  Density Effect of Change of Latitude on Density 56 ▪ At the surface, density increases as latitude increases. ▪ At about 26000 ft, density remains constant with an increase in latitude. ▪ Above 26000 ft, density decreases with an increase in latitude. Effect of Changes in Density on Aircraft Operations ▪ Accuracy of the aircraft instruments – ASI, Mach Meter. ▪ Aircraft and Engine Performance – less density = less lift, increase take-off run, reduce maximum take-off weight. Effect of latitude in Density We know, L = CL ½ ρ V2 S  57 Humidity  Humidity What is Humidity? 58 ▪ Humidity is the measurement of the amount of water vapour in the air. ▪ Water can be solid (ice), liquid (water), gas (vapour). The vapour component makes up for 99% of the all water held in the atmosphere. What is Latent Heat? ▪ The Latent heat is the heat required to change a state of substance without change of the temperature. Change of State: The picture below shows the various change of state of water.  Humidity Humidity Types 59 ▪ Absolute Humidity: Is the actual mass of water in a given volume of air. Usually expressed in g/m3. ▪ Relative Humidity (RH): The ratio of the actual water vapour in the air to the maximum amount the air could hold at that temperature and pressure. It is expressed in PERCENTAGE (%). AMOUNT OF WATER VAPOUR IN THE AIR (%) RH = AMOUNT OF WATER VAPOUR THE AIR CAN HOLD Some more Definitions ▪ Saturation: Air is saturated if it contains the maximum amount of water vapour that it can hold at that temperature. If saturated air is cooled, condensation will occur. ▪ Dew Point: The temperature at which air becomes saturated. Saturated air cannot hold any more water vapour without condensation.  60 Atmospheric Stability and Instability  Atmospheric Stability and Instability Adiabatic Processes 61 ▪ In order to understand the concepts of atmospheric Stability and Instability, it is necessary to understand the concepts of adiabatics. ▪ An adiabatic process is one in which the temperature changes within the system but there is no heat exchange of energy with the surroundings. ▪ E.g. Manual pump to inflate the bicycle tyre. The valve gets hot because of the compression of air. ▪ E.g. CO2 fire extinguisher discharge. Releasing the handle allows high pressure CO2 expands rapidly, reducing the gas temperature to extinguish the fire. The temperature change of air by compression or expansion  Atmospheric Stability and Instability Dry Adiabatic Lapse Rate (DALR) 62 ▪ When dry air (unsaturated air) is forced to rise, it cools at what is called Dry Adiabatic Lapse Rate (DALR). ▪ It has a constant value of 3⁰C/1000 ft. (1⁰C/100m). Saturated Adiabatic Lapse Rate (SALR) ▪ Saturated air, when forced to rise will also cool but as it cools, condensation will take place, releasing latent heat which slows the rate of cooling of air. This is called Saturated Adiabatic Lapse Rate (SALR). ▪ It has an average value of 1.5⁰C/1000 ft. (0.6⁰C/100m) Environmental Lapse Rate (ELR) ▪ The ELR is the lapse rate of the actual air in the environment. ▪ It is variable.  Atmospheric Stability and Instability Stability of the Air 63 ▪ Stability can be defined as being resistance to change. ▪ Air that is warmer than its surrounding environment is less dense and rises. This is called Instability. ▪ Air that is colder than its surrounding environment is more dense and sinks. This is called Stability. ▪ Air that is the same temperature as its surrounding environment neither rises nor sinks. It is Neutral. ▪ The stability of the atmosphere depends on the relationship between the ELR and the DALR and SALR. Summary of Stability Absolute Stability ELR < SALR < DALR Height Instability Absolute Instability ELR > DALR > SALR Stability Instability Conditional Instability DALR > ELR > SALR Temperature  Atmospheric Stability and Instability 64 Absolute Absolute Instability Stability ELR < SALR < DALR ELR > DALR > SALR DALR SALR ELR 1°C/1000 ft DALR SALR 11°C ELR 5°C/1000 ft 4000 ft 3°C 9°C 0°C 4000 ft 8°C 14°C 12°C 3000 ft 6°C 10.5°C 5°C 3000 ft 11°C 15.5°C 13°C 2000 ft 9°C 12°C 10°C 2000 ft 14°C 17°C 14°C 15°C 1000 ft 12°C 13.5°C 1000 ft 17°C 18.5°C 15°C 15°C 20°C 20°C Dry Air Saturated Dry Air Saturated Air Air Atmospheric Stability and Instability 65 Conditional Instability DALR > ELR > SALR  Atmospheric Stability and Instability Method to calculate an approximate Cloud Base height 66 ▪ If dewpoint is constant: H = (T – Td) ÷ 3 x 1000 Where, T = surface temperature in ⁰C, Td = dewpoint in ⁰C, H = Height of cloud base in ft. ▪ If dewpoint is not constant (reduces): H = (T – Td)400 or h = (T – Td)125 Where, T = surface temperature in ⁰C, Td = dewpoint in ⁰C, H = Height of cloud base in ft. h = Height of cloud base in m.  67 Thank you Dr Ivan Sikora Twitter: @Master_Mentor SKYPE: IvanS_Office WordPress: ivansikora.wordpress.com herts.ac.uk References 68 ▪ EASA Part-FCL/eRules, Dec 2021, Subpart C. ▪ Meteorology, CAE Oxford ATPL Series Books. (Including pictures) ▪ Meteorology, Atlantic Flight Training ATPL Series Books. (Including pictures) ▪ FAA Handbook of Aeronautical Knowledge. ▪ Aviation Law & Meteorology, Volume 2, Air Pilot’s Manual, Pooley’s Fourteenth Edition 2017. ▪ Navigation Meteorology, The PPL Course, AFE, Second Edition, Reprinted 2017. Images are from www.google.com for illustration purposes.  1 Meteorology Two 6ENT1169 Navigation, Human Factors and Meteorology Dr Ivan Sikora  2 Today’s Lecture Content  Today’s Lecture Content 3 ❑ Winds EASA Part-FCL / eRules ❑ Clouds Dec 2021 (Subpart C) ❑ Thunderstorm ❑ Visibility ❑ Air Masses ❑ Fronts  4 Winds  Winds What is Wind? 5 Wind is air in horizontal motion. ▪ Wind Velocity (W/V) has both direction and speed. The example below show a direction of 090⁰. Calm 20 kt, further additions up to 45 kt 1 to 2 kt 50 kt Click on the picture for video 5 kt 60 kt 10 kt 65 kt, further additions as necessary 15 kt ▪ Wind direction is always given as the direction from which is the wind the blowing. ▪ Wind speed is usually given in knots (kt). 1 knot = 1 Nm/hr. ▪ Wind Direction is usually given in ⁰T (true) but direction given by the ATC to the Pilot is in ⁰M (magnetic) because the runway direction is in magnetic.  Winds Veering: is a change of wind direction in a clockwise direction. 6 Backing: is a change of wind direction in an anticlockwise direction. Gust: is a sudden increase in wind speed and direction lasting for less than one minute. Lull: is a sudden decrease in wind speed. Squall: is sudden increase in wind speed often with direction lasting for more than one minute covering wide area. Gale: is a mean surface wind of 34 kt or more. Or gusting to 43 kt or more. Hurricane: is a wind with mean surface wind of 63 kt or more. Wind Gradient: is the gradual change in wind velocity between the surface and the top of the friction layer. Note: Friction layer is the layer of the air that is influenced by friction caused by the surface. The friction layer generally lies from earth surface to 3000 ft.  Winds Forces Acting Upon the Air: There are two main forces acting upon the air. 7 ▪ The Pressure Gradient Force (PGF) ▪ Geostrophic Force or Coriolis Force The Pressure Gradient Force (PGF): is the force caused by pressure difference. Air will flow from high pressure area to a lower pressure area. Geostrophic Force or Coriolis Force: is the force caused due to rotation of the earth. It makes moving mass of air turn RIGHT in the northern hemisphere and LEFT in southern hemisphere. The force is maximum at pole and minimum at equator. Note: the Pressure Gradient Force must initiate movement of a parcel of air before Geostrophic Force can come into play. Geostrophic Force has no effect on a stationary parcel of air. Click on picture for  Winds 8 The Geostrophic Wind: Wind which is blown as a result of balance between Geostrophic Force and Pressure Gradient Force. ▪ This wind flows parallel to the straight Isobars. ▪ Only above friction layer. The Gradient Wind: The gradient wind occurs when isobars are curved. The wind blows parallel to the curved isobars and hence the air starts to rotate around the centre of the system. This rotation brings in an additional force called, centrifugal force. This is a force acting outwards from the centre of the system.  Winds The Surface Wind: The wind on the surface is slower than at altitude. This is primarily due to friction layer. 9 Making a descent from 2000 ft towards earth surface, the wind speed reduces. As the wind speed reduces, Coriolis force has less effect and the direction of the wind will also change. ▪ In northern hemisphere, in a descent, the wind direction will back. The number of degrees of deflection and reduction in wind speed for different situation are shown in table below. Deflection of the surface Speed of the surface wind wind from 2000 ft wind as a % of the 2000 ft wind Over the Sea 15⁰ 75 Over the Land by Day 30⁰ 50 Over the Land by Night 45⁰ 25  Winds Diurnal Variation of The Surface Wind Measurement of the Surface Wind 10 Night to Veer and increase Surface Wind: day Day to Back and decrease night Night to Back and decrease 1500 ft Wind: day Day to Veer and increase night Night to Little Variation 2000 ft Wind: day Day to Little Variation night Wind Vane placed at 10 m above the ground surface  Winds Local Winds 11 Sea Breeze During the day, the land heats up quickly than the sea. The air in contact also heats up and rises by the convection which leads to low pressure at the surface and high pressure at 1000 ft. This causes the air to move from land to sea at 1000 ft creating a higher surface pressure over the sea and lower surface pressure over the land. As a result, the air flow from sea to land. Typical wind speed is around 10 kts in temperate latitude. In tropics speed is 15 kts and more. and extend on an average 8 to 14 nm either side of the coast. The wind direction is more or less at right angles to the coast but after sometime it veers under influence of Coriolis forced in norther hemisphere.  Winds Land Breeze 12 After sunset the situation is reversed. The land will cool rapidly whilst the sea will retain its heat. There will be an increase in pressure at the surface over the land whilst the pressure over the sea will fall - there will be a land breeze. The speed will be about 5 kts and the breeze will extend about 5 nm out to sea.  Winds Operational Implication of Sea and Land Breeze 13 LAND BREEZE Direction of T/O and Fog at coast can be blown Cloud Formation over a Landing reversed inland by day reducing Coastline visibility at coastal airfield  Winds Katabatic Wind 14 During the night a hillside cools down rapidly. The air in contact with it is cooled by conduction and becomes more dense than the free air next to it. It therefore flows down the hillside. The air remains in contact with the ground at all times and does not warm adiabatically. The average speed is 10 kt. If this wind occurs in a valley, cold air collects at the bottom increasing the likelihood of fog or frost.  Winds Anabatic Wind 15 Anabatic wind is the opposite of the Katabatic wind and occurs during the day on slopes which are subject to direct sunlight. As insolation increases, the air in contact with the land warms up, becomes less dense and flows up the slope. The Anabatic wind is typically weaker than the Katabatic (about 5 kt) since it flows against the force of gravity.  Winds Valley or Ravine or Funnel Wind 16 A wind blowing against a mountain is impeded. If the barrier is broken by a gap or valley, the wind will blow along the valley at an increased speed due to the restriction. Wind speeds of 70 kt can be experienced. A valley or ravine wind  Winds FÖHN WINDS 17 The Föhn Wind is a warm dry wind which blows on the downwind side of a mountain range. The Föhn Wind occurs when air is forced to rise up a mountain side in stable conditions. It cools initially at the DALR until it reaches saturation. At this point, cloud starts to form and the air continues to rise, but now cools at the SALR. Once it reaches the top of the mountain it starts to flow down the other side. Initially it warms at the SALR but quickly becomes unsaturated as much of its moisture has already been lost. It then warms at the DALR. The Föhn Effect  Winds Mountain Waves (MTW) 18 Mountain Waves also known as Standing Waves or Lee Waves are turbulent waves of air which can form above and downwind of a mountain range to an average distance of 50 to 100 nm at all heights up to, and even above, the tropopause MTW may form when: ▪ Wind direction at right angles to ridge (+/- 30°) and constant direction with height. ▪ Wind speed at summit is at least 15 kts and increasing with increase in altitudes. ▪ A marked layer of stability around the altitude of the summits. E.g. an isothermal layer or inversion, with less stable air above and below. A well developed mountain wave or lee wave  19 Clouds  Clouds Clouds are visible collections of water droplets, ice crystals, or a mixture of both. They provide indication of: 20 ▪ Possible Turbulence ▪ Poor Visibility ▪ Precipitation ▪ Lightning ▪ Icing Cloud Amount Cloud amounts are measured in OKTAS (eights). In aviation meteorology, it is assumed that sky is divided in to eight equal parts and total cloud amount is reported in terms of eights. The three letter abbreviation used in meteorological reports to indicate amount of clouds are: SKC Sky clear 0 oktas FEW Few 1 – 2 oktas SCT Scattered 3 – 4 oktas BKN Broken 5 – 7 oktas OVC Overcast 8 oktas  Clouds Cloud Base: The height of the base of the cloud above ground (official aerodrome level). 21 Clouds Ceiling: The height above the aerodrome level of the lowest layer of the cloud of more than 4 oktas. It is also referred to as a main cloud base. Method to calculate an approximate Cloud Base height ▪ If dewpoint is constant: H = (T – Td) ÷ 3 x 1000 Where, T = surface temperature in ⁰C, Td = dewpoint in ⁰C, H = Height of cloud base in ft. ▪ If dewpoint is not constant (reduces): H = (T – Td)400 or h = (T – Td)125 Where, T = surface temperature in ⁰C, Td = dewpoint in ⁰C, H = Height of cloud base in ft. h = Height of cloud base in m.  Clouds Cloud Classification 22 The classification of the cloud types are primarily based on the shape and form. The three basic forms are: Stratifor Cumuliform Cirrifor m m Stratiform cloud is a layered type of cloud of Cumuliform cloud is heaped cloud, displaying Cirriform cloud is a cloud which is fibrous, considerable horizontal extent, but little a marked vertical extent, of greater or lesser wispy or hair-like in appearance. This vertical extent. degree. type of cloud is found only at high levels in the Troposphere.  Clouds Clouds are also classified with reference to the height 23 The table and the picture below shows three levels and height of clouds at which they occur. Low Level Medium Level High Level Startocumulus SC Altocumulus AC Cirrus CI Stratus ST Altostratus AS Cirrocumulus CC Cumulus CU Nimbostratus NS Cirrostratus CS  Clouds A pictorial representation of the clouds is shown 24 below. Cumulonimbus clouds are clouds that the aviator should avoid. ▪ Cumulonimbus clouds consist of vigorous convective cloud cells of great vertical extent. ▪ The upper parts of a cumulonimbus cloud often consist of super-cooled water droplets and ice crystals. ▪ The base of cumulonimbus clouds is often very dark, with ragged cloud appearing beneath the main cloud cell. Usually the cloud base is between 2,000 ft and 5,000 ft.  Clouds 25 SUMMARY OF CLOUD TYPE AND CHARACTERISTICS Turbulenc Cloud Type Height Composition Icing Visibility Significance e 16 500 ft to Found 400 to 600 nm Cirrus CI Ice crystals Nil Nil 1000 m + 45 000 ft ahead of a warm front 16 500 ft to Found 400 to 600 nm Cirrostratus CS Ice crystals Nil Nil 1000 m + 45 000 ft ahead of a warm front Found 400 to 600 nm 16 500 ft to ahead of a warm front Cirrocumulus CC Ice crystals Light Nil 1000 m + 45 000 ft when turbulence exists  Clouds SUMMARY OF CLOUD TYPE AND CHARACTERISTICS 26 Turbulenc Cloud Type Height Composition Icing Visibility Significance e Water 20 to 6500 ft to Light to Light to Altocumulus AC 23 000 ft droplets and 1000 m Turbulence cloud moderate moderate ice crystals Warm front 200 nm Water 6500 ft to Light to Light to 20 to ahead. Merges with Altostratus AS droplets and 23 000 ft moderate moderate 1000 m NS as the front is ice crystals approached Ground level to Water 6500 ft. droplets but Can be 10 000 ft can be ice Moderate Moderate Warm front very Nimbostratus NS to 10 to 20 m 15 000 ft crystals at to severe to severe close merging into AS medium at higher levels levels  Clouds SUMMARY OF CLOUD TYPE AND CHARACTERISTICS 27 Compositio Turbulen Cloud Type Height Icing Visibility Significance n ce 1000 ft to Water Light to Light to Turbulence Stratocumulus SC 10 to 30 m 6500 ft droplets moderate moderate cloud Occasion Ground level Water ally light Turbulence Stratus ST Nil to light 10 to 30 m to 6500 ft droplets to cloud moderate Instability Water cloud. Large 1000 ft to droplets Moderate Moderate Less than Cumulus CU CU may 25 000 ft and ice to severe to severe 20 m develop into crystals CB  Clouds SUMMARY OF CLOUD TYPE AND CHARACTERISTICS 28 Compositio Turbulen Cloud Type Height Icing Visibility Significance n ce Cumulonimbus CB 1000 ft to Water Moderate Moderate 10 to 20 m Instability cloud 45 000 ft droplets and to severe to severe ice crystals Altocumulus AC 6500 ft to Water Moderate Moderate - An indication of castellanus C 23 000 ft droplets and to severe to severe unstable air at mid ice crystals levels; can indicate approaching CB Altocumulus AC 6500 ft to Water Moderate Moderate - Associated with Lenticularis L 23 000 ft droplets and to severe to severe mountain waves ice crystals  29 Thunderstorm  Thunderstorm Thunderstorm are associated with Cummulonimbus (CB) clouds. It requires a high relative humidity, instability 30 to the higher levels and some form of trigger action to create a lifting air. The three stages of development of a Thunderstorm Initial (Growth) Stage UPDRAUGH TS ONLY Several small Cu combine to form a large Cu cell about 5 nm across. There are strong up-currents of 1000 to 2000 fpm (exceptionally 6,000 fpm). Air from the sides and below is drawn in to replace the lifted air, thus causing turbulence. The initial stage lasts about 15 to 20 minutes and is characterized by only having up draughts. Click on picture for video  Thunderstorm 31 Mature Stage When precipitation occurs, the storm has reached the mature stage. The rain or hail will cause strong down currents of up to 2400 fpm and will also bring cold air to lower levels. These down drafts will warm initially at the SALR causing the air to warm very slowly, thereby staying colder than the surrounding air causing it to sink faster. Another factor aiding these down drafts is that some of the rain will evaporate which will absorb latent heat from the air making it even colder and more dense. UPDRAUGHTS AND DOWNDRAUGHTS  Thunderstorm 32 Mature Stage Up currents remain strong and can be up to 10,000 fpm. Tops may rise at 5,000 fpm or more. There can be extreme turbulence in, under and all around the cloud. Macro bursts are slightly larger in area than microbursts At the bottom leading edge of the storm and are said to affect an area between 3 and 5 miles there can be a roll of SC and a strong gust across as the entire cold air outflow leaves the front can be experienced up to 13 to17 nm thunderstorm or group of thunderstorms (classification Dr. (24 to 32km) ahead of the storm and be up Ted Fujita.). These are typically of more than 5 minutes to 6,000 feet in depth. Below the cloud a duration. squall and associated wind shear can be expected. Rising and falling water droplets will produce a considerable build-up of static electricity, usually of Microbursts are possible where the down positive charge at the top of the cloud and negative at the currents are very strong and are confined bottom. The build-ups eventually lead to lightning to a region in the cloud no more than 3nm discharge and thunder. (5km) across and a duration of less than 5 minutes. The mature stage lasts for a further 15 to 20 min and this stage is characterized by both up and down draughts.  Thunderstorm Dissipating Stage 33 At this stage there is a wider distribution of precipitation, which is heavy, and extreme turbulence. Thunder and lightning DOWNDRAUGH may possibly occur at this stage. This TS ONLY stage is characterized by predominantly downdraughts. The cloud extends to the tropopause, where it is spread out by the upper wind to form an anvil. At these levels the cloud thins to form Ci. Large variations in static charge in and around the cloud cause discharge in the form of lightning which can appear in the cloud, from the cloud to the ground, or from the cloud to the air alongside. The dissipating stage lasts for a further 1½ to 2½ hours.  Thunderstorm Electrostatic Charge on a Thundercloud 34 POSITI VE NEGATIV E Click on picture for video  Thunderstorm Hazards of Thunderstorms 35 Gust Front Microburst ▪ Turbulence and Wind shear ▪ Gust Front ▪ Microburst ▪ Hail and Icing ▪ Static ▪ Lightning ▪ Water Ingestion ▪ Tornadoes Icing  36 Thank you Dr Ivan Sikora Twitter: @Master_Mentor SKYPE: IvanS_Office WordPress: ivansikora.wordpress.com herts.ac.uk References 37 ▪ EASA Part-FCL/eRules, Dec 2021, Subpart C. ▪ Meteorology, CAE Oxford ATPL Series Books. (Including pictures) ▪ Meteorology, Atlantic Flight Training ATPL Series Books. (Including pictures) ▪ FAA Handbook of Aeronautical Knowledge. ▪ Aviation Law & Meteorology, Volume 2, Air Pilot’s Manual, Pooley’s Fourteenth Edition 2017. ▪ Navigation Meteorology, The PPL Course, AFE, Second Edition, Reprinted 2017. Images are from www.google.com for illustration purposes.  1 Meteorology Two 6ENT1169 Navigation, Human Factors and Meteorology Dr Ivan Sikora  2 Today’s Lecture Content Human Performance Today’s Lecture One Content ❑ Winds EASA Part-FCL / ❑ Clouds eRules Dec 2021 (Subpart C) ❑ Thunderstorm ❑ Visibility ❑ Air Masses ❑ Fronts  4 Visibility  Visibility Visibility is measure of atmospheric clarity, or obscurity. This can be caused by; 5 ▪ Water Droplets, such as cloud, fog or rain. ▪ Solid particle, like sand, dust or smoke. ▪ Ice, such as crystals, hail or snow. Visibility is generally better upwind of towns and industrial areas. Poor visibility is more common in stable conditions, such, underneath an inversion. Visibility Measurement By Day: Measurement are made by reference to suitable Objects at known distances from the observing position.  Visibility By Night: Transmissometer or forwards scatter meters are used. 6  Visibility Types of Visibility 7 Meteorological Visibility: is the furthest horizontal distance on the ground that an observer with normal eyesight can recognize a dark-colored object. At night, lights of known power are used. Readings are taken at a person’s eye level. Runway Visual Range (RVR): is the maximum distance in the direction of take-off or landing at which a pilot in the threshold area at 15 ft above ground can see marker boards by day, or runway lights by night. It is only used when the meteorological visibility is less than 1500m or when fog is reported or forecast. Oblique Visibility: When flying at altitude, slant visibility is the maximum distance a pilot can see to a point on the ground. The oblique visibility is the distance measured along the ground from the point directly beneath the aircraft to the furthest point the pilot can see. RVR VISIBILITY VISIBILITY  Visibility Types of Visibility Reduction 8 Mist: Caused by very small water droplets in a RH greater than 95%. The visibility is between 1000m to 5000m. Fog: Caused by water droplet. RH is almost 100% with visibility less than 1000m. Haze: Caused by solid particles. There is no lower or upper limit to visibility but haze is not reported above 5000m visibility. Type of FOGS There are several types of Fogs. The three main types are: 1) Radiation Fog 2) Advection Fog 3) Frontal Fog (Source: Li and Tang, 2022)  Visibility Radiation Fog 9 Radiation fog is caused by radiation of the earth’s heat at night, and the subsequent conductive cooling of the air in contact with the ground to below dew point. If there is a light wind, then fog will form, in calm conditions the result will be the formation of dew. The fog is not usually more than a few hundred feet thick.  Visibility Conditions necessary for Radiation Fog to form. 10 ▪ Clear Sky – to increase the rate of terrestrial radiation. ▪ High Relative Humidity – so that a little cooling will be enough to cause saturation and condensation. ▪ Light Wind – a 2 to 8 kt wind which mixes the air bringing warmer air from above to the surface to be cooled and thickening the fog. Times of Occurrence ▪ Predominantly in autumn and winter. ▪ Night and early Morning. Dispersal ▪ By insolation causing convection which will lift the fog. It will also help to evaporate the lower layers. ▪ By a strong wind lifting the fog to form stratus cloud.  Visibility Advection Fog 11 Advection fog is formed by the movement of warm, moist air over a cold surface. The surface can be land or sea. Condition necessary for Advection Fog to form ▪ A wind of up to 15 kt (20 kt over the sea). ▪ A high relative humidity so little cooling is required to bring the air to saturation. ▪ A cold surface with a temperature lower than the Dew Point (DP) of the moving air to ensure condensation.  Visibility Times of Occurrence and location of Advection Fog 12 ▪ Over land areas in winter and early spring. ▪ Over sea areas in early summer and late spring. ▪ Occurs particularly when a SW wind brings tropical maritime air to the UK. Dispersal of Advection Fog ▪ By a change of air-mass (Wind change). ▪ By a wind speed greater than 15 kts which will lift the fog to form stratus cloud.  Visibility Frontal Fog 13 Frontal fog occurs at a warm front or occlusion. The main cause is precipitation lowering the cloud base to the ground. Subsidiary causes are: ▪ Evaporation of standing water on the ground. ▪ Mixing of saturated air with non-saturated air below. The fog can form along a belt up to 200 nm wide which then travels with the front. Can be increased by orographic lifting. Will be dispersed by the passing of the front.  14 Air Masses  Air Masses What is an Air Mass? 15 An air mass is a large volume of air where the humidity and temperature in the horizontal are more or less constant. Classification based on temperature/latitude (source) Earth’s Climate Zones ▪ Tropical ▪ Polar ▪ Arctic Classification by Humidity ▪ Maritime (over sea) ▪ Continental (over land)  Air Masses 16 Air mases are identified according the moisture content, source or type and temperature using a 3 letter systems. ▪ First Letter: moisture content. c(ontinental) or m(aritime). ▪ Second Letter: source region. T(ropical), P(olar) or A(rctic). ▪ Third Letter: temperature. C=c(old) or w(arm). Hence the 5 air masses affecting Europe are: ▪ Arctic Maritime. mAc ▪ Polar Maritime. mPc ▪ Polar Continental. cPc ▪ Tropical Maritime. mTw ▪ Tropical Continental. cTw  Air Masses Air mases affecting British Isles are classified as shown in picture below from Met Office UK. 17 Click on picture for video  18 Fronts  Front s What is Front? 19 A front is a zone or surface of interaction of two air masses of different temperature. A front is usually only a few miles wide. If the term ZONE is used, than the region of interaction is much wider (up to 300 nm). Warm Front Where warm air replaces cold air, it is called a Warm Front. The symbol used on synoptic charts to represent the warm front is shown below. Click on picture for video  Front s Warm Front 20 A warm front has an approximate slope of 1:150 and a side view is as shown below. Generally as the warm front approaches the cloud will lower and thicken. Precipitation will start and gradually increase in intensity until the front passes. Visibility will also decrease and eventually fog may appear when the surface front arrives. Cross section through a warm front  Front s Cold Front 21 Where cold air replaces warm air, it is called a Cold Front. The symbol used on synoptic charts to represent the cold front is shown below. Click on picture for video  Front s Cold Front 22 The slope of a cold front is approximately 1:80 and a side view is shown below. A Winter cold front in Europe will usually produce more intense weather and precipitation. Cold fronts are marked by a sudden approach of cloud with embedded cumulonimbus. This gives precipitation in the form of showers of rain or even hail. After the cold front passes the weather should improve markedly but the temperature will be much lower. Cross section through a cold front  Front s Occluded Fronts/Occlusions 23 An occlusion occurs when the cold front in a depression catches up with or over takes the warm front. An occlusion forms because the cold front normally moves faster than the warm front. It usually forms when the pressure in the depression stops falling (frontolysis). An occlusion  Front s There are two types of occlusions: Warm and Cold. 24 Warm Type Occlusion If the air ahead of the warm front is colder than the air behind the cold front, then a warm type occlusion will be formed. This type of occlusion is more common in winter. The warm sector will be lifted above the surface and only a warm front will be apparent on the ground. There will be a wide rain belt, with mainly stability type precipitation. A Warm Occlusion as seen front a cross section and profile view  Front s Cold Type Occlusion 25 If the air behind the cold front is colder than the air ahead of the warm front, then a cold type occlusion will be formed. This type of occlusion is more common in summer. The warm sector will be lifted above the surface and only a cold front will be apparent on the ground. There will be a narrow rain belt, with CB and NS the most likely cloud. A Cold Occlusion as seen front a cross section and profile view  26 Thank you Dr Ivan Sikora Twitter: @Master_Mentor SKYPE: IvanS_Office WordPress: ivansikora.wordpress.com herts.ac.uk References 27 ▪ EASA Part-FCL/eRules, Dec 2021, Subpart C. ▪ Meteorology, CAE Oxford ATPL Series Books. (Including pictures) ▪ Meteorology, Atlantic Flight Training ATPL Series Books. (Including pictures) ▪ FAA Handbook of Aeronautical Knowledge. ▪ Aviation Law & Meteorology, Volume 2, Air Pilot’s Manual, Pooley’s Fourteenth Edition 2017. ▪ Navigation Meteorology, The PPL Course, AFE, Second Edition, Reprinted 2017. ▪ Li, Q. and Tang, S. (2022) 'Comparison of Visual Features for Image-Based Visibility Detection', Journal of Atmospheric and Oceanic Technology, 39 (6). Available at: DOI: 10.1175/JTECH-D-21-0170.1 Images are from www.google.com for illustration purposes.  1 Meteorology Three 6ENT1169 Navigation, Human Factors and Meteorology Dr Ivan Sikora  2 Today’s Lecture Content  Today’s Lecture Content 3 ❑ Icing EASA Part-FCL / eRules Dec 2021 (Subpart C) ❑ Meteorological Messages ❑ Briefing Charts  4 Icing  Icing Ice accretion on the airframe and engine induction systems can significantly reduce flight safety. 5 The Effects and Dangers of Icing are listed below: ▪ Aerodynamic effects: icing on airframe can modify the airflow pattern around aerofoils (i.e. wings and propellers), leading to loss of lift and increase in drag. - Fokker F-28 Fellowship 1000, 1989. ▪ A weight increase and change in CG position of the aircraft, unbalancing of the various control surfaces and the propeller, causing severe vibration and/or control difficulties. - ATR 42-312, 1987 ▪ Instruments effects: Ice can block pressure heads and the reading of ASI’s, VSI’s, Altimeters and Mach- meters can give erroneous readings. - Air France Flight 447, 2009. ▪ A loss of engine power, or even complete failure of engine, if ice blocks the air intake (in sub zero temperature) or carburettor ice forms (in moist air up to +25⁰C) - Douglas Dakota IV (DC-3),1947. and ▪ General effects: Windscreens and canopies can be obscured. Landing Gear wells can affect retraction. Aerials can cause static interference.  Icing Ice Formation 6 If the ambient air and airframe temperature is less than 0⁰C (freezing point of water), then ice may form, either: ▪ Directly from the water vapour (sublimation, causing hoar frost) or ▪ From water droplets freezing, causing rime ice and/or clear ice. Supercooled Water Droplets (SWD) A supercooled water droplet is a droplet of water still in the liquid state below 0⁰C. It can possibly exist at -40⁰C or even lower. Such a drop when comes in contact with a surface of an aircraft, freeze instantly. Types of Icing ▪ Clear (Glaze) Ice ▪ Rime Ice ▪ Mixed Ice ▪ Hoar Frost Source: University of Hertfordshire , 2023  Icing Clear (Glaze) Ice 7 Clear or Glaze Ice is a transparent form of ice formed by a large supercooled water droplets. It forms in NS, CU, and CB at temperatures from 0 to -20⁰C. The most dangerous type of airframe icing  Icing Rime Ice 8 Rime Ice is a white opaque or milky white form of ice formed by a small supercooled water droplets. The drop will freeze completely and quickly without spreading from the point of impact. It forms in NS, AS, SC, St and part of heap clouds at temperatures from 0 to -40⁰C.  Icing Mixed Ice 9 Mixed Ice as name suggest it is a mixture of both clear and rime ice. Large and small SWD co-exist. Appearance is whitish, irregular and rough.  Icing Hoar Frost 10 Hoar Frost is a white crystal deposit which appears similar to frost on the ground. It occurs in clear air. Water vapour in contact with the airframe converted to ice crystals via sublimation when airframe temperature is below 0⁰C.  Icing Piston Engine Induction Icing 11 1) Impact Icing: Ice in intake areas caused by snow, snow and rain mixed or supercooled water droplets. For turbo charged (fuel injection) engines, this is the only icing hazard. (Verma, 2014) 2) Fuel Icing: This is caused by water in the fuel freezing in the bends in the induction piping. (e.g. Boeing 777 at LHR January 2008, (Skybrary, 2021)) 3) Carburettor Icing: This is caused by: ▪ The sudden temperature drop as latent heat is absorbed when fuel is evaporates ▪ The temperature drop due to the adiabatic expansion of the air as it passes through the venture. I (Source: ADTW Study, 2022) Carburettor Icing is most dangerous within a temperature range of -10⁰C to +25⁰C, in cloud, fog, or precipitation at any power setting.  Icing Carburettor Icing 12 The Wide Range of Ambient Conditions Conducive to the Formation of Carburettor Icing  Icing Ice Protection 13 Anti – Icing Anti-icing measures are designed to prevent the formation of ice. They include: ❖ Kill-frost paste applied to the leading edges. ❖ Heated windscreen and pressure head. ❖ Hot air system on leading edges and tail plane. ❖ Hot air system on engine cowling lips and spinner. ❖ Anti-icing fluids. De- Icing Source: Boeing, 2010 De-icing measures are designed only to remove icing after it has formed, not to prevent its formation. Examples are: ❖ De – icing fluids. ❖ Pulsating rubber boots. ❖ Hot air systems. ❖ Electrical heating systems.  Icing Flight Crew Procedures (Boeing, 2010) 14 Prior to Taxi These are general guidelines; each aircraft manufacturer has additional considerations. ❖ Carefully inspect areas where surface snow, ice, or frost could change or affect normal system operations. ❖ Perform the normal engine start procedures. ❖ Displays may appear less bright than normal. ❖ Check the flight controls and flaps to ensure freedom of movement. Anti-icing fluids. During Taxi/ Landing Roll This guidance is applicable for normal operations during taxi. ❖ Allowing greater than normal distances between airplanes while taxiing will aid in stopping and turning in slippery conditions. ❖ Taxi at a reduced speed. Taxiing on slippery taxiways or runways at excessive speed or with strong crosswinds may cause the airplane to skid. Before/ During Takeoff ❖ Before brake release, check for stable engine operation. ❖ Check that flight deck indications are normal. ❖ A larger temperature difference from International Standard Atmosphere (ISA) results in larger altimeter errors. When the temperature is colder than ISA, true altitude is lower than indicated altitude. ❖ Coordination with local and en-route air traffic control facilities is recommended.  15 Meteorological Messages METAR (ICAO, 2010) Meteorological Messages METeorological Aerodrome Report contain coded messages pertaining to the actual weather conditions 16at a given aerodrome, at a stated time. Shown below is a good example of METAR taken from Met Office UK website. METAR EGLY 301220Z 24015KT 200V280 8000 —RA FEW010 BKN025 18/15 Q0983 TEMPO 3000 RA BKN008= Decoded: EGLY: Issued at 1220Z on 30th. Surface wind: mean 240 deg true, 15 KT; varying between 200 and 280 deg; prevailing vis 8 km; light rain; cloud; 1-2 oktas base 1000 ft , 5-7 oktas 2500 ft; temperature +18°C, dew point +15°C QNH 983 hPa; Trend: temporarily 3000 m in moderate rain with 5-7 oktas 800 ft. ▪ Issued generally every half hour during aerodrome operations. ▪ Example of METAR for practice: METAR EGPZ 301220Z 30025G37KT 270V360 6000 1200NE +SHSN SCT005 BKN010CB 03/M01 Q0999 RETS BECMG AT1300 9999 NSW SCT015= Decoded: EGPZ: Issued at 1220Z on the 30th. Surface wind: mean 300 deg true, 25 KT; maximum 37 KT, varying between 270 and 360 deg; prevailing vis 6 km, minimum vis 1200 m (to north-east); heavy shower of snow, Cloud; 3-4 oktas base 500 ft , 5-7 oktas CB base 1000 ft, temperature +3°C, dew point -1°C; QNH 999 hPa; Thunderstorm since the previous report; Trend: improving at 1300 Zulu to 10 km or more, nil significant weather, 3-4 oktas 1500 ft.  Meteorological Messages TAF 17 Terminal Aerodrome Forecast are forecasts of meteorological conditions at an aerodrome, as opposed to the report of actual, present conditions as given in a METAR. The format of the TAF is similar to that of METAR except few differences. Shown below is s good example of TAF taken from Met Office UK website. TAF EGPK 110500Z 1106/1206 13010KT 9000 BKN010 BECMG 1106/1108 BKN018 PROB30 TEMPO 1108/1116 17025G40KT 4000 TSRA BKN012CB BECMG 1118/1121 3000 BR NSC= Decoded: Twenty-four-hour TAF issued at 0500 Zulu on the 11th. Prestwick valid from oh six hundred on 11th to oh six hundred on 12th. Wind one three zero degrees ten knots. Nine kilometres visibility. Broken at one thousand feet. Becoming from oh six hundred on the 11th to oh eight hundred on the 11th, broken at one thousand eight hundred feet. 30% probability, temporarily between oh eight hundred on the 11th to sixteen hundred on the 11th, wind one seven zero degrees twenty five knots, gusting to forty knots. Four thousand metres visibility. Thunderstorm with rain. Broken cumulonimbus at one thousand two hundred feet. Becoming from eighteen hundred on the 11th to twenty one hundred on the 11th, three thousand metres visibility, mist, no significant cloud. ▪ TAF usually covers period of between 9 and 30 hours. ▪ Those valid for 9 hours are issued every 3 hours ▪ Those valid for 12 to 24 hours issued every 6 hours.  Meteorological Messages Example of TAF for practise: 18 TAF EGTE 300800Z 3009/3018 23010KT 9999 SCT010 BKN018 BECMG 3011/3014 6000 -RA BKN012 TEMPO 3014/3018 2000 DZ OVC004= Decode: Nine-hour TAF issued at 0800 Zulu on the 30th. Exeter valid from oh nine hundred on the 30th to eighteen hundred Zulu on the 30th. Wind two three zero degrees ten knots. Ten kilometres or more visibility. Scattered at one thousand feet. Broken at one thousand eight hundred feet. Becoming from eleven hundred on the 30th to fourteen hundred on the 30th, six kilometres, slight rain. Broken at one thousand two hundred feet. Temporarily between fourteen hundred on the 30th to eighteen hundred on the 30th. Two thousand metres visibility. Moderate drizzle. Overcast four hundred feet.  Meteorological Messages ATIS 19 ❖ Automatic Terminal Information Service is a continuous broadcast of the current aerodrome weather and other aerodrome information. It is broadcasted in plain language. ❖ The purpose is to improve controller efficiency and to reduce congestion on the busy ground, tower and approach frequencies by automatically transmitting on a discrete VHF radio frequency. ❖ ATIS message containing both arrival and departure information shall contain the following elements of information in the order listed: ▪ name of aerodrome ▪ visibility and, when applicable RVR ▪ arrival and/or departure indicator ▪ present weather ▪ contract type, if communication is via D-ATIS ▪ cloud below 1 500 m (5 000 ft) or below the highest ▪ designator minimum sector altitude, whichever is greater; ▪ time of observation, if appropriate ▪ air temperature ▪ type of approach to be expected ▪ dew point temperature ▪ the runways in use ▪ altimeter setting(s) ▪ significant runway surface conditions an