Meteorology in Aeronautics Part 7 PDF - Hazardous Weather Phenomena

Lecture Meteorology in Aeronautics Part 7 Hazardous weather phenomena Part 7 Hazardous weather phenomena 7.1 Thunderstorms 7.2 Aircraft icing Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 284 Thomas H...

Lecture Meteorology in Aeronautics Part 7 Hazardous weather phenomena Part 7 Hazardous weather phenomena 7.1 Thunderstorms 7.2 Aircraft icing Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 284 Thomas Hain 7.1 Thunderstorms Thunderstorm: Weather phenomenon generally associated with cumulonimbus clouds and is necessarily associated with lightning and thunder. Cumulonimbus cloud Photo: T. Hain Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 285 Thomas Hain Development of thunderstorms Conditions for thunderstorm development The following conditions are required for a thunderstorm to develop: ▪ high moisture content in the lower troposphere ▪ an unstably stratified troposphere ▪ a lifting process to lift the air parcels (to cooling down to saturation) Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 286 Thomas Hain Development of thunderstorms Lifting by: ▪ heating caused by the sun over land (e.g. thermals) or cooling aloft ▪ orography (uplift on the mountains) ▪ frontal processes Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 287 Thomas Hain Basic forms of thunderstorms Heat thunderstorm ▪ are caused by the heating of the air from the ground, occurring particularly frequently and strongly in the summer months over land ▪ First maximum in the afternoon (approx. 4 to 7 pm) strongest warming of the ground ▪ Second maximum in the first half of the night (approx. 9 p.m. to midnight) labilisation due to radiative cooling of the top of the (Cumulonimbus) cloud Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 288 Thomas Hain Basic forms of thunderstorms Heat thunderstorm ▪ occur especially from spring to autumn over the mainland ▪ in autumn and in the summer months at night over the seas (e.g. North Sea and Baltic Sea), as the warm water causes labilisation from below ▪ due to strong overheating of the cities often new formation / intensification = > Heat Island Effect (deutsch: Wärmeinseleffekt) ▪ usually only localised (SCT / ISOL) occurrence Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 289 Thomas Hain Basic forms of thunderstorms Heat thunderstorm ▪ Ideal conditions for formation are: high temperatures and high humidity / moisture low pressure gradient (little wind) cyclonically curved isobars or isohypses (small-scale heat low) Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 290 Thomas Hain Basic forms of thunderstorms Orographic thunderstorms ▪ are caused by the forced uplift of a conditionally unstable air mass at orographic obstacles => are therefore linked to orographic uplift areas ▪ even smallest mountain ranges are sufficient for thunderstorm formation ▪ are relatively independent of the diurnal temperature cycle, but are considerably intensified during the summer months due to the strong warming of the ground during the day Photo: T. Hain Thunderstorm over the mountains Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 291 Thomas Hain Basic forms of thunderstorms Orographic thunderstorms red = lightning Formation of orographic Source: DWD thunderstorms over the Black Forest Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 292 Thomas Hain Basic forms of thunderstorms Frontal thunderstorms ▪ On a cold front mostly linearly arranged and high-reaching cumulonimbus clouds shift quickly with the fast-moving cold front as its formation is based on the interaction of different air masses, occurring at all times of the year The cold air often flows far ahead into the warm sector => formation of strong thunderstorms with squall lines before the actual cold front (unstable active cold front) Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 293 Thomas Hain Basic forms of thunderstorms Frontal thunderstorms ▪ On a warm front In the summer months, the warm air from southern subtropical latitudes contains a lot of water vapour. If this condenses during uplift, considerable amounts of condensation heat are released, which can locally labilise the actually stable stratified atmosphere. embedded in the compact warm frontal cloud layer (embedded Cb) => not visible => danger for aviation Cumulonimbus embedded in warm frontal layer clouds on an unstable warm front Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 294 Thomas Hain Stages of thunderstorm development (thunderstorm theory by Byers and Braham) Developing stage ▪ begins with a strongly swelling "cumulus sky“ ▪ only up-drafts with approx. 10 to 25 kt exist with an increasing tendency ▪ horizontal extension approx. 2 to 8 km ▪ no precipitation, no hail and no lightning yet ▪ air is sucked in at the sides of the developing Cb (entrainment) ▪ light to moderate icing (clear ice) ▪ tops in summer approx. 20000 to 25000 feet ▪ duration of this development phase approx. 15 to 25 min Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 295 Thomas Hain Stages of thunderstorm development (thunderstorm theory by Byers and Braham) Developing stage Developing stage of a thunderstorm 2 to 8 km Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 296 Thomas Hain Stages of thunderstorm development (thunderstorm theory by Byers and Braham) Matura stage ▪ in addition to the extreme updrafts (up to 70 kt) now also downdrafts => close together => strong wind shear => strong turbulence ▪ heavy precipitation falls in a narrow temporal and localised area ▪ cold air often suddenly falling out of the cloud, which spreads in all directions when it hits the ground => dangerous microbursts ▪ often up to 20 km (in extreme cases up to 80 km) before the thunderstorm development of a outflow boundary (deutsch: Böenwalze) Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 297 Thomas Hain Stages of thunderstorm development (thunderstorm theory by Byers and Braham) Shower / 100 Outflow km Thunderstorm boundary (recognisable by line whirled up dust) Source: DWD Outflow boundary Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 298 Thomas Hain Stages of thunderstorm development (thunderstorm theory by Byers and Braham) Matura stage ▪ occurrence of sleet / hail from the ground to the cloud tops and outside (up to 20 km) of the cloud ▪ strong risk of icing within the cloud ▪ violent lightning activity reaches its maximum ▪ horizontal extension of up to 15 km ▪ it is not uncommon for cloud tops to reach the tropopause => formation of an anvil (still small) ▪ duration of this development phase approx. 25 to 40 minutes Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 299 Thomas Hain Stages of thunderstorm development (thunderstorm theory by Byers and Braham) Matura stage Matura stage of a thunderstorm about 15 km Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 300 Thomas Hain Stages of thunderstorm development (thunderstorm theory by Byers and Braham) Dissipating stage ▪ only downdrafts (10 to 20 kt), tendency decreasing ▪ heavy precipitation has turned into continuous rain ▪ no more hail ▪ decreasing risk of icing (still light to moderate => rough ice) ▪ lightning only sporadically ▪ horizontal extension of the thunderstorm cell up to approx. 20 km ▪ strong and large developed anvil ▪ duration of this development phase approx. 30 to 40 minutes Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 301 Thomas Hain Stages of thunderstorm development (thunderstorm theory by Byers and Braham) Dissipating stage Occasionally still low updrafts Dissipating stage of a thunderstorm up to 20 km Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 302 Thomas Hain Hazards of thunderstorms in aviation Icing ▪ strongest in the zone of mixed precipitation ▪ even at temperatures below -10° C Hail ▪ most frequently between 4.5 and 7.5 km ▪ also from overhanging cloud parts (anvil) => recommended distance cloud edge - aircraft during flights: - below zero degree line 5 NM - above zero degree line 10 NM Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 303 Thomas Hain Hazards of thunderstorms in aviation Turbulence ▪ There is a risk of turbulence in the transition zone between the upwind and downwind areas. => Formation of small turbulence eddies ranging from 15 to 150 m. ▪ Fast aircraft fly through the upwind and downwind areas very quickly. => strong and sudden accelerations upwards and downwards => material load => flying through the zone at reduced speed (turbulence penetration speed) ▪ also outside the Cb (squall line, microburst) Wind shear ▪ sudden change in wind speed and/or direction over a short distance Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 304 Thomas Hain Hazards of thunderstorms in aviation Lightning and electrical charge ▪ Most lightning strikes occur between +3°C and -5°C. ▪ As a result of the thermal effect of the lightning, damage to the sensors is possible. ▪ Passengers are protected by a Faraday cage. ▪ Electric fields can magnetise ferromagnetic materials. ▪ The flashes have a strong dazzling effect (especially at night). ▪ Electrical charging of the aircraft can lead to radio interference. Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 305 Thomas Hain Hazards of thunderstorms in aviation Heavy precipitation ▪ causes rapid and strong fluctuations in visibility Incorrect sensor displays ▪ Rapid changes in ground pressure (pressure mass) and turbulence can lead to incorrect altitude readings. ▪ Incorrect TAS readings occur as a result of the pitot tube becoming blocked by ice and snow. Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 306 Thomas Hain 7.2 Aircraft icing Aircraft icing: the deposition of ice, frost or snow on aircraft that are in the air or parked on the ground The intensity of icing in the presence of supercooled droplets depends on: ▪ the number ▪ the size ▪ the temperature of the supercooled droplets ▪ the aircraft's own speed ▪ duration of the flight in an icing zone Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 307 Thomas Hain Aircraft icing intensities The pilot finds information about icing in the Sign. WX - Charts SIGWX-(Forecast) Chart with information on aircraft icing conditions Source: WAFC London / DWD Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 308 Thomas Hain Aircraft icing intensities Symbol in weather maps Intensity no sign TRACE (barely perceptible, no significant accumulation) LIGHT (significant accumulations for prolonged flight (more than 1 hour)) MODERATE (significant accumulations for shorter periods of flight) SEVERE (rapid, dangerous accumulations) Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 309 Thomas Hain Types of aircraft icing Frost ▪ sublimation of water vapour on the aircraft when the temperature of the aircraft is below the frost point of the air ▪ white crystalline coating ▪ usually only to slight icing Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 310 Thomas Hain Types of aircraft icing Rime Ice ▪ is formed when small supercooled water droplets hit the surface ▪ density approx. less than 0.917 g/cm³ ▪ Water droplets freeze immediately on impact, causing the ice to adhere to the parts of the aircraft directly exposed to the airflow (leading edges of wings, antennas, etc.) => the ice build-up grows against the airflow. ▪ Air inclusions (air bubbles) give the rough ice a milky, opaque and porous (therefore easy to remove) character. Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 311 Thomas Hain Types of aircraft icing Rime Ice ▪ in STRATUS clouds only slight vertical movements and therefore only small water droplets exist e.g. in the St and As and in the lowlands in the Ns with light to moderate intensity temperature range -1°C and -15°C Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 312 Thomas Hain Types of aircraft icing Rime Ice ▪ in CUMULUS clouds above the -15°C isotherm, as the strong updrafts ensure a large number of small drops even at these altitudes e.g. in the Cb, Cu and Ac with moderate to strong intensity mostly light in the anvil of a Cb Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 313 Thomas Hain Types of aircraft icing Clear Ice ▪ is caused by the impact of very large and only slightly supercooled water droplets, which can spread out as a film of water before freezing => Icing also occurs in places on the aircraft that are not directly hit by the water droplets e.g. control surface gaps) ▪ is denser and more homogeneous than rime ice ▪ adheres very firmly to the aircraft (difficult to break off), is glassy, transparent and very hard ▪ mostly found in the temperature range 0°C and -6°C The ice formation severely disrupts the airflow and is responsible for an increase in drag that may be as much as 300 to 500%. Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 314 Thomas Hain Types of aircraft icing Clear Ice ▪ in STRATUS clouds only if there are strong vertical movements in it e.g. Ns in mountain congestion (often as a mixture of time and clear ice) or in the area of fronts with moderate to strong intensity Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 315 Thomas Hain Types of aircraft icing Clear Ice ▪ in CUMULUS clouds extreme risk of icing in the Cb, as the strong updrafts carry large droplets up to high altitudes and trigger condensation processes very quickly in exceptional cases at temperatures colder than -25°C with moderate to strong intensity strongest intensity in the Cb in temperature range 0°C to -15°C Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 316 Thomas Hain Types of aircraft icing Freezing Rain ▪ If snow falls from a layer with temperatures colder than 0°C into a layer with temperatures warmer than 0°C, melts into rain and this rain falls again into an underlying layer with negative temperatures, freezing rain occurs. Height Temperature T < 0° C / Snow 1500 ft * * * * * * * 900 ft T > 0° C / Rain * 300 ft T < 0° C / freez. Rain Development of freezing rain -4 0 +4 °C Temperature Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 317 Thomas Hain Types of aircraft icing Freezing Rain ▪ Moderate to heavy icing often occurs, whereby the aircraft can ice up completely in a very short time. ▪ The properties of the resulting ice are very similar to those of clear ice. ▪ Freezing rain occurs particularly frequently on warm winter fronts and warm front occlusions. Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 318 Thomas Hain Aircraft icing depending on the speed of the aircraft Aerodynamic heating ▪ During a flight, frictional heat is generated by the friction of the air on the aircraft parts exposed to the flow, which leads to an increase in temperature at the relevant points. => the icing zone shifts (vertically) upwards into an area of lower temperatures. ▪ The temperature increase is not the same on the entire aircraft. It is greatest on the surfaces exposed to the airflow (leading edges) => a different start of the ice build-up is often the result ▪ As part of the heat generated during a flight in cloud air is used to evaporate cloud droplets, the aerodynamic heating in cloud air is less than in dry air. Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 319 Thomas Hain Aircraft icing on fronts ▪ Fontal clouds have a higher icing probability than other clouds. ▪ In frontal zones, the strong lifting processes lead to the formation of very dense clouds, in which an increased number of supercooled water droplets are available in the mixing area. ▪ Fronts in particular, which are associated with convective rearrangements, show massive high-reaching icing zones. ▪ About 85 percent of the observed aircraft icing occurs in the vicinity of frontal zones. ▪ Some fronts with their typical icing zones are shown below. Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 320 Thomas Hain Aircraft icing on fronts Icing zone on a stable warm front Altitude 9 km 6 km ICING Cold air 3 km 200 km 0 km 200 km 400 km 600 km 800 km Icing zone on a stable warm front Distance Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 321 Thomas Hain Aircraft icing on fronts Icing zone on a unstable warm front Altitude 9 km 6 km ICING Cold air 3 km 200 km 0 km 200 km 400 km 600 km 800 km Icing zone on a unstable warm front Distance Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 322 Thomas Hain Aircraft icing on fronts Icing zone on an unstable cold front Altitude 9 km 6 km Cold air ICING 3 km Gusts 800 km 600 km 400 km 200 km 0 km 200 km 400 km Icing zone on a unstable cold front Distance Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 323 Thomas Hain Aircraft icing - forecast The pilot finds information about icing in the Sign. WX - Charts SIGWX- (Forecast) Chart with information on aircraft icing conditions 13 Jan 2025, 06 UTC Source: WAFC London / DWD Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 324 Thomas Hain Aircraft icing - forecast ADWICE The ADWICE product is one of the tools made available to pilots for No or Light ice forecasting aircraft icing. The strength of the icing and the altitude range in which icing occurs are indicated. Severe ice Moderate ice ADWICE Source: DWD Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 325 Thomas Hain Effects of aircraft icing on aircraft Icing of parts or the entire aircraft leads to: change in profile contour weight increase asymmetry and vibrations blocking of the flight control surfaces loss of power to the engines failure of displays and radio equipment loss of visibility due to freezing of aircraft windows or parts Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 326 Thomas Hain Effects of aircraft icing on aircraft The icing on the aircraft means that: the bouyance, thrust and rudder effect decrease the air resistance, the weight and the stall speed increase Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 327 Thomas Hain Technical options for preventing aircraft icing pneumatic de-icing (rubber mats (boots), which are inflated cyclically by compressed air during the flight) liquid de-icing (on the ground and in the air) electrical de-icing (heating) using of hot turbine air Meteorology in Aeronautics Part 7 Chair of Air Transport and Logistics 328 Thomas Hain