Basic Aviation Meteorology

5/20/2015

Basic Aviation Meteorology

Basic Aviation Meteorology Atmosphere Formation of Cloud Wind and windshear Thunderstorm

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Atmosphere Troposphere (7km-20km above surface) 99% of atmosphere water Most weather Higher altitude lower temperature

Tropopause (ceiling of Troposphere Most flight

Stratosphere (13km-50km above surface) Higher altitude higher temperature

Formation of Cloud Dew point – The temperature at which the water becomes saturated Associated with relative humidity (RH) When air is cooled to its dew point, water vapour condenses into droplets and forms cloud

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Formation of cloud Cloud base: height of cloud = (Ground temperature – dew point) x 400 Why cloud base? Formation of clouds: Orographic lift Advection Turbulence Convergence

Formation of cloud

Orographic lift

Advection (fog)

Turbulence Convergence

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Wind and Windshear Uneven heating of earth surface Different temperature, different rate Air rise – low pressure (air cool and condense) Air sink – high pressure Flow: High to low Wind

Wind and Windshear Lines joining points of equal sea-level pressure Coriolis force

isobars

Earth rotate anti-clockwise

Wind: vector of Pressure Gradient x Coriolis force

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Wind and Windshear Jet Stream Strong upper level winds Flow from West to East, stronger in Winter Japan 100-250 knots (Nautical mile/hr) HK-Vancouver shorter than reverse

Wind and Windshear Windshear Change of wind direction (head wind/tail wind) and/or speed Affect aircraft lift (and descend rate) May cause loss of control

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Wind and Windshear Common causes of windshear: Mountain wave Microburst Microburst: Intense localized cool air descends and spread onto the ground.

Diagram extracted from HKO website 2014

Wind and Wind shear Turbulence Rapid irregular motion of air Usually happen in clouds due to up and down movement of air mass Clear Air Turbulence (CAT) – dry therefore “Clear” or invisible Mountain wave Jet stream Weather radar impossible to detect

Source: SCMP http://www.scmp.com/news/hong-kong/article/1430508/eleveninjured-hong-kong-bound-cathay-flight-hit-turbulance-over?page=all

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Thunderstorm Contains nearly all weather hazards: Strong wind/ windshear/ turbulence Heavy rain (poor visibility) Lightning Severe icing Hails

Cause: 1. Unstable atmosphere (low pressure?) 2. Supply of moisture 3. Uplift of air mass

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Thunderstorm Uplift of air mass: Orographic lift Cold front

Phenomenon Towering cloud Cumulonimbus (Cb)

Avoid in all cases Safe to fly above? Near edge? Why Singapore no typhoon? QZ8501

Bibliography Aircraft General Knowledge, Navigation, Meteorology, Jeremy M Pratt, Airplane Flight Equipment Limited, 2003. ISBN: 9781874783183

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