AVIATION 120

1
AVIATION 120

• Meteorology

2
Todays Agenda

• Causes of instability
• Modifications
• Cloud development

3
Causes of Instability

• Increasing the steepness of the environmental
  lapse rate will increase the instability of the
  air
• Any process that will cool the air aloft and/or
  heat the air at the surface will steepen the ELR
• Such processes include
• Cooling aloft
• Warming at the surface
• Mixing
• Lifting

4
Causes of Instability (cont.)

• Cooling aloft can be caused by
• Cold air advection aloft
• Radiational cooling
• Warming at the surface can be caused by
• Air moving over a warm surface (Advective
  warming)
• Warm air advection
• Daytime heating of the surface
• Localized warming such as fires and industrial
  activity can cause instability

5
Causes of Instability (cont.)

• Mixing can be caused by
• Wind induced turbulent eddies (mechanical
  turbulence)
• Convection

6
Causes of Instability (cont.)

• Lifting
• Due to the fact that lifted air stretches out,
  the top of a lifted layer will cool more than the
  bottom
• Saturated lower level in a lifted layer can also
  enhance instability of a lifted layer
• Air may be lifted due to frontal lift, terrain,
  convergence at the surface and/or divergence aloft

7
Modification of Stability

• Not only can instability be caused by surface
  warming, cooling aloft, mixing or lifting, but
  stability can be modified by these same processes
• Stability will be increased with warming aloft,
  surface cooling, descending air and reduced
  mixing

8
Cloud Development

• Most clouds develop from one of the following
• Surface heating and free convection
• Widespread ascent due to convergence of surface
  air
• Frontal lift
• Topography

9
Categories of Cloud

• Layer type clouds form in stable air
• Fog, Stratus, Nimbostratus, Altostratus,
  Cirrostratus, cirrus, etc.
• Stable air moving over mountains can cause
  mountain wave type cloud
• Altocumulus Standing Lenticular (ACSL), banner
  clouds, rotor clouds
• Vertically developed clouds form in unstable air
• Cumulus, Altocumulus, Altocumulus Castellanus,
  Towering Cumulus, Cumulonimbus etc.

10
Cloud Development in Unstable Air

• Convection or forced lifting will cause air to
  rise and as a result, cool
• Initially, if the air is unsaturated, it will
  cool 10C for each 1000m (DALR) it rises
• If/When the air saturates, it will continue to
  cool, but a a much slower rate which averages 6C
  (SALR) for each 1000m it rises
• If the air saturates, this is the level of the
  base of any vertically developed cloud
• If the air is conditionally unstable, saturation
  will cause the air to become unstable and the air
  will continue to rise buoyantly
• Convective cloud bases can be estimated using the
  formula H(ft)228(T-Td) See Focus, pg 155,
  Meteorology Today

11
Development of a Cumulus Cloud
12
Types of Vertical Clouds
13
Cloud Development due to Topography
14
UACN01 CYEG 102227 EG UUA /OV CYXY 270130 2227
FL 330 /TP B747 /RM BRF 1 TO 2 MIN OF SVR WAVE
TURBC.... EGACC/FIC