meterolgy ( chapter 9 > required skills and knowledge )

Light turbulence

1. Momentarily causes slight, erratic changes in altitude

2. 0.5 g

3. Occupants may feel a slight strain against seat belts or shoulder straps

4. Unsecured object may be displaced slightly

5. Food service may be conducted

Moderate turbulence

1. Similar to light but greater intensity. Changes in altitude occur

2. 0.5 ~> 1.0 g

3. occupants definite strains against seat belts or shoulder straps

4. Unsecured objects are dislodged. Food service and walking are difficult

Severe turbulence

1. Causes large, abrupt changes in altitude. Aircraft may be momentarily out of control

2. Greater than 1.0 g

3. occupants are forced violently against seat belts or shoulder straps

4. Unsecured objects are tossed about. Food service and walking impossible

Gusts are

Rapid, temporary, localised increases in wind speed

Wind shear is

A strong difference in wind speed or direction over a relatively short distance

Vertical wind shear is

1. Is a change in horizontal wind direction and or speed and height

2. Often determined by two or more anemometers mounted at different heights

3. Expressed in kt / 100ft

Horizontal wind shear is

1. A change of horizontal wind direction and or speed and height

2. Often determined by two or more anemometers mounted at the same height along a runway

3. Expressed as kt / 1000ft

Low-level wind shear is

1. A string difference in wind speed or direction over a relatively short distance during thr approach and landing, or take-off

2. Potentially very dangerous

Wind shear is associated with

1. Thunderstorms ~ lots of gusts and micro / macro bursts

2. Fronts ~ large temperature difference

3. Inversions ~ change in wind speed or direction

4. Surface friction ~ large structures or buildings

Negative shear

A reduction in performance and airflow ~ dangerous

Positive shear

An increase in performance and airflow ~ causes deviations from intended flight path

Microbursts are

Small scale downbursts of 1 ~ 5 minutes, up to 4km across

Macro-bursts are

Larger scale downbursts, more than 4km across

Affects of downbursts are

1. Turbulence

2. Negative wind shear

3. Positive wind shear

What creates downbursts

1. String weather

2. Active weather

3. Convective weather

Development if downbursts

1. The large core of rain and hail, that the main updraft has been holding, collapses and falls rapidly

2. The rain and hail drags a lot of air along with it, gaining speed as it plummets earthward

3. Some of the rain evaporates, cooling the air, making it denser so the down draft becomes even stronger

Mountain waves

Form when the wind blows at approx 90 degrees relative to 5r mountain axis with a stable atmosphere. When crossing the ridge oscillates

The conditions necessary for thr formation of mountain waves are

1. Wind speed at mountain height must be at least 15 ~ 20 kts, increasing with height

2. Wind direction must be within 30 degrees of 5r perpendicular to the range of hills and mountains

3. Must be a region of marked stability

The common mechanisms for turbulence are

1. Convective ~ created by thermal activity as warm air will rise and cold air will sink

2. Mechanical ~ created by flow across trees, buildings

3. Orographic ~ created by flow across hills and mountains

4. Frontal ~ created by lifting of warm air by sloping front surface and friction between the two opposing air masses

5. Clear air turbulence ~ often associated with jet streams

Jet streams are

1. Narrow fast flowing currents of air

2. Have a speed of at least 60kts

3. About 2000NM long, 200NM wide, 2NM high