--- What is the relative importance of gravity wave breaking and Kelvin-Helmholtz instability to the turbulence hazard?
--- What are the processes leading to the enhanced hazard near thunderstorm anvils?
--- What is the structure and mechanism of turbulence in thunderstorm wakes?
From the animations above, its clear that shear layers of rapidly changing airspeeds, pressures, intensity and direction co-exist with the underlying structures of thunderstorms. Thunderstorm like those encountered by a
growing list of aircraft that have crashed when meeting them including
Malaysia QZ-8501
AF447
Incredible airspeed changes are possible when an airframe crosses boundary layers. By repeatedly crossing boundary layers between areas of high windspeed and low windspeed (and high pressure/low pressure zones), a kinetic transfer of airspeed gains are realized, and have been
looked at by NASA in research into perpetual flight, similar to the Albatross's seeming ability to cross oceans.
In Dynamic Soaring, a
3 Meter remote control glider has now been flown to 505 miles per hour -- airspeeds near the maximum airspeed attainable by an Airbus A320. Purely by repeatedly crossing boundary layers / shear layers, like the ones in the animation above, and gaining airspeed with each crossing.
High altitude windshear has similar effects and has the potential to overspeed an aircraft at cruise in one moment and then plunge it into a void of downwards stalling air the next moment, and repeat that process very quickly, confusing pilots, and taking auto-pilots offline.
Quote:
AIRBUS SAFETY LIBRARY
II.2 Defining Windshear
Windshear is defined as a sudden change of wind velocity and/or direction.
Windshear occurs in all directions, but for convenience, it is measured along vertical and horizontal axis, thus becoming vertical and horizontal windshear:
Vertical windshear:
−Variations of the horizontal wind component along the vertical axis, resulting in turbulence that may affect the aircraft airspeed when climbing or descending through the windshear layer
−Variations of the wind component of 20 kt per 1000 ft to 30 kt per 1000 ft are typical values, but a vertical windshear may reach up to 10 kt per 100 ft.
Windshear conditions usually are associated with the following weather situations:
•Jet streams
•Mountain waves
•Frontal surfaces
•Thunderstorms and convective clouds
•Microbursts.
Quote:
Influence of Windshear on Aircraft Performance The flight performance is affected as:
• Headwind gust instantaneously increases the aircraft speed and thus tends to make the aircraft fly above intended path and/or accelerate
• A downdraft affects both the aircraft Angle-Of-Attack (AOA), that increases, and the aircraft path since it makes the aircraft sink
• Tailwind gust instantaneously decreases the aircraft speed and thus tends to make the aircraft fly below intended path and/or decelerate.
I believe the effects upon airframes of thunderstorms and shear layers are not well enough understood and have played large roles in recent hull losses and life.
AF447's encounter with a the kinetic energy of a thunderstorm's 'turbulence':
Yemenia A310 Flight 626
A320 Alpha Floor Activation followed by initial overspeed and subsequent stall
The Pilot of this aircraft said :
I agree with the scientists studying these factors, that more research is needed.