Frost
Frost is frozen dew that has been left out over night. It can disrupt airflow over the wing causing a loss of lift and an increase in drag.
Hoar frost
When an aircraft has been cruising at high altitiude for a few hours It finally cools to the out side air temp
If it descends into a warmer layer of air sometimes the air will skip the water state and turn straight to ice.
The aircraft wont experience many problems and the ice will melt as it keeps descending to more hot atmosphere.
Thunderstorms conditions nessecary
The atmosphere must be condiotionally unstable or unstable from the surface to high levels (usually throughout the trophosphere)
Any mechanism that produces a rapid cooling of the enviroment with increased height, ie hgih enviromental lapse rate (ELR), will cause the atmosphere to tend towards instability. either heating of the bottom layers or cooling of the top layers increases the ELR and reduces atmospheric stability.
High humidity.
There must be sufficient water vapour present in the atmosphere to produce large, well developed cumulonimbus cloud. the latent heat realeased during the formation of these clouds increases there bouyancy and enhances their development.
A trigger mechanism
Some mechanism must be present to produce the intial lifting of the surface air. once it has been lifted, the latent heat realeased during the cloud formation and the conditioonally unstable atmosphere will ensure its continued ascent. thunderstorms are sometimes classified according to the trigger mechanism that was involved in the initial lifting of the surface air.
The different types of thunderstorms
Heat or convective thunderstorms thunderstorms
frontal thunderstorms.
cold stream thunderstorms
Heat or convective thunderstorms
These are formed when the initial lifting is caused by solar heating of the surface. these thunderstorms typically begin forming in mid afternoon during the summer months.
cold stream thunderstorms
Form in a cold airstream which moves rapidly across into warmer latitudes
good example is cold air moving south to north of the hemisphere. the latitudinal heating of the surface layers does not depend on direct solar heating, so it continues over day and night. the lighting from these storms can be seen over the ocean throughout the night.
frontal thunderstorms
are formed when the intial lifting is caused by solar heating of the surface. these thunderstorms typically begin forming in the mid afternoon during the summer months.
Nocturnal thunderstorms
Are named after a process that enhances the growth of a large cloud over the ocean at night.
After dark the temperature ocean surface remains almost the same as it was during the day.
Due to water being high specific so it stays hot at night but the air above it is cooled due to it being nighttime.
This causes aggresive convection and forming large towering cumuli cloud.
Orographic thunderstorms
These thunderstorms are triggered along a well formed trough of low pressure. as the surface- air veers across the iso bars towards the lowest pressure, the air along the trough line folds back on
Stages of development
The development of a thunderstorm is usually divided into 3 stages according to the nature of the air movement within the cloud
What does a thunderstorm need to form
For a thunderstorm to form it usually requires a large towering cumulus cloud with vigourous growth.
The developing stage
During this stage all of the air movement is upwards within the cloud.
The edges and top is growing rapidly and large water droplets and snow flakes are suspended in the strong updrafts.
there is no precipitation in this time of the cloud.
The mature stage (updrafts)
Water in the cloud begin to grow large and are to large to be supported by the updrafts
The mature stage (friction)
Friction between the falling droplets and surrounding air causes air to move down with them. Because of the unstable nature of the cloud, this downward movement becomes a strong downdraft.
Both updrafts and downdrafts exist in the cloud producing strong horizontal windshear and severe turbulence as they rush past eachother.
thunderstorm updrafts speed
The updrafts in a thunderstorm reaches vertical speeds as high as 10000ft per min and can reach heights of 40000ft
How is the anvil of a thunderstorm created.
The rapid ascent of air (updraft) accelerates towards the top of of the storm where its inertia actually causes it to overshoot where the air meets its enviroment air causing a overshoot dome. (mushroom)
