Thunderstorms
What are the 3 conditions necessary for thunderstorm formation?
-Moisture
-Unstable Air
-Lifting
Name the 3 types of ice and drop size.
- Clear (large drops)
- Rime (small drops)
- Mixed (combination of small and large drops)
What is a dry line?
The zone between two air masses differing only in moisture. Sometimes called a dew point line or Marfa Front.
What is a Jetstream?
It is a narrow band of high wind speed winds, 50 kts or greater.
What is the source of all earth's weather?
The sun, solar radiation
Which stage of a thunderstorm has predominantly downdrafts?
Dissipating
What conditions are necessary for icing?
Visible moisture and freezing temperatures
What is air density?
The mass of air molecules in a given space.
-Decreases with altitude and is affected by temperature and humidity.
-High density air = Low density altitude
-Low density air = High density altitude
How do the winds flow in relation to isobars?
Nearly parallel
What are the first 4 layers of atmosphere?
-Troposphere
-Tropopause
-Stratosphere
-Stratopause
What are the 3 stages of a thunderstorm?
- Cumulus
- Mature
- Dissipating
How does frost form and why is it dangerous to an aircraft?
- Forms on clear, cool nights, with light winds and the surface cools below to below freezing and the dew point is 0 C or less.
- Its dangerous because it disrupts the the airflow which prevents the aircraft from becoming airborne.
What is a ceiling?
Height above the earth's surface of the lowest cloud layer classified as broken or overcast, or vertical visibility into a surface based total obscuration.
What are the 2 primary forces that affect global winds? Explain each
-Pressure Gradient Force - Force driving winds from high to lower pressure
- Coriolis Force - Deflection force of winds due to the earth's rotation.
What determines stability?
Temperature Lapse Rate
Name some hazards associated with thunderstorms.
Lightning, Icing, Wind shear, Hail, Turbulence, Squall Lines, Tornadoes, and Microburst.
What is induction icing?
Air that is drawn into the engines creates an area of reduced pressure at the inlet, which lowers the temperature below that of the surrounding air. In conditions where icing is possible, this reduction in temperature may be sufficient to cause ice to form on the engine inlet, disrupting the airflow into the engine.
What are the characteristics of a Warm Front?
- Visibility is usually reduced.
-Cloud heights are typically very low.
- Usually slow moving and winds are usually light.
-In wintertime, expect icing conditions ahead of the front.
Explain how the winds flow around a Low and High Pressure system.
- Low Pressure System - Counter-clockwise, inward and upward
-High Pressure System - Clockwise, outward and downward
What is ISA?
International Standard Atmosphere (ISA)
It is the model atmosphere based on average distributions of pressure, temperature, and density.
Name the 2 classes of thunderstorms and explain how they formed.
-Air Mass Thunderstorms. Formed by convection.
-Steady State Thunderstorms. Formed by fronts and pressure systems.
Name the 5 effects of icing on an aircraft.
-Increased Stall Speed
-Increased Drag
-Increased Weight
-Decreased Lift
-Decreased Thrust
What are the characteristics of a Cold Front?
- Visibility is usually good and cloud heights are usually high.
-High winds may proceed and follow frontal passage.
- Fast moving fronts may contain supercell thunderstorms.
When flight planning east and west what are the pros and cons of riding the Jetstream?
- East - You can ride the Jetstream which will give you a greater tail wind saving you time and fuel, as well as increase your ground speed.
- West - Should avoid the Jetstream because you will be flying into a stronger headwind, which will decrease your ground speed and cause your flight time to be longer and to burn more fuel.
What is the Avg. temperature lapse rate, Avg. pressure lapse rate, standard temperature at sea level, and standard pressure at sea level?
Avg. Temp. Lapse Rate - 2 C / 1,000'
Avg. Pressure Lapse Rate - 1 in hg / 1,000'
Standard Temp. at sea level - 15 C or 59 F
Standard Pressure at sea level - 29.92 in hg or 1013.2 mb