Meterology Flashcards
What is an isobar?
Are lines of equal pressure and usually depicted at 4 hPa intervals. They indicate the rate of pressure change over a horizontal distance; the closer together higher-pressure gradient.
What is plotted on a synoptic chart?
isobars, lows, highs, troughs, ridges and cols.
What are ‘Lows/Depression’ or Cyclones?
Pressure is lowest at the centre and can vary in size from hundreds of feet to thousands of miles. They are by convention annotated with an ‘L’ at the centre.
What are Highs/Anticyclone?
The highest pressure is at the centre annotated with an ‘H’. This a stable air mass than can extend thousands of miles. The isobars tend to be more widely spaced than in a low.
What are Troughs?
Pressure is lower in the trough than at the two sides, indicated by isobars extending outwards from an area of low pressure. The isobars often appear in a sharp ‘V’ shape.
What are ridges?
A spur of higher-pressure extending form the high-pressure area. The associated isobars are always rounded, never V-shaped.
What are Cols?
A region of almost uniform pressure between two highs and two lows.
What are the ISA conditions?
Surface pressure = 1013.2 hPa (29.92 in Hg)
Surface temperature = 15 °C
Up to 11 km (approx. 36 000 ft) the temperature decreases at 6.5 °C/km (approx. 1.98 °C/1000 ft)
Above 11 km (approx. 36 000 ft) the temperature remains constant at -56.5 °C
At sea level the density (ρ) is 1.225 kg/m³
What is the height is the height of the tropopause?
On average the height of the tropopause is about 5 miles (25 000 ft) over the poles, 7 miles (35 000 ft) over the UK and 11 miles (55 000 ft) over the equator
What is the significance of the tropopause?
Wind speed is often at a maximum near (usually just below) the tropopause. This is where jet streams (winds in excess of 80 kts) can occur.
Since clouds rarely occur above/at the tropopause severe turbulence can be experienced without visible cues and is called Clear Air Turbulence (CAT). Long, persistent condensation trails (contrails) are most common around the tropopause.
Gas turbine engines are most fuel efficient at the tropopause. Efficiency increases as the ambient temperature drops. Above the tropopause, the reduction in density is not counterbalanced by any further reduction in temperature, so on any given day, the most fuel efficient level for a jet engine is the tropopause.
When do normal icing conditions occur?
Almost all icing occurs in air temperatures between 0°C and -20 °C, however, it can occur above 0 °C if the aircraft surface temperature is below 0°C. Below -20 °C icing is rare (the air is dry), though physical limit extends to -40 °C.
What are the general rules for icing related to convective clouds?
Below -40 °C: chance of icing is small
-40 °C to -20 °C: light icing possible; severe unlikely except in newly developed clouds
-20 °C to 0 °C: rate of icing may be severe over substantial depth of cloud
What are the types of icing severity?
Trace
Light - 0.5 cm in 15-60 minutes
Moderate - 0.5 cm in 5-15 minutes
Severe - 0.5 cm in less than 5 minutes - The ice protection systems fails to remove the accumulation of ice.
What are the hazards of Icing in flight?
Visibility
Weight
Engine Intake
Aerodynamic Effects
Undercarriage
Pitot Tubes and Antenna
Vibration
Communications
Control Services
What is an Air Mass?
Air masses are large volumes of air with largely uniform temperature and humidity.
