Aviation Meteorology

What is convective Turbulence, where are the updrafts more intense and what marks the top of these updrafts?

Convective Turbulence is the vertical movement of air caused by heating. Instability arises when air at lower levels is heated and becomes less dense than surrounding air and rises. Subsidence then occurs around the rising air. This creates eddies in between the rising and falling pockets of air. These updrafts are more intense over bare ground, rocky and paved areas. These updrafts are marked by fair weather cumulus clouds

What are the favourable conditions that a mountain wave needs to form?

Winds of 30kts or more at the mountain tops from a constant direction within 30 degrees of being perpendicular to the ridge line. And most importantly, a layer of stable air just above the mountaintop

What density altitude do you generally find in low pressure systems and why?

You usually find higher density altitudes because air molecules spread out in low pressure systems making the air thinner therefore making the aircraft feel like it is flying at a higher altitude

What factors determine the size and height of mountain and rotor eddies?

Roughness of terrain and convention as well as the speed and angle of the wind flowing over the mountain

What is subsidence?

Air descending from a higher altitude to a lower altitude

What is Evaporation Non-Expansional Cooling?

This phenomenon occurs during precipitation when some of falling rain evaporates into the surrounding air which results in energy or heat being absorbed therefore cooling surrounding air

What is an Isothermal Layer?

A layer of air where the temperature does not change with altitude

What is the Dry Adiabatic Lapse Rate

3 degrees Celsius per 1000ft

What is the Saturated Adiabatic Lapse Rate?

1.5-1.8 degrees Celsius per 1000ft

What does Adiabatic mean

It means a change in temperature caused by expansion or compression without exchanging heat from surrounding areas

What are isobars?

Isobars are lines drawn on a surface weather map that join areas of similar pressure at 4mb intervals

What is Pressure Gradient

Is the change in pressure in regards to distance. The shorter the distance the stronger the winds and vice versa

What is a Trough and what does it cause?

It is a line of low pressure that extends out from the centre of a low pressure system to such an extent that the pressure on either side is lower which causes lower level convergence and expansional cooling

What is the height of the troposphere?

It averages at about 36,000ft but can get as low as 26,000ft over the poles and 59,000ft at the equator

What are the 2 process that heat the Troposphere called?

Conduction and terrestrial radiation

Define Mechanical Turbulence

Mechanical turbulence and the irregular swirling motion of air that is caused when wind flows over surface obstacles such as hills, trees and city buildings. This friction breaks smooth horizontal winds into choppy eddies that affect the very lower levels of the atmosphere

Explain Anabatic and Katabatic Winds

Anabatic winds occur when the sun heats an ice and snow free mountain slope. This air becomes less dense and rises up the slope. Katabatic winds are the opposite. These slopes cool during the evenings and as the air becomes dense, it rides down the slope into the valley below. This can also occur during the day on snow and ice covered slopes.

Explain Land and Sea Breezes

During the day land warms faster than the oceans. Through conduction, the air over land warms and becomes less dense than the air over the sea and rises. The air over the water then moves in to replace the rising air creating what is known as a sea breeze. A land breeze is the exact opposite as land also cools faster than the sea during the evening and night

What are Diurnal Winds and what are some common examples?

Diurnal Winds are localised thermally driven wind cycles cause by the heating and cooling cycles of day and night time. The most common types are land, sea, valley and mountain breezes

What can prevent Nocturnal Cooling?

An overcast sky at night will reflect the infrared radiation released by the land and sea back towards the surface

What is Convection?

The vertical movement of air based on density

What is Saturation?

The point at which the moisture content of the air has reached the limit at that given temperature

Explain Dew Point

It is the temperature at which air must be cooled to as it rises to become saturated and produce visible condensation at that given pressure

What is Terrestrial Radiation?

Is UV radiation that is absorbed by the land or water than is then re-radiated back into the atmosphere as infrared radiation

Does land or water cool faster and night and why?

Land cools faster as water can hold roughly 4 times the heat and therefore has more heat to release

What are the 4 layers of the atmosphere called?

Troposphere, Stratosphere, Mesosphere and Thermosphere

Explain how temperature can affect an altimeter

An altimeter reads the weight of the atmosphere directly above it. Cooler air is denser and therefore weighs more and vice versa. If the temperature varies greatly from the MSLT then errors can occur.

What happens to the relative humidity as air cools or heats?

RH increases as air cools because cooler air cannot hold as much moisture as warmer air

What are the 3 things that can cause altimeter errors?

Pressure, Temperature and the Mountain Effect

What is Conduction and what height is affected?

A process where an object is heated or cooled by coming into contact with another. The affects of conduction do not typically exceed 4000ft

What is ISA Deviation used for?

To determine an aircraft’s performance compared to a standard atmospheric day

What is Latent Heat in meteorology?

Is energy that is absorbed or released as water vapour changes form in the atmosphere

What is Relative Humidity

The actual water content of the air compared to the potential content expressed as a percentage

What are condensation nuclei?

Particles that water vapour attaches to in the atmosphere

In which system does the centrifugal force move with the PGF

High pressure system

What are the 2 factors that affect the strength of the Coriolis Force?

Wind Speed - the stronger the winds the more the CF deflects the wind

Proximity to the Equator - the coriolis force has less of an affect closer to the equator

what are Geostrophic Winds

These are very rare but occur when the wind travels parallel to the isobars if they are straight and the coriolis force is equal to the pressure gradient force

What is the Pressure Gradient Force?

The movement of air from areas of high to low pressure

Which way to high pressure and low pressure systems rotate north of the equator?

High pressure rotates clockwise and lows rotate anticlockwise

Why are low pressure systems associated with clouds, rain and low visibility?

Upper level divergence acts as a ‘vacuum’ and causes air to rise. More air rushes in to replace the rising air. If rises enough it will eventually hit the dew point forming clouds, rains and low visibility

What happens when air rises to lower pressures?

It expands and cools because as molecules push outwards to occupy a larger a larger volume they lose kinetic energy and therefore heat

What is Orographic Lift?

Occurs when an airmass is forced to high elevations as it moves over higher terrain. This can cause expansional cooling and in increase in relative humidity

What is it called when the ELR is steeper than the DALR and the SALR?

Absolute Instability

What is it called then the ELR is steeper than the SALR but shallower than the DALR?

Conditional Instability. If the air is saturated the air mass becomes unstable but if it’s not saturated then it becomes stable

What is the ISA Mean Sea Level Pressure?

1013.25mb

What is the ISA Mean Sea Level Temperature?

15 degrees Celsius

Why are high pressure systems associated with fair weather?

Upper level convergence causes air to be forced down. Air falling means a more stable atmosphere as it resists air rising. Without air rising it’s less likely to hit the dew point and from clouds or precipitation. Also, as the air descends is goes through compressional heating, lowering the relative humidity and further moving the temperature away from the dew point

What are the processes that distribute heat to the upper levels of the atmosphere?

Convection, advection, compression, turbulent mixing and the release of latent heat

Define ELR

The actual observed rate at which air temperature decreases as elevation increases in a stationary atmosphere