Meteorology Flashcards
Describe the Tropopause
The Tropopause is the boundary between the Troposphere and the Stratosphere where temperature stops decreasing with altitude. It starts at approximately 8 km above the poles at -40C to 18km and -70C over the equator
Why does the stratosphere heat up with altitude above its isothermal layer?
Because the Ozone layer sits above the stratosphere. The ozone layer absorbs UV Ray’s which cause it to heat up.
What is radiation?
Radiation - anything with a temperature above absolute zero (-273 C) radiates heat energy in the form of electromagnetic waves.
As heat increases, wave length decreases. The Suns is short wave radiation, known as insolation, and the earths is long wave radiation, known as terrestrial radiation.
Heat transfer through radiation can occur in a vacuum.
What is convection?
The transfer of heat through movement of a body. The earths surface heats air which in turn decreases in pressure and rises. As it cools it travels horizontally, known as advection. It then sinks. Convection and advection together create circulation.
What is conduction?
Conduction is the transfer of heat through contact. The earths surface is heated by insolation from the sun which then heats the air on the surface through conduction. Air is a poor conductor so only the air close to the surface is heated. This is why temperature decreases with height close to the earth.
Less than half of the insolation from the sun is absorbed by the earths surface. Where is the rest lost?
Scattering by airborne particles and reflection from the ground and cloud tops.
What is the greenhouse effect?
Terrestrial radiation from the earth is absorbed by water and carbon dioxide molecules in the atmosphere and radiated back to the surface.
What is an isotherm?
A line on a weather map joining two places of the same temperature
What is diurnal variation?
The change of temperature over 24hours. Over sea is usually 1C due to the high specific heat of the ocean. Desert can be around 20C.
Wind will mix up air and reduce diurnal variation compared to calm conditions.
Cloud cover prevents heat transfer to and from the surface, thus reducing diurnal variation.
What is an isobar?
A line on a weather map joining places of equal pressure
What is QNE?
Question nil elevation. With 1013.2 set on a subscale the altimeter will read pressure height or QNE.
In what layer of the atmosphere is most of the water vapour, clouds and weather found?
The Troposphere
What three factors affect density?
Pressure and density are directly related.
Temperature and density are inversely related.
Humidity and density are inversely related.
How does an increase in density affect aircraft performance?
It improves aircraft performance.
What three effects cause air pressure to change?
The movement of pressure systems.
The change in intensity of pressure systems.
The expansion and contraction of the atmosphere as it heats and cools.(semi diurnal variation)
What is QNH?
QNH is the true sea level pressure. When set on a subscale it will read actual elevation AMSL.
Area QNH is the average for a given area and will not differ from an adjoining area or local QNH by more than 5 HPA
What is the transition layer?
The layer in which aircraft may not cruise. It’s base is 10,000’ and its ceiling is determined by QNH. FL110-FL125. A decrease of approximately 17HPA from 1013 will lead to an extra 500’.
FL110 not available below 1013
FL115 below 997
FL120 below 980
FL125 below 963
What will an altimeter read when flying level towards low pressure?
It will over read as if it were in a climb
What does a adiabatic mean?
A temperature change due to a change in pressure
What is a turbulence inversion?
Winds at low level may cause adiabatic expansion and cooling due to mixing. If the lower layer becomes cooler then an inversion forms.
What is a subsidence inversion?
As a column of air subsides, the top of the column undergoes greater heating and compression than the bottom. This creates an inversion.
What is a surface inversion?
Air close to the earths surface is cooled at night by conduction. Greatest at dawn
What is a frontal inversion?
The boundary of two masses can become an inversion as Warm air is lifted by cool air
Define stability, instability and conditional stability in the atmosphere.
Stability-when a parcel of air is lifted and its temperature becomes less than the surrounding environment and sinks once the lifting force is removed. ELR ELR > SALR
Instability - when a parcel of air is lifted and its temperature becomes more than the surrounding environment and continues to rise once the lifting force is removed. ELR > DALR
What are the lapse rates for; Dew point? Dry air? Saturated air? ISA? Actual Environment?
0.6*C per 1000’
3*C per 1000’
1.5*C per 1000’
2*C per 1000’
Must be measured in actual atmospheres
What is relative humidity?
The ratio of water in a sample of air compared to its water volume at saturation.
Relative humidity = actual mass of water vapour \ mass of water vapour at saturation
What is latent heat?
The heat which is required to change a substance to a higher state and released to change to a lower state.
There is no change in temperature, just state.
Lower - Solid, liquid, gas - higher
How can you can determine the base of a cloud base?
Surface Temperature - Surface Dew Point Temp
Divide by the DALR-DPLR (2.4)
Answer is in thousands of feet
What is a Fohn Wind?
Fohn wind is the warm dry air on the lee slide of a mountain.
Humid air is forced to rise over a mountain forming cloud as it cools adiabatically. Latent heat is
released by the process of condensation and carried with the air down the lee side of the mountain as warm dry air.
What do the terms veer and back mean?
Veer - wind changes in a clockwise direction
Back - wind changes in an anticlockwise direction
What is the difference between a squall and a gust?
Gusts are a sudden increase in wind lasting a short period of time.
Squalls are a sudden increase of wind of at least 16 knots and last for at least one minute reaching up to 22 knots
Describe pressure gradient force.
The tendency for air to flow from heigh to low pressure across isobars
Describe coriolis force
In the Southern Hemisphere the earths rotation causes air to deflect to the the left. The deflection is greatest at the poles and nil at the equator. The stronger the wind speed the greater the deflection
What is Buy Ballots Law?
With your back to the wind in the southern hemisphere, the wind will be on your right.
From the equator to the South Pole, list the main systems of the global circulation pattern.
Equatorial trough
Subtropical ridge
Sub polar low
Polar high
Why does Australia have a “wet season”?
In summer the equatorial trough moves poleward of the equator due to the tilt of the earths axis exposing one hemisphere to greater heating.
Air flowing towards the equatorial trough crosses the equator and is deflected by the Coriolis effect (left in SH) this gives rise to north westerly winds. As these winds pass over the sea they bring warm moist air.
As there is more land heating the equatorial trough in the northern hemisphere during summer it travels further poleward.
What winds form from the subtropical ridge in Australia during winter?
During winter in Australia air flows from the subtropical ridge to the equatorial trough. This brings moist air to the east coast but mostly dry air to northern Australia.
Strong north westerlies are generated below 40*S as air flows from the STR to the Sub Polar Low.
What are geostrophic and gradient winds?
Geostrophic winds flow parallel to straight isobars
Gradient winds flow parallel to curved isobars
What is the friction layer?
The lower 3000’ of the atmosphere. Wind speeds reduce by ~2/3 over land and ~1/3 over sea.
Reduction in speed reduces the coriolis effect and winds tend to veer compared to winds aloft. 30 degrees over land and 10 degrees over water due reduced friction.
Winds aloft tend to flow parallel to isobars. Surface winds flow across isobars from high to low pressure.
How are land and sea braces created?
The breeze flows towards the hotter of the two to replace the rising air. As land heats and cools quicker than the sea (sea has a height specific heat) it is common to have a sea breeze during the day and land breeze night.
What causes katabatic and a anabatic winds?
Anabatic - Air on a mountainside is heated by conduction, density reduces and rises up the hill
Katabatic - air on a mountainside is cooled by conduction density increases and sinks down the hill
What clouds form in the lower etage?
Cumulus: mound or tower like clouds formed from convection or other lifting. Made up from supercooled/water droplets & ice crystals. Showers of rain or snow with occasional virga. Little icing risk.
Stratus: flat, grey cloud formed from orographic lifting of stable air, made of water droplets & drizzle is typical. Usually no icing.
Stratocumulus: greyish layer formed from surface level turbulence or cumulus spreading out in an inversion. Consists of water droplets, light rain or drizzle & occasional rime ice if above freezing level.
Nimbostratus: dark, low ragged clouds at the base, heavy, continuous rain or snow. Common in slow moving fronts, usually formed by convergence. Moderate rime ice, clear ice at lower levels especially in turbulence.
Cumulonimbus: Heavy, dense clouds with great vertical extent. Developed from any lifting in a conditionally stable atmosphere. Composed of supercooled/water droplets, hail, snow & ice crystals. Clear icing.
What clouds form in the middle etage?
Altocumulus: clumpy white or grey clouds made of supercooled/water droplets, formed in turbulent middle levels usually below an inversion, convection, orographic lifting in low humidity. Light rain or snow may fall in the form of virga, light rime ice.
Altostratus: thin, grey cloud covering the sky, formed from frontal lifting or convergence. Contains supercooled/water droplets & ice crystals. When thick, can produce intermittent rain or snow sometimes as virga. Moderate rime ice; clear ice possible in lower levels.
What clouds form in the higher etage?
Cirrocumulus: thin layer of cloud made of ice crystals & liquid droplets, associated with frontal lifting or convergence. Occasional light to moderate turbulence. Too high for significant icing.
Cirrostratus: thin, transparent cloud often covering the entire sky, associated with frontal lifting or convergence, made of ice crystals. Occasional light to moderate turbulence. Too high for significant icing.
Cirrus: associated with frontal lifting or convergence in a low pressure system. Made of ice crystals. Occasional light turbulence, no icing
