Aviation Meteorology- Part 1

rc2017's version from 2017-09-05 16:10


Question Answer
IsothermsLines drawn on chart to depict areas of equal temperature
IsobarsIsobars are lines drawn on chart to depict areas of equal pressure
Dew Point temperatureThe dewpoint temperature is the temperature at which the air (at any given constant pressure + temperature) can no longer "hold" all of the water vapor which is mixed with it - reaches 100% humidity, so some of the water vapor condenses into liquid water when it comes in contact with any surface. A reducing gap between the actual temperature and the Dew Point temperature gives an indication of low visibility conditions
Dry Bulb TemperatureThe dry-bulb temperature is the temperature of air measured by a thermometer freely exposed to the air (shielded from moisture). It is usually thought of as true air temperature
What are the timings when minimum & maximum temperature are taken?Immediately after sunrise (min) & at app. 1400 hours (max)
If temperature is higher/lower, what happens to density? To pressure?Temperature and pressure are directly proportional to each other. This means that as the temperature decreases, the pressure also decreases & vice-versa. If temperature increases Volume increases therefore Density decreases. Inversely proportional.
What is sea breeze & when does it occur? & why?A coastal, localised, wind that blows from sea to land, it occurs in the day. Caused by the temperature difference when the sea surface is colder than the adjacent land
What is land breeze & when does it occur? & why?A coastal breeze blowing from land to sea, caused by the temperature difference when the sea surface is warmer than the adjacent land. A land breeze usually blows by night
Define MET visibilityIt is the lowest range of visibility within a whole of 360 deg of vision in all directions taken from a particular point of observation.
Fog, Mist, HazeMist and Fog are the terms used to describe low visibility caused by water droplets suspended in the air. Mist is a term used to describe visibility range 1-2 km while Fog is the term used when visibility is less than 1 km. Fog is like a surface cloud and affects the landing and take-off procedures. In haze visibility is reduced to lesser than 5 kms due to smoke, dust, water vapor
What are the groups of cloudCirriform (fibrous) Cumuliform (heaped) Stratiform (layered) Nimbus (rain-bearing)
Low level types of CloudsLow level cloud has a base below about 6,500 feet. Stratus (ST), Strato cumulus (SC), Nimbo Stratus (NS), Cumulus (CU) & Cumulo Nimbus (CB). Nimbostratus produces steady prec
Mid level types of CloudsMid level cloud range between 6,500 feet and 20,000 feet. Alto Stratus (AS), Alto Cumulus (AC)
High level types of CloudsHigh level cloud range the a base above 20,000 feet. Cirrus (CI), Cirro Stratus (CS), Cirro Cumulus (CC)
Which cloud is most hazardous to aviation? & why?CB Clouds or Cumulo Nimbus Clouds are most hazardous to aviation. They are associated with the following hazards: Base height of cloud is reduced Hail Icing Instrument Error Lightning Squall Windshear Microburst Precipitation (Rain, Snow, Mist, Fog …..) Thunderstorms Tornados Squall Water sprout V – poor visibility
What is RVR? When is RVR reported in METARRVR is the Runway Visual Range. It is reported in METAR when visibility is less than 1500 mtrs. RVR is measured with a transmissimeter (located end of runway)
What is METAR? Who issues them? Why are they important?METAR IS Routine Meteorological Aviation Report. They are issued by Aeronautical Class 1 Met Offices They are important because they give the current weather Wind direction, wind speed, visibility (RVR is less than 1500 mtrs), types of cloud & ceiling, temperature, pressure (QNH)
What is SPECI? Who issues them? Why are they important?SPECI is selected special report of an aerodrome issued by Aeronautical (class 1) Met offices whenever significant changes occur in the conditions given in the previous METAR. They are important because they give significant changes in wind, visibility, clouds, weather that occur between 2 METAR timings
What are air field warnings?Air field warnings are intended for protection of aircraft parked on the ground and include warnings for squall, wind, dust storm, thunderstorm, hail, frost, snow etc
Which form of airframe icing is most dangerous?Clear ice (a structural icing formed by large droplets in 2 degrees - 0 degrees celcius during freezing rain) is the most dangerous type of structural ice not only because it is hard to see, but also because it can change the shape of the airfoil.
Rime IceRime (a structural icing) ice forms when small droplets freeze immediately on contact with the aircraft surface. It typically occurs with temperatures between -15° C. and -20 ° C. Rime ice has a milky, opaque appearance resulting from air trapped when it strikes the leading edge of an airfoil and freezes.
Mixed IceMixed ice is a Structural icing that is a combination of clear and rime ice (usually occurs between -10 to -15 degrees celcius
What is the temperature range most favourable for severe icing?At just below zero, there is the highest threat of severe icing
What is validity of landing forecast2 hours
What is WAFC?World Area Forecast Centre – based in London & New York. India uses the London WAFC
What are the stages of thunderstorm?Cumulus stage updraft prevails, Mature stage both updraft and downdraft co-exists, Dissipating stage – only weak down draft exists.
Squall lineA squall line is a line of severe thunderstorms that can form along and/or ahead of a cold front. Lightning, tornadoes can occur in squall line
MicroburstsOnce during mature stage of a CB clouds happens, there is severe downdrafts. These vertical winds hit the ground surface and spreads in all directions producing strong winds upto a radius of 5 km. Such downdrafts are called Microbursts.
Gust FrontDuring mature stage of CB clouds, strong downdrafts occur. When the cold airflow hits the ground it moves outwards away. When this mass of cold air meets the surrounding warmer air, conditions similar to a Cold Front can occur. This cold front pushes up the warm air ahead of it creating a wall of strong winds called Gust Front. Very dangerous for landing and takeoff operations.
Wind ShearWind shear is defined as a sudden change of wind velocity and/or direction. There can be Vertical or Horizontal wind shears.
Mountain WavesMountain waves form when strong winds blow across a mountain range. The winds usually need to be at least 25 knots at the mountain peaks, and they need to blow perpendicular to the range.

Typically, a stable layer of air gets sandwiched between two less stable layers of air. Together the mountain thus looks like an Oscillating Wave/ Sine Wave pattern.

But at certain spots of mountain wave, usually on the Lee Side of the mountain, If a mountain wave is strong enough, parts of it can break away to form Rotor Winds.

One phenomenon associated with Mountain Waves is the formation of Lenticular/Cap clouds (which are associated with severe turbulences)
Clear Air TurbulenceClear Air Turbulence is defined as turbulence which is not associated with cloud and therefore cannot be detected visually or radar. It may occur due to change in terrain or vertical unstable air flow.
Adiabatic ProcessAnytime air moves upward, it expands because of decreasing atmospheric pressure.

Whereas if air is moving downward, it is compressed by due to higher pressure close to earth’s surface.

This increase or decrease in volume change causes the temperature to changes. When air expands, it cools; and when compresses, it warms. These changes are adiabatic, meaning that no heat has been removed from or added to the air...its pure volume depended.
Anabatic windAnabatic wind is the Air flow travelling up a slope of hill, mountain) during daytime. During day, air gets heated by conduction. As the air warms, its volume increases, and hence density and pressure decreases.
Katabatic windA cold flow of air travelling down hill/mountain slope during night time.

The cooler air at the mountain is denser and therefore heavier, so due to gravitation the flows down the Lee side of the mountain.

Katabatic, although a night phenomenon can be experienced during daytime also especially on the shady side of valleys. Therefore in mountainous terrain, it is advisable to fly on the sunny side in a single engine aircraft.
Coriolis ForceCoriolis Force is the result of Earth's rotation on weather patterns and ocean currents.

The “force” pulls an object to the right (clockwise) in the northern hemisphere and to the left (anticlockwise) in the southern hemisphere. This is caused by the rotation of the Earth from west to east.
Types of FogSteam Fog - Usually forms over the water surface. When the water surface warm meets a cooler air over water. Looks like steam over water.

Upslope Fog - Upslope Fog occurs when the air was forced to move up a mountain or raised terrain. Adiabatic cooling occurs, producing sufficient moisture.

Precipitation Fog - Occurs during rainfall. If the rain falls in an area that has prevailing cooler air.

Advection Fog- Advection fog usually forms in the coastal areas. Wherein the water is still warmer than land temperature and via advection, it meets the dewpoint to form the fog over water. But due to local sea breeze, the Advection Fog moves over on to the land surface.

Radiation Fog - Will form on calm, cool nights mainly because the cool ground surface (minus the sun's radiation) temperature will meet warm air temperature (that has already risen up during daytime) at the dewpoint and FOG occurs on the GROUND SURFACE usually at night, early morning.

Ice Fog - Any fog that occurs at temperatures below freezing point. It is composed on suspended ice crystals.