Aviation Weather Test 2 Study Lessons 6-9

Water Vapor

Water in gas form

Where is half of all water vapor found?

Below 6,500 feet

How does composition change with an increase of water vapor?

All gases decrease and water (h20) would increase.

What does water vapor do?

Helps transfer heat energy and helps regulate the temperature of earth.

How is water vapor measured?

Relative humidity and dew point

What is ITCZ?

Inter-tropical convergence zone at equator and has many cumulonimbus clouds because of the intense heat at the equator which causes severe thunderstorms.

Why are the highest clouds found at the ITCZ?

More heat which equals more water vapor.

Hydrologic Cycle

Involves the continuous circulation of water in Earth’s atmosphere.

When is the water cycle considered balanced?

When the amount of water evaporating is the same amount that falls back as precipitation.

Evaporation

When liquid becomes a gas.

Where is the primary source of evaporation?

The oceans

Transpiration

the evaporation of water from plants. It is largely controlled by the humidity of the atmosphere and the moisture content of the soil.

Condensation

Water vapor (gas) becomes liquid.

Precipitation

Water that falls onto earth (ex. rain, snow,hail,etc.)

Runoff

Eccessive precipitation leading to the ground becoming saturated and not able to absorb more water which flows into streams and rivers.

Sensible heating

An object temperature changes without changing its phase. (ex. heating water to less than 100 degrees C to increase temp w/o changing phase/ making it boil).

Latent heat

The heat required (absorbed or released) for an object to change phase, expressed in joules per gram.

What phases involve the absorption of heat?

Melting, evaporation, sublimation

What phases involve the release of heat?

Freezing, condensation, deposition

Deposition

Water vapor turns into ice w/o becoming liquid. (ex. frost)

Sublimation

Solid to gas w/o passing through liquid (ex. dry ice)

Saturation

Max amount of water vapor an air parcel can hold at a given temp and pressure. (Saturated= air parcel is full) (Unsaturated= air parcel is not full).

What forms when saturation occurs and water vapor condenses?

Clouds, fog, dew

Relative Humidity

How full the air is with water vapor. Amount of water vapor that air can hold depends on air temperature (%).

What relative humidity comes with warm temps?

Low

What relative humidity comes with cold temps?

High

Relative Humidity Equation

Water vapor content/ capacity x 100

Dew point

Temperature air parcel must be cooled to allow for saturation/ turn into liquid like dew or fog. (degrees C)

What does a higher dew point=?

More moisture, regardless of current temperature.

Is relative humidity or dew point a better indicator of how humid it feels outside?

Dew point

Atmospheric Pressure

The force exerted by the weight of the atmosphere.

Barometer

Device that measures pressure.

What does a barometer do when high pressure is present?

Contract

What does a barometer do when low pressure is present (up at altitude)?

Expands

Standard pressure (mb)

1013.2mb

Standard pressure (inHg)

29.92 inHg

Station Pressure

Pressure measured at an airport, this is what is put into an altimeter.

Is pressure higher or lower at high altitudes?

Lower

When does pressure vary?

With altitude, tempurature, and water vapor

Mean sea level (MSL)

Common reference to compare station pressures between stations at different altitudes.

Density

How closley molecules are packed together. The closer they are the greater the density.

Is density high or low with high temperatures?

Low

Is density high or low with low temperatures?

High

How does volume change with density?

As volume increases, density decreases, as volume decreases density increases.

How does density effect pressure?

An air parcel with a high pressure is denser than an air parcel with a low pressure.

Does density increase or decrease with height?

Decrease

Is it better for the aircraft to fly in cold or hot weather?

Cold

Is air with a greater amount of water vapor more or less dense than air with less water vapor?

less dense

Where do you enter the barometric pressure?

In the kollsman window

True altitude

Actual vertical distance above mean sea level.

Indicated altitude

What is indicated on the altimeter.

Pressure altitude

Altitude at standard temperature/ pressure (29.92)

Density Altitude

Pressure altitude corrected for non-standard temperatures.

Corrected altitude

Correcting true altitude for temperature

At what altitude does everyone set their altimeter to 29.92?

18,000 feet

What does higher density altitude do to aircraft performace?

Decreases performance

In what three ways does high density altitude reduce performance?

1. reduces power b/c engine takes in less air

2. reduces thrust b/c of less air for propeller

3. reduces lift because light air exerts less force on airplane

On cold days air is…

Denser which equals lower density altitude

On hot days air is…

Less dense which equals higher density altitudes.

Hadley Cell

Starts at equator and is a factor of tropical and subtropical climates.

Ferrel Cell

Mid latitude cell that distributes heat to polar and hadley cells.

Polar Cell

Cell over polar regions where air sinks once over pole

As air warms it…

Ascends, leading to low pressure at the surface.

As air cools it…

Descends, leading to high pressure at the surface.

Jet Streams

Narrow bands of strong wind in the upper levels of the atmosphere blowing from west to east. (found between each cell)

When are jet streams generally stronger?

In the winter

What do jet streams follow?

Boundaries of hot and cold air.

Where does the jet stream shift as the sun’s elevation increases in the spring?

North towards Canada

In autumn when the suns elevation decreases where does the jet stream move?

To the south towards the U.S.

How does high pressure move in the northern hemisphere?

Clockwise

How does low pressure move in the northern hemisphere?

Counterclockwise

Pressure gradient force

Force that pushes air from areas of high pressure to areas of low pressure

What three forces affect the wind?

Pressure gradient force, coriolis force, friction

What pressure is exerted from cold air?

High pressure due to cold air being more dense .

What pressure is exerted from warm air?

Low pressure due to warm air being less dense.

How do pressures follow each other?

High follows low

What does close spacing of isobars indicate?

Stronger pressure gradient force which results in stronger winds.

What does far spacing of isobars indicate?

Weaker pressure gradient force which results in weaker winds.

Coriolis force

Force that deflects air to the right in the northern hemisphere and to the left in the southern hemisphere.

What happens to the coriolis force as wind speed increases or decreases?

It increases or decreses with the wind.

Friction

Slows down the wind.

When you go higher in the atmosphere is there more or less friction?

Less

Sea Breeze

Coastal local wind that blows from the sea to the land.

What causes sea breezes?

Temperature differences when the sea is colder than the land.

What is the sea breeze direction at surface?

From sea to land.

What is the sea breeze direction at altitude?

From land to sea.

Sea breeze front

Boundary where cold air and warm air meet.

What is Florida?

A peninsula

What occurs with a sea breeze collision?

Causes air to rise which creates thunderstorms.

Land breeze

Coastal wind that blows from land to sea at night when the land’s temperature is cooler than the ocean’s.

Lake breeze

A local wind that blows from the surface of a large lake onto the shores.

How does a shallow lake warm up?

Warms up rapidly and is less effective than a deep lake.