PHAK 12: Weather Flashcards
How high does the Earth’s atmosphere extend vertically?
Almost 350 miles.
What is the composition of the atmosphere?
- 78% Nitrogen
- 21% Oxygen
- 1% Other gases (mostly Argon)
What are the layers of the atmosphere from Earth to space?
- Troposphere
- Tropopause
- Stratosphere
- Mesosphere
- Thermosphere
- Exosphere
Certain factors combine to set the atmosphere in motion, but a major factor is…
The uneven heating of the Earth’s surface.
What causes higher temperatures in equatorial areas?
Solar heating.
How much would a sealed column of air 350 miles high with a 1 square inch footprint weigh?
14.7 lbs
What is the Coriolis force?
A force caused by Earth’s rotation that deflects moving air and water.
Mercurial Barometer
A barometer that measures atmospheric pressure using a column of mercury.
Aneroid barometer
An instrument that measures the absolute pressure of the atmosphere by balancing the weight of the air above it against the spring action of the aneroid.
The Coriolis force deflects air to the ______ in the Northern Hemisphere.
Right
Standard Sea Level Pressure
- 59°F or 15°C
- 29.92” Hg or 1013.2 mb
What causes Convective Currents?
Plowed ground, rocks, sand, and barren land absorb solar energy quickly and can therefore give off a large amount of heat; whereas, water, trees, and other areas of vegetation tend to more slowly absorb heat and give off heat. The resulting uneven heating of the air creates small areas of local circulation called convective currents.
Effect of Obstructions on Wind
Obstructions on the ground affect the flow of wind and can be an unseen danger. Ground topography and large buildings can break up the flow of the wind and create wind gusts that change rapidly in direction and speed.
Depiction of winds on a surface weather chart.
Calm
Depiction of winds on a surface weather chart.
NW/5 kts
Depiction of winds on a surface weather chart.
SW/20 kts
Depiction of winds on a surface weather chart.
E/35 kts
Depiction of winds on a surface weather chart.
N/50 kts
Depiction of winds on a surface weather chart.
W/105 kts
Wind conditions
Each barb represents a speed of…
10 knots.
Wind conditions
Each half barb represents a speed of…
5 knots.
Wind conditions
Each pennant represents a speed of…
50 knots.
What are the characteristics of stable air?
Calm conditions and smooth airflow.
What type of clouds form in Stable Air?
Stratiform clouds
What is surface visibility typically like in Stable Air?
Poor surface visibility
What type of precipitation is found in Stable Air?
Steady or continuous precipitation.
What are the characteristics of unstable air?
Strong surface winds and turbulent airflow.
What type of clouds form in Unstable Air?
Cumulus clouds
What is surface visibility typically like in Unstable Air?
Good surface visibility.
What type of precipitation is found in Unstable Air?
Showery precipitation.
Trough
Elongated area of low pressure, rising air.
Ridge
Elongated area of high pressure, descending air.
Isobar
- Solid lines on a weather chart depicting lines of equal pressure.
- Lines closer together indicate steep pressure gradient and strong winds.
Wind Shear
- Sudden, drastic change in wind speed and/or direction over a very small area.
- Extremely dangerous at low altitudes.
Microburst
A small but intense downdraft causing extremely strong wind shear and hazardous winds.
3 Main Layers of Atmosphere that affect weather
- Troposphere
- Tropopause
- Stratosphere
Wind
Air movement caused by differences in atmospheric pressure.
Describe a High-Pressure Area
- Clockwise and dry.
- Descending air.
- Good weather.
- Clear skies.
Is a High-Pressure area typically moist or dry?
Dry
How does the air in a High-Pressure area move?
- Clockwise rotation
- Anticyclonic
- Descending
Describe a Low-Pressure Area
- Counterclockwise rotation.
- Cyclonic.
- Rising air.
- Poor visibility.
- Rain, fog, thunderstorms, cloudiness.
How does the air in a Low-Pressure area move?
- Counterclockwise rotation
- Cyclonic
- Rising
Dew Point
Temperature at which the air cannot hold any more moisture.
What happens when the air temperature reaches the Dew Point?
The air is completely saturated and moisture begins to condense out of the air in the form of fog, dew, frost, clouds, rain, or snow.
Radiation Fog
Forms on clear nights with little or no wind and generally over land.
As the Earth’s surface radiates its stored heat into space, it cools down.
When the near-surface air temperature drops to the dew point, humidity reaches 100%, and fog forms.
What type of fog forms on clear nights with little or no wind and generally over land.
Radiation Fog
Where does Radiation Fog form?
Always found at ground level.
How does Radiation Fog affect pilots?
Reduces visibility near the ground.
When does Radiation Fog dissipate?
Burns off once the sun rises and temperature increases.
Advection Fog
Wind blows moist, warm air over colder land or water. The air mass is cooled from below and the temperature is reduce to the dew point.
What type of fog occurs when wind blows moist, warm air over colder land or water.
Advection Fog
Where does Advection Fog form?
Common in coastal areas where sea breezes can blow the air over cooler landmasses.
Upslope Fog
Light wind pushes moist, stable air up a slope, such as a mountain range, to the level where air becomes saturated and condensation occurs.
Covers a large area.
Can persist for days.
What type of fog forms when light wind pushes moist, stable air up a slope, such as a mountain range, to the level where air becomes saturated and condensation occurs.
Upslope Fog
Steam Fog
“Sea Smoke”.
Cold, dry air moves over warm water.
As the water evaporates, it cools to its dew point, and the fog forms resembling smoke.
What type of fog forms when cold, dry air moves over warm water.
Steam Fog
What is Sea Smoke
A nickname for Steam Fog.
How much does Hg increase with altitude?
1 “Hg per 1,000 feet
ISA
International Standard Atmosphere
What happens to takeoff and landing distances with increased altitude?
They increase.
Are aircraft engines and propellers more or less efficient in higher density altitudes?
Less.
At what altitudes do people become impaired due to lack of oxygen?
The average person around 10,000 feet.
Some as low as 5,000 feet.
What is low-level wind shear commonly associated with?
- Passing frontal systems
- Thunderstorms
- Temperature inversions
- Strong upper level winds. (25+ knots)
What is a microburst typically associated with?
Convective precipitation into dry air at cloud base.
Generally the wind 2,000 feet AGL is what?
20° to 40° to the right of surface winds and greater in speed
Adiabatic heating
A process of heating dry air through compression. For example, as air moves down a slope it is compressed, which results in an increase in temperature.
Adiabatic cooling
A process of cooling the air through expansion. For example, as air moves up slope it expands with the reduction of atmospheric pressure and cools as it expands.
As a parcel of air rises…
Pressure decreases, volume increases, and temperature decreases.
As a parcel of air descends…
Pressure increases, volume decreases, temperature increases.
Lapse Rate
Change in temperature over altitude.
Average Lapse Rate
2 °C or 3.5 °F per 1,000 feet
up to 36,000’
Water vapor is ______ than air.
Lighter
Moisture ______ air density, causing it to ______.
Decreases, rise.
As moisture decreases, air becomes ______ and tends to ______.
Denser, sink
Moist air cools at a ______ rate and is generally ______ stable than dry air.
Slower, less.
Dry Adiabatic Lapse Rate
(unsaturated air)
3 °C or 5.4 °F
per 1,000 feet
Moist Adiabatic Lapse Rate
- Varies from 1.1 °C to 2.8 °C per 1,000 feet.
- Varies from 2 °F to 5 °F per 1,000 feet.
The combination of moisture and temperature determine the…
Stability of the air and the resulting weather.
Cool, dry air is very ______ and resists…
Stable, vertical movement.
Leads to good and generally clear weather.
The greatest instability occurs when the air is…
Moist and warm.
Altocumulus clouds
Several patchy white or gray layers, and seem to be made up of many small rows of fluffy ripples. They are lower than cirrus clouds, but still quite high. They are made of liquid water, but they don’t often produce rain.
Weather prediction: Fair
Altostratus clouds
Gray or blue-gray mid-level clouds composed of ice crystals and water droplets. The clouds usually cover the entire sky.
Weather prediction: Be prepared for continuous rain or snow!
Cirrocumulus clouds
Thin, sometimes patchy, sheet-like clouds. They sometimes look like they’re full of ripples or are made of small grains.
Weather prediction: Fair, but cold. However, if you live in a tropical region, these clouds could be a sign of an approaching hurricane!
Cirrostratus clouds
Thin, white clouds that cover the whole sky like a veil. These clouds are most commonly seen in the winter, and can cause the appearance of a halo around the sun or the moon.
Weather prediction: Rain or snow will arrive within 24 hours!
Cirrus clouds
Delicate, feathery clouds that are made mostly of ice crystals. Their wispy shape comes from wind currents which twist and spread the ice crystals into strands.
Weather prediction: A change is on its way!
Contrails
Made by high-flying jet airplanes. They are still clouds, though, because they are made of water droplets condensed from the water vapor in the exhaust of the jet engines.
Weather prediction: Contrails can provide information about the layers of moisture in the sky.
Cumulonimbus clouds
Grow on hot days when warm, wet air rises very high into the sky. From far away, they look like huge mountains or towers.
Weather prediction: Look out for rain, hail, and tornadoes!
Cumulus clouds
Fluffy, white cotton balls in the sky. They are beautiful in sunsets, and their varying sizes and shapes can make them fun to observe!
Weather prediction: Fair
Lenticular clouds
Shaped like lenses or almonds or…flying saucers! They may get their shape from hilly terrain or just the way the air is rising over flat terrain.
Weather prediction: None!
Mammatus clouds
Actually altocumulus, cirrus, cumulonimbus, or other types of clouds that have these pouch-like shapes hanging out of the bottom. The pouches are created when cold air within the cloud sinks down toward the Earth.
Weather prediction: Severe weather might be on its way!
Nimbostratus clouds
Dark, gray clouds that seem to fade into falling rain or snow. They are so thick that they often blot out the sunlight.
Weather prediction: Gloomy with continuous rain or snow
Orographic clouds
Get their shape from mountains or hills that force the air to move over or around them. They can also be formed by sea breezes and often appear as lines where two air masses meet.
Weather prediction: An early sign that the conditions might be right to form afternoon thunderstorms!
Stratocumulus clouds
Patchy gray or white clouds that often have a dark honeycomb-like appearance.
Weather prediction: Fair weather for now, but a storm might be on its way.
Stratus clouds
Often look like thin, white sheets covering the whole sky. Since they are so thin, they seldom produce much rain or snow. Sometimes, in the mountains or hills, these clouds appear to be fog.
Weather prediction: Fair, but gloomy
