Weather (atmosphere) Flashcards
Air flow aorund high/low pressure systems
Low - inward, upward, counterclockwise
High - Outward, downward, clockwise
Low/high pressure system characteristics
Low Pressure
Rising air
Cloudiness
Precipitation
bad weather
High Pressure
Descending air
dissipation of cloudiness
good weather
Fronts & descriptions
Cold: mass of cold dense stable air advances and replaces a body of warmer air
Occluded: fast moving cold front catches up with slow warm front (cold or warm front occlusion)
Warm: boundary area formed when warm air mass contacts and flows OVER a colder air mass
Stationery: forces of two air masses are about equal. Boundary or front that separates them remains stationary and influences local wx for days; a mixture of typical wx from warm and cold fronts
General warm and cold front characteristics
Cold: as the front passes expect towering cumulus or cumulonimbus, heavy rain with lightning, thunder, or hail, tornados possible. Durring passage poor visibility, winds variable/gusting, temp/dew point spreadand pressure drop
Warm: as the front passes expect straiform clouds, drizzle, low ceilings, poor visibility, variable winds, rise in temp
All depends on the amount of mositure , stability of air that is forced upward, slope of the front, speed of the movement, and upper wind flow
What is a trough? Ridge?
Trough: Elongated area of low pressure
Ridge: Elongated area of high pressure
Standar temps and pressures
59F/15C - 29.92 inches of Hg/1013.2 millibars
Isobars on surface weather chart/constant pressure chart
Spacing shows how steep or shallow pressure gradient is
Close: steep gradient; higher wind speeds
Farther: shallow/lower speeds
What force deflects winds to the right in northern hemisphere and to the left in the southern?
Coriolis
Pressure lapse rate per altitude
1 inch Hg / 1,000 feet
Dew Point means?
temperature to which air must be cooled to attain the state of saturation
What factor primarily determinds the type and vertical extent of clouds? WHy is it important?
Stability!
Stability depends on atmosphere’s ability to resist vertical motion
Unstable: turbulent airflow, convective activity, vertical clouds, severe weather
Effects of stable and undstable air on clouds, turbulence, precip, vis
Stable / unstable Clouds - stratiform / cumuliform Turbulence - smooth / rough Precip - Steady / showery Vis - Fair to poor / good
During preflight planning, what info should you be aware of for icing?
Location of fronts
Cloud layers
Freezing levels
Air temp and pressure
What is the freezing level?
Lowest altitude in the atmosphere over a location where temp is 0c/32f
What conditions necessary for structural icing?
Visible moisture / below freezing temps
Two categories of icing
Structural or induction
structural: on aircraft surfaces
Induction: in the engine’s induction system
Structrual icing types
Clear, rime, mixed ice
You encounter icing, now what?
Leave the area of visible moisture: climb or descend above or below cloud bases
turn away / different heading
Frost: is it bad?
Yes. It makes the surfaces rough and spoils smooth airflow arond them causing slower airflow and reduces lift
Thunderstorm formation factors
a. sufficient water vapor
b. unstable lapse rate
c. rising air
Thunderstorm stages
- cumulus: updrafts cause raindrops to get bigger
- Mature - rain, lightning, maybe roll clouds
- Dissipating - downdrafts and rain begin to dissipate
Temperature inversion
Increase in temp with height / reversal of normal decrease with height
How does fog form?
Temp and dewpoint become identical or nearly so
Cooling of air (radiation fog, advection fog, upslope fog)
Adding moisture and elevating the dewpoint (frontal fog or steam fog)
Name types of fog
Radiation, advection, upslope, frontal, precipitation induced, steam
What causes radiation fog?
The ground cools the adjacent air to the dewpoint on calm clear nights
What causes advection fog?
Results from the transport of warm humid air over a cold surface - primairly along coastal areas during the winter
What causes upslope fog?
Result of mosit stable air being cooled adiabatically as it moves up sloping terrain. Wind stops, fog goes away. Can be very dense and extends to high altitudes
What is wind shear, where is it likely to occur
Change of velocity and/or direction either horizontal or vertical.
a. low level temp inversion
b. frontal zone or t-storm
c. clear air turbulence (CAT) at high levels associated with a jet stream or strong circulation
