JX Weather (CBT) Flashcards
Change of 1.0 inHg changes the altimeter by how many feet
1,000 feet
You change your altimeter setting from 29.92 to 29.64. What will your altimeter indicate?
An decrease in altitude
You change your altimeter setting from 29.92 to 30.60. What will your altimeter indicate?
A increase in altitude
For every 11 deg C, how much of an altimeter error could you expect?
4%
With standard pressure (29.92), what will your altimeter indicate if OAT is lower than standard?
It will read an altitude higher than you actually are
With standard pressure (29.92), what will your altimeter indicate if OAT is higher than standard?
It will read an altitude lower than you actually are
Define indicated altitude
Altitude as it is displayed on your altimeter
Define absolute altitude
The acft’s altitude above the ground (AGL)
Define true altitude
The acft’s altitude references to sea level (MSL)
Define pressure altitude
Altitude above the standard datum plane (29.92 inHg)
Define density altitude
Pressure altitude corrected for nonstandard temperature deviations. (Not a reference altitude, but rather indication of acft performance)
Pure dry air contains what gasses and how much water vapor
Roughly:
78% nitrogen
21% oxygen
1% Other (10 gasses)
The atmosphere contains about 0-5% water vapor by volume
Troposphere dimensions
Average of 55,000 feet at the equator to 28,000 at the poles
Hight above the U.S. is about 36,000
Significance of the troposphere
Nearly all weather occurs in this layer
Define lapse rate
temp decrease with an increase of altitude
Define tropopause
- An abrupt change in temperature decrease with an increase of altitude
- Transition layer between the troposphere and the stratosphere
- Average hight of 36,000 over the U.S.
Where do the strongest winds occur
Just bellow the tropopause
Tropopause characteristics
- Strong winds
- Mod-sev turbulence
- Haze layer is common
- Temp is constant with altitude
- Normally the coldest area in the lower atmosphere
- Contrails occur… #Chemtrails
Stratosphere
Above the tropopause
Stratosphere characteristics
- increasing temperature as altitude increases (inversion) to approx 66,0000
- smooth air
- excellent visibility
What is an ELR
- Existing lapse rate
- Gives meteorologist the type of weather that exists
3 types of ELRs
- Standard
- Isothermal
- Inverted
What is the standard lapse rate (temp)
2 deg C (or 3.5 F) per 1,000 feet
What is Isothermal lapse rate
temp is constant with an increase in alt
What is inverted lapse rate
temp increases with an increase in alt (temp inversion)
Characteristics of an inverted lapse rate
- Few hundred - few thousand feet thick
- stable air
Average weight of air per square inch at sea level (standard conditions)
14.7 lbs
What is the relationship with altitude and pressure
- Always decreases with altitude
- pressure decreases more rapidly in the lower layers of the atmosphere (b/c air density)
What is inHg
measure of the high of a column of mercury that can be supported by atmospheric pressure
What is mb
The millibar is a direct measure of pressure defined by force per unit area
Standard day at sea level
- 29.92 inHg & 15 deg C (59 F)
or 1013.2 mb
What is the standard lapse rate (pressure)
1 inHg (or 34 mb) per 1,000 feet
What is station pressure
atmospheric pressure measured directly at an airfield or weather station
What do surface analysis charts show
- high and low pressure systems
- isobars
- ridges (high pressure/good wx)
- trough (low pressure/bad wx)
What are isobars
- Lines of equal (sea level) pressures
- depict horizontal distribution of pressure
Winds on charts will depict wind in relation to
True north
Winds reported from ATIS, tower, or RSU are in relation to
Magnetic north
What are the 3 station model wind indicators
- half barb = 5 kts
- barb = 10 kts
- penant = 50 kts
What weather conditions do a station model depict?
- Wind direction
- Wind speed
- sky cover (circle)
- temperature (top left)
- dew point (bottom left)
- sea level pressure (top right)
- pressure change (bottom right) +/- in last 3 hrs
How far apart are isobars spaced?
4 millibars apart
Wind characteristics in surface charts
- generally move in the same direction between pressure systems
- most cases, almost parallel to isobars
- High pressure system = clockwise
- Low pressure system = counterclockwise
Define pressure gradient
rate of change in a direction perpendicular to isobars
What is PGF
pressure gradient force
How is PGF represented
isobar spacing
Atmospheric circulation moves air by
mean of ascending and descending currents
descending air generates what pressure system
high pressure system
air moving upward generates what pressure system
low pressure system
Air spreads out, produces horizontal flow
high pressure system
air tries to converge toward the center
low pressure system
Coriolis force
- force created by earths rotation
- diverts wind to the right with respect to its initial direction (regardless of pressure system)
gradient winds
- combined force between the pressure gradient force and the Coriolis force
- flow perpendicular to pressure gradient force (parallel to isobars)
- results in northern hemisphere circulation (counterclockwise = low pressure system
clockwise = high pressure systems)
where are gradient winds found
above 2,000 ft AGL
When the PGF, Coriolis, and friction force balance (bellow 2,000ft AGL)
wind flows at a 45 deg across isobars from high to low pressure
wind speeds ______ with height through the troposphere; reach a maximum near the ______
increase; tropopause
Jet stream
- 50 knots or more (100-150; excess of 250)
- moves vertically and horizontally
two types of jet streams
- polar jet
- subtropical jet
characteristics of jet streams
- greatly influence weather patterns
- average height of 30,000 MSL
- wind speeds 100 - 150 kts (can reach in excess of 250 kts)
- 1,000 - 3,000 miles long
- 100 - 400 miles wide
- 3,000 - 7,000 feet deep
- move west to east
Valley wind
idk
Mountain wind
idk
dew point
the temperature that saturation occurs
difference between temperature and dewpoint
- dew point depression
- temperature dew point spread
relative humidity
percentage of the air saturation
3 characteristics of precipitation
- showers
- continuous
- intermittent
Characteristics of showery precipitation
- starts/stops
- changes intensity or sky conditions rapidly
- associated with cumuliform clouds
Characteristics of continuous precipitation
- steady
- gradual change
- associated with stratiform clouds
Characteristics of intermittent precipitation
- starts/stops at least once per hour
- can be showery or steady
- associated with both cumuliform and stratiform
precipitation forms
- rain
- drizzle
- frozen
how are clouds generally categorized
- high
- middle
- low
characteristics of low clouds
- surface to 6,500 agl
- hazardous to flight b/c of proximity to ground
- turbulence: non-moderate
- precipitation: drizzle or light rain
- if below freezing: can produce icing (accumulates faster due to clouds being denser)
characteristics of middle clouds
- 6,500 to 20,000 agl
- names contain “alto” prefix
- composed of ice crystals, water droplets, or a mix
- rain, snow
- icing is common
- turbulence may be encountered
characteristics of high clouds
- 20,000 to 40,000 agl
- names contain “cirro” prefix
- composed of primarily ice crystals
- contain no precipitation
- not an icing hazard
- little effect on flight ops except for mod turbulence
Special clouds (types)
- towering cumulous
- cumulonimbus
- nimbostratus
Cumulous & Cumulonimbus cloud characteristics
- found in low to middle and extend the the high cloud heights
- nearing thunderstorm stage
- produce heavy, showery precipitation
- mod turbulence
- icing common above the freezing level
Cumulonimbus cloud characteristics
- also referred to as “CB”
- very dangerous
- severe turb
- hail/icing
- lightening
- If extends past tropopause = severe thunderstorm
Nimbostratus cloud characteristics
- bases can be as low as 1,000 AGL
- heavy, continuous rain, snow, or ice pellets
- poor visibility
- low ceilings
What is denser, cold or warm air?
cold air
Four methods that air masses are lifted
- convergence
- frontal
- orographic
- thermal
convergent lifting
two air masses or parts of a single air mass converge
frontal lifting
cold fronts moving through the an area, lifting the warm front over it
orographic lifting
wind against a mountain side pushing up
thermal lifting
(Convective lifting) warm surface pushing cold air up by “intense solar heating”
Conditions you’d expect when stratiform clouds are present
- smooth air
- poor visibility
- steady winds
- steady precipitation
- rime icing
Conditions you’d expect when cumuliform clouds are present
- rough air
- good visibility
- gusty winds
- showery precipitation
- clear icing