Thunderstorms and Radar Flashcards
Other than the power control, the most important control on an airborne radar is the:
tilt control
Airborne weather radar typically has what wavelength? Ground Based Radar has what wavelength?
3 cm and 5cm respectively
The longer the wavelength of radar utilized, the larger:
the diameter of the antenna used
If you wanted to be able to “see” cloud droplets (not preceipitation) on an airborne radar, would a smaller or larger wavelegth work better?
smaller (around .5cm)
The intensity of the radar signal returned froma weather “target” is a function of what?
- droplet size
- droplet number density
- composition of the hydrometeors
With respect to radar beam width, greater accuracy occurs (at fixed wavelength) with a narrow beam, wide beam, or medium beam?
narrow beam
Range resolution refers to the ability of radar to what?
distinguish between two targets the same direction from the radar, but at different distances
In order to show as two separate targets, echoes must be separated by at least how many beam widths?
1 beam width
Attenuation is any process that what?
reduces the power density of a radar beam
Precipitation attenuation is worst for which band of radar?
x-band radar
Range attenuatation is normally proportional to what”
the inverse of the square of the distance to the target
a radar shadow occurs when what happens?
rain attenuates the signal so strongly that insufficient energy is returned to the radar receiver to be displayed
The fundamental difference between the echo image of a non-severe storm and that of a severe storm is that the sever storm will exhibit what?
scalloped contour outlines
You should avoid thunderstorms by what distance, when flying above the freezing level?
20 nm
You should avoid thunderstorms by what distance, when flying below the freezing level?
10 nm
The danger of flying into a radar shadow (on airborne radar) is what?
there may be undetected thunderstorm activity in the area of the radar shadow
A hook echo on a radar scope is the signature of what?
a mesocyclone
If a thunderstorm possesses a hook echo, in what quadrant of the storm would you expect to find it?
southwest
Do all tornadic thunderstorms exhibit a well-defined hook echo?
no
doppler radar measures what exactly?
- radial velocity relative to the radar antenna
- velocity shears
- areas of likely turbulence
What is a BWER?
bounded weak echo region, which is an area of low reflectivity radar returns, surrounded by high reflictivity returns, signifying an area of strong updrafts
What does TVS stand for?
tornado vortex signature
Stormscope and strikefinder detect what”
lightning discharges
What are some strengths of spheric detectors, compared to airborne radar (lightning detectors)
lower cost, easier to use, little or no precipitation attenuation, and it can be used safely on the ground
What are some weaknesses of spheric detectors compared to radar?
they are less precise than un-attenuated radar, can’t show precip not associated with a thunderstorm, they experience aliasing of pixels toward the aircraft position, particularly when severe thunderstorms are present
Most damage due to sever thudnerstorms is concentrated in which region of the US?
Central plains and east of mississippi river
What are the national weather service criteria for a severe thunderstorm?
- hail with diameter 1 in or greater, or
- wind damage or wind gusts greater than 58 mph, or
- a tornado
What is necessary for the formation of a thunderstorm?
- source of moisture
- conditionally unstable atmosphere
- a mechanism to trigger an updraft
In addition to the basic requirements, what additional requirement is necessary for a severe thunderstorm to occur?
strong vertical wind shear
Out of the three requirements of a thunderstorm, which is least responsible for how the storm organizes?
amount of moisture present
A front, terrain features, outflow from another t-storm, and differential heating of air over surfaces with different properties are all likely to create a boundary that could result in the lifting necessary to produce a t-storm. T/F?
True, a strong updraft however is not likely to create one
What spatial scale does the term “mesoscale” refer to?
a few to a few hundred kilometers
What type of t-storm always rotates?
supercell t-storm
what type of t-storm has an anvil?
all t-storms have anvils
What type of t-storm can have an overshooting top>
all t-storms can have an overshooting top
What develops when cool air generated by evaporation of rain within the downdrafts spreads outward away from the t-storm after reaching the surface?
gust front
What is the term used to describe the bulge at the top of a t-storm caused by strong updrafts?
overshooting top
What term describes the accumulation of rain-cooled air near the surface, under a t-storm
cold pool
What t-storm feature typically forms over the gust front as warm air is lifted?
shelf cloud
Most t-storms do not extend very far into the stratosphere, why?
because the air in the stratosphere is stable
A downdraft in a t-storm does what?
results from the drag created by falling precipitation particles, and is enhanced by evaporational cooling
A thunderstorm’s anvil is composed of what?
ice crystals
where do airmass t-storms tend to occur?
in environments where the winds do not increase substantially with height
Where and when would you most likely see an airmass t-storm?
far from any frontal boundaries, 4:00 PM
what is the primary mechanism that triggers the updraft of an airmass t-storm?
solar heating of the surface
Why is wind shear a key environmental condition for severe t-storm formation?
Strong winds cause the updraft to tilt and separate from the downdraft, allowing the inflow of warm, moist air to continue to feed the storm.
What type(s) of t-storms contain thunder and lightning?
All thunderstorms
What type of thunderstorms form far from frontal boundaries?
airmass t-storms
what type of t-storms appear as hook shaped echoes on radar reflectivity?
supercell t-storms
What type of t-storms commonly form along the tail of a comma cloud associated with an extratropical cyclone?
frontal squall line t-storms
what type of thunderstorms appear as a long continuous line on radar reflectivity, extending hundreds of miles?
frontal squall line t-storms
what type of t-storms account for most of the large, damaging tornadoes and large hail?
supercell t-storms
What type of t-storms are responsible for much of the summer rainfall on the Central Plains?
mesoscale convective system t-storms
What type of t-storm has an anvil that can grow to cover an area the size of an entire U.S. state?
mesoscale convective systems
What type of t-storm has an anvil and may have mammatus clouds on the underside of the anvil?
all t-storms
What type of t-storms form when a low level jet helps to transport warm moist air into the storm and provides the low-level wind shear that contributes to storm rotation?
supercell t-storms
What is true about a gust front?
it often produces a shelf cloud or a roll cloud, it can trigger new t-storm growth, and it is shallower than a t-storm
where is the most common location for a frontal squall line to form?
ahead of a cold front
what is a typical width of the region of heavy precipitation in an MCS squall line?
10 km
what is a typical width of the entire precipitation region in an MCS squall line?
100 km
What type of air is normally introduced into a t-storm by a rear inflow jet?
dry air
what is the term used to describe eddies that develop on either end of a bow echo?
bookend vortices
What feature of a t-storm sometimes appears as a fine line of lower radar reflectivity?
anvil
Which of the following is true near the end of the lifecycle of an MCS?
the trailing stratiform region decays, leaving a large area of clouds
what is the term used to describe the rotating region of slowly spinning clouds associated with MCS dissipation?
mesoscale convective vortex
When viewing an infrared satellite image, a large, semi-circular or obling region of high clouds covering the entire state of Missouri on a July evening is most likely what t-storm system?
mesoscale convective system
Along what type of front do frontal squall lines rarely form?
warm front
how long is a typical frontal squall line?
several hundred miles
how long does a typical frontal squall line last?
hours to days
how strong can the updrafts of a supercell t-torm be?
approximately 100 mph
What term is used to describe the rotating updraft within a supercell t-storm?
mesocyclone
On what side of a supercell t-storm is the updraft typiclly found?
southwest
what is the typical diameter of the updraft of a supercell t-storm?
3 to 6 miles
which statement regarding a wall cloud is not correct?
it develops when the cold pool lifts warm air
What order do you observe precipitation of a t-storm moving southwest to northeast over you?
virga, light rain, moderate rain, heavy rain, hail
What features of a supercell t-storm can produce an outflow boundary and gust front?
forward flank downdraft, and rear flank downdraft
In a strong t-storm, you can identify the location of the updraft by looking for what structural feature?
rain-free base
